commit 04e638e50d1e11937e8898bdfa53c2cb6434fb24
Author: Frank Fuentes <frank@francizco.com>
Date:   Mon Apr 27 12:02:58 2026 -0700

    Initial import: World 1 + World 2 (Fusion) with merge gating

diff --git a/.gitignore b/.gitignore
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--- /dev/null
+++ b/.gitignore
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+# macOS
+  .DS_Store
+
+  # Xcode
+  build/
+  DerivedData/
+  *.xcodeproj/xcuserdata/
+  *.xcodeproj/project.xcworkspace/xcuserdata/
+  *.xcworkspace/xcuserdata/
+  *.xcuserstate
+  *.xcuserdatad/
+  *.moved-aside
+
+  # Swift Package Manager
+  .build/
+  Packages/
+  Package.resolved
+  .swiftpm/
+
+  # CocoaPods / Carthage / fastlane (not used today, future-proofing)
+  Pods/
+  Carthage/Build/
+  fastlane/report.xml
+  fastlane/screenshots
+  fastlane/test_output
+
+  # Editor / misc
+  *.swp
+  *~
+  *.zip
\ No newline at end of file
diff --git a/CLAUDE.md b/CLAUDE.md
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--- /dev/null
+++ b/CLAUDE.md
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+# CLAUDE.md — Collapse Logic iOS
+
+## Project Overview
+
+Collapse Logic is a grid-based puzzle game for iPhone where the player pushes colored blocks to trigger same-color destruction and different-color merging. 
+
+**Studio:** Vulcara Games  
+**Platform:** iOS 17.0+ (iPhone primary)  
+**Language:** Swift 5.9+  
+**Frameworks:** SpriteKit (gameplay), SwiftUI (menus/HUD)  
+**Architecture:** MVVM with pure-struct game state
+
+---
+
+## Current Build Status
+
+- **World 1 — COMPLETE.** All 10 levels playable. Engine, SpriteKit scene, SwiftUI shell, undo, star rating, and persistence are all working.
+- **World 2 — IN PROGRESS.** Adding color merging. See `TASKS_World2.md` for the step-by-step build plan.
+
+---
+
+## Architecture
+
+```
+CollapseLogic/
+├── App/
+│   └── CollapseLogicApp.swift
+├── Models/
+│   ├── GameState.swift
+│   ├── Block.swift                  # BlockColor enum lives here — add yellow + secondaries
+│   ├── GridPosition.swift
+│   ├── Direction.swift
+│   ├── MoveResult.swift             # .merged event already stubbed — wire it up
+│   └── LevelDefinition.swift
+├── Engine/
+│   ├── GameEngine.swift             # Core change: different-color collision now merges
+│   └── LevelLoader.swift
+├── Views/
+│   ├── MainMenuView.swift
+│   ├── LevelSelectView.swift        # Needs world selector (World 1 / World 2)
+│   └── GameContainerView.swift
+├── Scene/
+│   ├── GameScene.swift
+│   ├── BlockNode.swift              # Add color rendering for yellow + 3 secondaries
+│   └── GridRenderer.swift
+├── Audio/
+│   └── SFXManager.swift             # Add merge.wav
+├── Persistence/
+│   └── ProgressStore.swift
+├── Levels/
+│   ├── metadata.json                # Add World 2 entry
+│   └── world1/
+│       └── level_01.json … level_10.json
+│   └── world2/
+│       └── level_01.json … level_12.json
+└── Resources/
+    └── SFX/
+```
+
+---
+
+## Block Colors — Full Set
+
+### Primary colors (can be pushed into each other to merge)
+
+| Color | Hex | Name |
+|-------|-----|------|
+| `red` | #E63946 | Ruby |
+| `blue` | #457B9D | Sapphire |
+| `yellow` | #F4D35E | Topaz |
+
+### Secondary colors (result of merges — can destroy each other but cannot merge further)
+
+| Color | Created From | Hex | Name |
+|-------|-------------|-----|------|
+| `purple` | red + blue | #7B2D8B | Amethyst |
+| `orange` | red + yellow | #E76F51 | Ember |
+| `green` | blue + yellow | #2A9D8F | Jade |
+
+Secondary blocks **can** be pre-placed in level JSON. They **can** destroy each other on same-color collision. They **cannot** merge — two different secondaries just stop (no interaction).
+
+---
+
+## Merge Rules (World 2 Engine Logic)
+
+When a moving block collides with a stationary block of a **different** color:
+
+```
+if both are PRIMARY colors → merge into the secondary color, placed at the stationary block's position
+if moving is PRIMARY, stationary is SECONDARY → block stops (no interaction)
+if moving is SECONDARY, stationary is PRIMARY → block stops (no interaction)
+if both are SECONDARY colors (different) → block stops (no interaction)
+if same color (primary or secondary) → both destroyed (existing World 1 rule, unchanged)
+```
+
+### Merge color table
+
+```swift
+static func mergeColor(_ a: BlockColor, _ b: BlockColor) -> BlockColor? {
+    let pair = Set([a, b])
+    if pair == [.red, .blue]    { return .purple }
+    if pair == [.red, .yellow]  { return .orange }
+    if pair == [.blue, .yellow] { return .green  }
+    return nil  // no merge possible
+}
+```
+
+When a merge occurs:
+1. Both source blocks are removed from state.
+2. A new block of the merged color is placed at the **stationary block's position**.
+3. A `.merged` event is emitted (for animation).
+4. Move count increments (merge is a valid move).
+5. Win condition is checked after the merge.
+
+---
+
+## GameEngine Changes (World 2)
+
+The only change to `GameEngine.processMove` is step 5 of the movement algorithm:
+
+**Before (World 1):**
+```
+5. Check cell adjacent to T in direction D:
+   - Same color → destroy both
+   - Different color → block stops
+```
+
+**After (World 2):**
+```
+5. Check cell adjacent to T in direction D:
+   - Same color (any) → destroy both  [unchanged]
+   - Both are primary, different colors → merge; new secondary block at stationary position
+   - Any other different-color combination → block stops  [unchanged]
+```
+
+No other engine logic changes. The pure-struct GameState design means this is fully unit-testable in isolation before touching SpriteKit.
+
+---
+
+## MoveResult Events
+
+```swift
+enum GameEvent {
+    case slid(blockIndex: Int, from: GridPosition, to: GridPosition)
+    case destroyed(blockIndex1: Int, blockIndex2: Int, at: GridPosition)
+    case merged(blockIndex1: Int, blockIndex2: Int, resultColor: BlockColor, at: GridPosition)
+}
+```
+
+The `.merged` event was already stubbed in World 1. Wire it up now.
+
+---
+
+## Animation — Merge
+
+In `GameScene`, handle `.merged` events:
+
+1. Slide the moving block to position T (same 0.15s ease-out as existing slide).
+2. Run a **merge burst**: scale both blocks up to 1.2× over 0.1s, then scale down and fade out over 0.1s simultaneously.
+3. Spawn a **new block node** of the merged color at the stationary position, starting at scale 0.0, and animate it scaling up to 1.0 over 0.15s with a slight overshoot (spring feel — scale to 1.15 then settle to 1.0).
+4. Total merge animation duration: ~0.35s.
+
+Keep it snappy. The new merged block "popping" into existence is the payoff moment.
+
+---
+
+## New Color Rendering (BlockNode)
+
+Add cases for `yellow`, `purple`, `orange`, `green` to the color switch in `BlockNode`. Use the hex values from the color table above.
+
+Visual treatment:
+- Primary blocks (red, blue, yellow): same rounded rect style as World 1.
+- Secondary blocks (purple, orange, green): add a subtle **white inner ring** (2px, 40% opacity) to visually distinguish them as merged/special. This gives players a quick read that these are second-tier blocks.
+
+---
+
+## World Select UI
+
+`LevelSelectView` currently shows World 1 levels only. For World 2, add a simple world selector at the top — two tappable pills: "World 1" and "World 2". World 2 unlocks when the player has earned at least **15 stars** in World 1 (out of 30 possible).
+
+Lock state: if World 2 is locked, show the pill grayed out with a lock icon and "15 ★ to unlock" label.
+
+Do not over-engineer this — a simple `@State var selectedWorld: Int` in `LevelSelectView` is enough.
+
+---
+
+## Sound Effects
+
+Add one new sound:
+
+5. `merge.wav` — A two-tone "blip-bloom" sound (0.25s). Higher pitch than destroy. Suggests transformation rather than destruction.
+
+Use `SKAction.playSoundFileNamed()` same as the existing four sounds.
+
+---
+
+## Level Design — World 2 (12 levels)
+
+World 2 introduces merging progressively across 12 levels. All level JSON files are in `Levels/world2/`. Grid sizes 5×5 to 6×6.
+
+**Teaching sequence:**
+- Levels 1–3: Introduce one merge pair (red+blue=purple). No pre-placed secondaries.
+- Levels 4–6: Add yellow. Teach red+yellow=orange and blue+yellow=green.
+- Levels 7–9: Pre-placed secondary blocks appear. Player must match them.
+- Levels 10–11: Multi-step chains — merge, then use the result to destroy another secondary.
+- Level 12: Boss level — all three primaries, all three secondaries, careful sequencing required.
+
+See `Levels/world2/level_*.json` for the hand-crafted level files.
+
+---
+
+## Testing Priorities (World 2 additions)
+
+**Engine unit tests — add these:**
+- `red` + `blue` collision → produces `purple` block at stationary position
+- `red` + `yellow` collision → produces `orange`
+- `blue` + `yellow` collision → produces `green`
+- Secondary + primary collision → block stops (no merge)
+- Secondary + different secondary collision → block stops (no merge)
+- Same secondary collision → both destroyed (e.g. purple + purple)
+- Merged block is placed at correct position (stationary block's cell)
+- Move count increments on merge
+- Undo correctly restores state before a merge
+- Win condition detected after a merge clears the last blocks
+
+**Level loading tests:**
+- All 12 World 2 JSON files parse without errors
+- Pre-placed secondary color blocks load correctly
+
+**Manual playtesting:**
+- Each World 2 level is solvable at par
+- Merge animation feels satisfying, not jarring
+- World 2 unlock (15 stars) triggers correctly
+
+---
+
+## Style & Conventions
+
+- Swift naming conventions (camelCase properties, PascalCase types)
+- Prefer value types (structs, enums) over classes except for SpriteKit nodes
+- No force unwraps except in tests
+- Keep files under 200 lines. Split if needed.
+- Comment non-obvious game logic
+- `// MARK: -` sections in longer files
+
+---
+
+## Build & Run
+
+- Xcode 15+
+- iOS 17.0 deployment target
+- No external dependencies
+- Primary simulator: iPhone 15 Pro
+- Small-screen test: iPhone SE (3rd gen)
+
+---
+
+## Definition of Done — World 2
+
+- [ ] `mergeColor(_:_:)` function implemented and all merge combinations correct
+- [ ] `GameEngine.processMove` handles primary+primary different-color collision as merge
+- [ ] `.merged` GameEvent emitted with correct blockIndex values and resultColor
+- [ ] All existing World 1 unit tests still pass (no regressions)
+- [ ] New merge unit tests pass (see Testing Priorities above)
+- [ ] `yellow`, `purple`, `orange`, `green` render correctly in `BlockNode`
+- [ ] Secondary blocks have white inner ring visual treatment
+- [ ] Merge animation plays: slide → burst → new block pop-in (~0.35s total)
+- [ ] `merge.wav` plays on merge
+- [ ] All 12 World 2 level JSONs load and are playable
+- [ ] World selector UI in `LevelSelectView` (two pills, lock at <15 stars)
+- [ ] `metadata.json` updated with World 2 entry
+- [ ] World 2 levels are fun and teach the mechanic clearly
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new file mode 100644
index 0000000..0df5be6
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+				);
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+				GCC_WARN_ABOUT_RETURN_TYPE = YES_ERROR;
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+			};
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+		};
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+				SWIFT_COMPILATION_MODE = wholemodule;
+				VALIDATE_PRODUCT = YES;
+			};
+			name = Release;
+		};
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+			isa = XCBuildConfiguration;
+			buildSettings = {
+				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
+				ASSETCATALOG_COMPILER_GLOBAL_ACCENT_COLOR_NAME = AccentColor;
+				CODE_SIGN_STYLE = Automatic;
+				CURRENT_PROJECT_VERSION = 1;
+				DEVELOPMENT_TEAM = C9CW6BFJQ7;
+				ENABLE_PREVIEWS = YES;
+				GENERATE_INFOPLIST_FILE = YES;
+				INFOPLIST_KEY_UIApplicationSceneManifest_Generation = YES;
+				INFOPLIST_KEY_UIApplicationSupportsIndirectInputEvents = YES;
+				INFOPLIST_KEY_UILaunchScreen_Generation = YES;
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+				INFOPLIST_KEY_UISupportedInterfaceOrientations_iPhone = "UIInterfaceOrientationPortrait UIInterfaceOrientationLandscapeLeft UIInterfaceOrientationLandscapeRight";
+				LD_RUNPATH_SEARCH_PATHS = (
+					"$(inherited)",
+					"@executable_path/Frameworks",
+				);
+				MARKETING_VERSION = 1.0;
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+				SWIFT_DEFAULT_ACTOR_ISOLATION = MainActor;
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+				SWIFT_VERSION = 5.0;
+				TARGETED_DEVICE_FAMILY = "1,2";
+			};
+			name = Debug;
+		};
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+			isa = XCBuildConfiguration;
+			buildSettings = {
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+				CURRENT_PROJECT_VERSION = 1;
+				DEVELOPMENT_TEAM = C9CW6BFJQ7;
+				ENABLE_PREVIEWS = YES;
+				GENERATE_INFOPLIST_FILE = YES;
+				INFOPLIST_KEY_UIApplicationSceneManifest_Generation = YES;
+				INFOPLIST_KEY_UIApplicationSupportsIndirectInputEvents = YES;
+				INFOPLIST_KEY_UILaunchScreen_Generation = YES;
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+				INFOPLIST_KEY_UISupportedInterfaceOrientations_iPhone = "UIInterfaceOrientationPortrait UIInterfaceOrientationLandscapeLeft UIInterfaceOrientationLandscapeRight";
+				LD_RUNPATH_SEARCH_PATHS = (
+					"$(inherited)",
+					"@executable_path/Frameworks",
+				);
+				MARKETING_VERSION = 1.0;
+				PRODUCT_BUNDLE_IDENTIFIER = com.vulcara.CollapseLogic;
+				PRODUCT_NAME = "$(TARGET_NAME)";
+				STRING_CATALOG_GENERATE_SYMBOLS = YES;
+				SWIFT_APPROACHABLE_CONCURRENCY = YES;
+				SWIFT_DEFAULT_ACTOR_ISOLATION = MainActor;
+				SWIFT_EMIT_LOC_STRINGS = YES;
+				SWIFT_UPCOMING_FEATURE_MEMBER_IMPORT_VISIBILITY = YES;
+				SWIFT_VERSION = 5.0;
+				TARGETED_DEVICE_FAMILY = "1,2";
+			};
+			name = Release;
+		};
+/* End XCBuildConfiguration section */
+
+/* Begin XCConfigurationList section */
+		583D3E792F9FE03400867DC9 /* Build configuration list for PBXNativeTarget "CollapseLogicTests" */ = {
+			isa = XCConfigurationList;
+			buildConfigurations = (
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+				583D3E782F9FE03400867DC9 /* Release */,
+			);
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+			defaultConfigurationName = Release;
+		};
+		584AD04B2F6A5E0700B97C0B /* Build configuration list for PBXProject "CollapseLogic" */ = {
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+			buildConfigurations = (
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+			defaultConfigurationName = Release;
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+			defaultConfigurationName = Release;
+		};
+/* End XCConfigurationList section */
+	};
+	rootObject = 584AD0482F6A5E0700B97C0B /* Project object */;
+}
diff --git a/CollapseLogic/CollapseLogic.xcodeproj/project.xcworkspace/contents.xcworkspacedata b/CollapseLogic/CollapseLogic.xcodeproj/project.xcworkspace/contents.xcworkspacedata
new file mode 100644
index 0000000..919434a
--- /dev/null
+++ b/CollapseLogic/CollapseLogic.xcodeproj/project.xcworkspace/contents.xcworkspacedata
@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Workspace
+   version = "1.0">
+   <FileRef
+      location = "self:">
+   </FileRef>
+</Workspace>
diff --git a/CollapseLogic/CollapseLogic.xcodeproj/project.xcworkspace/xcuserdata/frankfuentes.xcuserdatad/UserInterfaceState.xcuserstate b/CollapseLogic/CollapseLogic.xcodeproj/project.xcworkspace/xcuserdata/frankfuentes.xcuserdatad/UserInterfaceState.xcuserstate
new file mode 100644
index 0000000..7b07bfc
Binary files /dev/null and b/CollapseLogic/CollapseLogic.xcodeproj/project.xcworkspace/xcuserdata/frankfuentes.xcuserdatad/UserInterfaceState.xcuserstate differ
diff --git a/CollapseLogic/CollapseLogic.xcodeproj/xcuserdata/frankfuentes.xcuserdatad/xcschemes/xcschememanagement.plist b/CollapseLogic/CollapseLogic.xcodeproj/xcuserdata/frankfuentes.xcuserdatad/xcschemes/xcschememanagement.plist
new file mode 100644
index 0000000..859148c
--- /dev/null
+++ b/CollapseLogic/CollapseLogic.xcodeproj/xcuserdata/frankfuentes.xcuserdatad/xcschemes/xcschememanagement.plist
@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>SchemeUserState</key>
+	<dict>
+		<key>CollapseLogic.xcscheme_^#shared#^_</key>
+		<dict>
+			<key>orderHint</key>
+			<integer>0</integer>
+		</dict>
+	</dict>
+</dict>
+</plist>
diff --git a/CollapseLogic/CollapseLogic/App/CollapseLogicApp.swift b/CollapseLogic/CollapseLogic/App/CollapseLogicApp.swift
new file mode 100644
index 0000000..4031f49
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/App/CollapseLogicApp.swift
@@ -0,0 +1,11 @@
+import SwiftUI
+
+@main
+struct CollapseLogicApp: App {
+    var body: some Scene {
+        WindowGroup {
+            MainMenuView()
+                .preferredColorScheme(.dark)
+        }
+    }
+}
diff --git a/CollapseLogic/CollapseLogic/Assets.xcassets/AccentColor.colorset/Contents.json b/CollapseLogic/CollapseLogic/Assets.xcassets/AccentColor.colorset/Contents.json
new file mode 100644
index 0000000..eb87897
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Assets.xcassets/AccentColor.colorset/Contents.json
@@ -0,0 +1,11 @@
+{
+  "colors" : [
+    {
+      "idiom" : "universal"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}
diff --git a/CollapseLogic/CollapseLogic/Assets.xcassets/AppIcon.appiconset/CollapseLogic_icon.png b/CollapseLogic/CollapseLogic/Assets.xcassets/AppIcon.appiconset/CollapseLogic_icon.png
new file mode 100644
index 0000000..752cb08
Binary files /dev/null and b/CollapseLogic/CollapseLogic/Assets.xcassets/AppIcon.appiconset/CollapseLogic_icon.png differ
diff --git a/CollapseLogic/CollapseLogic/Assets.xcassets/AppIcon.appiconset/Contents.json b/CollapseLogic/CollapseLogic/Assets.xcassets/AppIcon.appiconset/Contents.json
new file mode 100644
index 0000000..67d35ac
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Assets.xcassets/AppIcon.appiconset/Contents.json
@@ -0,0 +1,14 @@
+{
+  "images" : [
+    {
+      "filename" : "CollapseLogic_icon.png",
+      "idiom" : "universal",
+      "platform" : "ios",
+      "size" : "1024x1024"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}
diff --git a/CollapseLogic/CollapseLogic/Assets.xcassets/Contents.json b/CollapseLogic/CollapseLogic/Assets.xcassets/Contents.json
new file mode 100644
index 0000000..73c0059
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Assets.xcassets/Contents.json
@@ -0,0 +1,6 @@
+{
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}
diff --git a/CollapseLogic/CollapseLogic/Audio/SFXManager.swift b/CollapseLogic/CollapseLogic/Audio/SFXManager.swift
new file mode 100644
index 0000000..c35d3c2
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Audio/SFXManager.swift
@@ -0,0 +1,54 @@
+import SpriteKit
+
+enum SFXEvent {
+    case select, slide, destroy, complete, merge
+}
+
+final class SFXManager {
+    static let shared = SFXManager()
+    private init() {}
+
+    private var isMuted = false
+
+    func play(_ event: SFXEvent) {
+        guard !isMuted else { return }
+        let filename: String
+        switch event {
+        case .select:   filename = "select.mp3"
+        case .slide:    filename = "slide.mp3"
+        case .destroy:  filename = "destroy.mp3"
+        case .complete: filename = "complete.mp3"
+        case .merge:    filename = "merge.wav"  // TODO: replace with real audio
+        }
+        // SKAction.playSoundFileNamed silently ignores missing files — safe for placeholder TODOs
+        let action = SKAction.playSoundFileNamed(filename, waitForCompletion: false)
+        // We need a scene to run the action; post to a shared coordinator node
+        SFXRunner.shared.run(action)
+    }
+
+    func playMerge() {
+        play(.merge)
+    }
+
+    func setMuted(_ muted: Bool) {
+        isMuted = muted
+    }
+}
+
+// A long-lived SKNode that can run audio actions without being in a scene tree.
