refactor(exec_bridge): add worker pool backpressure

codex_telegram_bridge/src/codex_telegram_bridge/exec_bridge.py

@@ -432,7 +432,6 @@ async def _drain_backlog(cfg: BridgeConfig, offset: int | None) -> int | None:
 async def _handle_message(
     cfg: BridgeConfig,
     *,
-    semaphore: asyncio.Semaphore,
     chat_id: int,
     user_msg_id: int,
     text: str,
@@ -523,27 +522,26 @@ async def _handle_message(
             _edit_progress(progress_renderer.render_progress(elapsed))
         )
 
-    async with semaphore:
-        try:
-            session_id, answer, saw_agent_message = await cfg.runner.run_serialized(
-                text, resume_session, on_event=on_event
-            )
-        except Exception as e:
-            if edit_task is not None:
-                await asyncio.gather(edit_task, return_exceptions=True)
+    try:
+        session_id, answer, saw_agent_message = await cfg.runner.run_serialized(
+            text, resume_session, on_event=on_event
+        )
+    except Exception as e:
+        if edit_task is not None:
+            await asyncio.gather(edit_task, return_exceptions=True)
 
-            err = _clamp_tg_text(f"Error:\n{e}")
-            logger.debug("[error] send reply_to=%s text=%s", user_msg_id, err)
-            await _send_or_edit_markdown(
-                cfg.bot,
-                chat_id=chat_id,
-                text=err,
-                edit_message_id=progress_id,
-                reply_to_message_id=user_msg_id,
-                disable_notification=True,
-                limit=TELEGRAM_MARKDOWN_LIMIT,
-            )
-            return
+        err = _clamp_tg_text(f"Error:\n{e}")
+        logger.debug("[error] send reply_to=%s text=%s", user_msg_id, err)
+        await _send_or_edit_markdown(
+            cfg.bot,
+            chat_id=chat_id,
+            text=err,
+            edit_message_id=progress_id,
+            reply_to_message_id=user_msg_id,
+            disable_notification=True,
+            limit=TELEGRAM_MARKDOWN_LIMIT,
+        )
+        return
 
     if edit_task is not None:
         await asyncio.gather(edit_task, return_exceptions=True)
@@ -621,29 +619,31 @@ async def poll_updates(cfg: BridgeConfig):
 
 
 async def _run_main_loop(cfg: BridgeConfig) -> None:
-    semaphore = asyncio.Semaphore(cfg.max_concurrency)
+    worker_count = max(1, min(cfg.max_concurrency, 16))
+    queue: asyncio.Queue[tuple[int, int, str, str | None]] = asyncio.Queue(
+        maxsize=worker_count * 2
+    )
 
-    async def _handle_message_task(
-        *,
-        chat_id: int,
-        user_msg_id: int,
-        text: str,
-        resume_session: str | None,
-    ) -> None:
-        try:
-            await _handle_message(
-                cfg,
-                semaphore=semaphore,
-                chat_id=chat_id,
-                user_msg_id=user_msg_id,
-                text=text,
-                resume_session=resume_session,
-            )
-        except Exception:
-            logger.exception("[handle] task failed")
+    async def worker() -> None:
+        while True:
+            chat_id, user_msg_id, text, resume_session = await queue.get()
+            try:
+                await _handle_message(
+                    cfg,
+                    chat_id=chat_id,
+                    user_msg_id=user_msg_id,
+                    text=text,
+                    resume_session=resume_session,
+                )
+            except Exception:
+                logger.exception("[handle] worker failed")
+            finally:
+                queue.task_done()
 
     try:
         async with asyncio.TaskGroup() as tg:
+            for _ in range(worker_count):
+                tg.create_task(worker())
             async for msg in poll_updates(cfg):
                 text = msg["text"]
                 user_msg_id = msg["message_id"]
@@ -651,13 +651,8 @@ async def _run_main_loop(cfg: BridgeConfig) -> None:
                 r = msg.get("reply_to_message") or {}
                 resume_session = resume_session or extract_session_id(r.get("text"))
 
-                tg.create_task(
-                    _handle_message_task(
-                        chat_id=msg["chat"]["id"],
-                        user_msg_id=user_msg_id,
-                        text=text,
-                        resume_session=resume_session,
-                    )
+                await queue.put(
+                    (msg["chat"]["id"], user_msg_id, text, resume_session)
                 )
     finally:
         await cfg.bot.close()

codex_telegram_bridge/tests/test_exec_bridge.py

@@ -111,7 +111,6 @@ def test_final_notify_sends_loud_final_message() -> None:
     asyncio.run(
         _handle_message(
             cfg,
-            semaphore=asyncio.Semaphore(1),
             chat_id=123,
             user_msg_id=10,
             text="hi",
@@ -141,7 +140,6 @@ def test_new_final_message_forces_notification_when_too_long_to_edit() -> None:
     asyncio.run(
         _handle_message(
             cfg,
-            semaphore=asyncio.Semaphore(1),
             chat_id=123,
             user_msg_id=10,
             text="hi",