fix: head-scope durable #332 review-decision locks (#620)

Prior REQUEST_CHANGES on head A no longer blocks formal re-review on
head B of the same open PR. Locks store reviewed head SHA, hard-stop and
mark_ready/submit gates allow a fresh decision boundary when the live
head differs, and same-head duplicates remain fail-closed. Open-PR lock
cleanup stays forbidden (#594); assessment reports locked vs current
head and stale_by_head / fresh_review_on_current_head_allowed.

Closes #620

gitea_mcp_server.py

@@ -3095,22 +3095,26 @@ def check_review_decision_gate(
         )
 
     prior = list(lock.get("live_mutations") or [])
-    if prior and not lock.get("correction_authorized"):
-        reasons.append(
-            "live review mutation already recorded in this run; only one live "
-            "review mutation is allowed unless "
-            "gitea_authorize_review_correction was invoked (fail closed)"
-        )
-    elif (
-        action in _TERMINAL_REVIEW_ACTIONS
-        and any(m.get("action") in _TERMINAL_REVIEW_ACTIONS for m in prior)
-        and not lock.get("correction_authorized")
+    ready_head = lock.get("ready_expected_head_sha")
+    if stale_review_decision_lock.prior_live_mutations_block_boundary(
+        lock, pr_number=pr_number, expected_head_sha=ready_head
     ):
-        reasons.append(
-            "terminal review decision already submitted on this PR in this "
-            "run; blocked unless an operator-approved correction was "
-            "authorized (fail closed)"
-        )
+        if prior and not lock.get("correction_authorized"):
+            reasons.append(
+                "live review mutation already recorded for this PR head in this "
+                "run; only one live review mutation is allowed per head unless "
+                "gitea_authorize_review_correction was invoked (fail closed, #620)"
+            )
+        elif (
+            action in _TERMINAL_REVIEW_ACTIONS
+            and any(m.get("action") in _TERMINAL_REVIEW_ACTIONS for m in prior)
+            and not lock.get("correction_authorized")
+        ):
+            reasons.append(
+                "terminal review decision already submitted for this PR head in "
+                "this run; blocked unless an operator-approved correction was "
+                "authorized (fail closed, #620)"
+            )
 
     return reasons
 
@@ -3118,12 +3122,18 @@ def check_review_decision_gate(
 def record_live_review_mutation(pr_number: int, action: str, review_id: int | None = None):
     lock = _load_review_decision_lock() or {}
     mutations = list(lock.get("live_mutations") or [])
-    mutations.append({
+    head_sha = stale_review_decision_lock.normalize_head_sha(
+        lock.get("ready_expected_head_sha")
+    )
+    entry = {
         "pr_number": pr_number,
         "action": action,
         "review_id": review_id,
         "review_state": action,
-    })
+    }
+    if head_sha:
+        entry["head_sha"] = head_sha
+    mutations.append(entry)
     lock["live_mutations"] = mutations
     if lock.get("correction_authorized"):
         lock["correction_authorized"] = False
@@ -3131,17 +3141,28 @@ def record_live_review_mutation(pr_number: int, action: str, review_id: int | No
     _save_review_decision_lock(lock)
 
 
-def terminal_review_hard_stop_reasons(pr_number: int, operation: str) -> list[str]:
-    """Session hard-stop after a terminal live review mutation (#332).
+def terminal_review_hard_stop_reasons(
+    pr_number: int,
+    operation: str,
+    expected_head_sha: str | None = None,
+) -> list[str]:
+    """Session hard-stop after a terminal live review mutation (#332 / #620).
 
-    After a terminal verdict is consumed in this run, the only permitted
-    continuation is the merge sequence for the same PR that was approved.
-    A REQUEST_CHANGES (or an approval of a different PR) blocks every
-    further review/mark-ready/merge mutation. An operator-approved
-    correction (#211) re-opens the review path only — never a cross-PR
-    merge.
+    After a terminal verdict is consumed for a given PR **head**, the only
+    permitted continuation is the merge sequence for that same approved PR
+    (merge does not require a new head). A REQUEST_CHANGES (or an approval of
+    a different PR, or the same head) blocks further review/mark-ready/merge
+    mutations for that boundary.
 
