feat: add Canonical Thread Handoff protocol (Closes #505)

Define CTH comment types, base template, parser/validator helpers, protocol documentation with examples, and workflow/runbook/prompt updates so agents discover and post authoritative thread handoffs before acting. Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
2026-07-08 03:44:58 -04:00
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+# Canonical Thread Handoff (CTH)
+
+**CTH** = **Canonical Thread Handoff**
+
+A CTH comment is the authoritative workflow handoff in a Gitea issue or PR
+thread. It records current state, decisions, blockers, proof, and the exact
+next prompt/action for the next LLM or person.
+
+CTH comments complement — but do not replace — formal Gitea review state.
+A CTH may summarize an APPROVE or REQUEST_CHANGES decision, yet merge gates
+still require the live Gitea review verdict.
+
+## CTH comment types
+
+- `CTH: State Handoff`
+- `CTH: Controller Decision`
+- `CTH: Author Handoff`
+- `CTH: Reviewer Handoff`
+- `CTH: Merger Handoff`
+- `CTH: Supersession Notice`
+- `CTH: Blocker`
+
+## Required base template
+
+```md
+## CTH: <Type>
+
+Status:
+Next owner:
+Current blocker:
+Decision:
+Proof:
+Next action:
+Ready-to-paste prompt:
+```
+
+Extended fields may map to canonical issue/PR state templates from #495 when
+that layer is available. Until then, keep the base fields complete.
+
+## Discovery and posting rules
+
+Before acting in an issue or PR thread:
+
+1. **Find the latest CTH comment** before doing work.
+2. Treat the **latest valid CTH** as the current handoff state.
+3. **Post a new CTH** when you finish, block, skip, supersede, request
+   changes, approve, or hand off.
+4. Do **not** rely on stale non-CTH comments when a newer CTH exists.
+5. Casual discussion comments do not need to be CTH comments.
+
+## Examples
+
+### PR approved and ready for merger
+
+```md
+## CTH: Reviewer Handoff
+
+Status: approved_at_current_head
+Next owner: merger
+Current blocker: none
+Decision: APPROVE recorded at head abc123...
+Proof: gitea_submit_pr_review performed; visible verdict APPROVE
+Next action: eligible merger merges PR #N with pinned expected_head_sha
+Ready-to-paste prompt: Merge PR #N for issue #M if live head still abc123... and merge gates pass.
+```
+
+### PR request-changes back to author
+
+```md
+## CTH: Reviewer Handoff
+
+Status: request_changes_at_current_head
+Next owner: author
+Current blocker: unresolved findings in validation report
+Decision: REQUEST_CHANGES at head def456...
+Proof: gitea_submit_pr_review performed; blocking review visible
+Next action: author fixes findings and pushes; reviewer re-validates fresh head
+Ready-to-paste prompt: Fix PR #N review findings, push to feat/issue-M-..., post Author Handoff CTH.
+```
+
+### Duplicate / superseded PR closure
+
+```md
+## CTH: Supersession Notice
+
+Status: superseded
+Next owner: controller
+Current blocker: duplicate branch/PR work
+Decision: close PR #N; continue on PR #M
+Proof: duplicate gate linked open PR #M for issue #K
+Next action: controller closes superseded PR and records canonical state
+Ready-to-paste prompt: Close superseded PR #N; confirm PR #M remains canonical for issue #K.
+```
+
+### Blocked workflow due to dirty root/worktree
+
+```md
+## CTH: Blocker
+
+Status: blocked_preflight
+Next owner: operator
+Current blocker: dirty control checkout / branches worktree mismatch
+Decision: stop before mutation
+Proof: verify_preflight_purity failed; workspace diagnostics attached
+Next action: repair worktree or relaunch MCP from branches/ worktree
+Ready-to-paste prompt: Repair dirty workspace, relaunch MCP from branches/review-prN, retry review.
+```
+
+### Stale head requiring fresh review
+
+```md
+## CTH: Reviewer Handoff
+
+Status: stale_head
+Next owner: reviewer
+Current blocker: live head differs from pinned review head
+Decision: prior approval not valid for current head
+Proof: expected_head_sha mismatch at merge gate
+Next action: re-run validation and post fresh review decision
+Ready-to-paste prompt: Re-validate PR #N at live head, dry-run review gates, submit fresh verdict.
+```
+
+### Issue implementation handoff
+
+```md
+## CTH: Author Handoff
+
+Status: implementation_complete_pending_review
+Next owner: reviewer
+Current blocker: none
+Decision: PR #N ready for review at head fedcba...
+Proof: tests passed in branches/issue-M-...; PR opened with Closes #M
+Next action: reviewer acquires lease and validates PR #N
+Ready-to-paste prompt: Review PR #N for issue #M; pin head fedcba... before mutations.
+```
+
+## Related
+
+- [`llm-workflow-runbooks.md`](llm-workflow-runbooks.md)
+- [`../skills/llm-project-workflow/templates/canonical-thread-handoff.md`](../skills/llm-project-workflow/templates/canonical-thread-handoff.md)
+- #495 — canonical next-action comment fields
+- #496 — fail-closed validation for workflow-changing comments
@@ -728,6 +728,27 @@ Never imply full-suite success unless the full-suite command itself passed
 (`full_suite_passed: true`). A report that hides a failed or skipped check
 is worse than a failing report.

+## Canonical Thread Handoff (CTH)
+
+**CTH** = **Canonical Thread Handoff** — the authoritative workflow handoff
+comment in a Gitea issue or PR thread. See
+[`canonical-thread-handoff.md`](canonical-thread-handoff.md) for types,
+templates, and examples.
+
+Before acting in an issue or PR thread:
+
+1. **Find the latest CTH comment** before doing work.
+2. Treat the **latest valid CTH** as the current handoff state.
+3. **Post a new CTH** when you finish, block, skip, supersede, request
+   changes, approve, or hand off.
+4. Do **not** rely on stale non-CTH comments when a newer CTH exists.
+
+A CTH summarizes workflow state for the next session. Formal Gitea review
+verdicts remain authoritative for merge gates — a CTH is not merge approval
+by itself.
+
+Template: [`../skills/llm-project-workflow/templates/canonical-thread-handoff.md`](../skills/llm-project-workflow/templates/canonical-thread-handoff.md)
+
 ## Controller Handoff (required, every task)

 Every task — implementation, review, merge, triage, documentation,