fix(feishu): preserve tool hints in final card content

Tool hints should be kept as permanent content in the streaming card
so users can see which tools were called (matching the standalone card
behavior). Previously, hints were stripped when new deltas arrived or
when the stream ended, causing tool call information to disappear.

Now:
- New delta: hint becomes permanent content, delta appends after it
- New tool hint: replaces the previous hint (unchanged)
- Resuming/stream_end: hint is preserved in the final text

Updated 3 tests to verify hint preservation semantics.

Made-with: Cursor

nanobot/channels/feishu.py

@@ -1287,9 +1287,7 @@ class FeishuChannel(BaseChannel):
                 # next segment appends to the same card.
                 buf = self._stream_bufs.get(chat_id)
                 if buf and buf.card_id and buf.text:
-                    if buf.tool_hint_len > 0:
-                        buf.text = buf.text[:-buf.tool_hint_len]
-                        buf.tool_hint_len = 0
+                    buf.tool_hint_len = 0
                     buf.sequence += 1
                     await loop.run_in_executor(
                         None, self._stream_update_text_sync, buf.card_id, buf.text, buf.sequence,
@@ -1299,9 +1297,7 @@ class FeishuChannel(BaseChannel):
             buf = self._stream_bufs.pop(chat_id, None)
             if not buf or not buf.text:
                 return
-            if buf.tool_hint_len > 0:
-                buf.text = buf.text[:-buf.tool_hint_len]
-                buf.tool_hint_len = 0
+            buf.tool_hint_len = 0
             if buf.card_id:
                 buf.sequence += 1
                 await loop.run_in_executor(
@@ -1338,7 +1334,6 @@ class FeishuChannel(BaseChannel):
             buf = _FeishuStreamBuf()
             self._stream_bufs[chat_id] = buf
         if buf.tool_hint_len > 0:
-            buf.text = buf.text[:-buf.tool_hint_len]
             buf.tool_hint_len = 0
         buf.text += delta
         if not buf.text.strip():