fix: separate Telegram connection pools and add timeout retry to prevent pool exhaustion

The root cause of "Pool timeout" errors is that long-polling (getUpdates)
and outbound API calls (send_message, send_photo, etc.) shared the same
HTTPXRequest pool — polling holds connections indefinitely, starving sends
under concurrent load (e.g. cron jobs + user chat).

- Split into two independent pools: API calls (default 32) and polling (4)
- Expose connection_pool_size / pool_timeout in TelegramConfig for tuning
- Add _call_with_retry() with exponential backoff (3 attempts) on TimedOut
- Apply retry to _send_text and remote media URL sends

nanobot/channels/telegram.py

@@ -11,6 +11,7 @@ from typing import Any, Literal
 from loguru import logger
 from pydantic import Field
 from telegram import BotCommand, ReplyParameters, Update
+from telegram.error import TimedOut
 from telegram.ext import Application, CommandHandler, ContextTypes, MessageHandler, filters
 from telegram.request import HTTPXRequest
 
@@ -151,6 +152,10 @@ def _markdown_to_telegram_html(text: str) -> str:
     return text
 
 
+_SEND_MAX_RETRIES = 3
+_SEND_RETRY_BASE_DELAY = 0.5  # seconds, doubled each retry
+
+
 class TelegramConfig(Base):
     """Telegram channel configuration."""
 
@@ -160,6 +165,8 @@ class TelegramConfig(Base):
     proxy: str | None = None
     reply_to_message: bool = False
     group_policy: Literal["open", "mention"] = "mention"
+    connection_pool_size: int = 32
+    pool_timeout: float = 5.0
 
 
 class TelegramChannel(BaseChannel):
@@ -226,15 +233,29 @@ class TelegramChannel(BaseChannel):
 
         self._running = True
 
-        # Build the application with larger connection pool to avoid pool-timeout on long runs
+        proxy = self.config.proxy or None
-        req = HTTPXRequest(
+
-            connection_pool_size=16,
+        # Separate pools so long-polling (getUpdates) never starves outbound sends.
-            pool_timeout=5.0,
+        api_request = HTTPXRequest(
+            connection_pool_size=self.config.connection_pool_size,
+            pool_timeout=self.config.pool_timeout,
             connect_timeout=30.0,
             read_timeout=30.0,
-            proxy=self.config.proxy if self.config.proxy else None,
+            proxy=proxy,
+        )
+        poll_request = HTTPXRequest(
+            connection_pool_size=4,
+            pool_timeout=self.config.pool_timeout,
+            connect_timeout=30.0,
+            read_timeout=30.0,
+            proxy=proxy,
+        )
+        builder = (
+            Application.builder()
+            .token(self.config.token)
+            .request(api_request)
+            .get_updates_request(poll_request)
         )
-        builder = Application.builder().token(self.config.token).request(req).get_updates_request(req)
         self._app = builder.build()
         self._app.add_error_handler(self._on_error)
 
@@ -365,7 +386,8 @@ class TelegramChannel(BaseChannel):
                     ok, error = validate_url_target(media_path)
                     if not ok:
                         raise ValueError(f"unsafe media URL: {error}")
-                    await sender(
+                    await self._call_with_retry(
+                        sender,
                         chat_id=chat_id,
                         **{param: media_path},
                         reply_parameters=reply_params,
@@ -401,6 +423,21 @@ class TelegramChannel(BaseChannel):
                 else:
                     await self._send_text(chat_id, chunk, reply_params, thread_kwargs)
 
+    async def _call_with_retry(self, fn, *args, **kwargs):
+        """Call an async Telegram API function with retry on pool/network timeout."""
+        for attempt in range(1, _SEND_MAX_RETRIES + 1):
+            try:
+                return await fn(*args, **kwargs)
+            except TimedOut:
+                if attempt == _SEND_MAX_RETRIES:
+                    raise
+                delay = _SEND_RETRY_BASE_DELAY * (2 ** (attempt - 1))
+                logger.warning(
+                    "Telegram timeout (attempt {}/{}), retrying in {:.1f}s",
+                    attempt, _SEND_MAX_RETRIES, delay,
+                )
+                await asyncio.sleep(delay)
+
     async def _send_text(
         self,
         chat_id: int,
@@ -411,7 +448,8 @@ class TelegramChannel(BaseChannel):
         """Send a plain text message with HTML fallback."""
         try:
             html = _markdown_to_telegram_html(text)
-            await self._app.bot.send_message(
+            await self._call_with_retry(
+                self._app.bot.send_message,
                 chat_id=chat_id, text=html, parse_mode="HTML",
                 reply_parameters=reply_params,
                 **(thread_kwargs or {}),
@@ -419,7 +457,8 @@ class TelegramChannel(BaseChannel):
         except Exception as e:
             logger.warning("HTML parse failed, falling back to plain text: {}", e)
             try:
-                await self._app.bot.send_message(
+                await self._call_with_retry(
+                    self._app.bot.send_message,
                     chat_id=chat_id,
                     text=text,
                     reply_parameters=reply_params,

tests/test_telegram_channel.py

@@ -18,6 +18,10 @@ class _FakeHTTPXRequest:
         self.kwargs = kwargs
         self.__class__.instances.append(self)
 