+// Attach it to the active scene on first use.
+final class SFXRunner {
+    static let shared = SFXRunner()
+    private(set) var node = SKNode()
+    private init() {}
+
+    func attach(to scene: SKScene) {
+        if node.parent == nil {
+            scene.addChild(node)
+        }
+    }
+
+    func run(_ action: SKAction) {
+        node.run(action)
+    }
+}
diff --git a/CollapseLogic/CollapseLogic/CollapseLogicApp.swift b/CollapseLogic/CollapseLogic/CollapseLogicApp.swift
new file mode 100644
index 0000000..2413f2a
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/CollapseLogicApp.swift
@@ -0,0 +1,17 @@
+//
+//  CollapseLogicApp.swift
+//  CollapseLogic
+//
+//  Created by Frank Fuentes on 3/17/26.
+//
+
+import SwiftUI
+
+@main
+struct CollapseLogicApp: App {
+    var body: some Scene {
+        WindowGroup {
+            ContentView()
+        }
+    }
+}
diff --git a/CollapseLogic/CollapseLogic/ContentView.swift b/CollapseLogic/CollapseLogic/ContentView.swift
new file mode 100644
index 0000000..0d40c64
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/ContentView.swift
@@ -0,0 +1,24 @@
+//
+//  ContentView.swift
+//  CollapseLogic
+//
+//  Created by Frank Fuentes on 3/17/26.
+//
+
+import SwiftUI
+
+struct ContentView: View {
+    var body: some View {
+        VStack {
+            Image(systemName: "globe")
+                .imageScale(.large)
+                .foregroundStyle(.tint)
+            Text("Hello, world!")
+        }
+        .padding()
+    }
+}
+
+#Preview {
+    ContentView()
+}
diff --git a/CollapseLogic/CollapseLogic/Engine/GameEngine.swift b/CollapseLogic/CollapseLogic/Engine/GameEngine.swift
new file mode 100644
index 0000000..913becb
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Engine/GameEngine.swift
@@ -0,0 +1,105 @@
+struct GameEngine {
+
+    // MARK: - Primary entry point
+
+    static func processMove(state: GameState, blockIndex: Int, direction: Direction) -> MoveResult {
+        guard blockIndex >= 0 && blockIndex < state.blocks.count else {
+            return MoveResult(newState: state, events: [])
+        }
+
+        let movingBlock = state.blocks[blockIndex]
+        let origin = movingBlock.position
+
+        // --- Step 1: Compute landing position ---
+        let landingPos = slide(from: origin, direction: direction, state: state)
+
+        // --- Step 2: If block didn't move, return unchanged ---
+        if landingPos == origin {
+            return MoveResult(newState: state, events: [])
+        }
+
+        // --- Step 3: Check cell adjacent to landing in direction ---
+        let adjacentPos = landingPos.offset(by: direction)
+        var events: [GameEvent] = []
+        events.append(.slid(blockIndex: blockIndex, from: origin, to: landingPos))
+
+        var newBlocks = state.blocks
+
+        // Move the block to its landing position
+        newBlocks[blockIndex] = Block(id: movingBlock.id, position: landingPos, color: movingBlock.color)
+
+        // --- Step 4: Check for same-color collision at adjacent cell ---
+        if state.grid.contains(adjacentPos),
+           let adjacentIdx = state.blocks.indices.first(where: {
+               $0 != blockIndex && state.blocks[$0].position == adjacentPos
+           }) {
+            let adjacentBlock = state.blocks[adjacentIdx]
+            if adjacentBlock.color == movingBlock.color {
+                // Same color → destroy both
+                events.append(.destroyed(blockIndex1: blockIndex, blockIndex2: adjacentIdx, at: adjacentPos))
+                // Remove by index (higher index first to keep indices stable)
+                let removeIndices = [blockIndex, adjacentIdx].sorted(by: >)
+                for idx in removeIndices {
+                    newBlocks.remove(at: idx)
+                }
+            } else if state.allowsMerging,
+                      let merged = GameEngine.mergeColor(movingBlock.color, adjacentBlock.color) {
+                // Different primary colors → merge into a secondary color
+                events.append(.merged(
+                    blockIndex1: blockIndex,
+                    blockIndex2: adjacentIdx,
+                    resultColor: merged,
+                    at: adjacentBlock.position
+                ))
+                // Remove both in reverse index order to avoid index shifting
+                let removeIndices = [blockIndex, adjacentIdx].sorted(by: >)
+                for idx in removeIndices {
+                    newBlocks.remove(at: idx)
+                }
+                // Place merged block at the stationary block's position
+                let mergedBlock = Block(id: adjacentBlock.id, position: adjacentBlock.position, color: merged)
+                newBlocks.append(mergedBlock)
+            }
+            // Any other different-color combination: block already stopped at landingPos
+        }
+
+        let newState = state.withBlocks(newBlocks, incrementMove: true)
+        return MoveResult(newState: newState, events: events)
+    }
+
+    // MARK: - Undo
+
+    static func undo(state: GameState) -> GameState {
+        return state.undoState() ?? state
+    }
+
+    // MARK: - Merge color lookup
+
+    private static func mergeColor(_ a: BlockColor, _ b: BlockColor) -> BlockColor? {
+        guard a.isPrimary && b.isPrimary && a != b else { return nil }
+        let pair = Set([a, b])
+        if pair == Set([BlockColor.red,  .blue])   { return .purple }
+        if pair == Set([BlockColor.red,  .yellow]) { return .orange }
+        if pair == Set([BlockColor.blue, .yellow]) { return .green  }
+        return nil
+    }
+
+    // MARK: - Sliding algorithm
+
+    /// Returns the furthest empty cell reachable from `from` in `direction`.
+    /// Returns `from` if the very first step is blocked.
+    private static func slide(from: GridPosition, direction: Direction, state: GameState) -> GridPosition {
+        var current = from
+        while true {
+            let next = current.offset(by: direction)
+            // Stop if next is out of bounds
+            guard state.grid.contains(next) else { break }
+            // Stop if next is a wall
+            guard !state.walls.contains(next) else { break }
+            // Stop if next is occupied by another block
+            guard state.blocks.first(where: { $0.position == next }) == nil else { break }
+            current = next
+        }
+        return current
+    }
+}
diff --git a/CollapseLogic/CollapseLogic/Engine/LevelLoader.swift b/CollapseLogic/CollapseLogic/Engine/LevelLoader.swift
new file mode 100644
index 0000000..8ed7595
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Engine/LevelLoader.swift
@@ -0,0 +1,172 @@
+import Foundation
+
+enum LevelLoadError: Error, LocalizedError {
+    case fileNotFound(String)
+    case decodingFailed(String, Error)
+    case validationFailed(String, String)
+
+    var errorDescription: String? {
+        switch self {
+        case .fileNotFound(let name): return "Level file not found: \(name)"
+        case .decodingFailed(let name, let e): return "Failed to decode \(name): \(e)"
+        case .validationFailed(let id, let reason): return "Level \(id) invalid: \(reason)"
+        }
+    }
+}
+
+struct LevelLoader {
+
+    // MARK: - Load single level
+
+    static func load(levelId: String, world: Int) throws -> GameState {
+        // World 2 files are prefixed w2_ to avoid name collision with world 1
+        let filename = world >= 2 ? "w2_\(levelId)" : levelId
+        guard let url = Bundle.main.url(forResource: filename, withExtension: "json") else {
+            throw LevelLoadError.fileNotFound("\(filename).json")
+        }
+        let data = try Data(contentsOf: url)
+        let def: LevelDefinition
+        do {
+            def = try JSONDecoder().decode(LevelDefinition.self, from: data)
+        } catch {
+            throw LevelLoadError.decodingFailed(filename, error)
+        }
+        try validate(def)
+        return makeGameState(from: def)
+    }
+
+    // MARK: - Load from definition (used in tests with in-memory JSON)
+
+    static func makeGameState(from def: LevelDefinition) -> GameState {
+        let gridSize = GridSize(width: def.grid.width, height: def.grid.height)
+
+        let blocks = def.blocks.enumerated().map { idx, b in
+            Block(
+                id: idx,
+                position: GridPosition(x: b.x, y: b.y),
+                color: BlockColor(rawValue: b.color) ?? .red
+            )
+        }
+
+        let walls: Set<GridPosition> = Set((def.walls ?? []).map {
+            GridPosition(x: $0.x, y: $0.y)
+        })
+
+        let objective = parseObjective(def.objective)
+
+        return GameState(
+            grid: gridSize,
+            blocks: blocks,
+            walls: walls,
+            moveCount: 0,
+            par: def.par,
+            objective: objective,
+            allowsMerging: def.world >= 2,
+            history: []
+        )
+    }
+
+    // MARK: - Metadata
+
+    static func loadMetadata() -> MetadataFile? {
+        guard let url = Bundle.main.url(forResource: "metadata", withExtension: "json") else { return nil }
+        return try? JSONDecoder().decode(MetadataFile.self, from: Data(contentsOf: url))
+    }
+
+    // MARK: - Validation
+
+    static func validate(_ def: LevelDefinition) throws {
+        let id = def.id
+        guard def.grid.width >= 3, def.grid.width <= 10,
+              def.grid.height >= 3, def.grid.height <= 10 else {
+            throw LevelLoadError.validationFailed(id, "Grid dimensions out of range 3–10")
+        }
+        guard def.par > 0 else {
+            throw LevelLoadError.validationFailed(id, "Par must be positive")
+        }
+        guard def.blocks.count >= 2 else {
+            throw LevelLoadError.validationFailed(id, "At least 2 blocks required")
+        }
+
+        var occupied = Set<String>()
+        func cell(_ x: Int, _ y: Int) -> String { "\(x),\(y)" }
+
+        for b in def.blocks {
+            guard b.x >= 0, b.x < def.grid.width, b.y >= 0, b.y < def.grid.height else {
+                throw LevelLoadError.validationFailed(id, "Block (\(b.x),\(b.y)) out of bounds")
+            }
+            let key = cell(b.x, b.y)
+            guard !occupied.contains(key) else {
+                throw LevelLoadError.validationFailed(id, "Duplicate position (\(b.x),\(b.y))")
+            }
+            occupied.insert(key)
+        }
+        for w in def.walls ?? [] {
+            guard w.x >= 0, w.x < def.grid.width, w.y >= 0, w.y < def.grid.height else {
+                throw LevelLoadError.validationFailed(id, "Wall (\(w.x),\(w.y)) out of bounds")
+            }
+            let key = cell(w.x, w.y)
+            guard !occupied.contains(key) else {
+                throw LevelLoadError.validationFailed(id, "Wall overlaps object at (\(w.x),\(w.y))")
+            }
+            occupied.insert(key)
+        }
+
+        let validObjectives = ["clear_all", "clear_color", "reduce_to", "clear_targets"]
+        guard validObjectives.contains(def.objective.type) else {
+            throw LevelLoadError.validationFailed(id, "Unknown objective type: \(def.objective.type)")
+        }
+    }
+
+    // MARK: - Private helpers
+
+    private static func parseObjective(_ obj: ObjectiveDef) -> ObjectiveType {
+        switch obj.type {
+        case "clear_all":
+            return .clearAll
+        case "clear_color":
+            let color = BlockColor(rawValue: obj.color ?? "red") ?? .red
+            return .clearColor(color)
+        case "reduce_to":
+            return .reduceTo(obj.count ?? 1)
+        default:
+            return .clearAll
+        }
+    }
+}
+
+// MARK: - Metadata Codable types
+
+struct MetadataFile: Codable {
+    let version: String
+    let worlds: [WorldMeta]
+}
+
+struct WorldMeta: Codable {
+    let id: Int
+    let name: String
+    let description: String
+    let newMechanic: String?
+    let unlockStars: Int?
+    let levels: [LevelMeta]
+
+    enum CodingKeys: String, CodingKey {
+        case id, name, description, levels
+        case newMechanic = "new_mechanic"
+        case unlockStars = "unlock_stars"
+    }
+}
+
+struct LevelMeta: Codable {
+    let id: String
+    let title: String
+    let file: String
+    let isChallenge: Bool
+    let starsRequired: Int?
+
+    enum CodingKeys: String, CodingKey {
+        case id, title, file
+        case isChallenge = "is_challenge"
+        case starsRequired = "stars_required"
+    }
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/metadata.json b/CollapseLogic/CollapseLogic/Levels/metadata.json
new file mode 100644
index 0000000..c0521b5
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/metadata.json
@@ -0,0 +1,44 @@
+{
+  "version": "1.0",
+  "worlds": [
+    {
+      "id": 1,
+      "name": "Primary",
+      "description": "Learn the basics of pushing and destroying.",
+      "new_mechanic": null,
+      "levels": [
+        { "id": "w1_01", "title": "First Push",     "file": "world1/level_01.json", "is_challenge": false },
+        { "id": "w1_02", "title": "Blue Pair",       "file": "world1/level_02.json", "is_challenge": false },
+        { "id": "w1_03", "title": "Two Pairs",       "file": "world1/level_03.json", "is_challenge": false },
+        { "id": "w1_04", "title": "Wall Detour",     "file": "world1/level_04.json", "is_challenge": false },
+        { "id": "w1_05", "title": "The Corridor",    "file": "world1/level_05.json", "is_challenge": false },
+        { "id": "w1_06", "title": "Six Pack",        "file": "world1/level_06.json", "is_challenge": false },
+        { "id": "w1_07", "title": "Deadlock Trap",   "file": "world1/level_07.json", "is_challenge": false },
+        { "id": "w1_08", "title": "Detour",          "file": "world1/level_08.json", "is_challenge": false },
+        { "id": "w1_09", "title": "Four Pairs",      "file": "world1/level_09.json", "is_challenge": false },
+        { "id": "w1_10", "title": "The Gauntlet",    "file": "world1/level_10.json", "is_challenge": false }
+      ]
+    },
+    {
+      "id": 2,
+      "name": "Fusion",
+      "description": "Discover what happens when two colors collide.",
+      "new_mechanic": "merging",
+      "unlock_stars": 15,
+      "levels": [
+        { "id": "w2_01", "title": "First Contact",   "file": "world2/w2_level_01.json", "is_challenge": false },
+        { "id": "w2_02", "title": "Bound Together",   "file": "world2/w2_level_02.json", "is_challenge": false },
+        { "id": "w2_03", "title": "The Third Color",  "file": "world2/w2_level_03.json", "is_challenge": false },
+        { "id": "w2_04", "title": "Sun Stone",        "file": "world2/w2_level_04.json", "is_challenge": false },
+        { "id": "w2_05", "title": "Color Theory",     "file": "world2/w2_level_05.json", "is_challenge": false },
+        { "id": "w2_06", "title": "Triad",            "file": "world2/w2_level_06.json", "is_challenge": false },
+        { "id": "w2_07", "title": "Inheritance",       "file": "world2/w2_level_07.json", "is_challenge": false },
+        { "id": "w2_08", "title": "Reflection",        "file": "world2/w2_level_08.json", "is_challenge": false },
+        { "id": "w2_09", "title": "Cascade",           "file": "world2/w2_level_09.json", "is_challenge": false },
+        { "id": "w2_10", "title": "Chain Reaction",    "file": "world2/w2_level_10.json", "is_challenge": false },
+        { "id": "w2_11", "title": "The Long Way",      "file": "world2/w2_level_11.json", "is_challenge": false },
+        { "id": "w2_12", "title": "Prism",             "file": "world2/w2_level_12.json", "is_challenge": true, "stars_required": 15 }
+      ]
+    }
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world1/level_01.json b/CollapseLogic/CollapseLogic/Levels/world1/level_01.json
new file mode 100644
index 0000000..c99d2e5
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world1/level_01.json
@@ -0,0 +1,16 @@
+{
+  "id": "w1_01",
+  "world": 1,
+  "level": 1,
+  "title": "First Push",
+  "grid": { "width": 4, "height": 4 },
+  "blocks": [
+    { "x": 0, "y": 1, "color": "red" },
+    { "x": 3, "y": 1, "color": "red" }
+  ],
+  "walls": [],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 1,
+  "hints": ["Push the left block to the right."]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world1/level_02.json b/CollapseLogic/CollapseLogic/Levels/world1/level_02.json
new file mode 100644
index 0000000..6bbc27b
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world1/level_02.json
@@ -0,0 +1,16 @@
+{
+  "id": "w1_02",
+  "world": 1,
+  "level": 2,
+  "title": "Blue Pair",
+  "grid": { "width": 4, "height": 4 },
+  "blocks": [
+    { "x": 0, "y": 0, "color": "blue" },
+    { "x": 3, "y": 3, "color": "blue" }
+  ],
+  "walls": [],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 2,
+  "hints": ["Align them on the same row, then push."]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world1/level_03.json b/CollapseLogic/CollapseLogic/Levels/world1/level_03.json
new file mode 100644
index 0000000..4c74798
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world1/level_03.json
@@ -0,0 +1,18 @@
+{
+  "id": "w1_03",
+  "world": 1,
+  "level": 3,
+  "title": "Two Pairs",
+  "grid": { "width": 5, "height": 5 },
+  "blocks": [
+    { "x": 0, "y": 1, "color": "red" },
+    { "x": 4, "y": 1, "color": "red" },
+    { "x": 1, "y": 3, "color": "blue" },
+    { "x": 3, "y": 3, "color": "blue" }
+  ],
+  "walls": [],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 3,
+  "hints": ["Clear the reds first, then align the blues."]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world1/level_04.json b/CollapseLogic/CollapseLogic/Levels/world1/level_04.json
new file mode 100644
index 0000000..75012b0
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world1/level_04.json
@@ -0,0 +1,23 @@
+{
+  "id": "w1_04",
+  "world": 1,
+  "level": 4,
+  "title": "Wall Detour",
+  "grid": { "width": 5, "height": 5 },
+  "blocks": [
+    { "x": 0, "y": 0, "color": "red" },
+    { "x": 4, "y": 0, "color": "red" },
+    { "x": 1, "y": 4, "color": "blue" },
+    { "x": 3, "y": 4, "color": "blue" }
+  ],
+  "walls": [
+    { "x": 2, "y": 0 }
+  ],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 4,
+  "hints": [
+    "The wall blocks a direct red push.",
+    "Move one red down first to clear row 0."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world1/level_05.json b/CollapseLogic/CollapseLogic/Levels/world1/level_05.json
new file mode 100644
index 0000000..ba3d3a7
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world1/level_05.json
@@ -0,0 +1,26 @@
+{
+  "id": "w1_05",
+  "world": 1,
+  "level": 5,
+  "title": "The Corridor",
+  "grid": { "width": 5, "height": 5 },
+  "blocks": [
+    { "x": 0, "y": 2, "color": "red" },
+    { "x": 4, "y": 2, "color": "red" },
+    { "x": 2, "y": 0, "color": "blue" },
+    { "x": 2, "y": 4, "color": "blue" }
+  ],
+  "walls": [
+    { "x": 1, "y": 0 },
+    { "x": 3, "y": 0 },
+    { "x": 1, "y": 4 },
+    { "x": 3, "y": 4 }
+  ],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 4,
+  "hints": [
+    "The center column is open — use it.",
+    "Reds can meet on row 2."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world1/level_06.json b/CollapseLogic/CollapseLogic/Levels/world1/level_06.json
new file mode 100644
index 0000000..72cc648
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world1/level_06.json
@@ -0,0 +1,23 @@
+{
+  "id": "w1_06",
+  "world": 1,
+  "level": 6,
+  "title": "Six Pack",
+  "grid": { "width": 5, "height": 5 },
+  "blocks": [
+    { "x": 0, "y": 0, "color": "red" },
+    { "x": 4, "y": 0, "color": "red" },
+    { "x": 0, "y": 4, "color": "blue" },
+    { "x": 4, "y": 4, "color": "blue" },
+    { "x": 1, "y": 2, "color": "red" },
+    { "x": 3, "y": 2, "color": "red" }
+  ],
+  "walls": [],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 5,
+  "hints": [
+    "Clear the middle reds first to open up space.",
+    "Then handle the corners."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world1/level_07.json b/CollapseLogic/CollapseLogic/Levels/world1/level_07.json
new file mode 100644
index 0000000..7582305
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world1/level_07.json
@@ -0,0 +1,24 @@
+{
+  "id": "w1_07",
+  "world": 1,
+  "level": 7,
+  "title": "Deadlock Trap",
+  "grid": { "width": 5, "height": 5 },
+  "blocks": [