-    *operation* is one of 'merge', 'mark_ready', or 'review'.
+    #620: when *expected_head_sha* differs from the last terminal's reviewed
+    head on the **same open PR**, mark_ready / review / resume may proceed so
+    a fresh formal decision can be recorded for the new head. Historical
+    mutations are preserved.
+
+    An operator-approved correction (#211) re-opens the review path only —
+    never a cross-PR merge.
+
+    *operation* is one of 'merge', 'mark_ready', 'review', or 'resume'.
     Returns [] when the operation may proceed.
     """
     lock = _load_review_decision_lock()
@@ -3160,8 +3181,19 @@ def terminal_review_hard_stop_reasons(pr_number: int, operation: str) -> list[st
         and last.get("pr_number") == pr_number
     ):
         return []
-    if operation in ("mark_ready", "review") and lock.get("correction_authorized"):
+    if operation in ("mark_ready", "review", "resume") and lock.get(
+        "correction_authorized"
+    ):
         return []
+    # #620: same PR, different reviewed head → fresh decision boundary.
+    if stale_review_decision_lock.terminal_boundary_allows_fresh_decision(
+        lock,
+        pr_number=pr_number,
+        expected_head_sha=expected_head_sha,
+        operation=operation,
+    ):
+        return []
+    locked_head = stale_review_decision_lock.mutation_head_sha(last, lock)
     if last.get("action") == "approve":
         guidance = (
             f"only the merge sequence for approved PR "
@@ -3169,15 +3201,22 @@ def terminal_review_hard_stop_reasons(pr_number: int, operation: str) -> list[st
         )
     else:
         guidance = "the session must stop and produce a final report"
+    head_note = (
+        f" at head {locked_head[:12]}…"
+        if locked_head
+        else ""
+    )
     recovery = (
         "if that PR is already merged/closed, use "
         "gitea_cleanup_stale_review_decision_lock (apply=true) after live-state "
-        "proof (#594); never delete session-state files by hand"
+        "proof (#594); if the PR is still open but the head moved, mark/submit "
+        "with the new expected_head_sha (#620); never delete session-state "
+        "files by hand"
     )
     return [
         "terminal review mutation already consumed in this run "
-        f"({last.get('action')} on PR #{last.get('pr_number')}); {guidance} "
-        f"(fail closed, #332); {recovery}"
+        f"({last.get('action')} on PR #{last.get('pr_number')}{head_note}); "
+        f"{guidance} (fail closed, #332); {recovery}"
     ]
 
 
@@ -3800,18 +3839,11 @@ def gitea_mark_final_review_decision(
             "reasons": workflow_blockers + (
                 review_workflow_load.recovery_handoff_without_replay()),
         }
-    hard_stop = terminal_review_hard_stop_reasons(pr_number, "mark_ready")
+    hard_stop = terminal_review_hard_stop_reasons(
+        pr_number, "mark_ready", expected_head_sha=expected_head_sha
+    )
     if hard_stop:
         return {"marked_ready": False, "reasons": hard_stop}
-    if lock.get("live_mutations") and not lock.get("correction_authorized"):
-        return {
-            "marked_ready": False,
-            "reasons": [
-                "cannot mark final decision after a live review mutation was "
-                "already recorded in this run unless an operator-approved "
-                "correction was authorized"
-            ],
-        }
     if action not in _REVIEW_ACTIONS:
         return {
             "marked_ready": False,
@@ -3828,6 +3860,17 @@ def gitea_mark_final_review_decision(
                 "decision (fail closed, #399)"
             ],
         }
+    if stale_review_decision_lock.prior_live_mutations_block_boundary(
+        lock, pr_number=pr_number, expected_head_sha=expected_head_sha
+    ):
+        return {
+            "marked_ready": False,
+            "reasons": [
+                "cannot mark final decision after a live review mutation was "
+                "already recorded for this PR head unless an operator-approved "
+                "correction was authorized (fail closed, #620)"
+            ],
+        }
     elig = gitea_check_pr_eligibility(
         pr_number=pr_number,
         action="review",
@@ -3880,6 +3923,8 @@ def gitea_mark_final_review_decision(
                     "#332)"
                 ],
             }
+    # Preserve historical terminal head boundaries before advancing ready_* (#620).
+    stale_review_decision_lock.backfill_terminal_heads_from_ready(lock)
     lock["final_review_decision_ready"] = True
     lock["ready_pr_number"] = pr_number
     lock["ready_action"] = action
@@ -3897,6 +3942,7 @@ def gitea_mark_final_review_decision(
         "org": org,
         "repo": repo,
         "final_review_decision_ready": True,
+        "head_scoped": True,
         "reasons": [],
     }
 
@@ -4063,6 +4109,12 @@ def gitea_cleanup_stale_review_decision_lock(
         "cleanup_allowed": assessment.get("cleanup_allowed"),
         "last_terminal_pr": assessment.get("last_terminal_pr"),
         "last_terminal_action": assessment.get("last_terminal_action"),
+        "locked_head_sha": assessment.get("locked_head_sha"),
+        "current_pr_head_sha": assessment.get("current_pr_head_sha"),
+        "stale_by_head": assessment.get("stale_by_head"),
+        "fresh_review_on_current_head_allowed": assessment.get(
+            "fresh_review_on_current_head_allowed"
+        ),
         "pr_state": assessment.get("pr_state"),
         "pr_merged": assessment.get("pr_merged"),
         "pr_merged_or_closed": assessment.get("pr_merged_or_closed"),

stale_review_decision_lock.py

@@ -1,4 +1,4 @@
-"""Stale / moot #332 review-decision lock detection and cleanup policy (#594).
+"""Stale / moot #332 review-decision lock detection and cleanup policy (#594/#620).
 
