Best possible solution:

Land the deterministic Slack traces as the Phase 0 conformance oracle after the branch receives the repository’s normal maintainer refresh and exact-head gates, preserving the documented intentional sensitivity to the pinned Slack SDK buffering contract.

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

Not applicable; this PR characterizes existing Slack delivery behavior rather than reporting a failing user-visible bug. The scenarios are source-verifiable against current production branches and the pinned Slack SDK.

Is this the best way to solve the issue?

Yes; extending the existing shared delivery-trace harness at the real Slack dispatch seam is the narrowest maintainable way to lock wire behavior before the channel refactor, without adding a parallel runtime path.

AGENTS.md: found and applied where relevant.

Codex review notes: model internal, reasoning high; reviewed against 702ba19e3aba.

Label changes:

• add P3: This is low-risk test infrastructure that strengthens refactor safety without changing runtime behavior.
• add rating: 🦞 diamond lobster: Overall readiness is 🦞 diamond lobster; proof is 🦞 diamond lobster and patch quality is 🦞 diamond lobster.
• add status: 👀 ready for maintainer look: ClawSweeper has no concrete contributor-facing blocker left for this PR. Not applicable: The protected maintainer-labeled, test-only PR is outside the external-contributor proof gate; its reported Testbox trace replay, full Slack suite, repeated golden verification, and Linux Node 24 run provide strong validation evidence.

Label justifications:

• P3: This is low-risk test infrastructure that strengthens refactor safety without changing runtime behavior.
• rating: 🦞 diamond lobster: Overall readiness is 🦞 diamond lobster; proof is 🦞 diamond lobster and patch quality is 🦞 diamond lobster.
• status: 👀 ready for maintainer look: ClawSweeper has no concrete contributor-facing blocker left for this PR. Not applicable: The protected maintainer-labeled, test-only PR is outside the external-contributor proof gate; its reported Testbox trace replay, full Slack suite, repeated golden verification, and Linux Node 24 run provide strong validation evidence.

PR surface:

Source +45, Tests +637. Total +682 across 6 files.

What I checked:

• Production-seam coverage: The test mocks only the core reply-turn boundary, then invokes the real dispatchPreparedSlackMessage path and records downstream Slack API behavior. (extensions/slack/src/delivery-trace.test.ts:90, 06468a6ed113)
• Reachable scenario branches: Current dispatch code contains the native-stream acknowledgement tracking, fallback, preview finalization, and cancellation paths represented by the five goldens; those production files have no drift between the PR head and reviewed current main. (extensions/slack/src/monitor/message-handler/dispatch.ts:714, 702ba19e3aba)
• Pinned dependency contract: The plugin pins @slack/web-api 7.18.0, whose ChatStreamer types and implementation confirm the 256-character default buffer, null pre-flush append result, first startStream flush, subsequent appendStream calls, and stop finalization captured by the tests. (extensions/slack/package.json:13, 702ba19e3aba)
• Established harness pattern: Current main already exports the shared delivery-trace harness and uses the same setup, recording, normalization, and golden-verification pattern for Feishu, Mattermost, and Microsoft Teams. (src/channels/plugins/contracts/trace/delivery-trace.ts:231, 702ba19e3aba)
• Validation evidence: The PR body reports focused 5/5 trace replay, the full Slack suite with 1,822 tests, check:changed, repeated byte-stability checks, and Linux Node 24 verification on Testbox. (extensions/slack/src/delivery-trace.test.ts:1, 06468a6ed113)
• Live protected state: The PR is open, non-draft, mergeable, behind current main, and labeled maintainer; repository policy therefore requires explicit maintainer handling rather than automatic cleanup closure. (06468a6ed113)

Likely related people:

• natedenh: Authored the merged PR that introduced Slack native text streaming, the central runtime behavior characterized here. (role: introduced behavior; confidence: high; commits: bb9a539d1d3f; files: extensions/slack/src/streaming.ts, extensions/slack/src/monitor/message-handler/dispatch.ts)
• Solvely-Colin: Authored the merged configurable Slack draft-preview streaming modes that underpin the preview-edit and cancellation scenarios. (role: feature contributor; confidence: high; commits: 89ce1460e15d; files: extensions/slack/src/stream-mode.ts, extensions/slack/src/monitor/message-handler/dispatch.ts)
• steipete: Recently authored the merged custom-identity streaming work and previously merged native Slack streaming changes, making this person closely connected to the identity and native-stream boundaries under test. (role: recent area contributor and merger; confidence: high; commits: be8b5f6c4f56, bb9a539d1d3f; files: extensions/slack/src/streaming.ts, extensions/slack/src/monitor/message-handler/dispatch.ts)

• 🦀 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.

• ClawSweeper keeps one durable marker-backed review comment per issue or PR.
• Re-runs edit this comment so the latest verdict, findings, and automation markers stay together instead of adding duplicate bot comments.
• A fresh review can be triggered by eligible @clawsweeper re-review comments, exact-item GitHub events, scheduled/background review runs, or manual workflow dispatch.
• PR/issue authors and users with repository write access can comment @clawsweeper re-review or @clawsweeper re-run on an open PR or issue to request a fresh review only.
• Maintainers can also comment @clawsweeper review to request a fresh review only.
• Fresh-review commands do not start repair, autofix, rebase, CI repair, or automerge.
• Maintainer-only repair and merge flows require explicit commands such as @clawsweeper autofix, @clawsweeper automerge, @clawsweeper fix ci, or @clawsweeper address review.
• Maintainers can comment @clawsweeper explain to ask for more context, or @clawsweeper stop to stop active automation.