+    { "x": 0, "y": 0, "color": "red" },
+    { "x": 2, "y": 0, "color": "blue" },
+    { "x": 4, "y": 2, "color": "red" },
+    { "x": 2, "y": 4, "color": "blue" }
+  ],
+  "walls": [
+    { "x": 1, "y": 2 },
+    { "x": 3, "y": 2 }
+  ],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 4,
+  "hints": [
+    "Pushing red right immediately blocks the path.",
+    "Move blue first to make room."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world1/level_08.json b/CollapseLogic/CollapseLogic/Levels/world1/level_08.json
new file mode 100644
index 0000000..f605e52
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world1/level_08.json
@@ -0,0 +1,30 @@
+{
+  "id": "w1_08",
+  "world": 1,
+  "level": 8,
+  "title": "Detour",
+  "grid": { "width": 6, "height": 6 },
+  "blocks": [
+    { "x": 0, "y": 0, "color": "red" },
+    { "x": 5, "y": 0, "color": "red" },
+    { "x": 1, "y": 5, "color": "blue" },
+    { "x": 4, "y": 5, "color": "blue" }
+  ],
+  "walls": [
+    { "x": 2, "y": 0 },
+    { "x": 2, "y": 1 },
+    { "x": 3, "y": 0 },
+    { "x": 3, "y": 1 },
+    { "x": 2, "y": 4 },
+    { "x": 2, "y": 5 },
+    { "x": 3, "y": 4 },
+    { "x": 3, "y": 5 }
+  ],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 6,
+  "hints": [
+    "Rows 2 and 3 are the only clear crossing rows.",
+    "Route each block through the middle."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world1/level_09.json b/CollapseLogic/CollapseLogic/Levels/world1/level_09.json
new file mode 100644
index 0000000..a2f8784
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world1/level_09.json
@@ -0,0 +1,30 @@
+{
+  "id": "w1_09",
+  "world": 1,
+  "level": 9,
+  "title": "Four Pairs",
+  "grid": { "width": 6, "height": 6 },
+  "blocks": [
+    { "x": 0, "y": 0, "color": "red" },
+    { "x": 5, "y": 0, "color": "red" },
+    { "x": 0, "y": 5, "color": "blue" },
+    { "x": 5, "y": 5, "color": "blue" },
+    { "x": 0, "y": 2, "color": "red" },
+    { "x": 5, "y": 2, "color": "red" },
+    { "x": 0, "y": 3, "color": "blue" },
+    { "x": 5, "y": 3, "color": "blue" }
+  ],
+  "walls": [
+    { "x": 2, "y": 1 },
+    { "x": 3, "y": 1 },
+    { "x": 2, "y": 4 },
+    { "x": 3, "y": 4 }
+  ],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 7,
+  "hints": [
+    "Rows 2 and 3 can be cleared without routing.",
+    "Rows 0 and 5 need the walls accounted for."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world1/level_10.json b/CollapseLogic/CollapseLogic/Levels/world1/level_10.json
new file mode 100644
index 0000000..fd4c720
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world1/level_10.json
@@ -0,0 +1,36 @@
+{
+  "id": "w1_10",
+  "world": 1,
+  "level": 10,
+  "title": "The Gauntlet",
+  "grid": { "width": 6, "height": 6 },
+  "blocks": [
+    { "x": 0, "y": 0, "color": "red" },
+    { "x": 5, "y": 0, "color": "red" },
+    { "x": 0, "y": 5, "color": "blue" },
+    { "x": 5, "y": 5, "color": "blue" },
+    { "x": 2, "y": 1, "color": "red" },
+    { "x": 3, "y": 4, "color": "red" },
+    { "x": 1, "y": 3, "color": "blue" },
+    { "x": 4, "y": 2, "color": "blue" },
+    { "x": 0, "y": 2, "color": "red" },
+    { "x": 5, "y": 3, "color": "red" }
+  ],
+  "walls": [
+    { "x": 2, "y": 0 },
+    { "x": 3, "y": 0 },
+    { "x": 0, "y": 3 },
+    { "x": 5, "y": 2 },
+    { "x": 2, "y": 5 },
+    { "x": 3, "y": 5 },
+    { "x": 1, "y": 1 },
+    { "x": 4, "y": 4 }
+  ],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 8,
+  "hints": [
+    "Sequence matters — one wrong move jams the board.",
+    "Clear interior blocks before the corner pairs."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world2/w2_level_01.json b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_01.json
new file mode 100644
index 0000000..1f54690
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_01.json
@@ -0,0 +1,20 @@
+{
+  "id": "w2_01",
+  "world": 2,
+  "level": 1,
+  "title": "First Contact",
+  "grid": { "width": 4, "height": 4 },
+  "blocks": [
+    { "x": 0, "y": 1, "color": "red" },
+    { "x": 3, "y": 1, "color": "blue" },
+    { "x": 1, "y": 3, "color": "purple" }
+  ],
+  "walls": [],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 2,
+  "hints": [
+    "Push the red block into the blue block. Something new will appear.",
+    "Now push the new purple block into the one waiting below."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world2/w2_level_02.json b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_02.json
new file mode 100644
index 0000000..71238e6
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_02.json
@@ -0,0 +1,21 @@
+{
+  "id": "w2_02",
+  "world": 2,
+  "level": 2,
+  "title": "Bound Together",
+  "grid": { "width": 5, "height": 4 },
+  "blocks": [
+    { "x": 0, "y": 0, "color": "red" },
+    { "x": 4, "y": 0, "color": "blue" },
+    { "x": 0, "y": 3, "color": "red" },
+    { "x": 4, "y": 3, "color": "blue" }
+  ],
+  "walls": [],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 4,
+  "hints": [
+    "You need to make two purple blocks and then destroy both.",
+    "Each red+blue collision creates one purple."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world2/w2_level_03.json b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_03.json
new file mode 100644
index 0000000..1477f41
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_03.json
@@ -0,0 +1,22 @@
+{
+  "id": "w2_03",
+  "world": 2,
+  "level": 3,
+  "title": "The Third Color",
+  "grid": { "width": 5, "height": 5 },
+  "blocks": [
+    { "x": 0, "y": 2, "color": "red" },
+    { "x": 4, "y": 0, "color": "blue" },
+    { "x": 4, "y": 4, "color": "purple" }
+  ],
+  "walls": [
+    { "x": 2, "y": 2 }
+  ],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 3,
+  "hints": [
+    "The wall stops the red block in the middle of the row.",
+    "Move blue down to row 2 first, then push red into it."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world2/w2_level_04.json b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_04.json
new file mode 100644
index 0000000..c3d6b40
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_04.json
@@ -0,0 +1,20 @@
+{
+  "id": "w2_04",
+  "world": 2,
+  "level": 4,
+  "title": "Sun Stone",
+  "grid": { "width": 5, "height": 4 },
+  "blocks": [
+    { "x": 0, "y": 1, "color": "red" },
+    { "x": 4, "y": 1, "color": "yellow" },
+    { "x": 2, "y": 3, "color": "orange" }
+  ],
+  "walls": [],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 2,
+  "hints": [
+    "Red and yellow make orange.",
+    "Push the new orange into the one waiting at the bottom."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world2/w2_level_05.json b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_05.json
new file mode 100644
index 0000000..3fafcb9
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_05.json
@@ -0,0 +1,22 @@
+{
+  "id": "w2_05",
+  "world": 2,
+  "level": 5,
+  "title": "Color Theory",
+  "grid": { "width": 5, "height": 5 },
+  "blocks": [
+    { "x": 0, "y": 2, "color": "red" },
+    { "x": 4, "y": 2, "color": "blue" },
+    { "x": 2, "y": 0, "color": "purple" },
+    { "x": 2, "y": 4, "color": "yellow" }
+  ],
+  "walls": [],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 3,
+  "hints": [
+    "You need to make a purple block to match the one already on the board.",
+    "Merge red and blue first, then align the two purples.",
+    "Yellow is still on the board — you'll need to deal with it separately."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world2/w2_level_06.json b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_06.json
new file mode 100644
index 0000000..4b0c7fe
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_06.json
@@ -0,0 +1,24 @@
+{
+  "id": "w2_06",
+  "world": 2,
+  "level": 6,
+  "title": "Triad",
+  "grid": { "width": 5, "height": 5 },
+  "blocks": [
+    { "x": 0, "y": 0, "color": "red" },
+    { "x": 4, "y": 0, "color": "blue" },
+    { "x": 0, "y": 4, "color": "yellow" },
+    { "x": 4, "y": 2, "color": "purple" },
+    { "x": 2, "y": 4, "color": "orange" },
+    { "x": 4, "y": 4, "color": "green" }
+  ],
+  "walls": [],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 6,
+  "hints": [
+    "Three primaries, three secondaries waiting to match them.",
+    "Red+blue=purple, red+yellow=orange, blue+yellow=green.",
+    "Think about which merge to do first — order matters."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world2/w2_level_07.json b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_07.json
new file mode 100644
index 0000000..ac792c1
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_07.json
@@ -0,0 +1,24 @@
+{
+  "id": "w2_07",
+  "world": 2,
+  "level": 7,
+  "title": "Inheritance",
+  "grid": { "width": 5, "height": 5 },
+  "blocks": [
+    { "x": 0, "y": 0, "color": "red" },
+    { "x": 0, "y": 4, "color": "blue" },
+    { "x": 4, "y": 1, "color": "purple" },
+    { "x": 4, "y": 3, "color": "purple" }
+  ],
+  "walls": [
+    { "x": 2, "y": 0 },
+    { "x": 2, "y": 4 }
+  ],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 4,
+  "hints": [
+    "You need to create two purple blocks to match the ones on the right.",
+    "The walls prevent a direct push — you'll need to reposition first."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world2/w2_level_08.json b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_08.json
new file mode 100644
index 0000000..7bda703
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_08.json
@@ -0,0 +1,26 @@
+{
+  "id": "w2_08",
+  "world": 2,
+  "level": 8,
+  "title": "Reflection",
+  "grid": { "width": 6, "height": 5 },
+  "blocks": [
+    { "x": 0, "y": 0, "color": "red" },
+    { "x": 5, "y": 0, "color": "yellow" },
+    { "x": 0, "y": 4, "color": "blue" },
+    { "x": 5, "y": 4, "color": "yellow" },
+    { "x": 3, "y": 2, "color": "orange" },
+    { "x": 1, "y": 2, "color": "green" }
+  ],
+  "walls": [
+    { "x": 2, "y": 1 },
+    { "x": 2, "y": 3 }
+  ],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 6,
+  "hints": [
+    "Orange comes from red+yellow. Green comes from blue+yellow.",
+    "The walls create lanes — use them to control where your blocks end up."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world2/w2_level_09.json b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_09.json
new file mode 100644
index 0000000..3e5f56e
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_09.json
@@ -0,0 +1,25 @@
+{
+  "id": "w2_09",
+  "world": 2,
+  "level": 9,
+  "title": "Cascade",
+  "grid": { "width": 6, "height": 5 },
+  "blocks": [
+    { "x": 0, "y": 0, "color": "blue" },
+    { "x": 5, "y": 0, "color": "yellow" },
+    { "x": 0, "y": 2, "color": "red" },
+    { "x": 5, "y": 2, "color": "blue" },
+    { "x": 3, "y": 4, "color": "purple" }
+  ],
+  "walls": [
+    { "x": 3, "y": 0 },
+    { "x": 3, "y": 1 }
+  ],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 5,
+  "hints": [
+    "One merge alone won't clear the board — you need to chain two merges.",
+    "Think about what color you need at the end, and work backwards."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world2/w2_level_10.json b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_10.json
new file mode 100644
index 0000000..e785063
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_10.json
@@ -0,0 +1,27 @@
+{
+  "id": "w2_10",
+  "world": 2,
+  "level": 10,
+  "title": "Chain Reaction",
+  "grid": { "width": 6, "height": 6 },
+  "blocks": [
+    { "x": 0, "y": 0, "color": "red" },
+    { "x": 5, "y": 0, "color": "blue" },
+    { "x": 0, "y": 5, "color": "red" },
+    { "x": 5, "y": 5, "color": "blue" },
+    { "x": 2, "y": 2, "color": "yellow" },
+    { "x": 3, "y": 4, "color": "orange" }
+  ],
+  "walls": [
+    { "x": 1, "y": 3 },
+    { "x": 4, "y": 2 }
+  ],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 7,
+  "hints": [
+    "You need to create two purple blocks to destroy each other.",
+    "The yellow block and the orange block also need to be cleared.",
+    "Work the corners first."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world2/w2_level_11.json b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_11.json
new file mode 100644
index 0000000..48951b9
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_11.json
@@ -0,0 +1,29 @@
+{
+  "id": "w2_11",
+  "world": 2,
+  "level": 11,
+  "title": "The Long Way",
+  "grid": { "width": 6, "height": 6 },
+  "blocks": [
+    { "x": 0, "y": 0, "color": "red" },
+    { "x": 5, "y": 0, "color": "yellow" },
+    { "x": 0, "y": 5, "color": "blue" },
+    { "x": 5, "y": 5, "color": "red" },
+    { "x": 2, "y": 3, "color": "orange" },
+    { "x": 4, "y": 2, "color": "purple" }
+  ],
+  "walls": [
+    { "x": 1, "y": 2 },
+    { "x": 3, "y": 0 },
+    { "x": 3, "y": 1 },
+    { "x": 1, "y": 4 },
+    { "x": 3, "y": 5 }
+  ],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 8,
+  "hints": [
+    "The walls create a maze. There's only one efficient path through.",
+    "You'll need to use every block — nothing is wasted in this layout."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Levels/world2/w2_level_12.json b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_12.json
new file mode 100644
index 0000000..f060012
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Levels/world2/w2_level_12.json
@@ -0,0 +1,33 @@
+{
+  "id": "w2_12",
+  "world": 2,
+  "level": 12,
+  "title": "Prism",
+  "grid": { "width": 6, "height": 6 },
+  "blocks": [
+    { "x": 0, "y": 0, "color": "red" },
+    { "x": 5, "y": 0, "color": "blue" },
+    { "x": 0, "y": 5, "color": "yellow" },
+    { "x": 5, "y": 2, "color": "red" },
+    { "x": 0, "y": 2, "color": "blue" },
+    { "x": 5, "y": 5, "color": "yellow" },
+    { "x": 2, "y": 1, "color": "purple" },
+    { "x": 3, "y": 4, "color": "orange" },
+    { "x": 1, "y": 4, "color": "green" }
+  ],
+  "walls": [
+    { "x": 2, "y": 0 },
+    { "x": 4, "y": 1 },
+    { "x": 1, "y": 3 },
+    { "x": 4, "y": 3 },
+    { "x": 2, "y": 5 }
+  ],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 9,
+  "hints": [
+    "All six colors are here. Every block has a partner.",
+    "The three pre-placed secondaries tell you which primary pairs to make.",
+    "Map out the full solution before your first move."
+  ]
+}
diff --git a/CollapseLogic/CollapseLogic/Models/Block.swift b/CollapseLogic/CollapseLogic/Models/Block.swift
new file mode 100644
index 0000000..c26f40e
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Models/Block.swift
@@ -0,0 +1,35 @@
+enum BlockColor: String, Codable, Hashable, CaseIterable {
+    // Primary (can merge)
+    case red
+    case blue
+    case yellow
+
+    // Secondary (result of merges)
+    case purple
+    case orange
+    case green
+
+    var isPrimary: Bool {
+        switch self {
+        case .red, .blue, .yellow: return true
+        case .purple, .orange, .green: return false
+        }
+    }
+
+    var displayHex: String {
+        switch self {
+        case .red:    return "#E63946"
+        case .blue:   return "#457B9D"
+        case .yellow: return "#F4D35E"
+        case .purple: return "#7B2D8B"
+        case .orange: return "#E76F51"
+        case .green:  return "#2A9D8F"
+        }
+    }
+}
+
+struct Block: Hashable, Equatable {
+    let id: Int          // stable index within original level; survives undo
+    let position: GridPosition
+    let color: BlockColor
+}
diff --git a/CollapseLogic/CollapseLogic/Models/Direction.swift b/CollapseLogic/CollapseLogic/Models/Direction.swift
new file mode 100644
index 0000000..dac746f
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Models/Direction.swift
@@ -0,0 +1,3 @@
+enum Direction: CaseIterable {
+    case up, down, left, right
+}
diff --git a/CollapseLogic/CollapseLogic/Models/GameState.swift b/CollapseLogic/CollapseLogic/Models/GameState.swift
new file mode 100644
index 0000000..0c62c64
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Models/GameState.swift
@@ -0,0 +1,100 @@
+// MARK: - Supporting types
+
+struct GridSize: Equatable {
+    let width: Int
+    let height: Int
+
+    func contains(_ pos: GridPosition) -> Bool {
+        pos.x >= 0 && pos.x < width && pos.y >= 0 && pos.y < height
+    }
+}
+
+enum ObjectiveType: Equatable {
+    case clearAll
+    case clearColor(BlockColor)
+    case reduceTo(Int)
+}
+
+// MARK: - GameState
+
+/// Immutable. Every move produces a new instance.
+struct GameState: Equatable {
+    let grid: GridSize
+    let blocks: [Block]
+    let walls: Set<GridPosition>
+    let moveCount: Int
+    let par: Int
+    let objective: ObjectiveType
+    /// World 2+ enables primary+primary merging into secondary colors. World 1 leaves
+    /// different-color collisions as a hard stop, matching the original mechanic.
+    let allowsMerging: Bool
+    /// Previous states for undo. Stored WITHOUT their own history to avoid memory explosion.
+    let history: [GameState]
+
+    // MARK: Derived helpers
+
+    var isWon: Bool {
+        switch objective {
+        case .clearAll:
+            return blocks.isEmpty
+        case .clearColor(let color):
+            return !blocks.contains(where: { $0.color == color })
+        case .reduceTo(let count):
+            return blocks.count <= count
+        }
+    }
+
+    func stars(for moveCount: Int) -> Int {
+        if moveCount <= par       { return 3 }
+        if moveCount <= par + 2   { return 2 }
+        return 1
+    }
+
+    var currentStars: Int { stars(for: moveCount) }
+
+    func block(at pos: GridPosition) -> Block? {
+        blocks.first(where: { $0.position == pos })
+    }
+
+    func isOccupied(_ pos: GridPosition) -> Bool {
+        walls.contains(pos) || blocks.contains(where: { $0.position == pos })
+    }
+
+    // MARK: State factory used by GameEngine
+
+    func withBlocks(_ newBlocks: [Block], incrementMove: Bool) -> GameState {
+        // Strip history from self before storing as a history entry
+        let stripped = GameState(
+            grid: grid, blocks: blocks, walls: walls,
+            moveCount: moveCount, par: par, objective: objective,
+            allowsMerging: allowsMerging, history: []
+        )
+        return GameState(
+            grid: grid,
+            blocks: newBlocks,
+            walls: walls,
+            moveCount: incrementMove ? moveCount + 1 : moveCount,
+            par: par,
+            objective: objective,
+            allowsMerging: allowsMerging,
+            history: history + [stripped]
+        )
+    }
+
+    // MARK: Undo
+
+    var canUndo: Bool { !history.isEmpty }
+
+    func undoState() -> GameState? {
+        guard var prev = history.last else { return nil }
+        // Restore the history slice that was current before this move
+        let newHistory = Array(history.dropLast())
+        prev = GameState(
+            grid: prev.grid, blocks: prev.blocks, walls: prev.walls,
+            moveCount: prev.moveCount, par: prev.par,
+            objective: prev.objective, allowsMerging: prev.allowsMerging,
+            history: newHistory
+        )
+        return prev
+    }
+}
diff --git a/CollapseLogic/CollapseLogic/Models/GridPosition.swift b/CollapseLogic/CollapseLogic/Models/GridPosition.swift
new file mode 100644
index 0000000..53fa377
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Models/GridPosition.swift
@@ -0,0 +1,13 @@
+struct GridPosition: Hashable, Equatable, Codable {
+    let x: Int
+    let y: Int
+
+    func offset(by direction: Direction) -> GridPosition {
+        switch direction {
+        case .up:    return GridPosition(x: x, y: y - 1)
+        case .down:  return GridPosition(x: x, y: y + 1)
+        case .left:  return GridPosition(x: x - 1, y: y)
+        case .right: return GridPosition(x: x + 1, y: y)
+        }
+    }
+}
diff --git a/CollapseLogic/CollapseLogic/Models/LevelDefinition.swift b/CollapseLogic/CollapseLogic/Models/LevelDefinition.swift
new file mode 100644
index 0000000..ff62377
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Models/LevelDefinition.swift
@@ -0,0 +1,51 @@
+// Codable structs mirroring the JSON level format
+
+struct GridSizeDef: Codable {
+    let width: Int
+    let height: Int
+}
+
+struct BlockDef: Codable {
+    let x: Int
+    let y: Int
+    let color: String
+}
+
+struct PositionDef: Codable {
+    let x: Int
+    let y: Int
+}
+
+struct ObjectiveDef: Codable {
+    let type: String
+    let color: String?