 #332 correctly hard-stops a reviewer session after a terminal live review
 mutation. After #559 those locks are durable on disk, so they can outlive the
@@ -6,6 +6,12 @@ work they protect: when the referenced PR is already merged or closed, no
 same-PR merge sequence remains, yet the durable ledger still blocks unrelated
 new terminal reviews.
 
+#620 scopes the terminal boundary by **reviewed head SHA**: a prior
+REQUEST_CHANGES (or APPROVE) on head A must not block a fresh formal decision
+on head B of the **same open PR**. Same-head duplicates remain fail-closed.
+Open-PR lock *cleanup* remains forbidden unless the PR is truly merged/closed
+(#594); new-head re-review is allowed without deleting the durable lock.
+
 This module is pure policy (no Gitea I/O). The MCP tool
 ``gitea_cleanup_stale_review_decision_lock`` fetches live PR state, calls these
 helpers, and only then clears durable state when cleanup is allowed.
@@ -23,6 +29,45 @@ from typing import Any
 TERMINAL_REVIEW_ACTIONS = frozenset({"approve", "request_changes"})
 
 
+def normalize_head_sha(value: Any) -> str | None:
+    """Normalize a git SHA for equality comparison; None if empty/invalid."""
+    if value is None:
+        return None
+    text = str(value).strip().lower()
+    if not text:
+        return None
+    return text
+
+
+def heads_equal(a: Any, b: Any) -> bool:
+    na = normalize_head_sha(a)
+    nb = normalize_head_sha(b)
+    if not na or not nb:
+        return False
+    return na == nb
+
+
+def mutation_head_sha(mutation: dict | None, lock: dict | None = None) -> str | None:
+    """Head SHA that bounds a live mutation (#620).
+
+    Prefers fields recorded on the mutation itself. For *legacy* mutations
+    that predate head-scoping, falls back to the lock's
+    ``ready_expected_head_sha`` only when that ready binding is for the same
+    PR number (the frozen durable PR #619-style ledger).
+    """
+    if not isinstance(mutation, dict):
+        return None
+    for key in ("head_sha", "expected_head_sha", "reviewed_head_sha"):
+        head = normalize_head_sha(mutation.get(key))
+        if head:
+            return head
+    if not isinstance(lock, dict):
+        return None
+    if lock.get("ready_pr_number") != mutation.get("pr_number"):
+        return None
+    return normalize_head_sha(lock.get("ready_expected_head_sha"))
+
+
 def last_terminal_mutation(lock: dict | None) -> dict | None:
     """Return the last terminal live mutation on *lock*, or None."""
     if not lock:
@@ -35,18 +80,125 @@ def last_terminal_mutation(lock: dict | None) -> dict | None:
     return terminals[-1] if terminals else None
 
