SessionEnd cleanup hook gets cancelled on exit — hooks.json ships no `timeout`, and Claude Code's default for SessionEnd hooks is only 1.5s

Problem

On session exit, the plugin's SessionEnd hook is reported as failed on every substantive session close:

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

This is not just a display artifact — the cleanup genuinely does not run. The session-scoped dedup temp files (<tmpdir>/vercel-plugin-<sessionId>-*, the claim dir / seen-skills state described in the plugin's own dedup contract) are left behind for closed sessions:

$ ls /tmp | grep vercel-plugin
vercel-plugin-1ec5a71c-...-greenfield.txt      # session closed at 22:10 — cleanup never ran
vercel-plugin-1ec5a71c-...-likely-skills.txt

Root cause

hooks/hooks.json declares the SessionEnd hook with no timeout field (current main, blob 3c6562c).

In Claude Code (verified in the 2.1.214 bundle), executeSessionEndHooks invokes the hook runner with a default timeoutMs of 1500 for SessionEnd specifically. Per hook, the budget is hook.timeout * 1000 if configured, else that 1500ms default. A hook that exceeds its budget is aborted (ABORT_ERR → "Hook cancelled").

session-end-cleanup.mjs itself is fast — standalone it exits 0 in ~50ms:

$ echo '{"session_id":"x"}' | node hooks/session-end-cleanup.mjs   # 0.047s, exit 0

But at a real session close the 1.5s window is easily consumed before the hook finishes: session teardown (notably with "tui": "fullscreen") plus sibling SessionEnd hooks run in the same instant. anthropics/claude-code#70465 (open) documents this exact class — a sub-second exit 0 SessionEnd hook cancelled alongside busy siblings. In my setup, user-configured SessionEnd hooks that declare explicit timeout values (10–30s) run to completion every close; the plugin's hook — the only SessionEnd hook without a timeout — is the only one that gets cancelled.

There's a second cost of not declaring a timeout: Claude Code derives its SessionEnd force-exit grace from the max configured timeout across all SessionEnd hooks, clamped to [1.5s, 60s]. For users whose only SessionEnd hook is this plugin's, everything collapses to the 1.5s floor.

Suggested fix

Declare a timeout on the SessionEnd hook (same one-field-per-hook shape as the shell fix proposed in #79):

     "SessionEnd": [
       {
         "hooks": [
           {
             "type": "command",
-            "command": "node \"${CLAUDE_PLUGIN_ROOT}/hooks/session-end-cleanup.mjs\""
+            "command": "node \"${CLAUDE_PLUGIN_ROOT}/hooks/session-end-cleanup.mjs\"",
+            "timeout": 15
           }
         ]
       }
     ]

This has no latency cost in the normal case — the hook still exits in milliseconds; the timeout only widens the abort window so teardown contention can't kill it. In the same environment, every SessionEnd hook that declares an explicit timeout completes on every close; only this one — the only one relying on the 1.5s default — gets cancelled.

timeout is a documented per-hook field in the hooks reference, and the plugin's own doctor already reasons about hook timeout risk, so this seems like the intended knob.

Environment

• Claude Code 2.1.214, "tui": "fullscreen"
• vercel-plugin 0.44.0 (marketplace install)
• Linux x86_64 (Arch-based)

Related

• anthropics/claude-code#70465 — open: SessionEnd hooks killed on exit, fast siblings included, no configurable grace
• anthropics/claude-code#63495 — closed: the display-only variant (hook exits 0 but message still shown). Distinct from this report: here the leftover temp files prove the cleanup really doesn't run.
• #79 — same file, precedent for adding per-hook fields to hooks.json

Start in hooks/hooks.json and inspect the SessionEnd hook for session-end-cleanup.mjs, then review the hook timeout reference and the precedent in #79. Verify the configured timeout prevents cancellation during session teardown and run the standalone node command from the report to confirm the cleanup hook exits successfully.