Three fixes for inline tool hints:
1. Consecutive tool hints now replace the previous one instead of
stacking — the old suffix is stripped before appending the new one.
2. When _resuming flushes the buffer, any trailing tool hint suffix
is removed so it doesn't persist into the next streaming segment.
3. When final _stream_end closes the card, tool hint suffix is
cleaned from the text before the final card update.
Adds 3 regression tests covering all three scenarios.
Made-with: Cursor