fix(weixin): raise exceptions instead of silently dropping messages

_send_text() swallowed API errors (non-zero errcode) with just a
warning log, and send() had three silent return paths (no client,
session paused, no context_token). Neither triggered ChannelManager's
retry logic, causing persistent message loss until a new inbound
message refreshed the context_token.

Now all failure paths raise RuntimeError, matching BaseChannel's
contract and enabling proper retry behavior.

tests/channels/test_weixin_channel.py

@@ -319,21 +319,22 @@ async def test_process_message_does_not_fallback_when_top_level_media_exists_but
 
 
 @pytest.mark.asyncio
-async def test_send_without_context_token_does_not_send_text() -> None:
+async def test_send_without_context_token_raises() -> None:
     channel, _bus = _make_channel()
     channel._client = object()
     channel._token = "token"
     channel._send_text = AsyncMock()
 
-    await channel.send(
-        type("Msg", (), {"chat_id": "unknown-user", "content": "pong", "media": [], "metadata": {}})()
-    )
+    with pytest.raises(RuntimeError, match="No context_token"):
+        await channel.send(
+            type("Msg", (), {"chat_id": "unknown-user", "content": "pong", "media": [], "metadata": {}})()
+        )
 
     channel._send_text.assert_not_awaited()
 
 
 @pytest.mark.asyncio
-async def test_send_does_not_send_when_session_is_paused() -> None:
+async def test_send_raises_when_session_is_paused() -> None:
     channel, _bus = _make_channel()
     channel._client = object()
     channel._token = "token"
@@ -341,9 +342,10 @@ async def test_send_does_not_send_when_session_is_paused() -> None:
     channel._pause_session(60)
     channel._send_text = AsyncMock()
 
-    await channel.send(
-        type("Msg", (), {"chat_id": "wx-user", "content": "pong", "media": [], "metadata": {}})()
-    )
+    with pytest.raises(RuntimeError, match="session paused"):
+        await channel.send(
+            type("Msg", (), {"chat_id": "wx-user", "content": "pong", "media": [], "metadata": {}})()
+        )
 
     channel._send_text.assert_not_awaited()
 
@@ -1213,3 +1215,38 @@ async def test_send_media_network_error_does_not_double_api_calls() -> None:
     # _send_media_file called once, _send_text never called
     channel._send_media_file.assert_awaited_once()
     channel._send_text.assert_not_awaited()
+
+
+# ---------------------------------------------------------------------------
+# Tests for _send_text raising on API errors (previously silently swallowed)
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_send_text_raises_on_api_error() -> None:
+    """_send_text must raise RuntimeError when the API returns a non-zero errcode,
+    matching _send_media_file behavior. This ensures ChannelManager can retry."""
+    channel, _bus = _make_channel()
+    channel._client = httpx.AsyncClient()
+    channel._token = "token"
+    channel._api_post = AsyncMock(
+        return_value={"errcode": -14, "errmsg": "session expired"}
+    )
+
+    with pytest.raises(RuntimeError, match="WeChat send text error.*-14"):
+        await channel._send_text("wx-user", "hello", "ctx-expired")
+
+    channel._api_post.assert_awaited_once()
+
+
+@pytest.mark.asyncio
+async def test_send_text_succeeds_on_zero_errcode() -> None:
+    """_send_text must NOT raise when errcode is 0."""
+    channel, _bus = _make_channel()
+    channel._client = httpx.AsyncClient()
+    channel._token = "token"
+    channel._api_post = AsyncMock(return_value={"errcode": 0})
+
+    await channel._send_text("wx-user", "hello", "ctx-ok")
+
+    channel._api_post.assert_awaited_once()