Busy Copilot CLI Swallowed Messages

[thsparks]

Describe the bug

Summary
While the CLI was running slowly, messages I typed and submitted disappeared from the input box and were never delivered. The option to force-send them never appeared.

/diagnose suggested I also include:

• Session ID: 08276f64-567c-4ea6-9c77-5f2abcda3eda (2026-09-23, ~18:26–18:41 UTC)

What happened

• The agent looked hung. The status indicator said it was working, but no output or thinking appeared for several minutes.
• I typed several "ping" messages and pressed Enter. Each one vanished from the input box without showing up in the chat, and no force-send option appeared.
• I pressed Ctrl+C. Stopping took about 80 seconds (abort at 18:39:29, turn ended at 18:40:51). After that, only my last message ("Are you stuck?") appeared in the chat.

What the session log shows (via /diagnose)

• Only one of the pings exists in events.jsonl ("Are you stuck?", delivered at 18:36:41). The earlier ones were never recorded, so they seem to have been dropped before reaching the session.
• That message reached the agent about 3 minutes before my Ctrl+C, and the agent replied at 18:37:47. The UI didn't show it until after the abort, so the display was minutes behind.
• The CLI appeared to be very slow in this window. Tool events land on even 10-second marks, and small edit calls took 70–110 seconds each. Hooks finished in under 1 second, so they weren't the cause.
• Likely trigger (not confirmed): a single create call writing a ~47K-character file at ~18:30. The slowdown starts right after it, possibly from drawing the large diff in the terminal.
• No local process log in ~/.copilot/logs covers this window.

Affected version

GitHub Copilot CLI 1.0.89

Steps to reproduce the behavior

Regrettably I don't have a consistent repro, but the conditions when it occurred were:

• Long-running session with many tool calls, including a denied permission prompt
• In a separate window, I had a different copilot-cli session running, also a long session
• Agent then generated a single ~47K-character create tool call (took ~4 min to stream, ~60s to execute)

Steps:

1. In a long session, ask the agent to create a very large file (~50K chars) in one create call.
2. While the agent is generating/executing that call, type a message (e.g. "ping") and press Enter. Repeat several times with slightly different messages.
3. Observe: messages disappear from the input box, are not shown as queued, and no "send now" option appears.
4. Press Ctrl+C. After a delay, only the last typed message is delivered

Expected behavior

Ideally there would still be some UI feedback for the messages that are submitted/queued while the agent is busy, or a way to ensure the force-sending option appears. I've seen this happen at other times, but when there was extreme lag it seemed to get dropped.

Additional context

No response