diff --git a/backend/app/channels/feishu.py b/backend/app/channels/feishu.py
index 32f71f1f6..6492d28e5 100644
--- a/backend/app/channels/feishu.py
+++ b/backend/app/channels/feishu.py
@@ -206,7 +206,9 @@ class FeishuChannel(Channel):
                     await asyncio.sleep(delay)
 
         logger.error("[Feishu] send failed after %d attempts: %s", _max_retries, last_exc)
-        raise last_exc  # type: ignore[misc]
+        if last_exc is None:
+            raise RuntimeError("Feishu send failed without an exception from any attempt")
+        raise last_exc
 
     async def send_file(self, msg: OutboundMessage, attachment: ResolvedAttachment) -> bool:
         if not self._api_client:
diff --git a/backend/app/channels/slack.py b/backend/app/channels/slack.py
index 760911083..32b42e5a8 100644
--- a/backend/app/channels/slack.py
+++ b/backend/app/channels/slack.py
@@ -126,7 +126,9 @@ class SlackChannel(Channel):
                 )
             except Exception:
                 pass
-        raise last_exc  # type: ignore[misc]
+        if last_exc is None:
+            raise RuntimeError("Slack send failed without an exception from any attempt")
+        raise last_exc
 
     async def send_file(self, msg: OutboundMessage, attachment: ResolvedAttachment) -> bool:
         if not self._web_client:
diff --git a/backend/app/channels/telegram.py b/backend/app/channels/telegram.py
index 97c50aa9f..9985fd43f 100644
--- a/backend/app/channels/telegram.py
+++ b/backend/app/channels/telegram.py
@@ -125,7 +125,9 @@ class TelegramChannel(Channel):
                     await asyncio.sleep(delay)
 
         logger.error("[Telegram] send failed after %d attempts: %s", _max_retries, last_exc)
-        raise last_exc  # type: ignore[misc]
+        if last_exc is None:
+            raise RuntimeError("Telegram send failed without an exception from any attempt")
+        raise last_exc
 
     async def send_file(self, msg: OutboundMessage, attachment: ResolvedAttachment) -> bool:
         if not self._application:
diff --git a/backend/app/gateway/routers/threads.py b/backend/app/gateway/routers/threads.py
index 562edfdb7..808604980 100644
--- a/backend/app/gateway/routers/threads.py
+++ b/backend/app/gateway/routers/threads.py
@@ -488,16 +488,19 @@ async def get_thread(thread_id: str, request: Request) -> ThreadResponse:
             "metadata": {k: v for k, v in ckpt_meta.items() if k not in ("created_at", "updated_at", "step", "source", "writes", "parents")},
         }
 
-    status = _derive_thread_status(checkpoint_tuple) if checkpoint_tuple is not None else record.get("status", "idle")  # type: ignore[union-attr]
+    if record is None:
+        raise HTTPException(status_code=404, detail=f"Thread {thread_id} not found")
+
+    status = _derive_thread_status(checkpoint_tuple) if checkpoint_tuple is not None else record.get("status", "idle")
     checkpoint = getattr(checkpoint_tuple, "checkpoint", {}) or {} if checkpoint_tuple is not None else {}
     channel_values = checkpoint.get("channel_values", {})
 
     return ThreadResponse(
         thread_id=thread_id,
         status=status,
-        created_at=str(record.get("created_at", "")),  # type: ignore[union-attr]
-        updated_at=str(record.get("updated_at", "")),  # type: ignore[union-attr]
-        metadata=record.get("metadata", {}),  # type: ignore[union-attr]
+        created_at=str(record.get("created_at", "")),
+        updated_at=str(record.get("updated_at", "")),
+        metadata=record.get("metadata", {}),
         values=serialize_channel_values(channel_values),
     )
 
diff --git a/backend/tests/test_channels.py b/backend/tests/test_channels.py
index c48137c76..fb58bcfb4 100644
--- a/backend/tests/test_channels.py
+++ b/backend/tests/test_channels.py
@@ -1854,6 +1854,20 @@ class TestSlackSendRetry:
 
         _run(go())
 
+    def test_raises_runtime_error_when_no_attempts_configured(self):
+        from app.channels.slack import SlackChannel
+
+        async def go():
+            bus = MessageBus()
+            ch = SlackChannel(bus=bus, config={"bot_token": "xoxb-test", "app_token": "xapp-test"})
+            ch._web_client = MagicMock()
+
+            msg = OutboundMessage(channel_name="slack", chat_id="C123", thread_id="t1", text="hello")
+            with pytest.raises(RuntimeError, match="without an exception"):
+                await ch.send(msg, _max_retries=0)
+
+        _run(go())
+
 
 # ---------------------------------------------------------------------------
 # Telegram send retry tests
@@ -1912,6 +1926,36 @@ class TestTelegramSendRetry:
 
         _run(go())
 
+    def test_raises_runtime_error_when_no_attempts_configured(self):
+        from app.channels.telegram import TelegramChannel
+
+        async def go():
+            bus = MessageBus()
+            ch = TelegramChannel(bus=bus, config={"bot_token": "test-token"})
+            ch._application = MagicMock()
+
+            msg = OutboundMessage(channel_name="telegram", chat_id="12345", thread_id="t1", text="hello")
+            with pytest.raises(RuntimeError, match="without an exception"):
+                await ch.send(msg, _max_retries=0)
+
+        _run(go())
+
+
+class TestFeishuSendRetry:
+    def test_raises_runtime_error_when_no_attempts_configured(self):
+        from app.channels.feishu import FeishuChannel
+
+        async def go():
+            bus = MessageBus()
+            ch = FeishuChannel(bus=bus, config={"app_id": "id", "app_secret": "secret"})
+            ch._api_client = MagicMock()
+
+            msg = OutboundMessage(channel_name="feishu", chat_id="chat", thread_id="t1", text="hello")
+            with pytest.raises(RuntimeError, match="without an exception"):
+                await ch.send(msg, _max_retries=0)
+
+        _run(go())
+
 
 # ---------------------------------------------------------------------------
 # Telegram private-chat thread context tests