 
+def prior_live_mutations_block_boundary(
+    lock: dict | None,
+    *,
+    pr_number: int,
+    expected_head_sha: str | None,
+) -> bool:
+    """True when prior live mutations block a new decision for PR+head (#620).
+
+    Historical terminals on a **different head of the same PR** do not block.
+    Any prior mutation on another PR, the same head, or without a comparable
+    head SHA fails closed (blocks).
+
+    Head resolution uses ``mutation_head_sha(m, lock)`` so pre-#620 ledgers
+    that only stored ``ready_expected_head_sha`` still compare correctly
+    (PR #619-style).
+    """
+    if not lock:
+        return False
+    if lock.get("correction_authorized"):
+        return False
+    prior = list(lock.get("live_mutations") or [])
+    if not prior:
+        return False
+    target = normalize_head_sha(expected_head_sha)
+    for m in prior:
+        if not isinstance(m, dict):
+            return True
+        m_pr = m.get("pr_number")
+        m_head = mutation_head_sha(m, lock)
+        if (
+            m_pr == pr_number
+            and target
+            and m_head
+            and not heads_equal(m_head, target)
+        ):
+            # Same open PR, different reviewed head — historical boundary only.
+            continue
+        return True
+    return False
+
+
+def terminal_boundary_allows_fresh_decision(
+    lock: dict | None,
+    *,
+    pr_number: int,
+    expected_head_sha: str | None,
+    operation: str,
+) -> bool:
+    """Whether #332 hard-stop should yield for a new PR+head boundary (#620).
+
+    Only for ``mark_ready`` / ``review`` / ``resume`` on the **same PR** when
+    the requested head differs from the last terminal's head. Merge is never
+    reopened by head change (approved head merge path is separate).
+    """
+    if operation not in ("mark_ready", "review", "resume"):
+        return False
+    if not lock:
+        return False
+    if lock.get("correction_authorized"):
+        return True
+    last = last_terminal_mutation(lock)
+    if last is None:
+        return True
+    if last.get("pr_number") != pr_number:
+        return False
+    locked_head = mutation_head_sha(last, lock)
+    target = normalize_head_sha(expected_head_sha)
+    if not locked_head or not target:
+        return False
+    return not heads_equal(locked_head, target)
+
+
+def backfill_terminal_heads_from_ready(lock: dict) -> dict:
+    """Stamp head_sha onto legacy terminal mutations before overwriting ready_*.
+
+    Called when marking a fresh decision on a new head so historical rows keep
+    their original boundary after ``ready_expected_head_sha`` advances (#620).
+    """
+    if not isinstance(lock, dict):
+        return lock
+    ready_pr = lock.get("ready_pr_number")
+    ready_head = normalize_head_sha(lock.get("ready_expected_head_sha"))
+    if ready_pr is None or not ready_head:
+        return lock
+    mutations = list(lock.get("live_mutations") or [])
+    changed = False
+    for m in mutations:
+        if not isinstance(m, dict):
+            continue
+        if m.get("action") not in TERMINAL_REVIEW_ACTIONS:
+            continue
+        if m.get("pr_number") != ready_pr:
+            continue
+        if mutation_head_sha(m):
+            continue
+        m["head_sha"] = ready_head
+        changed = True
+    if changed:
+        lock["live_mutations"] = mutations
+    return lock
+
+
 def classify_pr_live_state(pr_live: dict | None) -> dict[str, Any]:
     """Normalize a Gitea PR payload into merge/closed flags."""
     pr = pr_live or {}
     merged = bool(pr.get("merged") or pr.get("merged_at"))
     state = (pr.get("state") or "").strip().lower() or None
     closed = state == "closed"
+    head = pr.get("head") if isinstance(pr.get("head"), dict) else {}
+    head_sha = normalize_head_sha(
+        pr.get("head_sha") or pr.get("head_commit_sha") or head.get("sha")
+    )
     return {
         "pr_state": state,
         "pr_merged": merged,
         "pr_merged_or_closed": merged or closed,
         "merge_commit_sha": pr.get("merge_commit_sha")
         or pr.get("merged_commit_sha"),
+        "current_pr_head_sha": head_sha,
     }
 
 
@@ -56,6 +208,7 @@ def lock_summary(lock: dict | None) -> dict[str, Any] | None:
         return None
     last = last_terminal_mutation(lock)
     mutations = list(lock.get("live_mutations") or [])
+    last_head = mutation_head_sha(last, lock) if last else None
     return {
         "task": lock.get("task"),
         "remote": lock.get("remote"),
@@ -67,16 +220,21 @@ def lock_summary(lock: dict | None) -> dict[str, Any] | None:
         "session_profile": lock.get("session_profile"),
         "ready_pr_number": lock.get("ready_pr_number"),
         "ready_action": lock.get("ready_action"),
+        "ready_expected_head_sha": normalize_head_sha(
+            lock.get("ready_expected_head_sha")
+        ),
         "live_mutations_count": len(mutations),
         "last_terminal": (
             {
                 "pr_number": last.get("pr_number"),
                 "action": last.get("action"),
                 "review_id": last.get("review_id"),
+                "head_sha": last_head,
             }
             if last
             else None
         ),
+        "locked_head_sha": last_head,
         "correction_authorized": bool(lock.get("correction_authorized")),
         "updated_at": lock.get("updated_at") or lock.get("recorded_at"),
     }
@@ -88,13 +246,16 @@ def assess_stale_review_decision_lock(
     pr_live: dict | None = None,
     pr_lookup_error: str | None = None,
     active_profile_identity: str | None = None,
+    current_pr_head_sha: str | None = None,
 ) -> dict[str, Any]:
-    """Assess whether a durable review-decision lock is stale/moot (#594).
+    """Assess whether a durable review-decision lock is stale/moot (#594/#620).
 