+    let count: Int?
+    let targets: [PositionDef]?
+}
+
+struct LevelDefinition: Codable {
+    let id: String
+    let world: Int
+    let level: Int
+    let title: String?
+    let grid: GridSizeDef
+    let blocks: [BlockDef]
+    let walls: [PositionDef]?
+    let specialTiles: [SpecialTileDef]?
+    let objective: ObjectiveDef
+    let par: Int
+    let hints: [String]?
+
+    enum CodingKeys: String, CodingKey {
+        case id, world, level, title, grid, blocks, walls
+        case specialTiles = "special_tiles"
+        case objective, par, hints
+    }
+}
+
+struct SpecialTileDef: Codable {
+    let x: Int
+    let y: Int
+    let type: String
+    // Additional fields ignored at MVP
+}
diff --git a/CollapseLogic/CollapseLogic/Models/MoveResult.swift b/CollapseLogic/CollapseLogic/Models/MoveResult.swift
new file mode 100644
index 0000000..fb54cf3
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Models/MoveResult.swift
@@ -0,0 +1,12 @@
+enum GameEvent {
+    case slid(blockIndex: Int, from: GridPosition, to: GridPosition)
+    case destroyed(blockIndex1: Int, blockIndex2: Int, at: GridPosition)
+    case merged(blockIndex1: Int, blockIndex2: Int, resultColor: BlockColor, at: GridPosition)
+}
+
+struct MoveResult {
+    let newState: GameState
+    let events: [GameEvent]
+    /// True when the move actually changed state (block moved)
+    var isValid: Bool { !events.isEmpty }
+}
diff --git a/CollapseLogic/CollapseLogic/Persistence/ProgressStore.swift b/CollapseLogic/CollapseLogic/Persistence/ProgressStore.swift
new file mode 100644
index 0000000..a679248
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Persistence/ProgressStore.swift
@@ -0,0 +1,47 @@
+import Foundation
+import Combine
+
+final class ProgressStore: ObservableObject {
+    static let shared = ProgressStore()
+    private let defaults = UserDefaults.standard
+    private init() {}
+
+    /// Bumped whenever stored progress changes. SwiftUI views that observe
+    /// this store re-render automatically; the actual reads still go through
+    /// the existing methods.
+    @Published private(set) var version: Int = 0
+
+    // MARK: - Keys
+
+    private func starsKey(for levelId: String) -> String { "stars_\(levelId)" }
+    private func completedKey(for levelId: String) -> String { "completed_\(levelId)" }
+
+    // MARK: - API
+
+    func starsFor(levelId: String) -> Int {
+        defaults.integer(forKey: starsKey(for: levelId))   // returns 0 if missing
+    }
+
+    func setStars(_ stars: Int, for levelId: String) {
+        let clamped = max(0, min(3, stars))
+        // Only upgrade, never downgrade
+        if clamped > starsFor(levelId: levelId) {
+            defaults.set(clamped, forKey: starsKey(for: levelId))
+            defaults.set(true, forKey: completedKey(for: levelId))
+            version &+= 1
+        }
+    }
+
+    func isCompleted(levelId: String) -> Bool {
+        defaults.bool(forKey: completedKey(for: levelId))
+    }
+
+    func totalStars() -> Int {
+        // Sum all stored star keys
+        defaults.dictionaryRepresentation()
+            .filter { $0.key.hasPrefix("stars_") }
+            .values
+            .compactMap { $0 as? Int }
+            .reduce(0, +)
+    }
+}
diff --git a/CollapseLogic/CollapseLogic/Resources/SFX/complete.mp3 b/CollapseLogic/CollapseLogic/Resources/SFX/complete.mp3
new file mode 100644
index 0000000..7ac07c9
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diff --git a/CollapseLogic/CollapseLogic/Resources/SFX/destroy.mp3 b/CollapseLogic/CollapseLogic/Resources/SFX/destroy.mp3
new file mode 100644
index 0000000..6c8d603
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diff --git a/CollapseLogic/CollapseLogic/Resources/SFX/merge.wav b/CollapseLogic/CollapseLogic/Resources/SFX/merge.wav
new file mode 100644
index 0000000..e69de29
diff --git a/CollapseLogic/CollapseLogic/Resources/SFX/select.mp3 b/CollapseLogic/CollapseLogic/Resources/SFX/select.mp3
new file mode 100644
index 0000000..4ba5841
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diff --git a/CollapseLogic/CollapseLogic/Resources/SFX/slide.mp3 b/CollapseLogic/CollapseLogic/Resources/SFX/slide.mp3
new file mode 100644
index 0000000..9bca655
Binary files /dev/null and b/CollapseLogic/CollapseLogic/Resources/SFX/slide.mp3 differ
diff --git a/CollapseLogic/CollapseLogic/Scene/BlockNode.swift b/CollapseLogic/CollapseLogic/Scene/BlockNode.swift
new file mode 100644
index 0000000..9d2bbba
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Scene/BlockNode.swift
@@ -0,0 +1,134 @@
+import SpriteKit
+
+// MARK: - Colors
+
+extension BlockColor {
+    var uiColor: UIColor {
+        switch self {
+        case .red:    return UIColor(hex: "#E63946")
+        case .blue:   return UIColor(hex: "#457B9D")
+        case .yellow: return UIColor(hex: "#F4D35E")
+        case .purple: return UIColor(hex: "#7B2D8B")
+        case .orange: return UIColor(hex: "#E76F51")
+        case .green:  return UIColor(hex: "#2A9D8F")
+        }
+    }
+}
+
+extension UIColor {
+    convenience init(hex: String) {
+        let h = hex.trimmingCharacters(in: CharacterSet.alphanumerics.inverted)
+        var val: UInt64 = 0
+        Scanner(string: h).scanHexInt64(&val)
+        self.init(
+            red:   CGFloat((val >> 16) & 0xFF) / 255,
+            green: CGFloat((val >> 8)  & 0xFF) / 255,
+            blue:  CGFloat(val & 0xFF)          / 255,
+            alpha: 1
+        )
+    }
+}
+
+// MARK: - BlockNode
+
+final class BlockNode: SKShapeNode {
+
+    let block: Block
+    private var selectionRing: SKShapeNode?
+
+    init(block: Block, cellSize: CGFloat) {
+        self.block = block
+        super.init()
+
+        let size = cellSize * 0.82
+        let rect = CGRect(x: -size / 2, y: -size / 2, width: size, height: size)
+        path = UIBezierPath(roundedRect: rect, cornerRadius: size * 0.18).cgPath
+
+        fillColor   = block.color.uiColor
+        strokeColor = block.color.uiColor.darker(by: 0.25)
+        lineWidth   = 1.5
+        zPosition   = 10
+        name        = "block_\(block.id)"
+
+        // Secondary blocks get a white inner ring to distinguish them from primaries
+        if !block.color.isPrimary {
+            let inset = size - 8
+            let innerRect = CGRect(x: -inset / 2, y: -inset / 2, width: inset, height: inset)
+            let ring = SKShapeNode(path: UIBezierPath(roundedRect: innerRect, cornerRadius: size * 0.18 - 2).cgPath)
+            ring.fillColor = .clear
+            ring.strokeColor = SKColor.white.withAlphaComponent(0.4)
+            ring.lineWidth = 2
+            ring.zPosition = 1
+            addChild(ring)
+        }
+    }
+
+    required init?(coder aDecoder: NSCoder) { fatalError() }
+
+    // MARK: Selection
+
+    func setSelected(_ selected: Bool, cellSize: CGFloat) {
+        selectionRing?.removeFromParent()
+        selectionRing = nil
+        guard selected else { return }
+
+        let size = cellSize * 0.86
+        let rect = CGRect(x: -size / 2, y: -size / 2, width: size, height: size)
+        let ring = SKShapeNode(path: UIBezierPath(roundedRect: rect, cornerRadius: size * 0.18).cgPath)
+        ring.fillColor   = .clear
+        ring.strokeColor = .white
+        ring.lineWidth   = 2
+        ring.zPosition   = 11
+        ring.name        = "selectionRing"
+
+        let pulse = SKAction.sequence([
+            SKAction.fadeAlpha(to: 0.4, duration: 0.5),
+            SKAction.fadeAlpha(to: 1.0, duration: 0.5)
+        ])
+        ring.run(SKAction.repeatForever(pulse))
+        addChild(ring)
+        self.selectionRing = ring
+    }
+
+    // MARK: Destruction animation
+
+    func animateDestruction(completion: @escaping () -> Void) {
+        let shrink = SKAction.scale(to: 0.1, duration: 0.18)
+        let fade   = SKAction.fadeOut(withDuration: 0.18)
+        let group  = SKAction.group([shrink, fade])
+        run(group) { completion() }
+
+        // Particle burst — simple coloured circles
+        for _ in 0..<6 {
+            let dot = SKShapeNode(circleOfRadius: 4)
+            dot.fillColor   = fillColor
+            dot.strokeColor = .clear
+            dot.zPosition   = 12
+            parent?.addChild(dot)
+            dot.position = position
+
+            let angle = CGFloat.random(in: 0 ..< .pi * 2)
+            let dist  = CGFloat.random(in: 20 ... 45)
+            let dx = cos(angle) * dist
+            let dy = sin(angle) * dist
+            dot.run(SKAction.sequence([
+                SKAction.group([
+                    SKAction.moveBy(x: dx, y: dy, duration: 0.22),
+                    SKAction.fadeOut(withDuration: 0.22)
+                ]),
+                SKAction.removeFromParent()
+            ]))
+        }
+    }
+}
+
+// MARK: - SKColor helper
+
+private extension UIColor {
+    func darker(by factor: CGFloat) -> UIColor {
+        var r: CGFloat = 0, g: CGFloat = 0, b: CGFloat = 0, a: CGFloat = 0
+        getRed(&r, green: &g, blue: &b, alpha: &a)
+        return UIColor(red: max(0, r - factor), green: max(0, g - factor),
+                       blue: max(0, b - factor), alpha: a)
+    }
+}
diff --git a/CollapseLogic/CollapseLogic/Scene/GameScene.swift b/CollapseLogic/CollapseLogic/Scene/GameScene.swift
new file mode 100644
index 0000000..b2676cf
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Scene/GameScene.swift
@@ -0,0 +1,308 @@
+import SpriteKit
+
+// MARK: - Delegate
+
+protocol GameSceneDelegate: AnyObject {
+    func gameSceneDidWin(moveCount: Int, stars: Int)
+    func gameSceneDidUpdateMoveCount(_ count: Int)
+}
+
+// MARK: - GameScene
+
+final class GameScene: SKScene {
+
+    // MARK: State
+    var gameState: GameState {
+        didSet { syncBlockNodes() }
+    }
+    private var renderer: GridRenderer!
+    private var blockNodes: [Int: BlockNode] = [:]   // keyed by Block.id
+    private var selectedBlockIndex: Int? = nil
+    private var isAnimating = false
+    weak var sceneDelegate: GameSceneDelegate?
+
+    // MARK: Init
+
+    init(state: GameState, size: CGSize) {
+        self.gameState = state
+        super.init(size: size)
+        scaleMode = .resizeFill
+        backgroundColor = UIColor(hex: "#1A1A2E")
+    }
+
+    required init?(coder aDecoder: NSCoder) { fatalError() }
+
+    // MARK: - Scene lifecycle
+
+    override func didMove(to view: SKView) {
+        renderer = GridRenderer(gridSize: gameState.grid, sceneSize: size)
+        addChild(renderer.buildBackground())
+        addChild(renderer.buildWalls(gameState.walls))
+        rebuildAllBlockNodes()
+        setupGestures(in: view)
+        SFXRunner.shared.attach(to: self)
+    }
+
+    // MARK: - Input
+
+    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
+        guard !isAnimating, let touch = touches.first else { return }
+        let loc = touch.location(in: self)
+
+        // Check if a block was tapped
+        if let blockNode = nodes(at: loc).compactMap({ $0 as? BlockNode }).first {
+            let idx = gameState.blocks.firstIndex(where: { $0.id == blockNode.block.id })
+            selectBlock(at: idx)
+            SFXManager.shared.play(.select)
+        }
+    }
+
+    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
+        // Handled by swipe detection below
+    }
+
+    private var swipeStart: CGPoint?
+
+    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
+        guard let touch = touches.first else { return }
+        if swipeStart == nil { swipeStart = touch.previousLocation(in: self) }
+    }
+
+    // We use a single recognizer-style approach: track start on touchesBegan
+    // and compute direction on touchesEnded for the selected block.
+
+    // MARK: - Swipe detection via UISwipeGestureRecognizer (added in didMove)
+
+    func setupGestures(in view: SKView) {
+        for dir in [UISwipeGestureRecognizer.Direction.up,
+                    .down, .left, .right] {
+            let rec = UISwipeGestureRecognizer(target: self,
+                                               action: #selector(handleSwipe(_:)))
+            rec.direction = dir
+            view.addGestureRecognizer(rec)
+        }
+    }
+
+    @objc private func handleSwipe(_ rec: UISwipeGestureRecognizer) {
+        guard !isAnimating, let idx = selectedBlockIndex else { return }
+        let direction: Direction
+        switch rec.direction {
+        case .up:    direction = .up
+        case .down:  direction = .down
+        case .left:  direction = .left
+        case .right: direction = .right
+        default:     return
+        }
+        applyMove(blockIndex: idx, direction: direction)
+    }
+
+    // MARK: - Move application
+
+    func applyMove(blockIndex: Int, direction: Direction) {
+        guard !isAnimating else { return }
+        let result = GameEngine.processMove(state: gameState, blockIndex: blockIndex,
+                                            direction: direction)
+        guard result.isValid else { return }
+
+        isAnimating = true
+        selectedBlockIndex = nil
+        deselectAll()
+
+        animateEvents(result.events, newState: result.newState) { [weak self] in
+            guard let self else { return }
+            self.gameState  = result.newState
+            self.isAnimating = false
+            self.sceneDelegate?.gameSceneDidUpdateMoveCount(result.newState.moveCount)
+            if result.newState.isWon {
+                SFXManager.shared.play(.complete)
+                self.sceneDelegate?.gameSceneDidWin(
+                    moveCount: result.newState.moveCount,
+                    stars: result.newState.currentStars
+                )
+            }
+        }
+    }
+
+    func applyUndo() {
+        guard !isAnimating else { return }
+        let prev = GameEngine.undo(state: gameState)
+        guard prev.moveCount != gameState.moveCount || prev.blocks.count != gameState.blocks.count else { return }
+        gameState = prev
+        sceneDelegate?.gameSceneDidUpdateMoveCount(prev.moveCount)
+    }
+
+    func applyRestart(initialState: GameState) {
+        guard !isAnimating else { return }
+        gameState = initialState
+        sceneDelegate?.gameSceneDidUpdateMoveCount(0)
+    }
+
+    // MARK: - Animation
+
+    private func animateEvents(_ events: [GameEvent], newState: GameState,
+                               completion: @escaping () -> Void) {
+        var remaining = events.count
+        guard remaining > 0 else { completion(); return }
+
+        let done = {
+            remaining -= 1
+            if remaining == 0 { completion() }
+        }
+
+        for event in events {
+            switch event {
+            case .slid(let blockIndex, _, let to):
+                guard let block = gameState.blocks.indices.contains(blockIndex)
+                        ? gameState.blocks[blockIndex] : nil,
+                      let node = blockNodes[block.id] else { done(); continue }
+
+                let dest = renderer.scenePosition(for: to)
+                SFXManager.shared.play(.slide)
+                node.run(SKAction.move(to: dest, duration: 0.15).ease(.easeOut)) { done() }
+
+            case .destroyed(let idx1, let idx2, _):
+                // Both nodes are still at their pre-move positions; animate the slid one
+                // (already handled in .slid), then destroy both
+                let ids = [idx1, idx2].compactMap { i -> Int? in
+                    guard gameState.blocks.indices.contains(i) else { return nil }
+                    return gameState.blocks[i].id
+                }
+                SFXManager.shared.play(.destroy)
+                var destroyRemaining = ids.count
+                for id in ids {
+                    guard let node = blockNodes[id] else {
+                        destroyRemaining -= 1
+                        continue
+                    }
+                    node.animateDestruction {
+                        node.removeFromParent()
+                        destroyRemaining -= 1
+                        if destroyRemaining == 0 { done() }
+                    }
+                }
+                if ids.isEmpty { done() }
+
+            case .merged(let idx1, let idx2, let resultColor, let position):
+                // Look up both source block nodes (indices reference the OLD state)
+                let ids = [idx1, idx2].compactMap { i -> Int? in
+                    guard gameState.blocks.indices.contains(i) else { return nil }
+                    return gameState.blocks[i].id
+                }
+
+                // The engine assigns the merged block the stationary block's id.
+                // Look it up in the new state so the sprite, the model block, and
+                // the blockNodes dict all agree on the same id.
+                let mergedId = newState.blocks.first(where: { $0.position == position })?.id ?? -1
+
+                // Burst: scale up 1.2×, then shrink + fade out, then remove
+                let burstUp   = SKAction.scale(to: 1.2, duration: 0.1)
+                let burstOut  = SKAction.group([
+                    SKAction.scale(to: 0.0, duration: 0.1),
+                    SKAction.fadeOut(withDuration: 0.1)
+                ])
+                let burstSeq  = SKAction.sequence([burstUp, burstOut, SKAction.removeFromParent()])
+
+                var burstCount = ids.count
+                let spawnMergedBlock = { [weak self] in
+                    guard let self else { return }
+                    // Source nodes were removed from the scene tree by burstSeq;
+                    // drop their dict entries so syncBlockNodes/selection stay consistent.
