fix: anti-stomp capability auth, inventory wiring, side-effect proof (#604)

Address REQUEST_CHANGES on PR #680:

Blocker A — role vs capability agreement
- authorization_compatible allows reviewer/merger when they hold the task's
  required permission (e.g. gitea.issue.comment on comment_issue/mark_issue/
  set_issue_labels/lock_issue) without broad role-bypass.
- Unauthorized escalation without the permission remains fail closed.
- Regression coverage for allowed and denied reviewer/merger cases.

Blocker B — MUTATION_TASKS matches runtime wiring
- Remove unenforced entries; document dedicated-gate exclusions
  (mark_final_review_decision, save/resume_review_draft, etc.).
- Wire non-closing gitea_edit_pr as edit_pr; acquire lease uses
  acquire_reviewer_pr_lease task through verify_preflight_purity.
- Inventory↔wiring consistency tests replace set-membership-only coverage.

Blocker C — entrypoint side-effect ordering
- Behavioral tests for merge_pr, submit_pr_review, and comment_issue prove
  the assessor block aborts before Gitea API mutation and local durable writes.

Validation: 43 focused anti-stomp + related suites green; full suite
2639 passed / 6 skipped.

Closes #604

anti_stomp_preflight.py

@@ -0,0 +1,807 @@
+"""Common anti-stomp preflight for every MCP mutation tool (#604).
+
+Even with leases, mutation tools need a **shared** preflight that prevents
+stale sessions, wrong worktrees, wrong repos, old prompts, terminal locks,
+foreign leases, contaminated approvals, and root-checkout mutations from
+slipping through.
+
+This module is the pure assessment core. Callers (MCP mutation entrypoints)
+gather live facts and pass them in — nothing here performs git, network, or
+durable-state I/O. Existing happy-path guards remain authoritative; this
+module composes them into one typed, fail-closed result.
+
+Required checks (issue #604):
+
+* repo/org verification
+* profile/role verification
+* root checkout clean and not used for mutation (when role requires branches/)
+* worktree under branches when required
+* active lease ownership (when lease is required for the mutation)
+* terminal lock status (when applicable)
+* expected head SHA (when pinned)
+* stale runtime status
+* workflow hash (when a workflow load is required)
+* source contamination status
+* no manual state/mtime/source-file bypass
+
+Failure returns a typed blocker and an exact next action. There is **no**
+agent-facing bypass flag.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+import author_mutation_worktree
+import master_parity_gate
+import remote_repo_guard
+import root_checkout_guard
+import stable_branch_push_guard
+
+# ── public constants ──────────────────────────────────────────────────────────
+
+# Typed blocker kinds returned in the structured result.
+BLOCKER_WRONG_REPO = "wrong_repo"
+BLOCKER_WRONG_ROLE = "wrong_role"
+BLOCKER_ROOT_CHECKOUT = "root_checkout_mutation"
+BLOCKER_WRONG_WORKTREE = "wrong_worktree"
+BLOCKER_FOREIGN_LEASE = "foreign_lease"
+BLOCKER_TERMINAL_LOCK = "terminal_lock"
+BLOCKER_HEAD_SHA = "head_sha_mismatch"
+BLOCKER_STALE_RUNTIME = "stale_runtime"
+BLOCKER_WORKFLOW_HASH = "workflow_hash"
+BLOCKER_SOURCE_CONTAMINATION = "source_contamination"
+BLOCKER_MANUAL_BYPASS = "manual_bypass"
+
+BLOCKER_KINDS = frozenset({
+    BLOCKER_WRONG_REPO,
+    BLOCKER_WRONG_ROLE,
+    BLOCKER_ROOT_CHECKOUT,
+    BLOCKER_WRONG_WORKTREE,
+    BLOCKER_FOREIGN_LEASE,
+    BLOCKER_TERMINAL_LOCK,
+    BLOCKER_HEAD_SHA,
+    BLOCKER_STALE_RUNTIME,
+    BLOCKER_WORKFLOW_HASH,
+    BLOCKER_SOURCE_CONTAMINATION,
+    BLOCKER_MANUAL_BYPASS,
+})
+
+# Mutation tasks that must invoke the shared anti-stomp preflight before
+# acting (issue #604 AC1). Every member must appear as a live task= kwarg
+# to verify_preflight_purity / _run_anti_stomp_preflight (or the review