     *pr_live* must be the live Gitea payload for the **last terminal
     mutation's PR**. When no lock / no terminal mutation exists, cleanup is
     not applicable. When the PR is still open (or lookup fails), cleanup is
-    forbidden and #332 hard-stop remains in force.
+    forbidden (#594). Open PR + different live head reports
+    ``stale_by_head`` / ``fresh_review_on_current_head_allowed`` (#620)
+    without enabling cleanup.
     """
     summary = lock_summary(lock)
     result: dict[str, Any] = {
@@ -102,6 +263,10 @@ def assess_stale_review_decision_lock(
         "lock_summary": summary,
         "last_terminal_pr": None,
         "last_terminal_action": None,
+        "locked_head_sha": None,
+        "current_pr_head_sha": normalize_head_sha(current_pr_head_sha),
+        "stale_by_head": False,
+        "fresh_review_on_current_head_allowed": False,
         "is_moot": False,
         "cleanup_allowed": False,
         "profile_match": True,
@@ -141,8 +306,10 @@ def assess_stale_review_decision_lock(
 
     pr_number = last.get("pr_number")
     action = last.get("action")
+    locked_head = mutation_head_sha(last, lock)
     result["last_terminal_pr"] = pr_number
     result["last_terminal_action"] = action
+    result["locked_head_sha"] = locked_head
 
     if pr_number is None:
         result["reasons"].append(
@@ -165,25 +332,46 @@ def assess_stale_review_decision_lock(
         return result
 
     live = classify_pr_live_state(pr_live)
+    current_head = normalize_head_sha(
+        current_pr_head_sha or live.get("current_pr_head_sha")
+    )
     result.update(
         {
             "pr_state": live["pr_state"],
             "pr_merged": live["pr_merged"],
             "pr_merged_or_closed": live["pr_merged_or_closed"],
             "merge_commit_sha": live["merge_commit_sha"],
+            "current_pr_head_sha": current_head,
         }
     )
 
     if not live["pr_merged_or_closed"]:
-        result["reasons"].append(
-            f"terminal review mutation on open PR #{pr_number} is still active "
-            f"({action}); #332 hard-stop remains — cleanup forbidden (#594)"
+        stale_by_head = bool(
+            locked_head and current_head and not heads_equal(locked_head, current_head)
         )
+        result["stale_by_head"] = stale_by_head
+        # Fresh formal decision is allowed on the new head without cleanup (#620).
+        result["fresh_review_on_current_head_allowed"] = stale_by_head
+        if stale_by_head:
+            result["reasons"].append(
+                f"terminal {action} on PR #{pr_number} is bound to head "
+                f"{locked_head[:12]}…; live head is {current_head[:12]}… — "
+                "fresh formal review on current head is allowed without "
+                "cleanup (fail closed for cleanup, #620); #332 same-head "
+                "duplicate protection remains"
+            )
+        else:
+            result["reasons"].append(
+                f"terminal review mutation on open PR #{pr_number} is still active "
+                f"({action}); #332 hard-stop remains — cleanup forbidden (#594)"
+            )
         return result
 
     # Merged or closed: lock is moot. Same-PR merge continuation is impossible.
     result["is_moot"] = True
     result["cleanup_allowed"] = True
+    result["stale_by_head"] = False
+    result["fresh_review_on_current_head_allowed"] = False
     result["reasons"].append(
         f"terminal mutation ({action} on PR #{pr_number}) is moot: PR is "
         f"{'merged' if live['pr_merged'] else 'closed'}; canonical cleanup allowed (#594)"