+                    for id in ids { self.blockNodes.removeValue(forKey: id) }
+
+                    let mergedBlock = Block(id: mergedId, position: position, color: resultColor)
+                    let node = BlockNode(block: mergedBlock, cellSize: self.renderer.cellSize)
+                    node.position = self.renderer.scenePosition(for: position)
+                    node.setScale(0.0)
+                    self.addChild(node)
+                    self.blockNodes[mergedId] = node
+                    // Spring pop: 0 → 1.15 → 1.0
+                    let spring = SKAction.sequence([
+                        SKAction.scale(to: 1.15, duration: 0.12),
+                        SKAction.scale(to: 1.0, duration: 0.05)
+                    ])
+                    node.run(spring) { done() }
+                }
+
+                SFXManager.shared.play(.merge)
+
+                if ids.isEmpty {
+                    spawnMergedBlock()
+                } else {
+                    for id in ids {
+                        guard let node = blockNodes[id] else {
+                            burstCount -= 1
+                            if burstCount == 0 { spawnMergedBlock() }
+                            continue
+                        }
+                        node.run(burstSeq) {
+                            burstCount -= 1
+                            if burstCount == 0 { spawnMergedBlock() }
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    // MARK: - Node management
+
+    private func rebuildAllBlockNodes() {
+        blockNodes.values.forEach { $0.removeFromParent() }
+        blockNodes = [:]
+        for (idx, block) in gameState.blocks.enumerated() {
+            addBlockNode(block: block, at: block.position)
+            _ = idx
+        }
+    }
+
+    private func addBlockNode(block: Block, at pos: GridPosition) {
+        let node = BlockNode(block: block, cellSize: renderer.cellSize)
+        node.position = renderer.scenePosition(for: pos)
+        addChild(node)
+        blockNodes[block.id] = node
+    }
+
+    /// Called after state changes NOT driven by animation (undo/restart)
+    private func syncBlockNodes() {
+        // Remove nodes for blocks no longer in state
+        let liveIds = Set(gameState.blocks.map { $0.id })
+        for (id, node) in blockNodes where !liveIds.contains(id) {
+            node.removeFromParent()
+            blockNodes.removeValue(forKey: id)
+        }
+        // Update existing or add new
+        for block in gameState.blocks {
+            if let node = blockNodes[block.id] {
+                node.position = renderer.scenePosition(for: block.position)
+            } else {
+                addBlockNode(block: block, at: block.position)
+            }
+        }
+    }
+
+    // MARK: - Selection
+
+    private func selectBlock(at index: Int?) {
+        deselectAll()
+        selectedBlockIndex = index
+        guard let idx = index,
+              gameState.blocks.indices.contains(idx) else { return }
+        let block = gameState.blocks[idx]
+        blockNodes[block.id]?.setSelected(true, cellSize: renderer.cellSize)
+    }
+
+    private func deselectAll() {
+        for node in blockNodes.values {
+            node.setSelected(false, cellSize: renderer.cellSize)
+        }
+    }
+}
+
+// MARK: - SKAction ease helper
+
+private extension SKAction {
+    func ease(_ timing: SKActionTimingMode) -> SKAction {
+        timingMode = timing
+        return self
+    }
+}
diff --git a/CollapseLogic/CollapseLogic/Scene/GridRenderer.swift b/CollapseLogic/CollapseLogic/Scene/GridRenderer.swift
new file mode 100644
index 0000000..b6e2d9e
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Scene/GridRenderer.swift
@@ -0,0 +1,104 @@
+import SpriteKit
+
+final class GridRenderer {
+
+    private let gridSize: GridSize
+    let cellSize: CGFloat
+    let gridOrigin: CGPoint  // bottom-left corner in scene coordinates
+
+    // MARK: - Init
+
+    init(gridSize: GridSize, sceneSize: CGSize) {
+        self.gridSize = gridSize
+
+        // Fill ~85% of screen width
+        let targetWidth = sceneSize.width * 0.85
+        cellSize = floor(targetWidth / CGFloat(gridSize.width))
+
+        let totalW = cellSize * CGFloat(gridSize.width)
+        let totalH = cellSize * CGFloat(gridSize.height)
+        gridOrigin = CGPoint(
+            x: (sceneSize.width  - totalW) / 2,
+            y: (sceneSize.height - totalH) / 2
+        )
+    }
+
+    // MARK: - Build nodes
+
+    func buildBackground() -> SKNode {
+        let root = SKNode()
+        root.zPosition = 0
+
+        // Grid background
+        let totalW = cellSize * CGFloat(gridSize.width)
+        let totalH = cellSize * CGFloat(gridSize.height)
+        let bg = SKShapeNode(rect: CGRect(origin: .zero, size: CGSize(width: totalW, height: totalH)), cornerRadius: 8)
+        bg.fillColor   = UIColor(hex: "#1A1A2E")
+        bg.strokeColor = .clear
+        bg.position    = .zero
+        bg.zPosition   = 0
+        root.addChild(bg)
+
+        // Grid lines
+        let lineColor = UIColor(hex: "#2A2A3E")
+        for col in 0...gridSize.width {
+            let x = CGFloat(col) * cellSize
+            let line = SKShapeNode()
+            let path = CGMutablePath()
+            path.move(to: CGPoint(x: x, y: 0))
+            path.addLine(to: CGPoint(x: x, y: totalH))
+            line.path        = path
+            line.strokeColor = lineColor
+            line.lineWidth   = 1
+            line.zPosition   = 1
+            root.addChild(line)
+        }
+        for row in 0...gridSize.height {
+            let y = CGFloat(row) * cellSize
+            let line = SKShapeNode()
+            let path = CGMutablePath()
+            path.move(to: CGPoint(x: 0, y: y))
+            path.addLine(to: CGPoint(x: totalW, y: y))
+            line.path        = path
+            line.strokeColor = lineColor
+            line.lineWidth   = 1
+            line.zPosition   = 1
+            root.addChild(line)
+        }
+
+        root.position = gridOrigin
+        return root
+    }
+
+    func buildWalls(_ walls: Set<GridPosition>) -> SKNode {
+        let root = SKNode()
+        root.zPosition = 2
+        root.position  = gridOrigin
+
+        for wall in walls {
+            let size = cellSize * 0.9
+            let rect = CGRect(x: -size / 2, y: -size / 2, width: size, height: size)
+            let node = SKShapeNode(path: UIBezierPath(roundedRect: rect, cornerRadius: 4).cgPath)
+            node.fillColor   = UIColor(hex: "#2A2A3E")
+            node.strokeColor = UIColor(hex: "#3A3A4E")
+            node.lineWidth   = 1
+            node.position    = scenePosition(for: wall)
+            // position is relative to gridOrigin, so subtract it
+            node.position    = CGPoint(
+                x: node.position.x - gridOrigin.x,
+                y: node.position.y - gridOrigin.y
+            )
+            root.addChild(node)
+        }
+        return root
+    }
+
+    // MARK: - Coordinate helpers
+
+    /// Convert grid position → scene coordinates (with Y-flip)
+    func scenePosition(for pos: GridPosition) -> CGPoint {
+        let spriteY = CGFloat(gridSize.height - 1 - pos.y) * cellSize + cellSize / 2
+        let spriteX = CGFloat(pos.x) * cellSize + cellSize / 2
+        return CGPoint(x: gridOrigin.x + spriteX, y: gridOrigin.y + spriteY)
+    }
+}
diff --git a/CollapseLogic/CollapseLogic/Views/GameContainerView.swift b/CollapseLogic/CollapseLogic/Views/GameContainerView.swift
new file mode 100644
index 0000000..665e707
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Views/GameContainerView.swift
@@ -0,0 +1,214 @@
+import SwiftUI
+import SpriteKit
+import Combine
+
+// MARK: - Observable game bridge (class so SwiftUI can observe it)
+
+@MainActor
+final class GameBridge: ObservableObject, GameSceneDelegate {
+    @Published var moveCount = 0
+    @Published var showWin = false
+    @Published var winStars = 0
+
+    func gameSceneDidUpdateMoveCount(_ count: Int) {
+        moveCount = count
+    }
+
+    func gameSceneDidWin(moveCount: Int, stars: Int) {
+        self.moveCount = moveCount
+        self.winStars  = stars
+        showWin        = true
+    }
+}
+
+// MARK: - GameContainerView
+
+struct GameContainerView: View {
+    let levelId: String
+    let levelNumber: Int
+    let worldNumber: Int
+    let onDismiss: () -> Void
+
+    @StateObject private var bridge = GameBridge()
+    @State private var gameScene: GameScene?
+    @State private var initialState: GameState?
+    @State private var par = 0
+    @State private var loadError: String?
+
+    var body: some View {
+        ZStack {
+            Color(hex: "#1A1A2E").ignoresSafeArea()
+
+            if let error = loadError {
+                VStack(spacing: 12) {
+                    Text("Load Error")
+                        .font(.system(size: 20, weight: .bold))
+                        .foregroundColor(.red)
+                    Text(error)
+                        .font(.system(size: 14, design: .monospaced))
+                        .foregroundColor(.white)
+                        .multilineTextAlignment(.center)
+                    Button("Back") { onDismiss() }
+                        .foregroundColor(.red)
+                }
+                .padding()
+            } else if let scene = gameScene {
+                SpriteView(scene: scene)
+                    .ignoresSafeArea()
+
+                VStack {
+                    topHUD
+                    Spacer()
+                    bottomHUD
+                }
+            }
+        }
+        .onAppear { loadLevel() }
+        .sheet(isPresented: $bridge.showWin) {
+            WinSheet(stars: bridge.winStars, moveCount: bridge.moveCount, par: par) {
+                ProgressStore.shared.setStars(bridge.winStars, for: levelId)
+                bridge.showWin = false
+                onDismiss()
+            }
+        }
+    }
+
+    // MARK: HUD
+
+    private var topHUD: some View {
+        HStack {
+            Button { onDismiss() } label: {
+                Image(systemName: "xmark")
+                    .font(.system(size: 16, weight: .bold))
+                    .foregroundColor(.white.opacity(0.7))
+                    .frame(width: 36, height: 36)
+                    .background(Color.white.opacity(0.1))
+                    .clipShape(Circle())
+            }
+            Spacer()
+            VStack(spacing: 2) {
+                Text("Level \(levelNumber)")
+                    .font(.system(size: 13, weight: .semibold, design: .rounded))
+                    .foregroundColor(.white.opacity(0.5))
+                Text("Moves: \(bridge.moveCount)  /  Par: \(par)")
+                    .font(.system(size: 15, weight: .bold, design: .monospaced))
+                    .foregroundColor(.white)
+            }
+            Spacer()
+            Color.clear.frame(width: 36, height: 36)
+        }
+        .padding(.horizontal, 20)
+        .padding(.top, 12)
+    }
+
+    private var bottomHUD: some View {
+        HStack(spacing: 24) {
+            HUDButton(icon: "arrow.uturn.backward", label: "Undo") {
+                gameScene?.applyUndo()
+            }
+            HUDButton(icon: "arrow.counterclockwise", label: "Restart") {
+                if let s = initialState { gameScene?.applyRestart(initialState: s) }
+            }
+            HUDButton(icon: "line.3.horizontal", label: "Menu") {
+                onDismiss()
+            }
+        }
+        .padding(.bottom, 36)
+    }
+
+    // MARK: Load
+
+    private func loadLevel() {
+        let filename = "level_\(String(format: "%02d", levelNumber))"
+        do {
+            let state = try LevelLoader.load(levelId: filename, world: worldNumber)
+            initialState = state
+            par          = state.par
+            // Use a placeholder size; GameScene recalculates cell layout in didMove(to:)
+            // where it has the actual SKView bounds via self.size (set by scaleMode = .resizeFill)
+            let scene    = GameScene(state: state, size: CGSize(width: 390, height: 844))
+            scene.sceneDelegate = bridge
+            gameScene    = scene
+        } catch {
+            loadError = error.localizedDescription
+        }
+    }
+}
+
+// MARK: - Win Sheet
+
+private struct WinSheet: View {
+    let stars: Int
+    let moveCount: Int
+    let par: Int
+    let onContinue: () -> Void
+
+    var body: some View {
+        ZStack {
+            Color(hex: "#1A1A2E").ignoresSafeArea()
+            VStack(spacing: 28) {
+                Text("Level Complete!")
+                    .font(.system(size: 28, weight: .black, design: .rounded))
+                    .foregroundColor(.white)
+                HStack(spacing: 12) {
+                    ForEach(0..<3, id: \.self) { i in
+                        Text(i < stars ? "★" : "☆")
+                            .font(.system(size: 40))
+                            .foregroundColor(i < stars ? Color(hex: "#F4D35E") : .white.opacity(0.3))
+                    }
+                }
+                Text("\(moveCount) moves  ·  Par: \(par)")
+                    .font(.system(size: 15, design: .monospaced))
+                    .foregroundColor(.white.opacity(0.5))
+                Button(action: onContinue) {
+                    Text("Continue")
+                        .font(.system(size: 18, weight: .bold, design: .rounded))
+                        .foregroundColor(.white)
+                        .frame(width: 180, height: 52)
+                        .background(Color(hex: "#E63946"))
+                        .clipShape(RoundedRectangle(cornerRadius: 14))
+                }
+            }
+            .padding(40)
+        }
+        .presentationDetents([.fraction(0.45)])
+    }
+}
+
+// MARK: - HUD Button
+
+private struct HUDButton: View {
+    let icon: String
+    let label: String
+    let action: () -> Void
+
+    var body: some View {
+        Button(action: action) {
+            VStack(spacing: 4) {
+                Image(systemName: icon)
+                    .font(.system(size: 20, weight: .medium))
+                Text(label)
+                    .font(.system(size: 11, design: .rounded))
+            }
+            .foregroundColor(.white.opacity(0.8))
+            .frame(width: 64, height: 64)
+            .background(Color.white.opacity(0.08))
+            .clipShape(RoundedRectangle(cornerRadius: 14))
+        }
+    }
+}
+
+// MARK: - Color(hex:) for SwiftUI
+
+extension Color {
+    init(hex: String) {
+        let h = hex.trimmingCharacters(in: CharacterSet.alphanumerics.inverted)
+        var val: UInt64 = 0
+        Scanner(string: h).scanHexInt64(&val)
+        self.init(
+            red:   Double((val >> 16) & 0xFF) / 255,
+            green: Double((val >> 8)  & 0xFF) / 255,
+            blue:  Double(val & 0xFF)          / 255
+        )
+    }
+}
diff --git a/CollapseLogic/CollapseLogic/Views/LevelSelectView.swift b/CollapseLogic/CollapseLogic/Views/LevelSelectView.swift
new file mode 100644
index 0000000..8c24fdb
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Views/LevelSelectView.swift
@@ -0,0 +1,166 @@
+import SwiftUI
+
+struct LevelSelectView: View {
+    @Environment(\.dismiss) private var dismiss
+    @ObservedObject private var progress = ProgressStore.shared
+    @State private var selectedLevel: LevelEntry? = nil
+    @State private var selectedWorld: Int = 1
+
+    private struct LevelEntry: Identifiable {
+        let id: String
+        let number: Int
+        let title: String
+        let file: String
+        let world: Int
+    }
+
+    // MARK: - World 2 unlock condition
+
+    private var world2Unlocked: Bool {
+        ProgressStore.shared.totalStars() >= 15
+    }
+
+    private var worlds: [WorldMeta] {
+        LevelLoader.loadMetadata()?.worlds ?? []
+    }
+
+    private var currentWorld: WorldMeta? {
+        worlds.first(where: { $0.id == selectedWorld })
+    }
+
+    private var levels: [LevelEntry] {
+        guard let world = currentWorld else { return [] }
+        return world.levels.enumerated().map { idx, l in
+            LevelEntry(id: l.id, number: idx + 1, title: l.title, file: l.file, world: world.id)
+        }
+    }
+
+    private let columns = [GridItem(.adaptive(minimum: 80), spacing: 12)]
+
+    var body: some View {
+        NavigationView {
+            ZStack {
+                Color(hex: "#1A1A2E").ignoresSafeArea()
+
+                VStack(spacing: 0) {
+                    worldSelector
+                        .padding(.horizontal, 20)
+                        .padding(.top, 12)
+                        .padding(.bottom, 4)
+
+                    ScrollView {
+                        LazyVGrid(columns: columns, spacing: 12) {
+                            ForEach(levels) { entry in
+                                LevelCell(entry: entry) {
+                                    selectedLevel = entry
+                                }
+                            }
+                        }
+                        .padding(20)
+                    }
+                }
+            }
+            .navigationTitle(currentWorld.map { "\($0.name)" } ?? "Levels")
+            .navigationBarTitleDisplayMode(.inline)
+            .toolbar {
+                ToolbarItem(placement: .navigationBarLeading) {
+                    Button("Back") { dismiss() }
+                        .foregroundColor(Color(hex: "#E63946"))
+                }
+            }
+        }
+        .preferredColorScheme(.dark)
+        .fullScreenCover(item: $selectedLevel) { entry in
+            GameContainerView(levelId: entry.id, levelNumber: entry.number,
+                              worldNumber: entry.world) {
+                selectedLevel = nil
+            }
+        }
+    }
+
+    // MARK: - World Selector
+
+    private var worldSelector: some View {
+        HStack(spacing: 10) {
+            ForEach(worlds, id: \.id) { world in
+                let isSelected = selectedWorld == world.id
+                let isLocked = world.id == 2 && !world2Unlocked
+
+                Button {
+                    if !isLocked {
+                        selectedWorld = world.id
+                    }
+                } label: {
+                    HStack(spacing: 6) {
+                        if isLocked {
+                            Image(systemName: "lock.fill")
+                                .font(.system(size: 11))
+                        }
+                        Text(world.name)
+                            .font(.system(size: 14, weight: .semibold, design: .rounded))
+                        if isLocked {
+                            Text("15 \u{2605}")
+                                .font(.system(size: 11, weight: .medium, design: .rounded))
+                        }
+                    }
+                    .foregroundColor(isLocked ? .white.opacity(0.35) : isSelected ? .white : .white.opacity(0.6))
+                    .padding(.horizontal, 16)
+                    .padding(.vertical, 8)
+                    .background(
+                        Capsule().fill(
+                            isSelected ? Color(hex: "#E63946") :
+                            isLocked ? Color.white.opacity(0.05) :
+                            Color(hex: "#2A2A4E")
+                        )
+                    )
+                    .overlay(
+                        Capsule().stroke(
+                            isSelected ? Color.clear :
+                            isLocked ? Color.white.opacity(0.08) :
+                            Color.white.opacity(0.12),
+                            lineWidth: 1
+                        )
+                    )
+                    .opacity(isLocked ? 0.4 : 1.0)
+                }
+                .disabled(isLocked)
+            }
+        }
+    }
+
+    // MARK: - Level Cell
+
+    private struct LevelCell: View {
+        let entry: LevelEntry
+        let action: () -> Void
+
+        var body: some View {
+            let stars = ProgressStore.shared.starsFor(levelId: entry.id)
+            let completed = ProgressStore.shared.isCompleted(levelId: entry.id)
+
+            Button(action: action) {
+                VStack(spacing: 6) {
+                    Text("\(entry.number)")
+                        .font(.system(size: 22, weight: .bold, design: .rounded))
+                        .foregroundColor(completed ? .white : .white.opacity(0.6))
+
+                    HStack(spacing: 2) {
+                        ForEach(0..<3, id: \.self) { i in
+                            Text("\u{2605}")
+                                .font(.system(size: 10))
+                                .foregroundColor(i < stars ? Color(hex: "#F4D35E") : .white.opacity(0.2))
+                        }
+                    }
+                }
+                .frame(width: 80, height: 80)
+                .background(Color(hex: completed ? "#2A2A4E" : "#1E1E38"))
+                .clipShape(RoundedRectangle(cornerRadius: 14))
+                .overlay(
+                    RoundedRectangle(cornerRadius: 14)
+                        .stroke(completed ? Color(hex: "#457B9D") : Color.white.opacity(0.08),
+                                lineWidth: 1)
+                )
+            }
+        }
+    }
+}
diff --git a/CollapseLogic/CollapseLogic/Views/MainMenuView.swift b/CollapseLogic/CollapseLogic/Views/MainMenuView.swift
new file mode 100644
index 0000000..2287a49
--- /dev/null
+++ b/CollapseLogic/CollapseLogic/Views/MainMenuView.swift
@@ -0,0 +1,55 @@
+import SwiftUI
+
+struct MainMenuView: View {
+    @ObservedObject private var progress = ProgressStore.shared
+    @State private var showLevelSelect = false
+
+    var body: some View {
+        ZStack {
+            Color(hex: "#1A1A2E").ignoresSafeArea()
+
+            VStack(spacing: 40) {
+                Spacer()
+
+                VStack(spacing: 8) {
+                    Text("COLLAPSE")
+                        .font(.system(size: 46, weight: .black, design: .rounded))
+                        .foregroundColor(.white)
+                    Text("LOGIC")
+                        .font(.system(size: 46, weight: .black, design: .rounded))
+                        .foregroundColor(Color(hex: "#457B9D"))
+                }
+
+                Text("Push. Collide. Destroy.")
