## Problem

The Codex PR reviewer (`gautam-chatgpt`) intermittently failed with
`No valid JSON found in response` on `gbharg/pi-mono` PRs #28-32, posting
`⚠️ Codex: Review failed` instead of a real review. The same PR sometimes
parsed and sometimes did not, which pointed at output framing rather than a
broken model call.

## Root cause

`codex exec` does not always emit clean JSON on stdout. It can frame the
answer with a session transcript, a leading `codex` marker line, and a
trailing `tokens used` epilogue. That surrounding prose frequently contains
stray `{`/`}` (shell snippets, file trees, JSON examples in skill docs).

The old `parse-response.js` fell back to a naive `text.indexOf('{')` …
`text.lastIndexOf('}')` slice. When a stray brace appeared before the real
object, the slice spanned non-JSON prose and `JSON.parse` threw. Whether it
failed depended on whether the transcript happened to contain stray braces —
exactly the observed intermittency.

This is codex-specific framing; gemini/claude emit clean or fenced JSON.

## Fix (`pr-review-shared/lib`)

- `parse-response.js`: replace the first-`{`/last-`}` heuristic with a
  string-aware balanced-brace scan (a stack of open positions, so an
  unmatched stray `{` in prose can never absorb the real object). Prefer the
  LAST review-shaped object, since codex prints its answer after the
  transcript. Direct-parse and fence-strip fast paths are kept first, so
  gemini/claude are unaffected.
- `parseReviewWithRepair()`: one repair re-ask that demands pure JSON, as a
  last-resort net for genuinely truncated/empty output.
- `review-handler.js` (shared by codex/gemini/claude): call
  `parseReviewWithRepair`.

## Verification

- Replayed the real failing codex prompt: the new parser extracts the
  correct review from the full ~19 KB codex session transcript (the exact
  shape the old parser choked on), and from clean stdout.
- Added tests for transcript-framed, fenced, and stray-brace inputs plus the
  repair retry. `npm test` → **97 passed (97)**.
- Deploy copy at `/home/claude/repos/pr-review-shared` updated identically;
  `codex-pr-reviewer` restarted and confirmed posting structured reviews
  again on pi-mono.

Author: Gautam AI <gautamai@icloud.com>

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