tests/test_head_scoped_review_decision_lock.py

@@ -0,0 +1,397 @@
+"""Head-scoped #332 review-decision locks (#620).
+
+Proves:
+  * REQUEST_CHANGES on head A does not block mark_ready/submit on head B
+  * APPROVE on head B is allowed after RC on head A (same open PR)
+  * same-head duplicate terminal remains blocked
+  * open-PR cleanup remains forbidden; assessment reports stale_by_head
+  * historical mutations keep their head_sha (preserved ledger)
+  * PR #619-style: old RC at 036b78e…, current head 2429d9d…, approve allowed
+"""
+
+from __future__ import annotations
+
+import os
+import unittest
+from unittest.mock import patch
+
+import mcp_server
+import stale_review_decision_lock as srdl
+
+HEAD_A = "036b78e31ea5d036452b3a52e0e086b01e0c763f"
+HEAD_B = "2429d9d2e826e519eb8eb4ade45987c00838aefb"
+HEAD_C = "c" * 40
+
+
+def _lock(mutations=None, correction=False, ready_pr=None, ready_head=None, ready_action=None):
+    return {
+        "task": "review_pr",
+        "remote": "prgs",
+        "org": "Scaled-Tech-Consulting",
+        "repo": "Gitea-Tools",
+        "session_pid": os.getpid(),
+        "session_profile": "prgs-reviewer",
+        "session_profile_lock": "prgs-reviewer",
+        "profile_identity": "prgs-reviewer",
+        "final_review_decision_ready": False,
+        "ready_pr_number": ready_pr,
+        "ready_action": ready_action,
+        "ready_expected_head_sha": ready_head,
+        "ready_remote": "prgs" if ready_pr else None,
+        "ready_org": "Scaled-Tech-Consulting" if ready_pr else None,
+        "ready_repo": "Gitea-Tools" if ready_pr else None,
+        "live_mutations": list(mutations or []),
+        "correction_authorized": correction,
+        "correction_reason": None,
+    }
+
+
+RC_619_LEGACY = {
+    "pr_number": 619,
+    "action": "request_changes",
+    "review_id": 410,
+    "review_state": "request_changes",
+    # no head_sha — pre-#620 durable ledger shape
+}
+RC_619_HEAD_A = {
+    "pr_number": 619,
+    "action": "request_changes",
+    "review_id": 410,
+    "review_state": "request_changes",
+    "head_sha": HEAD_A,
+}
+APPROVE_619_HEAD_B = {
+    "pr_number": 619,
+    "action": "approve",
+    "review_id": 411,
+    "review_state": "approve",
+    "head_sha": HEAD_B,
+}
+
+
+def _seed(mutations=None, **kwargs):
+    import review_workflow_load
+
+    review_workflow_load.record_review_workflow_load(mcp_server.PROJECT_ROOT)
+    mcp_server._save_review_decision_lock(_lock(mutations, **kwargs))
+    mcp_server.gitea_load_review_workflow()
+
+
+def _open_pr(pr_number=619, head=HEAD_B):
+    return {
+        "number": pr_number,
+        "state": "open",
+        "merged": False,
+        "merged_at": None,
+        "head": {"sha": head},
+    }
+
+
+def _no_lease():
+    return {"block": False, "reasons": [], "mutation_allowed": True}
+
+
+def _feedback(blocking=False, stale=False, success=True):
+    return {
+        "success": success,
+        "has_blocking_change_requests": blocking,
+        "review_feedback_stale": stale,
+        "current_head_sha": HEAD_B,
+    }
+
+
+class TestPureHeadScopeHelpers(unittest.TestCase):
+    def test_mutation_head_prefers_recorded_sha(self):
+        m = {"pr_number": 1, "head_sha": HEAD_A}
+        self.assertEqual(srdl.mutation_head_sha(m), HEAD_A)
+
+    def test_legacy_mutation_uses_ready_expected_for_same_pr(self):
+        lock = _lock(
+            [RC_619_LEGACY],
+            ready_pr=619,
+            ready_head=HEAD_A,
+            ready_action="request_changes",
+        )
+        self.assertEqual(srdl.mutation_head_sha(RC_619_LEGACY, lock), HEAD_A)
+
+    def test_legacy_mutation_ignores_ready_for_other_pr(self):
+        lock = _lock([RC_619_LEGACY], ready_pr=1, ready_head=HEAD_A)
+        self.assertIsNone(srdl.mutation_head_sha(RC_619_LEGACY, lock))
+
+    def test_prior_blocks_same_head_not_other_head(self):
+        lock = _lock([RC_619_HEAD_A])
+        self.assertTrue(
+            srdl.prior_live_mutations_block_boundary(
+                lock, pr_number=619, expected_head_sha=HEAD_A
+            )
+        )
+        self.assertFalse(
+            srdl.prior_live_mutations_block_boundary(
+                lock, pr_number=619, expected_head_sha=HEAD_B
+            )
+        )
+
+    def test_backfill_stamps_legacy_terminals(self):
+        lock = _lock(
+            [dict(RC_619_LEGACY)],
+            ready_pr=619,
+            ready_head=HEAD_A,
+            ready_action="request_changes",
+        )
+        srdl.backfill_terminal_heads_from_ready(lock)
+        self.assertEqual(lock["live_mutations"][0]["head_sha"], HEAD_A)
+
+
+class TestHardStopHeadScope(unittest.TestCase):
+    def tearDown(self):