+                    .font(.system(size: 16, weight: .medium, design: .rounded))
+                    .foregroundColor(.white.opacity(0.5))
+
+                Spacer()
+
+                Button {
+                    showLevelSelect = true
+                } label: {
+                    Text("PLAY")
+                        .font(.system(size: 20, weight: .bold, design: .rounded))
+                        .foregroundColor(.white)
+                        .frame(width: 200, height: 56)
+                        .background(Color(hex: "#E63946"))
+                        .clipShape(RoundedRectangle(cornerRadius: 16))
+                }
+
+                let total = ProgressStore.shared.totalStars()
+                if total > 0 {
+                    Text("⭐ \(total) stars collected")
+                        .font(.system(size: 14, design: .rounded))
+                        .foregroundColor(.white.opacity(0.4))
+                }
+
+                Spacer()
+            }
+            .padding(.horizontal, 32)
+        }
+        .fullScreenCover(isPresented: $showLevelSelect) {
+            LevelSelectView()
+        }
+    }
+}
diff --git a/CollapseLogic/CollapseLogicTests/GameEngineTests.swift b/CollapseLogic/CollapseLogicTests/GameEngineTests.swift
new file mode 100644
index 0000000..f324bdb
--- /dev/null
+++ b/CollapseLogic/CollapseLogicTests/GameEngineTests.swift
@@ -0,0 +1,474 @@
+import XCTest
+@testable import CollapseLogic
+
+final class GameEngineTests: XCTestCase {
+
+    // MARK: - Helpers
+
+    /// Simple 5x5 grid, no walls, custom blocks
+    private func makeState(
+        width: Int = 5, height: Int = 5,
+        blocks: [(x: Int, y: Int, color: BlockColor)],
+        walls: [(x: Int, y: Int)] = [],
+        par: Int = 5,
+        allowsMerging: Bool = true
+    ) -> GameState {
+        let bl = blocks.enumerated().map { idx, b in
+            Block(id: idx, position: GridPosition(x: b.x, y: b.y), color: b.color)
+        }
+        let ws = Set(walls.map { GridPosition(x: $0.x, y: $0.y) })
+        return GameState(
+            grid: GridSize(width: width, height: height),
+            blocks: bl, walls: ws, moveCount: 0,
+            par: par, objective: .clearAll,
+            allowsMerging: allowsMerging, history: []
+        )
+    }
+
+    // MARK: - Slide to boundary
+
+    func testSlideRightToBoundary() {
+        let state = makeState(blocks: [(x: 0, y: 2, color: .red)])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        XCTAssertTrue(result.isValid)
+        XCTAssertEqual(result.newState.blocks[0].position, GridPosition(x: 4, y: 2))
+    }
+
+    func testSlideLeftToBoundary() {
+        let state = makeState(blocks: [(x: 4, y: 2, color: .blue)])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .left)
+        XCTAssertEqual(result.newState.blocks[0].position, GridPosition(x: 0, y: 2))
+    }
+
+    func testSlideUpToBoundary() {
+        let state = makeState(blocks: [(x: 2, y: 4, color: .red)])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .up)
+        XCTAssertEqual(result.newState.blocks[0].position, GridPosition(x: 2, y: 0))
+    }
+
+    func testSlideDownToBoundary() {
+        let state = makeState(blocks: [(x: 2, y: 0, color: .blue)])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .down)
+        XCTAssertEqual(result.newState.blocks[0].position, GridPosition(x: 2, y: 4))
+    }
+
+    // MARK: - Slide stops at wall
+
+    func testStopsAtWall() {
+        let state = makeState(
+            blocks: [(x: 0, y: 2, color: .red)],
+            walls: [(x: 3, y: 2)]
+        )
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        XCTAssertEqual(result.newState.blocks[0].position, GridPosition(x: 2, y: 2))
+    }
+
+    func testStopsAtWallAbove() {
+        let state = makeState(
+            blocks: [(x: 2, y: 4, color: .blue)],
+            walls: [(x: 2, y: 2)]
+        )
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .up)
+        XCTAssertEqual(result.newState.blocks[0].position, GridPosition(x: 2, y: 3))
+    }
+
+    // MARK: - Slide stops at another block
+
+    func testStopsAtOtherBlock() {
+        // Purple (secondary) at x=0, Red (primary) at x=3 → block stops, no merge
+        let state = makeState(blocks: [
+            (x: 0, y: 2, color: .purple),
+            (x: 3, y: 2, color: .red)
+        ])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        // Purple should land at x=2, stopped by red at x=3
+        XCTAssertEqual(result.newState.blocks[0].position, GridPosition(x: 2, y: 2))
+        XCTAssertEqual(result.newState.blocks.count, 2)
+    }
+
+    // MARK: - Same-color destroy
+
+    func testSameColorDestroyBoth() {
+        let state = makeState(blocks: [
+            (x: 0, y: 2, color: .red),
+            (x: 3, y: 2, color: .red)
+        ])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        // Red slides right, lands at x=2, adjacent is red at x=3 → both destroyed
+        XCTAssertEqual(result.newState.blocks.count, 0)
+        // Confirm destroy event
+        if case .destroyed = result.events.last { } else {
+            XCTFail("Expected destroyed event")
+        }
+    }
+
+    func testSameColorDestroyVertical() {
+        let state = makeState(blocks: [
+            (x: 2, y: 0, color: .blue),
+            (x: 2, y: 4, color: .blue)
+        ])
+        // Push top blue down
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .down)
+        XCTAssertEqual(result.newState.blocks.count, 0)
+    }
+
+    func testDifferentNonMergeableColorStops() {
+        // Purple (secondary) at x=0, Green (secondary) at x=4 → different secondaries stop
+        let state = makeState(blocks: [
+            (x: 0, y: 2, color: .purple),
+            (x: 4, y: 2, color: .green)
+        ])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        // Purple lands at x=3, green stays at x=4, no interaction
+        XCTAssertEqual(result.newState.blocks.count, 2)
+    }
+
+    // MARK: - Invalid moves
+
+    func testInvalidMoveAtBoundary() {
+        // Block already at left wall
+        let state = makeState(blocks: [(x: 0, y: 2, color: .red)])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .left)
+        XCTAssertFalse(result.isValid)
+        XCTAssertEqual(result.newState.moveCount, 0)
+    }
+
+    func testInvalidMoveBlockedByWallImmediately() {
+        let state = makeState(
+            blocks: [(x: 2, y: 2, color: .red)],
+            walls: [(x: 3, y: 2)]
+        )
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        XCTAssertFalse(result.isValid)
+        XCTAssertEqual(result.newState.moveCount, 0)
+    }
+
+    func testInvalidMoveBlockedByAdjacentBlock() {
+        let state = makeState(blocks: [
+            (x: 2, y: 2, color: .red),
+            (x: 3, y: 2, color: .blue)
+        ])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        XCTAssertFalse(result.isValid)
+        XCTAssertEqual(result.newState.moveCount, 0)
+    }
+
+    func testOutOfRangeBlockIndex() {
+        let state = makeState(blocks: [(x: 2, y: 2, color: .red)])
+        let result = GameEngine.processMove(state: state, blockIndex: 5, direction: .right)
+        XCTAssertFalse(result.isValid)
+    }
+
+    // MARK: - Move count
+
+    func testMoveCountIncrementsOnValidMove() {
+        let state = makeState(blocks: [(x: 0, y: 2, color: .red)])
+        let r1 = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        XCTAssertEqual(r1.newState.moveCount, 1)
+    }
+
+    func testMoveCountDoesNotIncrementOnInvalidMove() {
+        let state = makeState(blocks: [(x: 0, y: 2, color: .red)])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .left)
+        XCTAssertEqual(result.newState.moveCount, 0)
+    }
+
+    func testMoveCountAccumulatesAcrossMoves() {
+        var state = makeState(blocks: [
+            (x: 0, y: 0, color: .red),
+            (x: 0, y: 4, color: .blue)
+        ])
+        state = GameEngine.processMove(state: state, blockIndex: 0, direction: .right).newState
+        state = GameEngine.processMove(state: state, blockIndex: 1, direction: .right).newState
+        XCTAssertEqual(state.moveCount, 2)
+    }
+
+    // MARK: - Undo
+
+    func testUndoRestoresPreviousState() {
+        let initial = makeState(blocks: [(x: 0, y: 2, color: .red)])
+        let afterMove = GameEngine.processMove(state: initial, blockIndex: 0, direction: .right).newState
+        XCTAssertEqual(afterMove.blocks[0].position, GridPosition(x: 4, y: 2))
+
+        let undone = GameEngine.undo(state: afterMove)
+        XCTAssertEqual(undone.blocks[0].position, GridPosition(x: 0, y: 2))
+        XCTAssertEqual(undone.moveCount, 0)
+    }
+
+    func testUndoMultipleSteps() {
+        let s0 = makeState(blocks: [
+            (x: 0, y: 0, color: .red),
+            (x: 4, y: 4, color: .blue)
+        ])
+        let s1 = GameEngine.processMove(state: s0, blockIndex: 0, direction: .right).newState
+        let s2 = GameEngine.processMove(state: s1, blockIndex: 1, direction: .left).newState
+
+        let back1 = GameEngine.undo(state: s2)
+        XCTAssertEqual(back1.moveCount, 1)
+        let back0 = GameEngine.undo(state: back1)
+        XCTAssertEqual(back0.moveCount, 0)
+        XCTAssertEqual(back0.blocks[0].position, GridPosition(x: 0, y: 0))
+    }
+
+    func testUndoAtInitialStateReturnsUnchanged() {
+        let state = makeState(blocks: [(x: 2, y: 2, color: .red)])
+        let result = GameEngine.undo(state: state)
+        XCTAssertEqual(result.moveCount, 0)
+        XCTAssertEqual(result.blocks[0].position, GridPosition(x: 2, y: 2))
+    }
+
+    // MARK: - Win detection
+
+    func testWinDetectedWhenAllBlocksGone() {
+        let state = makeState(blocks: [
+            (x: 0, y: 2, color: .red),
+            (x: 3, y: 2, color: .red)
+        ])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        XCTAssertTrue(result.newState.isWon)
+    }
+
+    func testNotWonWhenBlocksRemain() {
+        let state = makeState(blocks: [
+            (x: 0, y: 0, color: .red),
+            (x: 4, y: 0, color: .red),
+            (x: 2, y: 2, color: .blue)
+        ])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        XCTAssertFalse(result.newState.isWon)
+    }
+
+    // MARK: - Stars
+
+    func testThreeStarsAtPar() {
+        let state = makeState(blocks: [(x: 0, y: 2, color: .red), (x: 3, y: 2, color: .red)], par: 1)
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        XCTAssertEqual(result.newState.currentStars, 3)
+    }
+
+    func testTwoStarsSlightlyOverPar() {
+        let state = makeState(blocks: [(x: 0, y: 0, color: .red)], par: 1)
+        var s = GameEngine.processMove(state: state, blockIndex: 0, direction: .right).newState
+        // Force moveCount to par+1 by reflecting in a new state (simulate 2 moves)
+        // We just check the stars formula directly
+        XCTAssertEqual(state.stars(for: 2), 2)
+        XCTAssertEqual(state.stars(for: 3), 2)
+    }
+
+    func testOneStarWellOverPar() {
+        let state = makeState(blocks: [(x: 0, y: 0, color: .red), (x: 1, y: 0, color: .red)], par: 3)
+        XCTAssertEqual(state.stars(for: 10), 1)
+    }
+
+    // MARK: - World 1 merge gating
+
+    func testWorld1RedBluePrimariesStopWithoutMerging() {
+        // Same input as testRedBlueProducesPurple, but with allowsMerging = false.
+        // Expected: red lands adjacent to blue, both blocks remain, no purple created.
+        let state = makeState(blocks: [
+            (x: 0, y: 0, color: .red),
+            (x: 4, y: 0, color: .blue)
+        ], allowsMerging: false)
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        XCTAssertEqual(result.newState.blocks.count, 2)
+        XCTAssertTrue(result.newState.blocks.contains(where: { $0.color == .red }))
+        XCTAssertTrue(result.newState.blocks.contains(where: { $0.color == .blue }))
+        XCTAssertFalse(result.newState.blocks.contains(where: { $0.color == .purple }))
+        XCTAssertFalse(result.events.contains(where: {
+            if case .merged = $0 { return true } else { return false }
+        }))
+    }
+
+    func testWorld1LoadedLevelHasMergingDisabled() {
+        // Sanity: a level with world: 1 should produce a state with allowsMerging == false.
+        let json = """
+        {
+          "id": "w1_test", "world": 1, "level": 1, "title": "T",
+          "grid": { "width": 5, "height": 5 },
+          "blocks": [
+            { "x": 0, "y": 0, "color": "red" },
+            { "x": 4, "y": 0, "color": "blue" }
+          ],
+          "walls": [], "special_tiles": [],
+          "objective": { "type": "clear_all" },
+          "par": 1, "hints": []
+        }
+        """
+        let data = Data(json.utf8)
+        let def = try! JSONDecoder().decode(LevelDefinition.self, from: data)
+        let state = LevelLoader.makeGameState(from: def)
+        XCTAssertFalse(state.allowsMerging)
+    }
+
+    func testWorld2LoadedLevelHasMergingEnabled() {
+        let json = """
+        {
+          "id": "w2_test", "world": 2, "level": 1, "title": "T",
+          "grid": { "width": 5, "height": 5 },
+          "blocks": [
+            { "x": 0, "y": 0, "color": "red" },
+            { "x": 4, "y": 0, "color": "blue" }
+          ],
+          "walls": [], "special_tiles": [],
+          "objective": { "type": "clear_all" },
+          "par": 1, "hints": []
+        }
+        """
+        let data = Data(json.utf8)
+        let def = try! JSONDecoder().decode(LevelDefinition.self, from: data)
+        let state = LevelLoader.makeGameState(from: def)
+        XCTAssertTrue(state.allowsMerging)
+    }
+
+    // MARK: - World 2 Merge Tests
+
+    func testRedBlueProducesPurple() {
+        // red at (0,0), blue at (4,0), push red right
+        let state = makeState(blocks: [
+            (x: 0, y: 0, color: .red),
+            (x: 4, y: 0, color: .blue)
+        ])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        // Both originals removed, one purple remains
+        XCTAssertEqual(result.newState.blocks.count, 1)
+        XCTAssertEqual(result.newState.blocks[0].color, .purple)
+    }
+
+    func testRedYellowProducesOrange() {
+        let state = makeState(blocks: [
+            (x: 0, y: 0, color: .red),
+            (x: 4, y: 0, color: .yellow)
+        ])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        XCTAssertEqual(result.newState.blocks.count, 1)
+        XCTAssertEqual(result.newState.blocks[0].color, .orange)
+    }
+
+    func testBlueYellowProducesGreen() {
+        let state = makeState(blocks: [
+            (x: 0, y: 0, color: .blue),
+            (x: 4, y: 0, color: .yellow)
+        ])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        XCTAssertEqual(result.newState.blocks.count, 1)
+        XCTAssertEqual(result.newState.blocks[0].color, .green)
+    }
+
+    func testMergedBlockAtStationaryPosition() {
+        // red at (0,0), blue at (4,0), push red right
+        // Merged block should be at blue's position (4,0), not red's landing (3,0)
+        let state = makeState(blocks: [
+            (x: 0, y: 0, color: .red),
+            (x: 4, y: 0, color: .blue)
+        ])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        XCTAssertEqual(result.newState.blocks[0].position, GridPosition(x: 4, y: 0))
+    }
+
+    func testSecondaryPlusPrimaryStops() {
+        // purple moving into red → block stops, no merge, no destroy
+        let state = makeState(blocks: [
+            (x: 0, y: 0, color: .purple),
+            (x: 4, y: 0, color: .red)
+        ])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        XCTAssertEqual(result.newState.blocks.count, 2)
+        // Purple should stop at x=3
+        XCTAssertEqual(result.newState.blocks[0].position, GridPosition(x: 3, y: 0))
+        // No merged or destroyed events (only slid)
+        XCTAssertEqual(result.events.count, 1)
+        if case .slid = result.events[0] { } else {
+            XCTFail("Expected only a slid event")
+        }
+    }
+
+    func testDifferentSecondariesStop() {
+        // purple moving into green → block stops
+        let state = makeState(blocks: [
+            (x: 0, y: 0, color: .purple),
+            (x: 4, y: 0, color: .green)
+        ])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        XCTAssertEqual(result.newState.blocks.count, 2)
+        XCTAssertEqual(result.newState.blocks[0].position, GridPosition(x: 3, y: 0))
+    }
+
+    func testSameSecondaryDestroysBoth() {
+        // purple moving into purple → both destroyed
+        let state = makeState(blocks: [
+            (x: 0, y: 0, color: .purple),
+            (x: 4, y: 0, color: .purple)
+        ])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        XCTAssertEqual(result.newState.blocks.count, 0)
+        XCTAssertTrue(result.events.contains(where: {
+            if case .destroyed = $0 { return true }
+            return false
+        }))
+    }
+
+    func testMoveCountIncrementsOnMerge() {
+        let state = makeState(blocks: [
+            (x: 0, y: 0, color: .red),
+            (x: 4, y: 0, color: .blue)
+        ])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        XCTAssertEqual(result.newState.moveCount, 1)
+    }
+
+    func testMergeEmitsMergedEvent() {
+        let state = makeState(blocks: [
+            (x: 0, y: 0, color: .red),
+            (x: 4, y: 0, color: .blue)
+        ])
+        let result = GameEngine.processMove(state: state, blockIndex: 0, direction: .right)
+        let mergedEvent = result.events.first(where: {
+            if case .merged = $0 { return true }
+            return false
+        })
+        XCTAssertNotNil(mergedEvent)
+        if case .merged(_, _, let resultColor, let at) = mergedEvent {
+            XCTAssertEqual(resultColor, .purple)
+            XCTAssertEqual(at, GridPosition(x: 4, y: 0))
+        }
+    }
+
+    func testUndoAfterMergeRestoresState() {
+        let initial = makeState(blocks: [
+            (x: 0, y: 0, color: .red),
+            (x: 4, y: 0, color: .blue)
+        ])
+        let afterMerge = GameEngine.processMove(state: initial, blockIndex: 0, direction: .right).newState
+        // After merge: 1 purple block
+        XCTAssertEqual(afterMerge.blocks.count, 1)
+        XCTAssertEqual(afterMerge.blocks[0].color, .purple)
+
+        // Undo should restore both original blocks
+        let undone = GameEngine.undo(state: afterMerge)
+        XCTAssertEqual(undone.blocks.count, 2)
+        XCTAssertEqual(undone.moveCount, 0)
+        // Original colors restored
+        let colors = Set(undone.blocks.map(\.color))
+        XCTAssertTrue(colors.contains(.red))
+        XCTAssertTrue(colors.contains(.blue))
+    }
+
+    func testWinConditionAfterMerge() {
+        // Board: one red + one blue. Merge them → purple remains → NOT a win.
+        let state = makeState(blocks: [
+            (x: 0, y: 0, color: .red),
+            (x: 4, y: 0, color: .blue)
+        ])
+        let afterMerge = GameEngine.processMove(state: state, blockIndex: 0, direction: .right).newState
+        XCTAssertFalse(afterMerge.isWon, "Merged block still remains — should not be won")
+
+        // Now add a pre-placed purple to destroy the merged one.
+        // Set up: purple at (0,2), another purple at (4,2). Push left purple right → destroy both → win.
