Best possible solution:

Preserve independent Testbox sessions unless maintainers explicitly approve a one-active-session-per-ref policy; if cancellation is still desired, key it on an explicit supersession/session identity rather than only github.ref.

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

Yes from source inspection: the workflow is manually dispatched with a per-session testbox_id, while the PR groups cancellation only by github.ref. A live Blacksmith run was not needed to see that two documented main dispatches would share one concurrency group.

Is this the best way to solve the issue?

No, not as-is: a ref-only key is too broad for a session-oriented workflow_dispatch workflow. The narrow maintainable fix is an explicit supersession key, or a maintainer-approved policy that one active Testbox per ref is intentional.

Full review comments:

• [P1] Narrow Testbox cancellation key — .github/workflows/ci-check-testbox.yml:15-16
  This workflow is dispatched per Testbox session using testbox_id, and the documented Crabbox path runs against --blacksmith-ref main. Keying cancellation only on github.ref means a second independent main-session dispatch cancels the first one instead of only cancelling a superseded registration. Please include an explicit session or supersession identity in the group, or document and get approval for a one-active-session-per-ref policy before enabling cancellation.
  Confidence: 0.89

Overall correctness: patch is incorrect
Overall confidence: 0.87

AGENTS.md: not found in the target repository.

Codex review notes: model internal, reasoning high; reviewed against 18fb855c8ccd.

Label changes:

• add P2: The PR affects repository automation and can cancel active validation sessions, but the blast radius is limited to the Testbox workflow.
• add merge-risk: 🚨 automation: The diff changes GitHub Actions scheduling semantics by cancelling in-progress Testbox workflow runs after merge.
• add rating: 🧂 unranked krab: Overall readiness is 🧂 unranked krab; proof is 🌊 off-meta tidepool and patch quality is 🧂 unranked krab.
• add status: ⏳ waiting on author: ClawSweeper has contributor-facing work open and is waiting for author action. Not applicable: The external-contributor proof gate does not apply because the PR is member-authored and changes workflow scheduling policy rather than an externally demonstrated runtime behavior.

Label justifications:

• P2: The PR affects repository automation and can cancel active validation sessions, but the blast radius is limited to the Testbox workflow.
• merge-risk: 🚨 automation: The diff changes GitHub Actions scheduling semantics by cancelling in-progress Testbox workflow runs after merge.
• rating: 🧂 unranked krab: Overall readiness is 🧂 unranked krab; proof is 🌊 off-meta tidepool and patch quality is 🧂 unranked krab.
• status: ⏳ waiting on author: ClawSweeper has contributor-facing work open and is waiting for author action. Not applicable: The external-contributor proof gate does not apply because the PR is member-authored and changes workflow scheduling policy rather than an externally demonstrated runtime behavior.

What I checked:

• Target AGENTS.md check: No AGENTS.md is tracked or present inside the target repository checkout, so no target-specific AGENTS policy applied.
• Current Testbox workflow is per session: Current main exposes a required workflow_dispatch input named testbox_id and passes it to useblacksmith/begin-testbox@v2, so individual dispatches represent separate Testbox sessions. (.github/workflows/ci-check-testbox.yml:4, 18fb855c8ccd)
• Documented Crabbox path defaults to main: The workflow README documents crabbox run --provider blacksmith-testbox with --blacksmith-ref main, meaning independent normal Testbox sessions commonly share the same Git ref. (.github/workflows/README.md:24, 18fb855c8ccd)
• PR concurrency key is ref-only: The PR adds group: clawbench-testbox-${{ github.ref }} and cancel-in-progress: true, which cannot distinguish separate testbox_id dispatches on the same ref. (.github/workflows/ci-check-testbox.yml:15, 34c7e0d08339)
• Diff validation: The PR diff is narrow and YAML parsing plus whitespace checks did not report syntax problems. (.github/workflows/ci-check-testbox.yml:14, 34c7e0d08339)
• Workflow history: The Testbox workflow was introduced by commit fc86dd6, and adjacent CI runner-burst work was merged in fix(ci): serialize Clawbench test runners #33. (.github/workflows/ci-check-testbox.yml:1, fc86dd615523)

Likely related people:

• vincentkoc: They introduced the Blacksmith Testbox workflow on main and recently merged adjacent CI runner-serialization work, so they are the strongest routing candidate for this workflow behavior. (role: feature history owner and recent area contributor; confidence: high; commits: fc86dd615523, 18fb855c8ccd; files: .github/workflows/ci-check-testbox.yml, .github/workflows/README.md, .github/workflows/ci.yml)
• scoootscooob: They introduced the original CI workflow and the repository's existing github.ref concurrency pattern, which is relevant comparison context but not the Testbox session owner. (role: adjacent workflow introducer; confidence: medium; commits: b6f07d9a8796; files: .github/workflows/ci.yml)

• 🦀 challenger crab: rare, exceptional readiness with strong proof, clean implementation, and convincing validation.
• 🦞 diamond lobster: very strong readiness with only minor maintainer review expected.
• 🐚 platinum hermit: good normal PR, likely mergeable with ordinary maintainer review.
• 🦐 gold shrimp: useful signal, but proof or patch confidence is still limited.
• 🦪 silver shellfish: thin signal; proof, validation, or implementation needs work.
• 🧂 unranked krab: not merge-ready because proof is missing/unusable or there are serious correctness or safety concerns.
• 🌊 off-meta tidepool: rating does not apply to this item.

Shiny media proof means a screenshot, video, or linked artifact directly shows the changed behavior. Runtime, network, CSP, and security claims still need visible diagnostics.

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