Fix Stop hook example prompt to prevent JSON parsing failures

[Haikane]

Summary

• Adds a JSON-only output instruction to the Stop hook example prompt in the README
• Adds a timeout field to the example (missing from original)
• Documents the pitfall so others don't hit it

Problem

The anti-rationalization Stop hook example asks Haiku to respond with {"ok": true} or {"ok": false, "reason": "..."}. Without an explicit formatting constraint, Haiku responds with:

```json
{"ok": true}
```

or:

The work appears complete. {"ok": true}

Both fail JSON parsing, producing Hooks: error parsing response as JSON in debug logs. The hook silently does nothing.

Fix

Prepend the prompt with:

You are a JSON-only evaluator. You MUST respond with a single JSON object and NOTHING else. No markdown, no code fences, no explanation, no preamble. Just the raw JSON object.

This is a README-only change. The Stop hook is intentionally not in settings.json (it's an opt-in pattern per the "patterns to adapt, not drop-in configs" guidance).

Test plan

• Copy the example into ~/.claude/settings.json and run a session with --verbose
• Verify debug logs show Model response: {"ok": true} (clean JSON, no fences)

🤖 Generated with Claude Code

[CLAassistant]

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