fix: include room ID in message permalink for cross-room navigation

Links now use #roomId/messageHash format so the app can load the correct
room before scrolling to the target message. Handles hashchange events
and auto-navigates on page load.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

client/src/components/app.riot

@@ -190,10 +190,9 @@
         // Register global 401 handler so any expired-token API call triggers logout
         setOnUnauthorized(() => this.handleLogout())
 
-        // Listen for hash changes to scroll to linked messages
+        // Listen for hash changes to navigate to linked messages
         this._onHashChange = () => {
-          const hash = window.location.hash?.slice(1)
+          this.navigateToMessageLink()
-          if (hash) this.scrollToHash(hash)
         }
         window.addEventListener('hashchange', this._onHashChange)
 
@@ -365,6 +364,9 @@
 
         // Process any pending invite token
         await this.processInviteToken()
+
+        // Check for a message permalink in the URL hash (e.g. #roomId/messageHash)
+        this.navigateToMessageLink()
       },
 
       handleLogin(data) {
@@ -408,14 +410,7 @@
             typingUsers: [],
           })
           ws.joinRoom(roomId)
-
-          // Check for hash in URL to scroll to a specific message
-          const targetHash = window.location.hash?.slice(1)
-          if (targetHash) {
-            this.scrollToHash(targetHash)
-          } else {
           this.scrollToBottom()
-          }
         } catch (e) {
           console.error('Failed to load room:', e)
         }
@@ -504,12 +499,35 @@
         })
       },
 
+      /** Parse #roomId/messageHash from URL, load the room, and scroll to the message */
+      async navigateToMessageLink() {
+        const fragment = window.location.hash?.slice(1)
+        if (!fragment) return
+        const slashIdx = fragment.indexOf('/')
+        if (slashIdx === -1) return // not a room/hash link
+
+        const roomId = fragment.slice(0, slashIdx)
+        const msgHash = fragment.slice(slashIdx + 1)
+        if (!roomId || !msgHash) return
+
+        // Store the target hash before selecting the room
+        this._pendingScrollHash = msgHash
+
+        // Select the room if not already active
+        if (this.state.activeRoomId !== roomId) {
+          await this.selectRoom(roomId)
+        }
+
+        // Scroll to the message after render
+        this.scrollToHash(this._pendingScrollHash)
+        this._pendingScrollHash = null
+      },
+
       scrollToHash(hash) {
         requestAnimationFrame(() => {
           const el = document.getElementById('msg-' + hash)
           if (el) {
             el.scrollIntoView({ behavior: 'smooth', block: 'center' })
-            // Briefly highlight the message
             el.classList.add('hash-highlight')
             setTimeout(() => el.classList.remove('hash-highlight'), 3000)
           }

client/src/components/message-bubble.riot

@@ -478,7 +478,9 @@
         e.stopPropagation()
         const hash = this.props.message?.hash
         if (!hash) return
-        const url = `${window.location.origin}${window.location.pathname}#${hash}`
+        const roomId = this.props.message?.room_id
+        if (!roomId) return
+        const url = `${window.location.origin}${window.location.pathname}#${roomId}/${hash}`
         const btn = e.currentTarget
         navigator.clipboard.writeText(url).then(() => {
           btn.classList.add('copied')