fix(telegram): preserve final-edit retry contract in rich stream upgrade

Address review feedback on the rich edit error classification:

- Transport, rate-limit, and unexpected errors now propagate instead of
  returning False. Returning False made send_delta fall through to an
  immediate legacy edit_message_text, which under connection-pool
  exhaustion doubled demand and discarded the buffered retry state that
  ChannelManager relies on.
- 'Message is not modified' is treated as success: when the rich edit is
  applied server-side but its response times out, the retry inside
  _call_with_retry reports the edit as already applied, and the previous
  BadRequest branch would have let the legacy edit overwrite the
  successful rich result.
- False is now returned only for capability errors (pre-10.1 servers,
  which still trip the rich latch) and content-shaped rejections, where
  the legacy HTML path is the intended fallback.

Adds regression coverage for a direct NetworkError (propagates, buffer
kept for manager retry) and TimedOut followed by Message-is-not-modified
(treated as success, no legacy overwrite).

nanobot/channels/telegram/runtime.py

@@ -902,9 +902,16 @@ class TelegramChannel(BaseChannel):
 
         Editing in place keeps the message identity, so the streaming preview is
         upgraded without the delete-and-resend pattern that caused flickering and
-        dropped line breaks (issue #4470). Returns True on success; on capability
-        errors (server older than Bot API 10.1) the rich latch is tripped so the
-        legacy HTML path is used from then on.
+        dropped line breaks (issue #4470).
+
+        Returns True when the rich edit is in place (including the ambiguous
+        "message is not modified" retry outcome after a response timeout).
+        Returns False only when the legacy HTML path should take over:
+        capability errors (server older than Bot API 10.1, which also trip the
+        rich latch) and content-shaped BadRequest rejections. Transport,
+        rate-limit, and unexpected errors propagate so the final-edit retry
+        contract is preserved — ChannelManager retries the buffered send
+        instead of an immediate legacy edit doubling connection demand.
         """
         if not self._app:
             return False
@@ -924,19 +931,27 @@ class TelegramChannel(BaseChannel):
             )
             return True
         except BadRequest as exc:
+            if self._is_not_modified_error(exc):
+                # Ambiguous success: the rich edit was applied server-side but
+                # its response timed out, so the retry hit "message is not
+                # modified". Treat it as done rather than letting the legacy
+                # edit overwrite the already-successful rich result.
+                self.logger.debug("Rich stream edit already applied for {}", chat_id)
+                return True
             if self._is_rich_capability_error(exc):
                 self.logger.debug("editMessageText rich_message not available, disabling")
                 self._rich_send_disabled = True
-            else:
-                self.logger.debug("editMessageText rich_message rejected: {}", exc)
-            return False
-        except Exception as exc:
-            err_str = str(exc).lower()
-            if "timed out" in err_str or isinstance(exc, TimedOut):
-                self.logger.debug("editMessageText rich_message timeout, falling back to legacy path")
                 return False
-            self.logger.debug("editMessageText rich_message failed: {}", exc)
+            # Content-shaped rejections (invalid markdown, unsupported media in
+            # the rich payload, …) fall back to the legacy HTML edit.
+            self.logger.debug("editMessageText rich_message rejected: {}", exc)
             return False
+        except Exception:
+            # Transport, rate-limit, and unexpected errors propagate so the
+            # final-edit retry contract stays intact: ChannelManager retries
+            # the buffered send instead of this handler doubling connection
+            # demand with an immediate legacy edit.
+            raise
 
     async def send(self, msg: OutboundMessage) -> None:
         """Send a message through Telegram."""

nanobot/channels/telegram/tests/test_telegram_channel.py

@@ -2808,3 +2808,54 @@ async def test_send_delta_stream_end_rich_disabled_uses_legacy_html() -> None:
     channel._app.bot.do_api_request.assert_not_called()
     channel._app.bot.edit_message_text.assert_awaited_once()
     assert "123" not in channel._stream_bufs
+
+
+@pytest.mark.asyncio
+async def test_send_delta_stream_end_rich_network_error_propagates_for_retry() -> None:
+    """A transport failure on the rich edit must propagate so ChannelManager
+    retries the buffered send — not fall through to an immediate legacy edit
+    that doubles connection demand during pool exhaustion."""
+    from telegram.error import NetworkError
+
+    channel = TelegramChannel(
+        TelegramConfig(enabled=True, token="123:abc", allow_from=["*"], rich_messages=True),
+        MessageBus(),
+    )
+    _install_ready_app(channel)
+    channel._app.bot.do_api_request = AsyncMock(side_effect=NetworkError("pool exhausted"))
+    channel._app.bot.edit_message_text = AsyncMock()
+    channel._stream_bufs["123"] = _StreamBuf(text="hello", message_id=7, last_edit=0.0)
+
+    with pytest.raises(NetworkError):
+        await channel.send_delta("123", "", stream_end=True)
+
+    # No legacy fallback edit: the buffered state stays for the manager retry.
+    channel._app.bot.edit_message_text.assert_not_awaited()
+    assert "123" in channel._stream_bufs
+
+
+@pytest.mark.asyncio
+async def test_send_delta_stream_end_rich_not_modified_after_timeout_is_success() -> None:
+    """Ambiguous success: the rich edit applied server-side but its response
+    timed out, so the retry hit "message is not modified". That is a completed
+    rich upgrade — the legacy edit must not overwrite it."""
+    from telegram.error import BadRequest, TimedOut
+
+    channel = TelegramChannel(
+        TelegramConfig(enabled=True, token="123:abc", allow_from=["*"], rich_messages=True),
+        MessageBus(),
+    )
+    _install_ready_app(channel)
+    # First attempt (inside _call_with_retry) times out, retry reports the
+    # edit as already applied.
+    channel._app.bot.do_api_request = AsyncMock(
+        side_effect=[TimedOut(), BadRequest("Message is not modified")]
+    )
+    channel._app.bot.edit_message_text = AsyncMock(side_effect=AssertionError("must not overwrite rich result"))
+    channel._stream_bufs["123"] = _StreamBuf(text="hello", message_id=7, last_edit=0.0)
+
+    await channel.send_delta("123", "", stream_end=True)
+
+    assert channel._app.bot.do_api_request.await_count == 2
+    channel._app.bot.edit_message_text.assert_not_awaited()
+    assert "123" not in channel._stream_bufs