+        mcp_server._save_review_decision_lock(None)
+        mcp_server.review_workflow_load.clear_review_workflow_load()
+
+    def test_rc_head_a_allows_mark_ready_head_b(self):
+        _seed(
+            [RC_619_HEAD_A],
+            ready_pr=619,
+            ready_head=HEAD_A,
+            ready_action="request_changes",
+        )
+        self.assertEqual(
+            mcp_server.terminal_review_hard_stop_reasons(
+                619, "mark_ready", expected_head_sha=HEAD_B
+            ),
+            [],
+        )
+
+    def test_rc_head_a_blocks_mark_ready_same_head(self):
+        _seed(
+            [RC_619_HEAD_A],
+            ready_pr=619,
+            ready_head=HEAD_A,
+            ready_action="request_changes",
+        )
+        reasons = mcp_server.terminal_review_hard_stop_reasons(
+            619, "mark_ready", expected_head_sha=HEAD_A
+        )
+        self.assertTrue(reasons)
+        self.assertIn("#332", reasons[0])
+
+    def test_rc_head_a_blocks_other_pr(self):
+        _seed([RC_619_HEAD_A], ready_pr=619, ready_head=HEAD_A)
+        reasons = mcp_server.terminal_review_hard_stop_reasons(
+            700, "mark_ready", expected_head_sha=HEAD_B
+        )
+        self.assertTrue(reasons)
+
+    def test_legacy_619_ledger_allows_new_head(self):
+        """PR #619-style durable lock without mutation head_sha."""
+        _seed(
+            [RC_619_LEGACY],
+            ready_pr=619,
+            ready_head=HEAD_A,
+            ready_action="request_changes",
+        )
+        self.assertEqual(
+            mcp_server.terminal_review_hard_stop_reasons(
+                619, "mark_ready", expected_head_sha=HEAD_B
+            ),
+            [],
+        )
+
+
+class TestMarkFinalAndRecord(unittest.TestCase):
+    def tearDown(self):
+        mcp_server._save_review_decision_lock(None)
+        mcp_server.review_workflow_load.clear_review_workflow_load()
+
+    def _mark(self, pr, action, head, feedback=None):
+        with patch("mcp_server._list_pr_lease_comments", return_value=[]), patch(
+            "mcp_server._pr_work_lease_reviewer_block", return_value=_no_lease()
+        ), patch.object(
+            mcp_server,
+            "gitea_get_pr_review_feedback",
+            return_value=feedback or _feedback(blocking=False, stale=True),
+        ), patch.object(
+            mcp_server,
+            "gitea_check_pr_eligibility",
+            return_value={"eligible": True, "head_sha": head},
+        ):
+            return mcp_server.gitea_mark_final_review_decision(
+                pr_number=pr,
+                action=action,
+                expected_head_sha=head,
+                remote="prgs",
+                org="Scaled-Tech-Consulting",
+                repo="Gitea-Tools",
+            )
+
+    def test_rc_then_rc_on_new_head(self):
+        _seed(
+            [RC_619_HEAD_A],
+            ready_pr=619,
+            ready_head=HEAD_A,
+            ready_action="request_changes",
+        )
+        # Prior RC at head A is unresolved but head moved → feedback stale.
+        res = self._mark(
+            619,
+            "request_changes",
+            HEAD_B,
+            feedback=_feedback(blocking=True, stale=True),
+        )
+        self.assertTrue(res.get("marked_ready"), res)
+        lock = mcp_server._load_review_decision_lock()
+        # Historical head A preserved on mutation after backfill.
+        heads = {
+            m.get("head_sha")
+            for m in lock["live_mutations"]
+            if m.get("action") == "request_changes"
+        }
+        self.assertIn(HEAD_A, heads)
+        self.assertEqual(lock["ready_expected_head_sha"], HEAD_B)
+
+    def test_rc_then_approve_on_new_head(self):
+        _seed(
+            [RC_619_HEAD_A],
+            ready_pr=619,
+            ready_head=HEAD_A,
+            ready_action="request_changes",
+        )
+        res = self._mark(619, "approve", HEAD_B)
+        self.assertTrue(res.get("marked_ready"), res)
+        self.assertTrue(res.get("head_scoped"))
+
+    def test_same_head_rc_still_blocked_by_hard_stop(self):
+        _seed(
+            [RC_619_HEAD_A],
+            ready_pr=619,
+            ready_head=HEAD_A,
+            ready_action="request_changes",
+        )
+        res = self._mark(619, "approve", HEAD_A)
+        self.assertFalse(res.get("marked_ready"))
+        self.assertTrue(any("#332" in r for r in res.get("reasons") or []))
+
+    def test_pr619_style_legacy_lock_approve_on_current_head(self):
+        _seed(
+            [RC_619_LEGACY],
+            ready_pr=619,
+            ready_head=HEAD_A,
+            ready_action="request_changes",
+        )
+        res = self._mark(619, "approve", HEAD_B)
