killAgent() is a no-op — sidebar agent subprocess not terminated on kill/stop

[mr-k-man]

Summary

killAgent() in browse/src/server.ts:471 signals agentProcess, but agentProcess is never assigned after the queue-based refactor. spawnClaude() writes to sidebar-agent-queue.jsonl instead of spawning directly. The /sidebar-agent/kill and /sidebar-agent/stop endpoints reset local state (status, timestamps) but the actual claude subprocess in sidebar-agent.ts keeps running.

Impact

Users clicking "Stop" in the sidebar UI see the agent marked as stopped, but the real claude process continues executing — consuming API tokens and potentially making changes.

Fix

PR #664 adds a cancel-file protocol: killAgent() writes a cancel file, sidebar-agent.ts polls for it every 500ms during active processing, and kills the subprocess on detection.

Found via sqry AST-based semantic code graph analysis.