diff --git a/Agents.md b/Agents.md
index 0404c5d..a076a99 100644
--- a/Agents.md
+++ b/Agents.md
@@ -203,6 +203,138 @@ Button("Save") { state.save() }
 - Avoid UIKit colors in SwiftUI code.
 
 
+## watchOS Development (CRITICAL)
+
+**Read this entire section before implementing any watch functionality.**
+
+### Creating a Watch Target
+
+When adding a watchOS target to an existing iOS app:
+
+1. **File → New → Target → "Watch App for watchOS"**
+2. Choose **"Watch App for Existing iOS App"** (NOT standalone)
+3. Name it appropriately (e.g., `AppNameWatch`)
+4. Xcode creates a folder like `AppNameWatch Watch App/`
+
+### CRITICAL: Embedding the Watch App
+
+⚠️ **THIS IS THE #1 CAUSE OF "WATCH APP NOT INSTALLED" ERRORS** ⚠️
+
+The watch app MUST be embedded in the iOS app for deployment to real devices:
+
+1. Select the **iOS target** in Xcode
+2. Go to **Build Phases** tab
+3. Verify there's an **"Embed Watch Content"** phase
+4. **CRITICAL**: Ensure **"Code Sign On Copy"** is CHECKED ✓
+
+If "Embed Watch Content" doesn't exist:
+1. Click **"+"** → **"New Copy Files Phase"**
+2. Rename to **"Embed Watch Content"**
+3. Set **Destination** to **"Products Directory"**
+4. Set **Subpath** to `$(CONTENTS_FOLDER_PATH)/Watch`
+5. Add the watch app (e.g., `AppNameWatch Watch App.app`)
+6. **CHECK "Code Sign On Copy"** ← This is critical!
+
+Without proper embedding, the iOS app installs but the watch app does NOT install on the paired Apple Watch.
+
+### Bundle Identifiers
+
+Watch app bundle IDs MUST be prefixed with the iOS app's bundle ID:
+
+```
+iOS app:    com.company.AppName
+Watch app:  com.company.AppName.watchkitapp  ← MUST start with iOS bundle ID
+```
+
+Also verify `WKCompanionAppBundleIdentifier` in the watch target's build settings matches the iOS app's bundle ID exactly.
+
+### Data Sync: WatchConnectivity (NOT App Groups)
+
+**DO NOT use App Groups for iPhone ↔ Watch data sharing.**
+
+App Groups:
+- ❌ Do NOT work between iPhone and Apple Watch
+- ❌ Different container paths on each device
+- ❌ Will waste hours debugging why data isn't syncing
+- ✅ Only work between an app and its extensions on the SAME device
+
+**Use WatchConnectivity framework instead:**
+
+```swift
+// iOS side - WatchConnectivityService.swift
+import WatchConnectivity
+
+@MainActor
+final class WatchConnectivityService: NSObject, WCSessionDelegate {
+    static let shared = WatchConnectivityService()
+    
+    private override init() {
+        super.init()
+        if WCSession.isSupported() {
+            WCSession.default.delegate = self
+            WCSession.default.activate()
+        }
+    }
+    
+    func syncData(_ data: [String: Any]) {
+        guard WCSession.default.activationState == .activated,
+              WCSession.default.isPaired,
+              WCSession.default.isWatchAppInstalled else { return }
+        
+        try? WCSession.default.updateApplicationContext(data)
+    }
+}
+```
+
+### WatchConnectivity Methods
+
+| Method | Use Case |
+|--------|----------|
+| `updateApplicationContext` | Latest state that persists (use this for most syncs) |
+| `sendMessage` | Immediate delivery when counterpart is reachable |
+| `transferUserInfo` | Queued delivery, guaranteed but not immediate |
+
+### watchOS Framework Limitations
+
+These iOS frameworks are NOT available on watchOS:
+
+- ❌ `CoreImage` - Generate QR codes on iOS, send image data to watch
+- ❌ `UIKit` (mostly) - Use SwiftUI
+- ❌ `AVFoundation` (limited)
+
+### Simulator Limitations
+
+WatchConnectivity on simulators is **unreliable**:
+
+- `isWatchAppInstalled` often returns `false` even when running
+- `isReachable` may be `false` even with both apps running
+- `updateApplicationContext` may fail with "counterpart not installed"
+
+**Workarounds for simulator testing:**
+1. Add `#if targetEnvironment(simulator)` blocks with sample data
+2. Test real sync functionality on physical devices only
+
+### Debugging Watch Sync Issues
+
+If `isWatchAppInstalled` returns `false`:
+
+1. ✅ Check "Embed Watch Content" build phase exists
+2. ✅ Check "Code Sign On Copy" is enabled
+3. ✅ Verify bundle ID is prefixed correctly
+4. ✅ Clean build folder (⇧⌘K) and rebuild
+5. ✅ On iPhone, open Watch app → verify app appears under "Installed"
+
+### NSObject Requirement
+
+`WCSessionDelegate` is an Objective-C protocol, so conforming classes must inherit from `NSObject`:
+
+```swift
+final class WatchConnectivityService: NSObject, WCSessionDelegate {
+    // NSObject is required for WCSessionDelegate conformance
+}
+```
+
+
 ## SwiftData Instructions
 
 If SwiftData is configured to use CloudKit:
diff --git a/README.md b/README.md
index b37cf46..c420ba7 100644
--- a/README.md
+++ b/README.md
@@ -177,6 +177,16 @@ BusinessCardTests/       # Unit tests
 **watchOS Target:**
 
 - WatchConnectivity (for receiving cards from iPhone)
+- Bundle ID must be prefixed with iOS bundle ID (e.g., `com.mbrucedogs.BusinessCard.watchkitapp`)
+
+### Watch App Embedding (CRITICAL)
+
+The watch app must be embedded in the iOS app for deployment. In the iOS target's **Build Phases**:
+
+1. **"Embed Watch Content"** phase must exist
+2. **"Code Sign On Copy"** must be CHECKED ✓
+
+Without this, the iOS app installs but the watch app does NOT install on the paired Apple Watch. See `Agents.md` for full troubleshooting guide.
 
 ### CloudKit Container