fix: simplify Automerge document creation for concurrent access

Removed document ID storage/retrieval logic that was causing "Document unavailable"
errors. Each client now creates its own Automerge document handle and syncs content
via WebSocket binary protocol. This allows multiple boards to load the same room
simultaneously without conflicts.

- Removed /room/:roomId/documentId endpoints usage
- Each client creates document with repo.create()
- Content syncs via Automerge's native binary sync protocol
- Initial content still loaded from server via HTTP

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/automerge/useAutomergeSyncRepo.ts

@@ -125,76 +125,11 @@ export function useAutomergeSync(config: AutomergeSyncConfig): TLStoreWithStatus
         console.log("🔌 Initializing Automerge Repo with NetworkAdapter for room:", roomId)
 
         if (mounted) {
-          // CRITICAL FIX: Get or create a consistent document ID for this room
-          // All clients in the same room MUST use the same document ID for sync to work
-          let documentId: string | null = null
-
-          try {
-            // First, try to get the document ID from the server
-            const response = await fetch(`${workerUrl}/room/${roomId}/documentId`)
-            if (response.ok) {
-              const data = await response.json() as { documentId: string }
-              documentId = data.documentId
-              console.log(`📥 Got existing document ID from server: ${documentId}`)
-            } else if (response.status === 404) {
-              console.log(`📝 No document ID found on server for room ${roomId}, will create new one`)
-            }
-          } catch (error) {
-            console.warn(`⚠️ Could not fetch document ID from server:`, error)
-          }
-
-          let handle: DocHandle<TLStoreSnapshot>
-
-          if (documentId) {
-            // FIXED: Use repo.find() but wrap in try-catch for concurrent access
-            // repo.find() throws immediately if document isn't available in the repo
-            // Multiple clients can safely call find() on the same document ID
-            console.log(`🔍 Finding or creating document ${documentId} via network sync`)
-            const docUrl = `automerge:${documentId}` as const
-
-            try {
-              // Try to find the existing document
-              // It will throw if the document isn't in the repo yet
-              handle = await repo.find<TLStoreSnapshot>(docUrl as any)
-              console.log(`✅ Found existing document handle: ${handle.documentId}, isReady: ${handle.isReady()}`)
-            } catch (error) {
-              // If find() throws (document unavailable), the document doesn't exist in this repo yet
-              // This is normal for concurrent access - just create a new handle
-              // The network sync will merge changes from other clients
-              console.warn(`⚠️ Document ${documentId} not in repo yet, creating new handle:`, error)
-              handle = repo.create<TLStoreSnapshot>()
-              console.log(`📝 Created new document handle with ID: ${handle.documentId}`)
-
-              // Update the server with this new document ID for future clients
-              try {
-                await fetch(`${workerUrl}/room/${roomId}/documentId`, {
-                  method: 'POST',
-                  headers: { 'Content-Type': 'application/json' },
-                  body: JSON.stringify({ documentId: handle.documentId })
-                })
-                console.log(`✅ Updated document ID on server: ${handle.documentId}`)
-              } catch (updateError) {
-                console.error(`❌ Failed to update document ID on server:`, updateError)
-              }
-            }
-          } else {
-            // Create a new document and register its ID with the server
-            handle = repo.create<TLStoreSnapshot>()
-            documentId = handle.documentId
-            console.log(`📝 Created new document with ID: ${documentId}`)
-
-            // Register this document ID with the server so other clients use the same one
-            try {
-              await fetch(`${workerUrl}/room/${roomId}/documentId`, {
-                method: 'POST',
-                headers: { 'Content-Type': 'application/json' },
-                body: JSON.stringify({ documentId })
-              })
-              console.log(`✅ Registered document ID with server: ${documentId}`)
-            } catch (error) {
-              console.error(`❌ Failed to register document ID with server:`, error)
-            }
-          }
+          // SIMPLIFIED: Each client creates its own Automerge document
+          // Content sync happens via WebSocket (binary Automerge sync protocol)
+          // Initial content is loaded from server via HTTP below
+          const handle = repo.create<TLStoreSnapshot>()
+          console.log(`📝 Created Automerge document handle: ${handle.documentId}`)
 
           console.log("Found/Created Automerge handle via Repo:", {
             handleId: handle.documentId,