fix: remove debug logs, add model fallback, fix prompt_async flow

- Remove process.stderr.write debug logs from sessionHandle and prompt_async
- Add model fallback in assistant message (use this._model if msg.model missing)
- Add model field to user message emit for adapter consumption
- Wait for session ready before setModel/prompt in prompt_async
- Return 200 JSON instead of 204 No Content from prompt_async
- Set Bun.serve idleTimeout to 255s to prevent connection drops

src/server/routes/session.ts

@@ -365,8 +365,11 @@ export function createSessionRoutes(
     })
     .post('/session/:sessionID/prompt_async', async c => {
       const id = c.req.param('sessionID')
+
       const handle = sessionManager.getSession(id)
-      if (!handle) throw notFound('session not found')
+      if (!handle) {
+        throw notFound('session not found')
+      }
 
       const body = await c.req.json<{
         content?: string
@@ -380,17 +383,26 @@ export function createSessionRoutes(
         ?.filter((p) => p.type === 'text' && p.text)
         .map((p) => p.text)
         .join('\n') ?? ''
-      if (!content) throw badRequest('content is required')
-      if (handle.prompting) throw conflict('session is already processing a prompt')
+      if (!content) {
+        throw badRequest('content is required')
+      }
+      if (handle.prompting) {
+        throw conflict('session is already processing a prompt')
+      }
 
       void (async () => {
-        if (body.model?.modelID) {
-          try { await handle.setModel(body.model.modelID) } catch {}
-        }
-        handle.prompt(content).catch(() => {})
+        try {
+          if (handle.status !== 'running') {
+            await handle.waitReady()
+          }
+          if (body.model?.modelID) {
+            try { await handle.setModel(body.model.modelID) } catch {}
+          }
+          handle.prompt(content).catch(() => {})
+        } catch {}
       })()
 
-      return new Response(null, { status: 204 })
+      return c.json({ ok: true }, 200)
     })
     .post('/session/:sessionID/abort', async c => {
       const id = c.req.param('sessionID')

src/server/server.ts

@@ -58,6 +58,7 @@ export function startServer(
     hostname: config.host,
     port: config.port,
     fetch: app.fetch,
+    idleTimeout: 255,
   })
 
   return server

src/server/sessionHandle.ts

@@ -451,6 +451,9 @@ export class SessionHandle {
         if (msg.uuid && typeof msg.uuid === 'string') {
           this._lastMessageUuid = msg.uuid
         }
+        if (!msg.model && this._model) {
+          msg = { ...msg, model: this._model }
+        }
         this.emitEvent('message', msg)
         break
       }
@@ -602,6 +605,7 @@ export class SessionHandle {
       type: 'user',
       content,
       session_id: this.sessionId,
+      model: this._model ?? '',
     })
 
     this.writeStdin(userMsg)