+        self.assertTrue(res.get("marked_ready"), res)
+        lock = mcp_server._load_review_decision_lock()
+        # Backfill should have stamped HEAD_A onto the legacy mutation.
+        self.assertEqual(lock["live_mutations"][0].get("head_sha"), HEAD_A)
+        self.assertEqual(lock["ready_expected_head_sha"], HEAD_B)
+
+    def test_record_live_mutation_stores_head(self):
+        _seed(ready_pr=619, ready_head=HEAD_B, ready_action="approve")
+        lock = mcp_server._load_review_decision_lock()
+        lock["final_review_decision_ready"] = True
+        lock["ready_pr_number"] = 619
+        lock["ready_expected_head_sha"] = HEAD_B
+        mcp_server._save_review_decision_lock(lock)
+        mcp_server.record_live_review_mutation(619, "approve", review_id=99)
+        stored = mcp_server._load_review_decision_lock()["live_mutations"][-1]
+        self.assertEqual(stored["head_sha"], HEAD_B)
+        self.assertEqual(stored["pr_number"], 619)
+
+    def test_submit_gate_allows_new_head_after_prior_terminal(self):
+        """check_review_decision_gate must not block different-head submit."""
+        mutations = [RC_619_HEAD_A]
+        _seed(
+            mutations,
+            ready_pr=619,
+            ready_head=HEAD_B,
+            ready_action="approve",
+        )
+        lock = mcp_server._load_review_decision_lock()
+        lock["final_review_decision_ready"] = True
+        lock["ready_pr_number"] = 619
+        lock["ready_action"] = "approve"
+        lock["ready_expected_head_sha"] = HEAD_B
+        lock["ready_remote"] = "prgs"
+        lock["ready_org"] = "Scaled-Tech-Consulting"
+        lock["ready_repo"] = "Gitea-Tools"
+        mcp_server._save_review_decision_lock(lock)
+        reasons = mcp_server.check_review_decision_gate(
+            619,
+            "approve",
+            final_review_decision_ready=True,
+            remote="prgs",
+            org="Scaled-Tech-Consulting",
+            repo="Gitea-Tools",
+        )
+        self.assertEqual(reasons, [], reasons)
+
+    def test_submit_gate_blocks_same_head_duplicate(self):
+        mutations = [RC_619_HEAD_A]
+        _seed(
+            mutations,
+            ready_pr=619,
+            ready_head=HEAD_A,
+            ready_action="request_changes",
+        )
+        lock = mcp_server._load_review_decision_lock()
+        lock["final_review_decision_ready"] = True
+        lock["ready_pr_number"] = 619
+        lock["ready_action"] = "request_changes"
+        lock["ready_expected_head_sha"] = HEAD_A
+        lock["ready_remote"] = "prgs"
+        lock["ready_org"] = "Scaled-Tech-Consulting"
+        lock["ready_repo"] = "Gitea-Tools"
+        mcp_server._save_review_decision_lock(lock)
+        reasons = mcp_server.check_review_decision_gate(
+            619,
+            "request_changes",
+            final_review_decision_ready=True,
+            remote="prgs",
+            org="Scaled-Tech-Consulting",
+            repo="Gitea-Tools",
+        )
+        self.assertTrue(reasons)
+
+
+class TestAssessmentOpenPrHead(unittest.TestCase):
+    def test_open_pr_stale_by_head_no_cleanup(self):
+        lock = _lock(
+            [RC_619_HEAD_A],
+            ready_pr=619,
+            ready_head=HEAD_A,
+            ready_action="request_changes",
+        )
+        a = srdl.assess_stale_review_decision_lock(
+            lock, pr_live=_open_pr(619, HEAD_B)
+        )
+        self.assertTrue(a["has_lock"])
+        self.assertFalse(a["is_moot"])
+        self.assertFalse(a["cleanup_allowed"])
+        self.assertTrue(a["stale_by_head"])
+        self.assertTrue(a["fresh_review_on_current_head_allowed"])
+        self.assertEqual(a["locked_head_sha"], HEAD_A)
+        self.assertEqual(a["current_pr_head_sha"], HEAD_B)
+
+    def test_open_pr_same_head_no_fresh(self):
+        lock = _lock([RC_619_HEAD_A], ready_pr=619, ready_head=HEAD_A)
+        a = srdl.assess_stale_review_decision_lock(
+            lock, pr_live=_open_pr(619, HEAD_A)
+        )
+        self.assertFalse(a["stale_by_head"])
+        self.assertFalse(a["fresh_review_on_current_head_allowed"])
+        self.assertFalse(a["cleanup_allowed"])
+
+    def test_historical_mutation_preserved_in_summary(self):
+        lock = _lock(
+            [RC_619_HEAD_A, APPROVE_619_HEAD_B],
+            ready_pr=619,
+            ready_head=HEAD_B,
+            ready_action="approve",
+        )
+        summary = srdl.lock_summary(lock)
+        self.assertEqual(summary["live_mutations_count"], 2)
+        self.assertEqual(summary["last_terminal"]["head_sha"], HEAD_B)
+        self.assertEqual(summary["locked_head_sha"], HEAD_B)
+
+
+if __name__ == "__main__":
+    unittest.main()