vercel plugin: SessionEnd hook (session-end-cleanup.mjs) intermittently fails with "Hook cancelled" — missing timeout in hooks.json

[jg-shoealls]

Title

vercel plugin: SessionEnd hook (session-end-cleanup.mjs) intermittently fails with "Hook cancelled" — missing timeout in hooks.json

Environment

• Plugin: vercel@claude-plugins-official, version 0.45.1 (confirmed latest via claude plugin update)
• OS: Windows 10, Git Bash shell
• Node: v24.15.0
• Trigger context observed: non-interactive claude -p "<prompt>" session

Summary

The vercel plugin's SessionEnd hook (hooks/session-end-cleanup.mjs) occasionally fails at session teardown with:

SessionEnd hook [node "${CLAUDE_PLUGIN_ROOT}/hooks/session-end-cleanup.mjs"] failed: Hook cancelled

Root cause (as far as I could determine)

Looking at hooks/hooks.json in the installed plugin:

"SessionEnd": [
  {
    "hooks": [
      {
        "type": "command",
        "command": "node \"${CLAUDE_PLUGIN_ROOT}/hooks/session-end-cleanup.mjs\""
      }
    ]
  }
]

This is the only hook entry in the file with no "timeout" field — every other hook in the same plugin (and in other plugins, e.g. claude-mem) declares one.

session-end-cleanup.mjs reads its session id synchronously from stdin:

function parseSessionIdFromStdin() {
  return normalizeSessionEndSessionId(parseSessionEndHookInput(readFileSync(0, "utf8")));
}

Manually piping valid input into the script completes instantly and exits 0:

echo '{"session_id":"abc123"}' | node session-end-cleanup.mjs
# exit 0, immediate

So the script logic itself is not the problem. The suspicion is that when the harness doesn't close stdin promptly for this hook (observed specifically after a non-interactive claude -p session on Windows), the blocking readFileSync(0, ...) call hangs until some default/harness-level cancellation kicks in — which would explain "Hook cancelled" rather than a script error or non-zero exit.

Impact

Low / cosmetic. The hook only deletes temp files matching vercel-plugin-<sessionId>-* in the OS temp dir. A cancelled run just leaves those temp files behind; no data loss or effect on session behavior.

Suggested fix

• Add an explicit "timeout" to the SessionEnd hook entry in hooks.json, consistent with the other hooks in the plugin.
• Consider making the stdin read robust to a not-yet-closed stream (e.g., an explicit read timeout/fallback inside session-end-cleanup.mjs itself) rather than relying solely on the harness's hook-level timeout.

Repro steps

1. Install vercel@claude-plugins-official (v0.45.1).
2. Run a non-interactive session: claude -p "<any task-oriented prompt>" on Windows.
3. Observe the SessionEnd hook [...] failed: Hook cancelled message at teardown (intermittent, not on every run).