Best possible solution:

Keep the PR focused on the heartbeat failure-copy fix, but classify both stale generic rewrites and direct heartbeat-specific runner-failure payloads as failed heartbeat events before merge.

Do we have a high-confidence way to reproduce the issue?

Yes, at source level: current main can convert an unclassified heartbeat runner error into the generic foreground failure payload, and the linked issue includes a live Discord report. I did not execute the repro in this read-only review.

Is this the best way to solve the issue?

No, not quite: the copy split is in the right area, but the delivery-side failure classification only handles stale generic rewrites and misses the new direct heartbeat-specific failure path.

Full review comments:

• [P2] Classify direct heartbeat failures as failed — src/infra/heartbeat-runner.ts:1829
  The new agent-runner path returns HEARTBEAT_EXTERNAL_RUN_FAILURE_TEXT for raw heartbeat failures before the heartbeat runner sees the payload. Because deliveredAgentRunFailure is only replacement.replaced, that normal path sends the fixed copy but still emits a sent heartbeat event with no agent-runner-failure reason. Treat the heartbeat-specific failure copy or metadata as an agent-runner failure too, and cover the full runner path.
  Confidence: 0.87

Overall correctness: patch is incorrect
Overall confidence: 0.84

Acceptance criteria:

• node scripts/run-vitest.mjs src/auto-reply/reply/agent-runner-execution.test.ts src/infra/heartbeat-runner.tool-response.test.ts
• .agents/skills/codex-review/scripts/codex-review --mode auto

What I checked:

• Current main source path: Current main still defines the generic external runner failure text with /new guidance and uses it as the fallback for unclassified external runner errors before the PR changes this path. (src/auto-reply/reply/agent-runner-execution.ts:582, d887eb8dc2cc)
• PR direct heartbeat copy path: On the PR head, buildExternalRunFailureReply returns HEARTBEAT_EXTERNAL_RUN_FAILURE_TEXT whenever isHeartbeat is set, before later generic/CLI mismatch fallbacks run. (src/auto-reply/reply/agent-runner-execution.ts:607, 0a87501f4cb5)
• PR delivery classification gap: The heartbeat runner only sets deliveredAgentRunFailure from replacement.replaced, so an already heartbeat-specific failure payload from the new direct path is delivered with sentStatus = "sent". (src/infra/heartbeat-runner.ts:1829, 0a87501f4cb5)
• Regression coverage shape: The new heartbeat-runner test covers a stale generic payload rewrite and expects a failed heartbeat event, while the direct raw external error test stops at runAgentTurnWithFallback and does not cover the full heartbeat runner event path. (src/infra/heartbeat-runner.tool-response.test.ts:273, 0a87501f4cb5)
• Related canonical issue: GitHub search found the linked bug report and this PR as the matching heartbeat /new failure-copy cluster; no more canonical merged fix was found in that search result set.
• Real behavior proof in PR body: The PR body reports a Crabbox AWS run (cbx_a7790d85a34e, run_c01ca3c5129b) where the Discord heartbeat message used heartbeat-specific failure copy and did not include /new. (0a87501f4cb5)

Likely related people:

• steipete: Recent commits touch both heartbeat runner behavior and agent-runner fallback/failure paths, including heartbeat reply fallback binding and auto-fallback probing. (role: recent area contributor; confidence: high; commits: bea4f0d2f4b4, c8782d18ebd4, 391b4916dcf2; files: src/infra/heartbeat-runner.ts, src/auto-reply/reply/agent-runner-execution.ts)
• zeroaltitude: Authored a recent multi-agent heartbeat cadence and session-target fix touching the central heartbeat runner area. (role: heartbeat feature contributor; confidence: medium; commits: b247b1432fc2; files: src/infra/heartbeat-runner.ts)
• joshavant: Beyond authoring this PR, recent current-main history shows a merged fallback provenance fix in the agent-runner execution area. (role: adjacent fallback-path contributor; confidence: medium; commits: 1dac68c0bbe7; files: src/auto-reply/reply/agent-runner-execution.ts)
• hclsys: Recent heartbeat-runner history includes pending-delivery replay behavior, adjacent to the heartbeat delivery normalization path touched here. (role: adjacent heartbeat contributor; confidence: medium; commits: 06d8cd1b230b; files: src/infra/heartbeat-runner.ts)

Remaining risk / open question:

• Focused tests and Crabbox proof are reported in the PR body, but this read-only review did not execute tests locally.
• The PR body says broad GitHub CI was still pending.

Codex review notes: model gpt-5.5, reasoning high; reviewed against d887eb8dc2cc.