Ask before kill_window, kill_pane and kill_server #152

Summary

#149 makes kill_session ask the user before killing, when the client supports MCP elicitation. kill_window, kill_pane and kill_server still kill without asking, so the confirmation covers one of the four kill tools.

Motivation

Each of these ends processes the user may care about: every pane in a window, the process in a pane, or every session on a server. A user who sees kill_session ask would expect the others to ask too.

Proposal

Move the confirmation from session_tools.py into _utils.py as one helper, _ask_before_teardown(ctx, question, declined=..., identity=...), and call it from all four tools. A local spike did this.

• Questions name what the user would lose: the window's name, the command running in the pane, and the server's socket and session count.
• The target's identity is #{pid}:#{start_time}:<id>, using #{window_id} or #{pane_id}, and plain #{pid}:#{start_time} for the server. tmux numbers sessions, windows and panes from process-global counters that restart at zero with each server (session.c, window.c at 3.8). So an id alone can name a new object after a restart. start_time has one-second resolution, and pid separates two servers started in the same second.
• display-message -p '#{pid}:#{start_time}' works on a server with no attached client, so kill_server can carry an identity too.
• The tools become async and take a Context. fastmcp hides ctx from the input schema and drops InputRequiredResult from the output schema, so the tool-surface snapshot showed no change for the three tools.
• Tests: accept, decline, and a client without elicitation, for each tool on 2025-11-25 and 2026-07-28. Existing tests that call these tools directly need asyncio.run.

The delete_buffer and clear_pane tools also sit in the teardown toolset; whether they should ask is a separate question.

References

• mcp(feat): Confirm kill_session, add pane viewer and icons #149 adds the confirmation to kill_session
• tmux session.c session-id counter at 3.8
• tmux window.c window and pane id counters at 3.8