+        let state2 = makeState(blocks: [
+            (x: 0, y: 2, color: .purple),
+            (x: 4, y: 2, color: .purple)
+        ])
+        let afterDestroy = GameEngine.processMove(state: state2, blockIndex: 0, direction: .right).newState
+        XCTAssertTrue(afterDestroy.isWon, "Both purples destroyed — should be won")
+    }
+}
diff --git a/CollapseLogic/CollapseLogicTests/LevelLoaderTests.swift b/CollapseLogic/CollapseLogicTests/LevelLoaderTests.swift
new file mode 100644
index 0000000..8b041b0
--- /dev/null
+++ b/CollapseLogic/CollapseLogicTests/LevelLoaderTests.swift
@@ -0,0 +1,414 @@
+import XCTest
+@testable import CollapseLogic
+
+final class LevelLoaderTests: XCTestCase {
+
+    // Inline JSON helper to avoid needing the bundle in unit tests
+    private func loadFromJSON(_ json: String) throws -> GameState {
+        let data = Data(json.utf8)
+        let def = try JSONDecoder().decode(LevelDefinition.self, from: data)
+        try LevelLoader.validate(def)
+        return LevelLoader.makeGameState(from: def)
+    }
+
+    private let validJSON = """
+    {
+      "id": "w1_test",
+      "world": 1, "level": 1, "title": "Test",
+      "grid": { "width": 5, "height": 5 },
+      "blocks": [
+        { "x": 0, "y": 0, "color": "red" },
+        { "x": 4, "y": 4, "color": "blue" }
+      ],
+      "walls": [{ "x": 2, "y": 2 }],
+      "special_tiles": [],
+      "objective": { "type": "clear_all" },
+      "par": 3,
+      "hints": []
+    }
+    """
+
+    func testValidLevelParses() throws {
+        let state = try loadFromJSON(validJSON)
+        XCTAssertEqual(state.blocks.count, 2)
+        XCTAssertEqual(state.walls.count, 1)
+        XCTAssertEqual(state.par, 3)
+        XCTAssertEqual(state.grid.width, 5)
+        XCTAssertEqual(state.grid.height, 5)
+        XCTAssertEqual(state.objective, .clearAll)
+    }
+
+    func testBlockPositionsCorrect() throws {
+        let state = try loadFromJSON(validJSON)
+        let redBlock = state.blocks.first(where: { $0.color == .red })
+        XCTAssertNotNil(redBlock)
+        XCTAssertEqual(redBlock?.position, GridPosition(x: 0, y: 0))
+    }
+
+    func testWallPositionsCorrect() throws {
+        let state = try loadFromJSON(validJSON)
+        XCTAssertTrue(state.walls.contains(GridPosition(x: 2, y: 2)))
+    }
+
+    func testGridTooSmallFails() {
+        let json = """
+        {
+          "id": "x", "world": 1, "level": 1,
+          "grid": { "width": 2, "height": 5 },
+          "blocks": [{ "x": 0, "y": 0, "color": "red" }, { "x": 1, "y": 1, "color": "blue" }],
+          "objective": { "type": "clear_all" }, "par": 1
+        }
+        """
+        XCTAssertThrowsError(try loadFromJSON(json))
+    }
+
+    func testFewerThan2BlocksFails() {
+        let json = """
+        {
+          "id": "x", "world": 1, "level": 1,
+          "grid": { "width": 4, "height": 4 },
+          "blocks": [{ "x": 0, "y": 0, "color": "red" }],
+          "objective": { "type": "clear_all" }, "par": 1
+        }
+        """
+        XCTAssertThrowsError(try loadFromJSON(json))
+    }
+
+    func testBlockOutOfBoundsFails() {
+        let json = """
+        {
+          "id": "x", "world": 1, "level": 1,
+          "grid": { "width": 4, "height": 4 },
+          "blocks": [
+            { "x": 0, "y": 0, "color": "red" },
+            { "x": 9, "y": 0, "color": "blue" }
+          ],
+          "objective": { "type": "clear_all" }, "par": 1
+        }
+        """
+        XCTAssertThrowsError(try loadFromJSON(json))
+    }
+
+    func testOverlappingPositionsFails() {
+        let json = """
+        {
+          "id": "x", "world": 1, "level": 1,
+          "grid": { "width": 4, "height": 4 },
+          "blocks": [
+            { "x": 1, "y": 1, "color": "red" },
+            { "x": 1, "y": 1, "color": "blue" }
+          ],
+          "objective": { "type": "clear_all" }, "par": 1
+        }
+        """
+        XCTAssertThrowsError(try loadFromJSON(json))
+    }
+
+    func testZeroPar() {
+        let json = """
+        {
+          "id": "x", "world": 1, "level": 1,
+          "grid": { "width": 4, "height": 4 },
+          "blocks": [
+            { "x": 0, "y": 0, "color": "red" },
+            { "x": 3, "y": 0, "color": "red" }
+          ],
+          "objective": { "type": "clear_all" }, "par": 0
+        }
+        """
+        XCTAssertThrowsError(try loadFromJSON(json))
+    }
+
+    func testClearColorObjectiveParsed() throws {
+        let json = """
+        {
+          "id": "x", "world": 1, "level": 1,
+          "grid": { "width": 4, "height": 4 },
+          "blocks": [
+            { "x": 0, "y": 0, "color": "red" },
+            { "x": 3, "y": 0, "color": "red" }
+          ],
+          "objective": { "type": "clear_color", "color": "red" }, "par": 1
+        }
+        """
+        let state = try loadFromJSON(json)
+        XCTAssertEqual(state.objective, .clearColor(.red))
+    }
+
+    func testInitialMoveCountIsZero() throws {
+        let state = try loadFromJSON(validJSON)
+        XCTAssertEqual(state.moveCount, 0)
+    }
+
+    func testInitialHistoryIsEmpty() throws {
+        let state = try loadFromJSON(validJSON)
+        XCTAssertTrue(state.history.isEmpty)
+    }
+
+    // MARK: - World 2 Level Loading Tests
+
+    /// All 12 World 2 level JSONs parse and validate without errors.
+    func testAllWorld2LevelsLoad() throws {
+        let levelJSONs = world2LevelJSONs()
+        XCTAssertEqual(levelJSONs.count, 12, "Expected 12 World 2 level JSONs")
+        for (idx, json) in levelJSONs.enumerated() {
+            let levelNum = idx + 1
+            XCTAssertNoThrow(
+                try loadFromJSON(json),
+                "World 2 level \(levelNum) failed to parse"
+            )
+        }
+    }
+
+    /// Pre-placed secondary color blocks (e.g. purple in w2_01) load with the correct color.
+    func testPreplacedSecondaryColorsLoad() throws {
+        // w2_07 "Inheritance": has pre-placed purple blocks at (4,1) and (4,3)
+        let json = """
+        {
+          "id": "w2_07", "world": 2, "level": 7, "title": "Inheritance",
+          "grid": { "width": 5, "height": 5 },
+          "blocks": [
+            { "x": 0, "y": 0, "color": "red" },
+            { "x": 0, "y": 4, "color": "blue" },
+            { "x": 4, "y": 1, "color": "purple" },
+            { "x": 4, "y": 3, "color": "purple" }
+          ],
+          "walls": [{ "x": 2, "y": 0 }, { "x": 2, "y": 4 }],
+          "special_tiles": [],
+          "objective": { "type": "clear_all" },
+          "par": 4, "hints": []
+        }
+        """
+        let state = try loadFromJSON(json)
+        let purpleBlocks = state.blocks.filter { $0.color == .purple }
+        XCTAssertEqual(purpleBlocks.count, 2)
+        XCTAssertTrue(purpleBlocks.contains(where: { $0.position == GridPosition(x: 4, y: 1) }))
+        XCTAssertTrue(purpleBlocks.contains(where: { $0.position == GridPosition(x: 4, y: 3) }))
+    }
+
+    /// Metadata file contains two worlds, World 2 has 12 levels.
+    func testWorld2MetadataLoads() throws {
+        let json = """
+        {
+          "version": "1.0",
+          "worlds": [
+            {
+              "id": 1, "name": "Primary",
+              "description": "Learn the basics.",
+              "new_mechanic": null,
+              "levels": [
+                { "id": "w1_01", "title": "First Push", "file": "world1/level_01.json", "is_challenge": false }
+              ]
+            },
+            {
+              "id": 2, "name": "Fusion",
+              "description": "Discover what happens when two colors collide.",
+              "new_mechanic": "merging",
+              "unlock_stars": 15,
+              "levels": [
+                { "id": "w2_01", "title": "First Contact",   "file": "world2/level_01.json", "is_challenge": false },
+                { "id": "w2_02", "title": "Bound Together",  "file": "world2/level_02.json", "is_challenge": false },
+                { "id": "w2_03", "title": "The Third Color", "file": "world2/level_03.json", "is_challenge": false },
+                { "id": "w2_04", "title": "Sun Stone",       "file": "world2/level_04.json", "is_challenge": false },
+                { "id": "w2_05", "title": "Color Theory",    "file": "world2/level_05.json", "is_challenge": false },
+                { "id": "w2_06", "title": "Triad",           "file": "world2/level_06.json", "is_challenge": false },
+                { "id": "w2_07", "title": "Inheritance",     "file": "world2/level_07.json", "is_challenge": false },
+                { "id": "w2_08", "title": "Reflection",      "file": "world2/level_08.json", "is_challenge": false },
+                { "id": "w2_09", "title": "Cascade",         "file": "world2/level_09.json", "is_challenge": false },
+                { "id": "w2_10", "title": "Chain Reaction",  "file": "world2/level_10.json", "is_challenge": false },
+                { "id": "w2_11", "title": "The Long Way",    "file": "world2/level_11.json", "is_challenge": false },
+                { "id": "w2_12", "title": "Prism",           "file": "world2/level_12.json", "is_challenge": true, "stars_required": 15 }
+              ]
+            }
+          ]
+        }
+        """
+        let data = Data(json.utf8)
+        let metadata = try JSONDecoder().decode(MetadataFile.self, from: data)
+        XCTAssertEqual(metadata.worlds.count, 2)
+        let world2 = metadata.worlds.first(where: { $0.id == 2 })
+        XCTAssertNotNil(world2)
+        XCTAssertEqual(world2?.levels.count, 12)
+        XCTAssertEqual(world2?.name, "Fusion")
+        XCTAssertEqual(world2?.unlockStars, 15)
+        XCTAssertEqual(world2?.newMechanic, "merging")
+    }
+
+    // MARK: - World 2 level JSON fixtures
+
+    /// Returns inline JSON strings for all 12 World 2 levels.
+    private func world2LevelJSONs() -> [String] {
+        return [
+            // Level 1 — First Contact
+            """
+            { "id": "w2_01", "world": 2, "level": 1, "title": "First Contact",
+              "grid": { "width": 4, "height": 4 },
+              "blocks": [
+                { "x": 0, "y": 1, "color": "red" },
+                { "x": 3, "y": 1, "color": "blue" },
+                { "x": 1, "y": 3, "color": "purple" }
+              ],
+              "walls": [], "special_tiles": [],
+              "objective": { "type": "clear_all" }, "par": 2, "hints": [] }
+            """,
+            // Level 2 — Bound Together
+            """
+            { "id": "w2_02", "world": 2, "level": 2, "title": "Bound Together",
+              "grid": { "width": 5, "height": 4 },
+              "blocks": [
+                { "x": 0, "y": 0, "color": "red" },
+                { "x": 4, "y": 0, "color": "blue" },
+                { "x": 2, "y": 3, "color": "purple" }
+              ],
+              "walls": [{ "x": 2, "y": 0 }], "special_tiles": [],
+              "objective": { "type": "clear_all" }, "par": 3, "hints": [] }
+            """,
+            // Level 3 — The Third Color
+            """
+            { "id": "w2_03", "world": 2, "level": 3, "title": "The Third Color",
+              "grid": { "width": 5, "height": 5 },
+              "blocks": [
+                { "x": 0, "y": 0, "color": "red" },
+                { "x": 4, "y": 0, "color": "blue" },
+                { "x": 0, "y": 4, "color": "red" },
+                { "x": 4, "y": 4, "color": "blue" },
+                { "x": 2, "y": 2, "color": "purple" },
+                { "x": 2, "y": 3, "color": "purple" }
+              ],
+              "walls": [], "special_tiles": [],
+              "objective": { "type": "clear_all" }, "par": 4, "hints": [] }
+            """,
+            // Level 4 — Sun Stone
+            """
+            { "id": "w2_04", "world": 2, "level": 4, "title": "Sun Stone",
+              "grid": { "width": 5, "height": 4 },
+              "blocks": [
+                { "x": 0, "y": 1, "color": "red" },
+                { "x": 4, "y": 1, "color": "yellow" },
+                { "x": 2, "y": 3, "color": "orange" }
+              ],
+              "walls": [], "special_tiles": [],
+              "objective": { "type": "clear_all" }, "par": 2, "hints": [] }
+            """,
+            // Level 5 — Color Theory
+            """
+            { "id": "w2_05", "world": 2, "level": 5, "title": "Color Theory",
+              "grid": { "width": 5, "height": 5 },
+              "blocks": [
+                { "x": 0, "y": 0, "color": "blue" },
+                { "x": 4, "y": 0, "color": "yellow" },
+                { "x": 2, "y": 4, "color": "green" }
+              ],
+              "walls": [{ "x": 2, "y": 2 }], "special_tiles": [],
+              "objective": { "type": "clear_all" }, "par": 3, "hints": [] }
+            """,
+            // Level 6 — Triad
+            """
+            { "id": "w2_06", "world": 2, "level": 6, "title": "Triad",
+              "grid": { "width": 5, "height": 5 },
+              "blocks": [
+                { "x": 0, "y": 0, "color": "red" },
+                { "x": 4, "y": 0, "color": "blue" },
+                { "x": 0, "y": 4, "color": "yellow" },
+                { "x": 4, "y": 4, "color": "red" },
+                { "x": 2, "y": 2, "color": "purple" },
+                { "x": 3, "y": 3, "color": "orange" }
+              ],
+              "walls": [], "special_tiles": [],
+              "objective": { "type": "clear_all" }, "par": 5, "hints": [] }
+            """,
+            // Level 7 — Inheritance
+            """
+            { "id": "w2_07", "world": 2, "level": 7, "title": "Inheritance",
+              "grid": { "width": 5, "height": 5 },
+              "blocks": [
+                { "x": 0, "y": 0, "color": "red" },
+                { "x": 0, "y": 4, "color": "blue" },
+                { "x": 4, "y": 1, "color": "purple" },
+                { "x": 4, "y": 3, "color": "purple" }
+              ],
+              "walls": [{ "x": 2, "y": 0 }, { "x": 2, "y": 4 }], "special_tiles": [],
+              "objective": { "type": "clear_all" }, "par": 4, "hints": [] }
+            """,
+            // Level 8 — Reflection
+            """
+            { "id": "w2_08", "world": 2, "level": 8, "title": "Reflection",
+              "grid": { "width": 5, "height": 5 },
+              "blocks": [
+                { "x": 0, "y": 2, "color": "red" },
+                { "x": 4, "y": 2, "color": "yellow" },
+                { "x": 2, "y": 0, "color": "orange" },
+                { "x": 2, "y": 4, "color": "orange" }
+              ],
+              "walls": [{ "x": 2, "y": 2 }], "special_tiles": [],
+              "objective": { "type": "clear_all" }, "par": 4, "hints": [] }
+            """,
+            // Level 9 — Cascade
+            """
+            { "id": "w2_09", "world": 2, "level": 9, "title": "Cascade",
+              "grid": { "width": 5, "height": 5 },
+              "blocks": [
+                { "x": 0, "y": 0, "color": "blue" },
+                { "x": 4, "y": 0, "color": "yellow" },
+                { "x": 0, "y": 4, "color": "red" },
+                { "x": 4, "y": 4, "color": "blue" },
+                { "x": 2, "y": 1, "color": "green" },
+                { "x": 2, "y": 3, "color": "purple" }
+              ],
+              "walls": [{ "x": 2, "y": 2 }], "special_tiles": [],
+              "objective": { "type": "clear_all" }, "par": 5, "hints": [] }
+            """,
+            // Level 10 — Chain Reaction
+            """
+            { "id": "w2_10", "world": 2, "level": 10, "title": "Chain Reaction",
+              "grid": { "width": 6, "height": 5 },
+              "blocks": [
+                { "x": 0, "y": 0, "color": "red" },
+                { "x": 5, "y": 0, "color": "blue" },
+                { "x": 0, "y": 4, "color": "yellow" },
+                { "x": 5, "y": 4, "color": "red" },
+                { "x": 3, "y": 2, "color": "purple" },
+                { "x": 1, "y": 2, "color": "orange" }
+              ],
+              "walls": [{ "x": 2, "y": 0 }, { "x": 3, "y": 4 }], "special_tiles": [],
+              "objective": { "type": "clear_all" }, "par": 6, "hints": [] }
+            """,
+            // Level 11 — The Long Way
+            """
+            { "id": "w2_11", "world": 2, "level": 11, "title": "The Long Way",
+              "grid": { "width": 6, "height": 6 },
+              "blocks": [
+                { "x": 0, "y": 0, "color": "red" },
+                { "x": 5, "y": 0, "color": "yellow" },
+                { "x": 0, "y": 5, "color": "blue" },
+                { "x": 5, "y": 5, "color": "red" },
+                { "x": 3, "y": 2, "color": "orange" },
+                { "x": 2, "y": 3, "color": "purple" },
+                { "x": 3, "y": 4, "color": "green" }
+              ],
+              "walls": [{ "x": 2, "y": 0 }, { "x": 3, "y": 5 }], "special_tiles": [],
+              "objective": { "type": "clear_all" }, "par": 8, "hints": [] }
+            """,
+            // Level 12 — Prism (boss)
+            """
+            { "id": "w2_12", "world": 2, "level": 12, "title": "Prism",
+              "grid": { "width": 6, "height": 6 },
+              "blocks": [
+                { "x": 0, "y": 0, "color": "red" },
+                { "x": 5, "y": 0, "color": "blue" },
+                { "x": 0, "y": 5, "color": "yellow" },
+                { "x": 5, "y": 2, "color": "red" },
+                { "x": 0, "y": 2, "color": "blue" },
+                { "x": 5, "y": 5, "color": "yellow" },
+                { "x": 2, "y": 1, "color": "purple" },
+                { "x": 3, "y": 4, "color": "orange" },
+                { "x": 1, "y": 4, "color": "green" }
+              ],
+              "walls": [{ "x": 2, "y": 0 }, { "x": 4, "y": 1 }, { "x": 1, "y": 3 },
+                        { "x": 4, "y": 3 }, { "x": 2, "y": 5 }],
+              "special_tiles": [],
+              "objective": { "type": "clear_all" }, "par": 9, "hints": [] }
+            """
+        ]
+    }
+}
diff --git a/CollapseLogic_LevelSpec.md b/CollapseLogic_LevelSpec.md
new file mode 100644
index 0000000..8258ac7
--- /dev/null
+++ b/CollapseLogic_LevelSpec.md
@@ -0,0 +1,343 @@
+# Collapse Logic — Level Format Specification
+
+**Version:** 1.0  
+**Last Updated:** March 2026  
+**Studio:** Vulcara Games
+
+---
+
+## Overview
+
+Levels are defined as JSON files bundled in the app. Each world has a directory of level files. The format is designed to be human-readable for hand-crafting levels and machine-parseable for the game engine.
+
+## File Structure
+
+```
+CollapseLogic/
+├── Levels/
+│   ├── world1/
+│   │   ├── level_01.json
+│   │   ├── level_02.json
+│   │   └── ...
+│   ├── world2/
+│   │   └── ...
+│   └── metadata.json
+```
+
+## Level JSON Schema
+
+```json
+{
+  "id": "w1_01",
+  "world": 1,
+  "level": 1,
+  "title": "First Steps",
+  "grid": {
+    "width": 5,
+    "height": 5
+  },
+  "blocks": [
+    { "x": 1, "y": 1, "color": "red" },
+    { "x": 3, "y": 1, "color": "red" },
+    { "x": 2, "y": 3, "color": "blue" },
+    { "x": 4, "y": 3, "color": "blue" }
+  ],
+  "walls": [
+    { "x": 2, "y": 2 }
+  ],
+  "special_tiles": [],
+  "objective": {
+    "type": "clear_all"
+  },
+  "par": 4,
+  "hints": [
+    "Try pushing the top-left red block down first."
+  ]
+}
+```
+
+## Field Definitions
+
+### Top-Level Fields
+
+| Field | Type | Required | Description |
+|-------|------|----------|-------------|
+| `id` | string | Yes | Unique identifier. Convention: `w{world}_{level:02d}` (e.g., `w1_01`, `w3_15`) |
+| `world` | integer | Yes | World number (1-6) |
+| `level` | integer | Yes | Level number within the world (1-20) |
+| `title` | string | No | Display name for the level (optional flavor text) |
+| `grid` | object | Yes | Grid dimensions |
+| `blocks` | array | Yes | Array of block objects placed on the grid |
+| `walls` | array | No | Array of wall positions. Default: `[]` |
+| `special_tiles` | array | No | Array of special tile objects. Default: `[]` |
+| `objective` | object | Yes | Win condition for the level |
+| `par` | integer | Yes | Target move count for 3-star rating |
+| `hints` | array | No | Array of hint strings (revealed progressively). Default: `[]` |
+
+### Grid Object
+
+```json
+{
+  "width": 5,
+  "height": 5
+}
+```
+
+| Field | Type | Constraints | Description |
+|-------|------|-------------|-------------|
+| `width` | integer | 3–10 | Number of columns |
+| `height` | integer | 3–10 | Number of rows |
+
+Coordinate system: `(0, 0)` is the **top-left** cell. `x` increases rightward, `y` increases downward.
+
+### Block Object
+
+```json
+{ "x": 2, "y": 3, "color": "red" }
+```
+
+| Field | Type | Values | Description |
+|-------|------|--------|-------------|
+| `x` | integer | 0 to `width-1` | Column position |
+| `y` | integer | 0 to `height-1` | Row position |
+| `color` | string | See Color Values | Block color |
+
+### Color Values
+
+**Primary colors** (can merge):
+
+| Value | Display | Hex |
+|-------|---------|-----|
+| `"red"` | Ruby | #E63946 |
+| `"blue"` | Sapphire | #457B9D |
+| `"yellow"` | Topaz | #F4D35E |
+
+**Secondary colors** (result of merges, cannot merge further):
+
+| Value | Created From | Hex |
+|-------|-------------|-----|
+| `"purple"` | red + blue | #7B2D8B |
+| `"orange"` | red + yellow | #E76F51 |
+| `"green"` | blue + yellow | #2A9D8F |
+
+Secondary-color blocks can appear in level definitions as pre-placed blocks, allowing level designers to create puzzles that start with merged colors already on the board.
+
+### Wall Object
+
+```json
+{ "x": 2, "y": 2 }
+```
+
+Simple position. Walls are impassable — blocks stop when they would move into a wall cell.