+    @classmethod
+    def clear(cls) -> None:
+        cls.instances.clear()
+
 
 class _FakeUpdater:
     def __init__(self, on_start_polling) -> None:
@@ -144,7 +148,8 @@ def _make_telegram_update(
 
 
 @pytest.mark.asyncio
-async def test_start_uses_request_proxy_without_builder_proxy(monkeypatch) -> None:
+async def test_start_creates_separate_pools_with_proxy(monkeypatch) -> None:
+    _FakeHTTPXRequest.clear()
     config = TelegramConfig(
         enabled=True,
         token="123:abc",
@@ -164,10 +169,106 @@ async def test_start_uses_request_proxy_without_builder_proxy(monkeypatch) -> No
 
     await channel.start()
 
-    assert len(_FakeHTTPXRequest.instances) == 1
+    assert len(_FakeHTTPXRequest.instances) == 2
-    assert _FakeHTTPXRequest.instances[0].kwargs["proxy"] == config.proxy
+    api_req, poll_req = _FakeHTTPXRequest.instances
-    assert builder.request_value is _FakeHTTPXRequest.instances[0]
+    assert api_req.kwargs["proxy"] == config.proxy
-    assert builder.get_updates_request_value is _FakeHTTPXRequest.instances[0]
+    assert poll_req.kwargs["proxy"] == config.proxy
+    assert api_req.kwargs["connection_pool_size"] == 32
+    assert poll_req.kwargs["connection_pool_size"] == 4
+    assert builder.request_value is api_req
+    assert builder.get_updates_request_value is poll_req
+
+
+@pytest.mark.asyncio
+async def test_start_respects_custom_pool_config(monkeypatch) -> None:
+    _FakeHTTPXRequest.clear()
+    config = TelegramConfig(
+        enabled=True,
+        token="123:abc",
+        allow_from=["*"],
+        connection_pool_size=32,
+        pool_timeout=10.0,
+    )
+    bus = MessageBus()
+    channel = TelegramChannel(config, bus)
+    app = _FakeApp(lambda: setattr(channel, "_running", False))
+    builder = _FakeBuilder(app)
+
+    monkeypatch.setattr("nanobot.channels.telegram.HTTPXRequest", _FakeHTTPXRequest)
+    monkeypatch.setattr(
+        "nanobot.channels.telegram.Application",
+        SimpleNamespace(builder=lambda: builder),
+    )
+
+    await channel.start()
+
+    api_req = _FakeHTTPXRequest.instances[0]
+    poll_req = _FakeHTTPXRequest.instances[1]
+    assert api_req.kwargs["connection_pool_size"] == 32
+    assert api_req.kwargs["pool_timeout"] == 10.0
+    assert poll_req.kwargs["pool_timeout"] == 10.0
+
+
+@pytest.mark.asyncio
+async def test_send_text_retries_on_timeout() -> None:
+    """_send_text retries on TimedOut before succeeding."""
+    from telegram.error import TimedOut
+
+    channel = TelegramChannel(
+        TelegramConfig(enabled=True, token="123:abc", allow_from=["*"]),
+        MessageBus(),
+    )
+    channel._app = _FakeApp(lambda: None)
+
+    call_count = 0
+    original_send = channel._app.bot.send_message
+
+    async def flaky_send(**kwargs):
+        nonlocal call_count
+        call_count += 1
+        if call_count <= 2:
+            raise TimedOut()
+        return await original_send(**kwargs)
+
+    channel._app.bot.send_message = flaky_send
+
+    import nanobot.channels.telegram as tg_mod
+    orig_delay = tg_mod._SEND_RETRY_BASE_DELAY
+    tg_mod._SEND_RETRY_BASE_DELAY = 0.01
+    try:
+        await channel._send_text(123, "hello", None, {})
+    finally:
+        tg_mod._SEND_RETRY_BASE_DELAY = orig_delay
+
+    assert call_count == 3
+    assert len(channel._app.bot.sent_messages) == 1
+
+
+@pytest.mark.asyncio
+async def test_send_text_gives_up_after_max_retries() -> None:
+    """_send_text raises TimedOut after exhausting all retries."""
+    from telegram.error import TimedOut
+
+    channel = TelegramChannel(
+        TelegramConfig(enabled=True, token="123:abc", allow_from=["*"]),
+        MessageBus(),
+    )
+    channel._app = _FakeApp(lambda: None)
+
+    async def always_timeout(**kwargs):
+        raise TimedOut()
+
+    channel._app.bot.send_message = always_timeout
+
+    import nanobot.channels.telegram as tg_mod
+    orig_delay = tg_mod._SEND_RETRY_BASE_DELAY
+    tg_mod._SEND_RETRY_BASE_DELAY = 0.01
+    try:
+        await channel._send_text(123, "hello", None, {})
+    finally:
+        tg_mod._SEND_RETRY_BASE_DELAY = orig_delay
+
+    assert channel._app.bot.sent_messages == []
 
 
 def test_derive_topic_session_key_uses_thread_id() -> None: