feat(#496): fail-closed canonical comment validation before Gitea posts

Add canonical_comment_validator and wire it into issue comments, PR review
bodies, reconcile post_comment, and structured comment helpers. Workflow-changing
comments without complete next-action state are rejected before any API call.
Includes unit/MCP integration tests, runbook docs, and a final-report rule
blocking false "comment posted" claims when validation failed.

canonical_comment_validator.py

@@ -0,0 +1,408 @@
+"""Fail-closed validation for workflow-changing Gitea comments (#496)."""
+
+from __future__ import annotations
+
+import re
+from typing import Any
+
+VALID_ROLES = frozenset({
+    "controller",
+    "author",
+    "reviewer",
+    "merger",
+    "reconciler",
+    "user",
+})
+
+_BASE_REQUIRED = ("STATE", "WHO_IS_NEXT", "NEXT_ACTION", "NEXT_PROMPT", "WHY")
+
+_ISSUE_REQUIRED = _BASE_REQUIRED + ("BLOCKERS", "VALIDATION")
+_PR_REQUIRED = _BASE_REQUIRED + (
+    "ISSUE",
+    "HEAD_SHA",
+    "REVIEW_STATUS",
+    "MERGE_READY",
+    "BLOCKERS",
+    "VALIDATION",
+)
+_SUPERSESSION_REQUIRED = _BASE_REQUIRED + (
+    "CANONICAL_ITEM",
+    "SUPERSEDED_ITEM",
+    "CLOSE_OR_KEEP_OPEN",
+)
+
+_MACHINE_MARKERS = (
+    "<!-- mcp-review-lease:v1 -->",
+    "<!-- mcp-conflict-fix-lease:v1 -->",
+    "<!-- gitea-issue-claim-heartbeat:v1 -->",
+)
+
+_WORKFLOW_TRIGGERS = re.compile(
+    r"\b(?:"
+    r"blocked|unblocked|ready(?:\s+for\s+(?:review|merge|author))?|"
+    r"ready-to-merge|approved|approve|request\s+changes|changes\s+requested|"
+    r"superseded|duplicate|canonical|next\s+action|next\s+actor|who\s+is\s+next|"
+    r"author\s+should|reviewer\s+should|merger\s+should|reconciler\s+should|"
+    r"controller\s+should|issue\s+complete|pr\s+open|pr\s+merged|close\s+this|"
+    r"do\s+not\s+merge|needs?\s+rebase|stale\s+approval|contaminated\s+review|"
+    r"merge\s+ready|ready\s+for\s+merge"
+    r")\b",
+    re.IGNORECASE,
+)
+
+_CANONICAL_HEADINGS = (
+    "## Canonical Issue State",
+    "## Canonical PR State",
+    "## Canonical Discussion Summary",
+)
+
+_FIELD_RE = re.compile(
+    r"^([A-Z][A-Z0-9_]*)\s*:\s*(.*)$",
+    re.MULTILINE,
+)
+
+_VAGUE_NEXT_ACTIONS = frozenset({
+    "continue",
+    "handle this",
+    "fix it",
+    "follow up",
+    "follow-up",
+    "see above",
+    "see review",
+    "tbd",
+    "todo",
+    "as needed",
+    "proceed",
+    "next steps",
+    "will check",
+    "investigate",
+})
+
+_FULL_SHA_RE = re.compile(r"\b[0-9a-f]{40}\b", re.IGNORECASE)
+_SHORT_SHA_RE = re.compile(r"\b[0-9a-f]{7,40}\b", re.IGNORECASE)
+_PR_REF_RE = re.compile(r"(?:PR\s*#|pull\s*#)\d+|\b#\d{2,}\b", re.IGNORECASE)
+_APPROVAL_PROOF_RE = re.compile(
+    r"\b(?:approved|approval_at_current_head|APPROVE)\b",
+    re.IGNORECASE,
+)
+_UNBLOCK_RE = re.compile(
+    r"\b(?:unblock|until|after|once|when|requires?|must)\b",
+    re.IGNORECASE,
+)
+
+
+def _parse_fields(body: str) -> dict[str, str]:
+    """Parse KEY: value fields, including values continued on following lines."""
+    fields: dict[str, str] = {}
+    current_key: str | None = None
+    current_lines: list[str] = []
+
+    def _flush() -> None:
+        nonlocal current_key, current_lines
+        if current_key is not None:
+            fields[current_key] = "\n".join(current_lines).strip()
+        current_key = None
+        current_lines = []
+
+    for line in (body or "").splitlines():
+        if line.startswith("## "):
+            _flush()
+            continue
+        match = re.match(r"^([A-Z][A-Z0-9_]*)\s*:\s*(.*)$", line)
+        if match:
+            _flush()
+            current_key = match.group(1).strip().upper()
+            rest = match.group(2)
+            current_lines = [rest] if rest else []
+        elif current_key is not None:
+            current_lines.append(line)
+    _flush()
+    return fields
+
+
+def _is_machine_generated(body: str) -> bool:
+    text = body or ""
+    return any(marker in text for marker in _MACHINE_MARKERS)
+
+
+def _has_canonical_heading(body: str) -> bool:
+    return any(h in (body or "") for h in _CANONICAL_HEADINGS)
+
+
+def is_workflow_changing_comment(body: str) -> bool:
+    """True when comment text implies a workflow/state transition."""
+    text = (body or "").strip()
+    if not text:
+        return False
+    if _is_machine_generated(text):
+        return False
+    if _has_canonical_heading(text):
+        return True
+    if _WORKFLOW_TRIGGERS.search(text):
+        return True
+    fields = _parse_fields(text)
+    if "STATE" in fields or "WHO_IS_NEXT" in fields:
+        return True
+    return False
+
+
+def infer_comment_context(body: str, *, explicit: str | None = None) -> str:
+    if explicit:
+        return explicit
+    text = body or ""
+    if "## Canonical Discussion Summary" in text:
+        return "discussion_summary"
+    if "## Canonical PR State" in text:
+        return "pr_comment"
+    if "## Canonical Issue State" in text:
+        return "issue_comment"
+    fields = _parse_fields(text)
+    if fields.get("CANONICAL_ITEM") or fields.get("SUPERSEDED_ITEM"):
+        return "supersession"
+    if any(k in fields for k in ("HEAD_SHA", "REVIEW_STATUS", "MERGE_READY", "ISSUE")):
+        return "pr_comment"
+    return "issue_comment"
+
+
+def _required_fields_for_context(context: str) -> tuple[str, ...]:
+    if context in ("pr_comment", "pr_review"):
+        return _PR_REQUIRED
+    if context == "supersession":
+        return _SUPERSESSION_REQUIRED
+    if context == "discussion_summary":
+        return _BASE_REQUIRED + ("DECISION", "SUBSTANTIVE_COMMENTS")
+    return _ISSUE_REQUIRED
+
+
+def _is_vague_next_action(value: str) -> bool:
+    normalized = re.sub(r"\s+", " ", (value or "").strip().lower())
+    normalized = normalized.rstrip(".")
+    if not normalized:
+        return True
+    if normalized in _VAGUE_NEXT_ACTIONS:
+        return True
+    if len(normalized) < 12:
+        return True
+    return False
+
+
+def _next_prompt_ok(value: str) -> bool:
+    text = (value or "").strip()
+    if len(text) < 40:
+        return False
+    if text.lower() in {"n/a", "none", "tbd", "todo"}:
+        return False
+    return True
+
+
+def _state_value(fields: dict[str, str]) -> str:
+    return (fields.get("STATE") or "").strip().lower()
+
+
+def _suggested_template(context: str) -> str:
+    if context == "pr_comment" or context == "pr_review":
+        return (
+            "## Canonical PR State\n\n"
+            "STATE:\n"
+            "WHO_IS_NEXT:\n"
+            "NEXT_ACTION:\n"
+            "NEXT_PROMPT:\n"
+            "```text\n<paste-ready prompt>\n```\n"
+            "WHAT_HAPPENED:\n"
+            "WHY:\n"
+            "ISSUE:\n"
+            "HEAD_SHA:\n"
+            "REVIEW_STATUS:\n"
+            "MERGE_READY:\n"
+            "BLOCKERS:\n"
+            "VALIDATION:\n"
+            "LAST_UPDATED_BY:\n"
+        )
+    if context == "supersession":
+        return (
+            "## Canonical PR State\n\n"
+            "STATE:\nsuperseded\n"
+            "WHO_IS_NEXT:\nreconciler\n"
+            "NEXT_ACTION:\n"
+            "NEXT_PROMPT:\n"
+            "WHY:\n"
+            "CANONICAL_ITEM:\n"
+            "SUPERSEDED_ITEM:\n"
+            "CLOSE_OR_KEEP_OPEN:\n"
+        )
+    if context == "discussion_summary":
+        return (
+            "## Canonical Discussion Summary\n\n"
+            "STATE:\n"
+            "WHO_IS_NEXT:\n"
+            "DECISION:\n"
+            "WHY:\n"
+            "SUBSTANTIVE_COMMENTS:\n"
+            "NEXT_ACTION:\n"
+            "NEXT_PROMPT:\n"
+        )
+    return (
+        "## Canonical Issue State\n\n"
+        "STATE:\n"
+        "WHO_IS_NEXT:\n"
+        "NEXT_ACTION:\n"
+        "NEXT_PROMPT:\n"
+        "```text\n<paste-ready prompt>\n```\n"
+        "WHAT_HAPPENED:\n"
+        "WHY:\n"
+        "RELATED_PRS:\n"
+        "BLOCKERS:\n"
+        "VALIDATION:\n"
+        "LAST_UPDATED_BY:\n"
+    )
+
+
+def _build_correction_message(
+    *,
+    missing_fields: list[str],
+    vague_fields: list[str],
+    extra_reasons: list[str],
+    context: str,
+) -> str:
+    parts = [
+        "Canonical comment validation failed (fail closed before posting).",
+    ]
+    if missing_fields:
+        parts.append("Missing fields: " + ", ".join(missing_fields) + ".")
+    if vague_fields:
+        parts.append("Vague or invalid fields: " + ", ".join(vague_fields) + ".")
+    parts.extend(extra_reasons)
+    parts.append("Fill the suggested template and retry.")
+    parts.append("Suggested template:\n" + _suggested_template(context))
+    return "\n".join(parts)
+
+
+def assess_canonical_comment(
+    body: str,
+    *,
+    context: str | None = None,
+    force_workflow: bool = False,
+) -> dict[str, Any]:
+    """Validate outgoing comment text before a Gitea mutation."""
+    text = (body or "").strip()
+    ctx = infer_comment_context(text, explicit=context)
+
+    if not text:
+        return {
+            "allowed": True,
+            "is_workflow_comment": False,
+            "context": ctx,
+            "missing_fields": [],
+            "vague_fields": [],
+            "correction_message": "",
+            "suggested_template": "",
+        }
+
+    if _is_machine_generated(text):
+        return {
+            "allowed": True,
+            "is_workflow_comment": False,
+            "context": ctx,
+            "missing_fields": [],
+            "vague_fields": [],
+            "correction_message": "",
+            "suggested_template": "",
+        }
+
+    workflow = force_workflow or is_workflow_changing_comment(text)
+    if not workflow:
+        return {
+            "allowed": True,
+            "is_workflow_comment": False,
+            "context": ctx,
+            "missing_fields": [],
+            "vague_fields": [],
+            "correction_message": "",
+            "suggested_template": "",
+        }
+
+    fields = _parse_fields(text)
+    required = _required_fields_for_context(ctx)
+    missing = [name for name in required if not (fields.get(name) or "").strip()]
+
+    vague: list[str] = []
+    extra: list[str] = []
+
+    who = (fields.get("WHO_IS_NEXT") or "").strip().lower()
+    if who and who not in VALID_ROLES:
+        vague.append("WHO_IS_NEXT")
+        extra.append(
+            f"WHO_IS_NEXT must be one of: {', '.join(sorted(VALID_ROLES))}."
+        )
+
+    next_action = fields.get("NEXT_ACTION") or ""
+    if next_action and _is_vague_next_action(next_action):
+        vague.append("NEXT_ACTION")
+
+    next_prompt = fields.get("NEXT_PROMPT") or ""
+    if not _next_prompt_ok(next_prompt):
+        if "NEXT_PROMPT" not in missing:
+            vague.append("NEXT_PROMPT")
+
+    state = _state_value(fields)
+    blockers = (fields.get("BLOCKERS") or "").strip()
+    if "blocked" in state:
+        if not blockers or blockers.lower() in {"none", "n/a"}:
+            missing.append("BLOCKERS (unblock condition)")
+        elif not _UNBLOCK_RE.search(blockers):
+            vague.append("BLOCKERS")
+            extra.append("BLOCKED state requires an explicit unblock condition in BLOCKERS.")
+
+    if "superseded" in state:
+        canon = (fields.get("CANONICAL_ITEM") or fields.get("SUPERSEDED_BY") or "").strip()
+        superseded = (fields.get("SUPERSEDED_ITEM") or fields.get("SUPERSEDES") or "").strip()
+        if not canon and "CANONICAL_ITEM" not in missing:
+            missing.append("CANONICAL_ITEM")
+        if not superseded and "SUPERSEDED_ITEM" not in missing:
+            missing.append("SUPERSEDED_ITEM")
+
+    if "ready-to-merge" in state or "ready to merge" in state:
+        head_sha = fields.get("HEAD_SHA") or ""
+        merge_ready = fields.get("MERGE_READY") or ""
+        review_status = fields.get("REVIEW_STATUS") or ""
+        validation = fields.get("VALIDATION") or ""
+        proof_blob = " ".join((head_sha, merge_ready, review_status, validation))
+        has_sha = bool(_FULL_SHA_RE.search(proof_blob) or _SHORT_SHA_RE.search(proof_blob))
+        has_approval = bool(_APPROVAL_PROOF_RE.search(proof_blob))
+        if not has_sha or not has_approval:
+            extra.append(
+                "ready-to-merge STATE requires approval proof and HEAD_SHA in "
+                "REVIEW_STATUS, MERGE_READY, HEAD_SHA, or VALIDATION."
+            )
+
+    if ctx in ("pr_comment", "pr_review"):
+        head_sha = (fields.get("HEAD_SHA") or "").strip()
+        if not head_sha or not _SHORT_SHA_RE.search(head_sha):
+            if "HEAD_SHA" not in missing:
+                missing.append("HEAD_SHA")
+
+    if ctx == "issue_comment" and _PR_REF_RE.search(text):
+        related = (fields.get("RELATED_PRS") or "").strip()
+        if not related or related.lower() in {"none", "n/a", "-"}:
+            missing.append("RELATED_PRS")
+
+    allowed = not missing and not vague and not extra
+    correction = ""
+    if not allowed:
+        correction = _build_correction_message(
+            missing_fields=missing,
+            vague_fields=vague,
+            extra_reasons=extra,
+            context=ctx,
+        )
+
+    return {
+        "allowed": allowed,
+        "is_workflow_comment": True,
+        "context": ctx,
+        "missing_fields": missing,
+        "vague_fields": vague,
+        "extra_reasons": extra,
+        "correction_message": correction,
+        "suggested_template": _suggested_template(ctx) if not allowed else "",
+    }

docs/llm-workflow-runbooks.md

@@ -818,6 +818,55 @@ touched release state names the exact tag/commit and why. Design debates
 belong in **discussion/RFC issues** (e.g. #100 `profiles.json v2`) — comment
 on the issue, create no branches/PRs, and end the comment with this handoff.
 
+## Canonical comment validation (#496)
+
+Workflow-changing issue/PR/review comments must carry durable next-action
+state. Casual discussion is still allowed.
+
+The MCP server runs `canonical_comment_validator.assess_canonical_comment`
+**before** posting through:
+
+- `gitea_create_issue_comment`
+- `gitea_submit_pr_review` / `gitea_dry_run_pr_review` (non-empty review bodies)
+- `gitea_reconcile_already_landed_pr` when `post_comment=True`
+- internal structured comment helpers (machine lease/heartbeat markers stay exempt)
+
+Detection examples:
+
+- **Allowed:** `Thanks, I will check this.`
+- **Rejected:** `Blocked, author should fix.` (workflow trigger without canonical fields)
+
+When validation fails, the tool returns `canonical_comment_validation` with
+`allowed: false`, `missing_fields`, `vague_fields`, `correction_message`, and
+`suggested_template`. **No Gitea API call is made.**
+
+Minimum workflow comment fields:
+
+```text
+STATE:
+WHO_IS_NEXT:
+NEXT_ACTION:
+NEXT_PROMPT:
+WHY:
+```
+
+`WHO_IS_NEXT` must be one of: `controller`, `author`, `reviewer`, `merger`,
+`reconciler`, `user`.
+
+Issue comments also require `RELATED_PRS`, `BLOCKERS`, and `VALIDATION` when
+they mention PR work. PR comments/reviews also require `ISSUE`, `HEAD_SHA`,
+`REVIEW_STATUS`, `MERGE_READY`, `BLOCKERS`, and `VALIDATION`.
+
+Special states:
+
+- `STATE: blocked` — `BLOCKERS` must name an explicit unblock condition.
+- `STATE: superseded` — requires `CANONICAL_ITEM` and `SUPERSEDED_ITEM`.
+- `STATE: ready-to-merge` — requires approval proof and head SHA in
+  `HEAD_SHA`, `REVIEW_STATUS`, `MERGE_READY`, or `VALIDATION`.
+
+Final reports must not claim a comment was posted when
+`canonical_comment_validation.allowed` is false (#496 AC14).
+
 ## Fail-closed behavior
 
 Before any mutating action the workflow verifies identity, active profile,

final_report_validator.py

@@ -194,6 +194,23 @@ _PAGINATION_PROOF_RE = re.compile(
     re.IGNORECASE,
 )
 _GIT_FETCH_RE = re.compile(r"\bgit\s+fetch\b", re.IGNORECASE)
+_CANONICAL_VALIDATION_REJECTED_RE = re.compile(
+    r"canonical comment validation failed|"
+    r"canonical_comment_validation|"
+    r'"allowed"\s*:\s*false',
+    re.IGNORECASE,
+)
+_COMMENT_POSTED_CLAIM_RE = re.compile(
+    r"(?:issue comments posted\s*:\s+(?!none\b)\S|"
+    r"pr comments posted\s*:\s+(?!none\b)\S|"
+    r"comment_id\s*[:=]\s*\d+|"
+    r"gitea comment (?:was )?posted|"
+    r"posted (?:issue|pr|canonical) (?:state )?comment|"
+    r"comment posted successfully|"
+    r"mcp/gitea mutations\s*:\s*[^;\n]*comment posted|"
+    r"reconciliation mutations\s*:\s*[^;\n]*comment posted)",
+    re.IGNORECASE,
+)
 _READONLY_DIAG_RE = re.compile(
     r"read[- ]only diagnostics\s*:\s*(.+)$",
     re.IGNORECASE | re.MULTILINE,
@@ -348,6 +365,43 @@ def _rule_shared_email_disclosure(report_text: str) -> list[dict[str, str]]:
     )
 
 
+def _rule_shared_canonical_comment_post_claim(
+    report_text: str,
+    *,
+    action_log: list[dict] | None = None,
+) -> list[dict[str, str]]:
+    """#496: reports must not claim comment posted when validator rejected."""
+    text = report_text or ""
+    rejected_in_report = bool(_CANONICAL_VALIDATION_REJECTED_RE.search(text))
+    rejected_in_log = False
+    if action_log:
+        for entry in action_log:
+            validation = entry.get("canonical_comment_validation") or {}
+            if validation.get("allowed") is False:
+                rejected_in_log = True
+                break
+            result = entry.get("result") or {}
+            nested = result.get("canonical_comment_validation") or {}
+            if nested.get("allowed") is False:
+                rejected_in_log = True
+                break
+    if not (rejected_in_report or rejected_in_log):
+        return []
+    if not _COMMENT_POSTED_CLAIM_RE.search(text):
+        return []
+    return [
+        validator_finding(
+            "shared.canonical_comment_post_claim",
+            "block",
+            "MCP/Gitea mutations",
+            "report claims a Gitea comment was posted while canonical comment "
+            "validation rejected the workflow comment",
+            "do not claim comment posted when validator fail-closed; repair "
+            "the canonical comment body and retry posting",
+        )
+    ]
+
+
 def _rule_reviewer_legacy_workspace_mutations(
     report_text: str,
     *,
@@ -1279,10 +1333,15 @@ _SHARED_CLEANUP_PROOF_RULES = (
     _rule_shared_mcp_native_cleanup_proof,
 )
 
+_SHARED_CANONICAL_COMMENT_RULES = (
+    _rule_shared_canonical_comment_post_claim,
+)
+
 _RULES_BY_TASK: dict[str, list[Callable[..., list[dict[str, str]]]]] = {
     "review_pr": [
         _rule_shared_controller_handoff,
         _rule_shared_email_disclosure,
+        *_SHARED_CANONICAL_COMMENT_RULES,
         *_SHARED_ISSUE_LOCK_RULES,
         _rule_reviewer_legacy_workspace_mutations,
         _rule_reviewer_vague_mutations_none,
@@ -1311,6 +1370,7 @@ _RULES_BY_TASK: dict[str, list[Callable[..., list[dict[str, str]]]]] = {
     "reconcile_already_landed": [
         _rule_reconcile_controller_handoff,
         _rule_shared_email_disclosure,
+        *_SHARED_CANONICAL_COMMENT_RULES,
         *_SHARED_ISSUE_LOCK_RULES,
         *_SHARED_CLEANUP_PROOF_RULES,
         _rule_reconcile_stale_author_fields,
@@ -1326,12 +1386,14 @@ _RULES_BY_TASK: dict[str, list[Callable[..., list[dict[str, str]]]]] = {
     "author_issue": [
         _rule_shared_controller_handoff,
         _rule_shared_email_disclosure,
+        *_SHARED_CANONICAL_COMMENT_RULES,
         *_SHARED_ISSUE_LOCK_RULES,
         _rule_reviewer_vague_mutations_none,
     ],
     "work_issue": [
         _rule_shared_controller_handoff,
         _rule_shared_email_disclosure,
+        *_SHARED_CANONICAL_COMMENT_RULES,
         *_SHARED_ISSUE_LOCK_RULES,
         _rule_shared_issue_acceptance_gate,
         _rule_reviewer_vague_mutations_none,
@@ -1341,17 +1403,20 @@ _RULES_BY_TASK: dict[str, list[Callable[..., list[dict[str, str]]]]] = {
     "issue_filing": [
         _rule_shared_controller_handoff,
         _rule_shared_email_disclosure,
+        *_SHARED_CANONICAL_COMMENT_RULES,
         *_SHARED_ISSUE_LOCK_RULES,
     ],
     "inventory": [
         _rule_shared_controller_handoff,
         _rule_shared_email_disclosure,
+        *_SHARED_CANONICAL_COMMENT_RULES,
         *_SHARED_ISSUE_LOCK_RULES,
         _rule_reconcile_pagination_proof,
     ],
     "issue_selection": [
         _rule_shared_controller_handoff,
         _rule_shared_email_disclosure,
+        *_SHARED_CANONICAL_COMMENT_RULES,
         *_SHARED_ISSUE_LOCK_RULES,
     ],
 }

gitea_mcp_server.py

@@ -829,6 +829,7 @@ import review_merge_state_machine  # noqa: E402
 import pr_work_lease  # noqa: E402
 import native_mcp_preference  # noqa: E402
 import worktree_cleanup_audit  # noqa: E402
+import canonical_comment_validator as ccv  # noqa: E402
 
 
 # Keyed issue-lock storage (#443): per remote/org/repo/issue files under
@@ -3268,6 +3269,13 @@ def _evaluate_pr_review_submission(
         result["pr_work_lease"] = lease_block
         return result
 
+    if (body or "").strip():
+        gate = _canonical_comment_gate(body, context="pr_review")
+        if gate["blocked"]:
+            reasons.extend(gate["reasons"])
+            result["canonical_comment_validation"] = gate["canonical_comment_validation"]
+            return result
+
     result["would_perform"] = True
     if not live:
         reasons.append(
@@ -5207,6 +5215,12 @@ def gitea_reconcile_already_landed_pr(
                 "gitea.pr.comment"
             )
             return result
+        gate = _canonical_comment_gate(comment_body)
+        if gate["blocked"]:
+            result["success"] = False
+            result["reasons"].extend(gate["reasons"])
+            result["canonical_comment_validation"] = gate["canonical_comment_validation"]
+            return result
         comment_url = f"{base}/issues/{pr_number}/comments"
         with _audited(
             "comment_pr",
@@ -6444,6 +6458,15 @@ def gitea_create_issue_comment(
             blocked["permission_report"] = _permission_block_report(
                 "gitea.issue.comment")
         return blocked
+    canon_gate = _canonical_comment_gate(body, context="issue_comment")
+    if canon_gate["blocked"]:
+        return {
+            "success": False,
+            "performed": False,
+            "issue_number": issue_number,
+            "reasons": canon_gate["reasons"],
+            "canonical_comment_validation": canon_gate["canonical_comment_validation"],
+        }
     h, o, r = _resolve(remote, host, org, repo)
     auth = _auth(h)
     api = f"{repo_api_url(h, o, r)}/issues/{issue_number}/comments"
@@ -7973,6 +7996,34 @@ def gitea_audit_config() -> dict:
     return report
 
 
+def _canonical_comment_gate(
+    body: str,
+    *,
+    context: str | None = None,
+    force_workflow: bool = False,
+) -> dict:
+    """Fail-closed canonical state validation before comment/review POST (#496)."""
+    assessment = ccv.assess_canonical_comment(
+        body,
+        context=context,
+        force_workflow=force_workflow,
+    )
+    if assessment.get("allowed"):
+        return {
+            "blocked": False,
+            "canonical_comment_validation": assessment,
+            "reasons": [],
+        }
+    correction = (assessment.get("correction_message") or "").strip()
+    return {
+        "blocked": True,
+        "canonical_comment_validation": assessment,
+        "reasons": [
+            correction or "canonical comment validation failed (fail closed before posting)"
+        ],
+    }
+
+
 def _post_structured_issue_comment(
     *,
     issue_number: int,
@@ -7982,8 +8033,18 @@ def _post_structured_issue_comment(
     org: str | None,
     repo: str | None,
     audit_op: str = "create_issue_comment",
+    comment_context: str | None = None,
 ) -> dict:
     """Post an issue-thread comment after permission gates already passed."""
+    gate = _canonical_comment_gate(body, context=comment_context)
+    if gate["blocked"]:
+        return {
+            "success": False,
+            "performed": False,
+            "issue_number": issue_number,
+            "reasons": gate["reasons"],
+            "canonical_comment_validation": gate["canonical_comment_validation"],
+        }
     h, o, r = _resolve(remote, host, org, repo)
     auth = _auth(h)
     api = f"{repo_api_url(h, o, r)}/issues/{issue_number}/comments"

tests/test_canonical_comment_validator.py

@@ -0,0 +1,217 @@
+"""Unit tests for canonical_comment_validator (#496)."""
+
+import unittest
+
+import canonical_comment_validator as ccv
+
+FULL_SHA = "a" * 40
+
+_VALID_ISSUE = f"""## Canonical Issue State
+
+STATE: ready-for-author
+WHO_IS_NEXT: author
+NEXT_ACTION: Implement canonical comment validator and wire MCP gates
+NEXT_PROMPT:
+```text
+You are the author LLM for issue #496. Add canonical_comment_validator.py
+and wire fail-closed gates into gitea_create_issue_comment.
+```
+WHAT_HAPPENED: Issue filed for MCP validation wall
+WHY: Workflow comments must carry durable next-action state
+RELATED_PRS: none
+BLOCKERS: none
+VALIDATION: unit tests not yet run
+LAST_UPDATED_BY: prgs-author
+"""
+
+_VALID_PR = f"""## Canonical PR State
+
+STATE: ready-for-review
+WHO_IS_NEXT: reviewer
+NEXT_ACTION: Run focused pytest and review the validator wiring diff
+NEXT_PROMPT:
+```text
+Review PR for issue #496. Confirm casual comments still post and workflow
+comments without canonical fields are rejected before the Gitea API call.
+```
+WHAT_HAPPENED: Author opened PR with validator module
+WHY: Fail-closed enforcement belongs at the MCP boundary
+ISSUE: #496
+HEAD_SHA: {FULL_SHA}
+REVIEW_STATUS: pending
+MERGE_READY: false
+BLOCKERS: none
+VALIDATION: not yet run
+LAST_UPDATED_BY: prgs-author
+"""
+
+_VALID_SUPERSEDED = """## Canonical PR State
+
+STATE: superseded
+WHO_IS_NEXT: reconciler
+NEXT_ACTION: Close superseded issue after canonical issue #495 lands
+NEXT_PROMPT:
+```text
+Close issue #494 as superseded by #495 once templates and docs are merged.
+```
+WHY: Duplicate tracking issue replaced by durable canonical template work
+CANONICAL_ITEM: issue #495
+SUPERSEDED_ITEM: issue #494
+CLOSE_OR_KEEP_OPEN: close superseded issue #494 after #495 merges
+"""
+
+_VALID_BLOCKED = """## Canonical Issue State
+
+STATE: blocked
+WHO_IS_NEXT: author
+NEXT_ACTION: Fix failing validator unit tests before requesting re-review
+NEXT_PROMPT:
+```text
+Run pytest tests/test_canonical_comment_validator.py and repair failures.
+```
+WHAT_HAPPENED: Validator tests failed in CI
+WHY: Blocked until test suite is green
+RELATED_PRS: PR #500
+BLOCKERS: pytest failures; unblock after all validator tests pass
+VALIDATION: pytest failed
+LAST_UPDATED_BY: prgs-author
+"""
+
+_VALID_READY_TO_MERGE = f"""## Canonical PR State
+
+STATE: ready-to-merge
+WHO_IS_NEXT: merger
+NEXT_ACTION: Merge PR after confirming approval_at_current_head
+NEXT_PROMPT:
+```text
+Merge PR #500 for issue #496 after live mergeable check passes.
+```
+WHAT_HAPPENED: Reviewer approved at current head
+WHY: All gates passed and head SHA is current
+ISSUE: #496
+HEAD_SHA: {FULL_SHA}
+REVIEW_STATUS: approved / approval_at_current_head
+MERGE_READY: true
+BLOCKERS: none
+VALIDATION: pytest passed; reviewer approved at head {FULL_SHA}
+LAST_UPDATED_BY: prgs-reviewer
+"""
+
+
+class TestCanonicalCommentDetection(unittest.TestCase):
+    def test_casual_comment_not_workflow(self):
+        self.assertFalse(ccv.is_workflow_changing_comment("Thanks, I will check this."))
+
+    def test_workflow_trigger_detected(self):
+        self.assertTrue(ccv.is_workflow_changing_comment("Blocked, author should fix."))
+
+    def test_machine_marker_exempt(self):
+        body = "<!-- mcp-review-lease:v1 -->\nphase: claimed"
+        self.assertFalse(ccv.is_workflow_changing_comment(body))
+
+
+class TestCanonicalCommentValidation(unittest.TestCase):
+    def test_casual_comment_allowed(self):
+        result = ccv.assess_canonical_comment("Thanks, I will check this.")
+        self.assertTrue(result["allowed"])
+        self.assertFalse(result["is_workflow_comment"])
+
+    def test_workflow_comment_missing_fields_rejected(self):
+        result = ccv.assess_canonical_comment("Blocked, author should fix.")
+        self.assertFalse(result["allowed"])
+        self.assertTrue(result["is_workflow_comment"])
+        self.assertIn("WHO_IS_NEXT", result["missing_fields"])
+        self.assertIn("correction_message", result)
+        self.assertIn("Suggested template", result["correction_message"])
+
+    def test_missing_next_prompt_rejected(self):
+        body = """STATE: blocked
+WHO_IS_NEXT: author
+NEXT_ACTION: Repair the failing validator unit tests in CI
+WHY: Tests must pass before merge
+BLOCKERS: pytest failed; unblock after tests pass
+VALIDATION: failed
+"""
+        result = ccv.assess_canonical_comment(body)
+        self.assertFalse(result["allowed"])
+        self.assertIn("NEXT_PROMPT", result["missing_fields"] + result["vague_fields"])
+
+    def test_vague_next_action_rejected(self):
+        body = _VALID_ISSUE.replace(
+            "Implement canonical comment validator and wire MCP gates",
+            "continue",
+        )
+        result = ccv.assess_canonical_comment(body)
+        self.assertFalse(result["allowed"])
+        self.assertIn("NEXT_ACTION", result["vague_fields"])
+
+    def test_invalid_who_is_next_rejected(self):
+        body = _VALID_ISSUE.replace("WHO_IS_NEXT: author", "WHO_IS_NEXT: llm")
+        result = ccv.assess_canonical_comment(body)
+        self.assertFalse(result["allowed"])
+        self.assertIn("WHO_IS_NEXT", result["vague_fields"])
+
+    def test_valid_issue_comment_allowed(self):
+        result = ccv.assess_canonical_comment(_VALID_ISSUE)
+        self.assertTrue(result["allowed"])
+
+    def test_issue_comment_mentioning_pr_requires_related_prs(self):
+        body = _VALID_ISSUE.replace("RELATED_PRS: none", "RELATED_PRS:")
+        body = body.replace("Issue filed", "Issue filed; see PR #500")
+        result = ccv.assess_canonical_comment(body)
+        self.assertFalse(result["allowed"])
+        self.assertIn("RELATED_PRS", result["missing_fields"])
+
+    def test_pr_review_requires_head_sha(self):
+        body = _VALID_PR.replace(f"HEAD_SHA: {FULL_SHA}", "HEAD_SHA:")
+        result = ccv.assess_canonical_comment(body, context="pr_review")
+        self.assertFalse(result["allowed"])
+        self.assertIn("HEAD_SHA", result["missing_fields"])
+
+    def test_ready_to_merge_requires_approval_and_sha_proof(self):
+        body = _VALID_READY_TO_MERGE.replace("approval_at_current_head", "pending")
+        body = body.replace(f"HEAD_SHA: {FULL_SHA}", "HEAD_SHA: pending")
+        body = body.replace("reviewer approved at head", "reviewer pending at head")
+        body = body.replace("approved /", "pending /")
+        result = ccv.assess_canonical_comment(body, context="pr_comment")
+        self.assertFalse(result["allowed"])
+        self.assertTrue(result["extra_reasons"])
+
+    def test_ready_to_merge_valid_allowed(self):
+        result = ccv.assess_canonical_comment(_VALID_READY_TO_MERGE, context="pr_comment")
+        self.assertTrue(result["allowed"])
+
+    def test_superseded_requires_canonical_and_superseded_items(self):
+        body = _VALID_SUPERSEDED.replace("CANONICAL_ITEM: issue #495", "CANONICAL_ITEM:")
+        result = ccv.assess_canonical_comment(body, context="supersession")
+        self.assertFalse(result["allowed"])
+        self.assertIn("CANONICAL_ITEM", result["missing_fields"])
+
+    def test_superseded_valid_allowed(self):
+        result = ccv.assess_canonical_comment(_VALID_SUPERSEDED, context="supersession")
+        self.assertTrue(result["allowed"])
+
+    def test_blocked_requires_unblock_condition(self):
+        body = _VALID_BLOCKED.replace(
+            "BLOCKERS: pytest failures; unblock after all validator tests pass",
+            "BLOCKERS: pytest failures",
+        )
+        result = ccv.assess_canonical_comment(body)
+        self.assertFalse(result["allowed"])
+        self.assertIn("BLOCKERS", result["vague_fields"])
+
+    def test_blocked_valid_allowed(self):
+        result = ccv.assess_canonical_comment(_VALID_BLOCKED)
+        self.assertTrue(result["allowed"])
+
+    def test_correction_lists_missing_fields(self):
+        result = ccv.assess_canonical_comment("ready for merge")
+        self.assertFalse(result["allowed"])
+        message = result["correction_message"]
+        self.assertIn("Missing fields", message)
+        self.assertIn("WHO_IS_NEXT", message)
+        self.assertIn("Suggested template", message)
+
+
+if __name__ == "__main__":
+    unittest.main()