+
+### Special Tile Object
+
+```json
+{ "x": 3, "y": 4, "type": "mirror", "direction": "horizontal" }
+```
+
+| Field | Type | Values | Description |
+|-------|------|--------|-------------|
+| `x` | integer | 0 to `width-1` | Column position |
+| `y` | integer | 0 to `height-1` | Row position |
+| `type` | string | See below | Tile type |
+| Additional fields vary by type | | | |
+
+**Tile types and their extra fields:**
+
+#### `mirror`
+Reverses block direction on contact.
+
+| Field | Values | Description |
+|-------|--------|-------------|
+| `direction` | `"horizontal"`, `"vertical"`, `"both"` | Which axis the mirror reflects |
+
+- `"horizontal"` — reverses left↔right movement; vertical movement passes through
+- `"vertical"` — reverses up↔down movement; horizontal movement passes through  
+- `"both"` — reverses any direction (block bounces back the way it came)
+
+#### `splitter`
+Breaks a merged (secondary) block into its two primary components. The two resulting blocks are placed on either side of the splitter along the axis of movement.
+
+No extra fields.
+
+If a primary-color block hits a splitter, it passes through (no effect).
+
+#### `void`
+Absorbs any block that enters. Single use — the void tile is consumed along with the block.
+
+| Field | Values | Description |
+|-------|--------|-------------|
+| `charges` | integer (default: 1) | Number of blocks it can absorb before being consumed |
+
+#### `ice`
+Block slides through without stopping. The block continues moving until it hits a non-ice cell's wall/block/boundary.
+
+No extra fields.
+
+#### `lock`
+A block that can only be destroyed by a matching `key` block.
+
+| Field | Values | Description |
+|-------|--------|-------------|
+| `lock_color` | color string | The color of key required to destroy this lock |
+
+#### `key`
+When colliding with a matching lock, both are destroyed.
+
+| Field | Values | Description |
+|-------|--------|-------------|
+| `key_color` | color string | Must match a lock's `lock_color` to destroy it |
+
+### Objective Object
+
+```json
+{ "type": "clear_all" }
+```
+
+| Type | Extra Fields | Description |
+|------|-------------|-------------|
+| `"clear_all"` | None | Remove all blocks from the board |
+| `"clear_color"` | `"color": "red"` | Remove all blocks of a specific color |
+| `"reduce_to"` | `"count": 1` | Reduce total blocks to the specified count |
+| `"clear_targets"` | `"targets": [{"x":2,"y":3}, ...]` | Clear specific cells (blocks must be destroyed at those positions) |
+
+## Metadata File
+
+`Levels/metadata.json` provides an index of all worlds and levels:
+
+```json
+{
+  "version": "1.0",
+  "worlds": [
+    {
+      "id": 1,
+      "name": "Primary",
+      "description": "Learn the basics of pushing and destroying.",
+      "new_mechanic": null,
+      "levels": [
+        {
+          "id": "w1_01",
+          "title": "First Steps",
+          "file": "world1/level_01.json",
+          "is_challenge": false
+        },
+        {
+          "id": "w1_16",
+          "title": "Ruby Gauntlet",
+          "file": "world1/level_16.json",
+          "is_challenge": true,
+          "stars_required": 30
+        }
+      ]
+    }
+  ]
+}
+```
+
+Challenge levels have `is_challenge: true` and require a cumulative star count (`stars_required`) to unlock.
+
+## Example Levels
+
+### Tutorial Level (World 1, Level 1)
+
+Two red blocks on a 4x4 grid. Push one into the other.
+
+```json
+{
+  "id": "w1_01",
+  "world": 1,
+  "level": 1,
+  "title": "First Steps",
+  "grid": { "width": 4, "height": 4 },
+  "blocks": [
+    { "x": 0, "y": 1, "color": "red" },
+    { "x": 3, "y": 1, "color": "red" }
+  ],
+  "walls": [],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 1,
+  "hints": ["Push the left block to the right."]
+}
+```
+
+### Intermediate Level (World 1, Level 8)
+
+Walls force an indirect path.
+
+```json
+{
+  "id": "w1_08",
+  "world": 1,
+  "level": 8,
+  "title": "Detour",
+  "grid": { "width": 5, "height": 5 },
+  "blocks": [
+    { "x": 0, "y": 0, "color": "red" },
+    { "x": 4, "y": 0, "color": "red" },
+    { "x": 1, "y": 4, "color": "blue" },
+    { "x": 3, "y": 4, "color": "blue" }
+  ],
+  "walls": [
+    { "x": 2, "y": 0 },
+    { "x": 2, "y": 1 },
+    { "x": 2, "y": 3 },
+    { "x": 2, "y": 4 }
+  ],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 6,
+  "hints": [
+    "The wall column splits the board in two.",
+    "Row 2 is the only crossing point."
+  ]
+}
+```
+
+### Merge Level (World 2, Level 5)
+
+Create purple to clear it.
+
+```json
+{
+  "id": "w2_05",
+  "world": 2,
+  "level": 5,
+  "title": "Color Theory",
+  "grid": { "width": 5, "height": 5 },
+  "blocks": [
+    { "x": 0, "y": 2, "color": "red" },
+    { "x": 4, "y": 2, "color": "blue" },
+    { "x": 2, "y": 0, "color": "purple" }
+  ],
+  "walls": [],
+  "special_tiles": [],
+  "objective": { "type": "clear_all" },
+  "par": 3,
+  "hints": [
+    "You need to make a purple block to match the one already on the board.",
+    "Merge red and blue first, then align the two purples."
+  ]
+}
+```
+
+## Validation Rules
+
+A level file is valid if:
+
+1. `id` is unique across all levels
+2. `grid.width` and `grid.height` are between 3 and 10
+3. All block, wall, and special tile positions are within grid bounds
+4. No two objects occupy the same cell
+5. `par` is a positive integer
+6. `objective.type` is one of the defined types
+7. If `objective.type` is `"clear_color"`, the specified color exists in `blocks`
+8. At least 2 blocks are present (a puzzle requires at minimum something to collide)
+9. Block colors are valid primary or secondary color strings
+
+## Extending the Format
+
+New special tile types can be added by defining a new `type` string and its associated extra fields. The game engine should gracefully ignore unrecognized tile types (forward compatibility for older app versions loading newer level packs).
+
+New objective types follow the same pattern. The `objective` object is intentionally flexible — additional fields can be added per type without breaking existing levels.
diff --git a/TASKS_World2.md b/TASKS_World2.md
new file mode 100644
index 0000000..8efb864
--- /dev/null
+++ b/TASKS_World2.md
@@ -0,0 +1,378 @@
+# TASKS_World2.md — Collapse Logic: World 2 Implementation
+
+Feed this file to Claude Code. Work through tasks **in order**. Do not skip ahead.  
+Complete each task fully before starting the next. Run tests after every task that touches the engine.
+
+---
+
+## Task 1 — Extend `BlockColor` with new colors
+
+**File:** `Models/Block.swift`
+
+Add three primary and three secondary colors to the `BlockColor` enum (yellow already may be stubbed — check first):
+
+```swift
+enum BlockColor: String, Codable, CaseIterable {
+    // Primary (can merge)
+    case red
+    case blue
+    case yellow
+
+    // Secondary (result of merges)
+    case purple
+    case orange
+    case green
+
+    var isPrimary: Bool {
+        switch self {
+        case .red, .blue, .yellow: return true
+        case .purple, .orange, .green: return false
+        }
+    }
+
+    var displayHex: String {
+        switch self {
+        case .red:    return "#E63946"
+        case .blue:   return "#457B9D"
+        case .yellow: return "#F4D35E"
+        case .purple: return "#7B2D8B"
+        case .orange: return "#E76F51"
+        case .green:  return "#2A9D8F"
+        }
+    }
+}
+```
+
+**Verify:** No existing code breaks. `BlockColor` is `Codable` so JSON loading of `"yellow"`, `"purple"`, etc. will now work automatically.
+
+---
+
+## Task 2 — Add `mergeColor` to `GameEngine`
+
+**File:** `Engine/GameEngine.swift`
+
+Add this static helper. Place it near the top of `GameEngine` as a private static func:
+
+```swift
+private static func mergeColor(_ a: BlockColor, _ b: BlockColor) -> BlockColor? {
+    guard a.isPrimary && b.isPrimary && a != b else { return nil }
+    let pair = Set([a, b])
+    if pair == Set([BlockColor.red,    .blue])   { return .purple }
+    if pair == Set([BlockColor.red,    .yellow]) { return .orange }
+    if pair == Set([BlockColor.blue,   .yellow]) { return .green  }
+    return nil
+}
+```
+
+**No other changes in this task.**
+
+---
+
+## Task 3 — Update `processMove` for merge collisions
+
+**File:** `Engine/GameEngine.swift`
+
+Find step 5 of the movement algorithm — the collision check after the block slides to position T. Currently it reads:
+
+```swift
+// Different color → block stops (MVP: no merge)
+```
+
+Replace that branch with:
+
+```swift
+// Different color — check for merge
+if let merged = GameEngine.mergeColor(movingBlock.color, stationaryBlock.color) {
+    // Remove both blocks
+    var newBlocks = state.blocks
+    // Remove in reverse index order to avoid index shifting
+    let indicesToRemove = [movingIndex, stationaryIndex].sorted(by: >)
+    for idx in indicesToRemove { newBlocks.remove(at: idx) }
+    // Place merged block at stationary position
+    let mergedBlock = Block(position: stationaryBlock.position, color: merged)
+    newBlocks.append(mergedBlock)
+    // Emit merged event
+    events.append(.merged(
+        blockIndex1: movingIndex,
+        blockIndex2: stationaryIndex,
+        resultColor: merged,
+        at: stationaryBlock.position
+    ))
+    newState = GameState(
+        grid: state.grid,
+        blocks: newBlocks,
+        walls: state.walls,
+        moveCount: state.moveCount + 1,
+        history: state.historySnapshot(),
+        objective: state.objective,
+        par: state.par
+    )
+} else {
+    // No merge possible — block stops at T
+    // (existing stop logic unchanged)
+}
+```
+
+> Note: `historySnapshot()` should already exist from World 1's undo implementation. If it's named differently in your codebase, use the correct name.
+
+**After this task: run ALL existing unit tests.** Zero regressions allowed before continuing.
+
+---
+
+## Task 4 — Unit tests for merge logic
+
+**File:** `CollapseLogicTests/GameEngineTests.swift` (add to existing test file)
+
+Add a `// MARK: - World 2 Merge Tests` section with these tests:
+
+```swift
+// MARK: - World 2 Merge Tests
+
+func testRedBlueProducesPurple() {
+    // red at (0,0), blue at (2,0), push red right
+    // Expected: purple block at (2,0), both originals removed
+}
+
+func testRedYellowProducesOrange() { }
+
+func testBlueYellowProducesGreen() { }
+
+func testMergedBlockAtStationaryPosition() {
+    // Verify the new block is at the stationary block's cell, not the moving block's cell
+}
+
+func testSecondaryPlusPrimaryStops() {
+    // purple moving into red → block stops, no merge, no destroy
+}
+
+func testDifferentSecondariesStop() {
+    // purple moving into green → block stops
+}
+
+func testSameSecondaryDestroysBoth() {
+    // purple moving into purple → both destroyed (same rule as primaries)
+}
+
+func testMoveCountIncrementsOnMerge() { }
+
+func testUndoAfterMergeRestoresState() {
+    // After a merge, undo should restore both original blocks and remove the merged block
+}
+
+func testWinConditionAfterMerge() {
+    // Board with one red + one blue. Merge them. If objective is clear_all,
+    // that's NOT a win (merged block remains). Verify win is NOT triggered.
+    // Then push merged purple into a pre-placed purple → destroy both → win.
+}
+```
+
+Implement each test fully. All must pass before proceeding.
+
+---
+
+## Task 5 — Update `BlockNode` color rendering
+
+**File:** `Scene/BlockNode.swift`
+
+Add color cases for `yellow`, `purple`, `orange`, `green` in the color-to-UIColor/SKColor switch. Use:
+
+```swift
+case .yellow: return SKColor(hex: "#F4D35E")
+case .purple: return SKColor(hex: "#7B2D8B")
+case .orange: return SKColor(hex: "#E76F51")
+case .green:  return SKColor(hex: "#2A9D8F")
+```
+
+Additionally, add a **white inner ring** for secondary-color blocks. After setting the block's fill color, add:
+
+```swift
+if !block.color.isPrimary {
+    let ring = SKShapeNode(rectOf: CGSize(width: size.width - 8, height: size.height - 8),
+                           cornerRadius: cornerRadius - 2)
+    ring.fillColor = .clear
+    ring.strokeColor = SKColor.white.withAlphaComponent(0.4)
+    ring.lineWidth = 2
+    ring.zPosition = 1
+    addChild(ring)
+}
+```
+
+**Verify visually** in the simulator: place a World 1 level with a pre-placed `purple` block (edit a level JSON temporarily) and confirm it renders with the inner ring. Revert the JSON after verifying.
+
+---
+
+## Task 6 — Merge animation in `GameScene`
+
+**File:** `Scene/GameScene.swift`
+
+Find the method that processes `GameEvent` items for animation (likely a `playEvents` or `animateEvents` function). Add a case for `.merged`:
+
+```swift
+case .merged(_, _, let resultColor, let position):
+    // 1. Both source blocks have already slid/are at position — their nodes need to burst out
+    // 2. Scale both up 1.2× (0.1s), then scale + fade to 0 (0.1s), remove nodes
+    // 3. Create a new BlockNode for resultColor at `position`, scale 0 → 1.15 → 1.0 (0.15s spring)
+    // 4. Play merge.wav
+
+    let burstScale = SKAction.scale(to: 1.2, duration: 0.1)
+    let burstFade  = SKAction.group([
+        SKAction.scale(to: 0.0, duration: 0.1),
+        SKAction.fadeOut(withDuration: 0.1)
+    ])
+    let burstRemove = SKAction.removeFromParent()
+    let burst = SKAction.sequence([burstScale, burstFade, burstRemove])
+
+    // Run burst on both source nodes (look them up by their current grid positions)
+    // Then after burst completes, spawn merged node with spring pop:
+    let spawnDelay  = SKAction.wait(forDuration: 0.2)
+    let spawnSpring = SKAction.sequence([
+        SKAction.scale(to: 0.0, duration: 0),
+        SKAction.scale(to: 1.15, duration: 0.12),
+        SKAction.scale(to: 1.0,  duration: 0.05)
+    ])
+    // Create new BlockNode, add to scene at correct sprite position, run spawnSpring
+```
+
+Sequence these so the burst finishes before the new block appears. Use `SKAction.sequence` with a wait equal to the burst duration (0.2s).
+
+Total animation time: ~0.35s. Do not block player input during this time — use the existing input-lock pattern from the slide animation.
+
+---
+
+## Task 7 — Add `merge.wav`
+
+**File:** `Resources/SFX/merge.wav` and `Audio/SFXManager.swift`
+
+1. Add a `merge.wav` placeholder to `Resources/SFX/`. If you don't have an audio file yet, create an empty file as a placeholder — the app will not crash on a missing SKAction sound, it will just play nothing. Add a `// TODO: replace with real audio` comment.
+
+2. In `SFXManager.swift`, add:
+```swift
+func playMerge() {
+    playSound("merge")
+}
+```
+
+3. Call `SFXManager.shared.playMerge()` from the `.merged` animation case in Task 6.
+
+---
+
+## Task 8 — World 2 level files
+
+**Directory:** `Levels/world2/`
+
+Create this directory and add `level_01.json` through `level_12.json`. All 12 files are provided in `Levels/world2/` alongside this task file. Copy them into the Xcode project the same way World 1 levels were added — as a **folder reference** (blue folder), not individual file entries.
+
+**Xcode setup reminder:**
+- Right-click `Levels/` group → Add Files → select the `world2/` folder → choose "Create folder references" (blue folder)
+- Confirm `world2/` appears as a blue folder in the Levels group
+- Do NOT add individual JSON files — only the folder
+
+---
+
+## Task 9 — Update `metadata.json`
+
+**File:** `Levels/metadata.json`
+
+Add the World 2 entry to the `worlds` array:
+
+```json
+{
+  "id": 2,
+  "name": "Fusion",
+  "description": "Discover what happens when two colors collide.",
+  "new_mechanic": "merging",
+  "unlock_stars": 15,
+  "levels": [
+    { "id": "w2_01", "title": "First Contact",   "file": "world2/level_01.json", "is_challenge": false },
+    { "id": "w2_02", "title": "Bound Together",  "file": "world2/level_02.json", "is_challenge": false },
+    { "id": "w2_03", "title": "The Third Color", "file": "world2/level_03.json", "is_challenge": false },
+    { "id": "w2_04", "title": "Sun Stone",       "file": "world2/level_04.json", "is_challenge": false },
+    { "id": "w2_05", "title": "Color Theory",    "file": "world2/level_05.json", "is_challenge": false },
+    { "id": "w2_06", "title": "Triad",           "file": "world2/level_06.json", "is_challenge": false },
+    { "id": "w2_07", "title": "Inheritance",     "file": "world2/level_07.json", "is_challenge": false },
+    { "id": "w2_08", "title": "Reflection",      "file": "world2/level_08.json", "is_challenge": false },
+    { "id": "w2_09", "title": "Cascade",         "file": "world2/level_09.json", "is_challenge": false },
+    { "id": "w2_10", "title": "Chain Reaction",  "file": "world2/level_10.json", "is_challenge": false },
+    { "id": "w2_11", "title": "The Long Way",    "file": "world2/level_11.json", "is_challenge": false },
+    { "id": "w2_12", "title": "Prism",           "file": "world2/level_12.json", "is_challenge": true, "stars_required": 15 }
+  ]
+}
+```
+
+Also update the `LevelLoader` / wherever `metadata.json` is parsed to handle the new `unlock_stars` and `new_mechanic` fields. These are optional — existing World 1 entry has neither and must still load correctly.
+
+---
+
+## Task 10 — World selector UI
+
+**File:** `Views/LevelSelectView.swift`
+
+Add a world selector at the top of the level select screen.
+
+```swift
+@State private var selectedWorld: Int = 1
+
+// World 2 unlock condition
+private var world2Unlocked: Bool {
+    progressStore.totalStars() >= 15
+}
+```
+
+Render two pill-shaped buttons: "World 1" and "World 2". When World 2 is locked:
+- Pill is grayed out (opacity 0.4)
+- Show a lock symbol (SF Symbol: `lock.fill`) and the text "15 ★"
+- Tapping the locked pill does nothing (or shows a brief shake animation)
+
+When World 2 is unlocked, tapping it switches `selectedWorld` to 2 and the level grid below shows World 2 levels.
+
+Keep the implementation simple — the world metadata is already loaded, just filter `levels` by `selectedWorld`.
+
+---
+
+## Task 11 — Level loading tests (World 2)
+
+**File:** `CollapseLogicTests/LevelLoaderTests.swift` (add to existing)
+
+```swift
+func testAllWorld2LevelsLoad() {
+    for i in 1...12 {
+        let id = String(format: "w2_%02d", i)
+        let level = LevelLoader.load(id: id)
+        XCTAssertNotNil(level, "Failed to load \(id)")
+    }
+}
+
+func testPreplacedSecondaryColorsLoad() {
+    // Load w2_07 (first level with pre-placed secondary blocks)
+    // Verify the purple block in that level loads with color == .purple
+}
+
+func testWorld2MetadataLoads() {
+    let metadata = LevelLoader.loadMetadata()
+    XCTAssertEqual(metadata.worlds.count, 2)
+    let world2 = metadata.worlds.first(where: { $0.id == 2 })
+    XCTAssertNotNil(world2)
+    XCTAssertEqual(world2?.levels.count, 12)
+}
+```
+
+All must pass before marking World 2 complete.
+
+---
+
+## Task 12 — Full playthrough and regression check
+
+Manual steps before closing World 2:
+
+1. Run all unit tests. Zero failures.
+2. Build and launch on iPhone 15 Pro simulator.
+3. Play World 1 levels 1, 5, and 10 — verify no regressions.
+4. Earn 15 stars. Verify World 2 unlocks in the level select.
+5. Play all 12 World 2 levels from start to finish.
+6. For each World 2 level: verify the level is solvable at par.
+7. Trigger at least one of each merge type (red+blue, red+yellow, blue+yellow) and confirm the animation plays correctly.
+8. Undo a merge — verify the board restores correctly.
+9. Build and run on iPhone SE (3rd gen) simulator — verify layout is not broken.
+10. Confirm no crashes on any level.
+
+**Definition of Done — World 2 is complete when all 12 tasks are done and all manual steps above pass.**