feat: server-first terminal creation, broadcast-only WS clients

- Add POST /create-terminal endpoint with MAX_TERMINALS=5 limit
- Server creates PTY, runs command, registers and broadcasts atomically
- Frontend startTerminal() calls server first, connects in reconnect mode
- Remove registerTerminalOnServer() — server handles registration
- Separate broadcast-only WS clients from PTY clients (no phantom "main" PTY)
- All broadcast functions use broadcastToAll() helper
- Fix resume existing flow to create terminal with --resume flag

frontend/src/components/FloatingTranscriptDebug.vue

@@ -40,6 +40,9 @@ const {
   switchAgent,
   selectSession,
   createNewSession,
+  startTerminal,
+  parkCurrentTerminal,
+  fetchSessionContent,
   switchToTerminal,
   closeTerminal,
   disconnectRealtime,
@@ -468,7 +471,11 @@ async function handleModalResume(sessionId: string, agent: AgentName) {
   if (agent !== selectedAgent.value) {
     await switchAgent(agent)
   }
-  selectSession(sessionId)
+  // Load transcript + create terminal with --resume
+  parkCurrentTerminal()
+  selectedSessionId.value = sessionId
+  await fetchSessionContent(sessionId)
+  await startTerminal(sessionId)
 }
 
 // ============================================================================

frontend/src/composables/transcript-debug/useTranscriptDebug.ts

@@ -92,30 +92,6 @@ export function useTranscriptDebug() {
 
   // ── Server registry HTTP helpers ──
 
-  async function registerTerminalOnServer(
-    ephemeralSessionId: string,
-    transcriptSessionId: string,
-    agent: AgentName,
-    label: string,
-    command: string
-  ) {
-    try {
-      await fetch(terminalApiUrl('/register-terminal'), {
-        method: 'POST',
-        headers: { 'Content-Type': 'application/json' },
-        body: JSON.stringify({
-          ephemeralSessionId,
-          transcriptSessionId,
-          agent,
-          label,
-          command,
-          createdAt: new Date().toISOString()
-        })
-      })
-      // Server broadcasts change → all clients pick it up via WS
-    } catch { /* best effort */ }
-  }
-
   async function updateTerminalOnServer(
     ephemeralSessionId: string,
     updates: { transcriptSessionId?: string; label?: string }
@@ -150,26 +126,44 @@ export function useTranscriptDebug() {
     return sessionId.slice(0, 12) + '...'
   }
 
-  function startTerminal(sessionId?: string) {
+  async function startTerminal(sessionId?: string) {
     const key = sessionId || '__new__'
     const cmd = sessionId
       ? `${AGENT_CMD[selectedAgent.value]} --resume "${sessionId}"`
       : AGENT_CMD[selectedAgent.value]
 
-    const term = useEphemeralTerminal(cmd)
-    localTerminals.set(key, term)
-    activeTerminalSessionId.value = key
+    console.log(`[TranscriptDebug] startTerminal called — key=${key} cmd=${cmd} url=${terminalApiUrl('/create-terminal')}`)
 
-    term.start()
+    try {
+      // Server creates PTY, runs command, registers in registry, broadcasts
+      const res = await fetch(terminalApiUrl('/create-terminal'), {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({
+          agent: selectedAgent.value,
+          transcriptSessionId: key,
+          label: sessionId ? getSessionLabel(sessionId) : 'New session',
+          command: cmd
+        })
+      })
 
-    // Register on server
-    registerTerminalOnServer(
-      term.ephemeralSessionId,
-      key,
-      selectedAgent.value,
-      sessionId ? getSessionLabel(sessionId) : 'New session',
-      cmd
-    )
+      if (!res.ok) {
+        const err = await res.json().catch(() => ({ error: 'Unknown error' }))
+        console.error(`[TranscriptDebug] Failed to create terminal: ${err.error}`)
+        return
+      }
+
+      const { ephemeralSessionId } = await res.json()
+
+      // Connect to the existing PTY in reconnect mode
+      const term = useEphemeralTerminal(cmd, ephemeralSessionId)
+      localTerminals.set(key, term)
+      activeTerminalSessionId.value = key
+
+      term.start()
+    } catch (e: any) {
+      console.error('[TranscriptDebug] Terminal creation failed:', e.message)
+    }
   }
 
   function parkCurrentTerminal() {
@@ -281,7 +275,7 @@ export function useTranscriptDebug() {
     pendingPrompt.value = initialPrompt?.trim() || null
 
     awaitingNewSession.value = true
-    startTerminal() // no sessionId → brand new session
+    await startTerminal() // no sessionId → brand new session
   }
 
   // ── WebSocket realtime ──
@@ -949,6 +943,9 @@ export function useTranscriptDebug() {
     switchAgent,
     selectSession,
     createNewSession,
+    startTerminal,
+    parkCurrentTerminal,
+    fetchSessionContent,
     switchToTerminal,
     closeTerminal,
     connectRealtime,