Stop review gate fails open when hook stdin is malformed JSON

Description

stop-review-gate-hook.mjs parses hook stdin before entering the review-gate logic. A malformed non-empty JSON payload throws an uncaught SyntaxError, exits with status 1, and emits no decision: "block" response. When the host treats a crashed Stop hook as having supplied no block decision, the review gate can fail open.

Reproduction

With plugin 1.0.2:

printf '%s' '{not-json' | node scripts/stop-review-gate-hook.mjs

Observed result:

SyntaxError: Expected property name or '}' in JSON at position 1
    at JSON.parse
    at readHookInput (.../stop-review-gate-hook.mjs:26:15)
    at main (.../stop-review-gate-hook.mjs:143:17)

The process exits 1 without emitting hook JSON.

Root cause

readHookInput() calls JSON.parse(raw) without a catch, and main() calls readHookInput() before any fail-closed handling:

function readHookInput() {
  const raw = fs.readFileSync(0, "utf8").trim();
  if (!raw) return {};
  return JSON.parse(raw);
}

Expected behavior

Any failure to read or parse Stop-hook input should emit a valid fail-closed response, for example:

{"decision":"block","reason":"The stop review gate could not parse hook input; refusing to fail open."}

A regression test should feed malformed non-empty stdin and assert exit 0 plus a valid decision: "block" payload.

Related

• #120 reports a separate readHookInput() failure mode (EAGAIN). The malformed-JSON case is deterministic and specifically requires fail-closed Stop-gate behavior.

Environment

• Codex plugin: 1.0.2
• Claude Code: 2.1.241
• Node.js: 24.17.0
• OS: WSL2 / Linux

Start with scripts/stop-review-gate-hook.mjs and reproduce the issue using the provided printf and node command. Trace readHookInput() into main(), then add a regression test that feeds malformed non-empty stdin and verifies exit 0 with a valid decision: "block" response. Done means malformed input cannot make the Stop hook fail open.