tests/test_final_report_validator.py

@@ -573,6 +573,31 @@ class TestReconcilerCloseProof(unittest.TestCase):
         )
 
 
+class TestCanonicalCommentPostClaim(unittest.TestCase):
+    def test_blocks_post_claim_when_validator_rejected_in_report(self):
+        report = "\n".join([
+            "## Controller Handoff",
+            "- MCP/Gitea mutations: issue comment posted",
+            "- Issue comments posted: 1 canonical state comment",
+            "canonical comment validation failed (fail closed before posting).",
+            '- canonical_comment_validation: {"allowed": false}',
+        ])
+        result = assess_final_report_validator(report, "work_issue")
+        rule_ids = [f["rule_id"] for f in result["findings"]]
+        self.assertIn("shared.canonical_comment_post_claim", rule_ids)
+        self.assertTrue(result["blocked"])
+
+    def test_allows_none_when_validator_rejected_without_post_claim(self):
+        report = "\n".join([
+            "## Controller Handoff",
+            "- Issue comments posted: none",
+            "canonical comment validation failed (fail closed before posting).",
+        ])
+        result = assess_final_report_validator(report, "work_issue")
+        rule_ids = [f["rule_id"] for f in result["findings"]]
+        self.assertNotIn("shared.canonical_comment_post_claim", rule_ids)
+
+
 class TestEntryPoint(unittest.TestCase):
     def test_unknown_task_kind_blocks(self):
         result = assess_final_report_validator("report", "unknown_mode")

tests/test_mcp_server.py

@@ -3102,6 +3102,36 @@ class TestIssueCommentTools(unittest.TestCase):
         self.assertFalse(result["success"])
         mock_api.assert_not_called()
 
+    @patch("mcp_server.api_request")
+    @patch("mcp_server.get_auth_header", return_value=FAKE_AUTH)
+    def test_create_casual_comment_allowed(self, _auth, mock_api):
+        mock_api.return_value = self._comment(556, "gitea-author", "casual")
+        with patch.dict(os.environ, self.AUTHOR_ENV, clear=True):
+            result = gitea_create_issue_comment(
+                issue_number=9,
+                body="Thanks, I will check this.",
+                remote="prgs",
+            )
+        self.assertTrue(result["success"])
+        self.assertTrue(result["performed"])
+        mock_api.assert_called_once()
+
+    @patch("mcp_server.api_request")
+    @patch("mcp_server.get_auth_header", return_value=FAKE_AUTH)
+    def test_create_workflow_comment_missing_fields_blocked(self, _auth, mock_api):
+        with patch.dict(os.environ, self.AUTHOR_ENV, clear=True):
+            result = gitea_create_issue_comment(
+                issue_number=9,
+                body="Blocked, author should fix.",
+                remote="prgs",
+            )
+        self.assertFalse(result["success"])
+        self.assertFalse(result["performed"])
+        self.assertIn("canonical_comment_validation", result)
+        self.assertFalse(result["canonical_comment_validation"]["allowed"])
+        self.assertTrue(result["canonical_comment_validation"]["is_workflow_comment"])
+        mock_api.assert_not_called()
+
     @patch("mcp_server.api_request")
     @patch("mcp_server.get_auth_header", return_value=FAKE_AUTH)
     def test_create_missing_issue_error_is_redacted(self, _auth, mock_api):