[Bug] Auto-updater in-place binary overwrite causes SIGKILL on subsequent launches (macOS)

_Drafted by Claude Code itself during a live debugging session. I (the OP) reviewed and approved the wording before filing. The main use case is VS Code terminal and/or Cursor._

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Bug Description
Auto-update overwrites the binary in place; every new launch then dies with Killed: 9 (macOS)

Install: npm global (/opt/homebrew/lib/node_modules/@anthropic-ai/claude-code/), Apple Silicon, Darwin 23.5.0.
Seen twice: 2026-08-21, and 2026-09-28 on the 2.1.283 -> 2.1.284 update.

Symptom: after the auto-updater runs while a session is open, every new claude exits immediately with Killed: 9 (exit 137). There is no crash report. The session that ran the update keeps working.

Evidence (2026-09-28):

• bin/claude.exe mtime matches the timestamp in .last-update-result.json to the second.
• A byte-identical cp of claude.exe in the same directory (same SHA-256) runs fine and prints 2.1.284.
• mv-ing that copy over claude.exe fixes it with no reboot.
• First time (2026-08-21): quitting every claude process did not fix it; a reboot did. Second time (2026-09-28): replacing the binary as above fixed it without a reboot.
• Ruled out: memory pressure, code signing (codesign --verify --deep --strict and spctl both pass), and antivirus.

Likely cause: the updater rewrites claude.exe in place while a running process has it memory-mapped, so macOS's cached code-signing state for that inode goes stale and every new exec is killed.

Suggested fix: write the new binary to a temp file in the same directory and rename() it over the old one, so each update gets a fresh inode.

Environment Info

• Platform: darwin
• Terminal: Apple_Terminal
• Version: 2.1.284
• Feedback ID: 2e79a919-3475-49ad-ad54-13d9333832e0

Errors

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