fix(examples): improve gemini.py CLI experience

- Support --acp flag with --experimental-acp fallback for older versions
- Suppress Gemini CLI stderr noise in non-debug mode
- Drain stdin before terminating subprocess for cleaner shutdown
- Catch KeyboardInterrupt in main() to avoid noisy traceback

Co-Authored-By: Claude Sonnet 4 <noreply@anthropic.com>

Author: whhe

docs/quickstart.md

@@ -16,7 +16,7 @@ Spin up a working ACP agent/client loop in minutes. Keep this page beside the te
 
 - Python 3.10–3.14 with `pip` or `uv`
 - An ACP-capable client such as Zed (recommended for validation)
-- Optional: the Gemini CLI (`gemini --experimental-acp`) for the bridge example
+- Optional: the Gemini CLI (`gemini --acp`; use `--experimental-acp` for older versions) for the bridge example
 
 ## Step 1 — Install the SDK
 
@@ -145,7 +145,7 @@ Run it with `run_agent()` inside an async entrypoint and wire it to your client.
 - [`examples/echo_agent.py`](https://github.com/agentclientprotocol/python-sdk/blob/main/examples/echo_agent.py) for the smallest streaming agent
 - [`examples/agent.py`](https://github.com/agentclientprotocol/python-sdk/blob/main/examples/agent.py) for an implementation that negotiates capabilities and streams richer updates
 - [`examples/duet.py`](https://github.com/agentclientprotocol/python-sdk/blob/main/examples/duet.py) to see `spawn_agent_process` in action alongside the interactive client
-- [`examples/gemini.py`](https://github.com/agentclientprotocol/python-sdk/blob/main/examples/gemini.py) to drive the Gemini CLI (`--acp`) directly from Python
+- [`examples/gemini.py`](https://github.com/agentclientprotocol/python-sdk/blob/main/examples/gemini.py) to drive the Gemini CLI (`--acp`; use `--experimental-acp` for older versions) directly from Python
 
 Need builders for common payloads? `acp.helpers` mirrors the Go/TS helper APIs:
 

examples/gemini.py

@@ -328,7 +328,8 @@ async def run(argv: list[str]) -> int:  # noqa: C901
             *cmd,
             stdin=asyncio.subprocess.PIPE,
             stdout=asyncio.subprocess.PIPE,
-            stderr=None,
+            # Suppress Gemini CLI diagnostic noise unless debugging
+            stderr=None if args.debug else asyncio.subprocess.DEVNULL,
         )
     except FileNotFoundError as exc:
         print(f"Failed to start Gemini CLI: {exc}", file=sys.stderr)
@@ -412,6 +413,10 @@ def _print_request_error(stage: str, err: RequestError) -> None:
 async def _shutdown(proc: asyncio.subprocess.Process, conn: ClientSideConnection) -> None:
     with contextlib.suppress(Exception):
         await asyncio.wait_for(conn.close(), timeout=2)
+    if proc.stdin is not None:
+        with contextlib.suppress(Exception):
+            proc.stdin.close()
+            await asyncio.wait_for(proc.stdin.wait_closed(), timeout=2)
     if proc.returncode is None:
         proc.terminate()
         try:
@@ -424,7 +429,10 @@ async def _shutdown(proc: asyncio.subprocess.Process, conn: ClientSideConnection
 
 def main(argv: list[str] | None = None) -> int:
     args = sys.argv if argv is None else argv
-    return asyncio.run(run(list(args)))
+    try:
+        return asyncio.run(run(list(args)))
+    except KeyboardInterrupt:
+        return 1
 
 
 if __name__ == "__main__":