+# anti_task map) in gitea_mcp_server.py. Inventory↔wiring tests fail if
+# a declared task is not wired.
+MUTATION_TASKS = frozenset({
+    "create_issue",
+    "comment_issue",
+    "close_issue",
+    "mark_issue",
+    "lock_issue",
+    "set_issue_labels",
+    "create_label",
+    "create_pr",
+    "close_pr",
+    "edit_pr",
+    "commit_files",
+    "gitea_commit_files",
+    "delete_branch",
+    "cleanup_merged_pr_branch",
+    "cleanup_stale_claims",
+    "reconcile_merged_cleanups",
+    "reconcile_already_landed_pr",
+    "reconcile_close_superseded_pr",
+    "post_heartbeat",
+    "acquire_reviewer_pr_lease",
+    "gitea_acquire_reviewer_pr_lease",
+    "adopt_merger_pr_lease",
+    "review_pr",
+    "submit_pr_review",
+    "approve_pr",
+    "request_changes_pr",
+    "merge_pr",
+})
+
+# Intentionally excluded from MUTATION_TASKS. Each has a dedicated
+# fail-closed gate that preserves decision-lock ownership, workflow-hash,
+# head-SHA, and repository consistency. Do not re-add without either
+# wiring shared preflight or updating this rationale (#604 Blocker B).
+DEDICATED_GATE_MUTATIONS: dict[str, str] = {
+    "mark_final_review_decision": (
+        "Local review-decision lock only. Enforced by session lock ownership, "
+        "workflow-hash, expected head SHA, PR work lease, eligibility, and "
+        "terminal-lock gates. No Gitea review POST; shared anti-stomp would "
+        "duplicate without side-effect-ordering value."
+    ),
+    "save_review_draft": (
+        "Local session-state draft save with live PR head/base consistency "
+        "checks. Not a Gitea review/merge mutation; dedicated head-SHA and "
+        "worktree resolution gates apply."
+    ),
+    "resume_review_draft": (
+        "Live-state resume with terminal lock, lease ownership, head/base SHA, "
+        "and parity checks. When submit=True, delegates to gitea_submit_pr_review "
+        "which runs shared anti-stomp before the Gitea review POST."
+    ),
+    "cleanup_stale_review_decision_lock": (
+        "Moot-lock cleanup with identity match, live PR merged/closed proof, "
+        "and reviewer capability gate (#594). Distinct from shared anti-stomp."
+    ),
+    "gitea_cleanup_stale_review_decision_lock": (
+        "Alias of cleanup_stale_review_decision_lock; dedicated #594 path."
+    ),
+    "heartbeat_reviewer_pr_lease": (
+        "Lease heartbeat posts via verify_preflight_purity(task='review_pr') "
+        "plus in-session lease ownership checks; not a separate mutation class."
+    ),
+    "release_reviewer_pr_lease": (
+        "Lease release uses workspace binding + ownership checks; posts only "
+        "when the session owns the active lease."
+    ),
+}
+
+# Roles that must mutate from a branches/ worktree (not the control checkout).
+_BRANCHES_REQUIRED_ROLES = frozenset({"author"})
+
+# Reviewer/merger mutations that require an owned lease + head pinning when
+# the caller supplies those facts.
+_LEASE_AWARE_TASKS = frozenset({
+    "review_pr",
+    "submit_pr_review",
+    "approve_pr",
+    "request_changes_pr",
+    "merge_pr",
+    "acquire_reviewer_pr_lease",
+    "gitea_acquire_reviewer_pr_lease",
+    "adopt_merger_pr_lease",
+})
+
+_NEXT_ACTIONS: dict[str, str] = {
+    BLOCKER_WRONG_REPO: (
+        "Pass explicit org= and repo= matching the local git remote "
+        "(e.g. org=Scaled-Tech-Consulting repo=Gitea-Tools) and retry."
+    ),
+    BLOCKER_WRONG_ROLE: (
+        "Call gitea_resolve_task_capability, switch to the required "
+        "namespace/profile, re-verify with gitea_whoami, then retry."
+    ),
+    BLOCKER_ROOT_CHECKOUT: (
+        "Leave the root control checkout on clean master; create or switch "
+        "to a session-owned worktree under branches/ and retry the mutation "
+        "with worktree_path set."
+    ),
+    BLOCKER_WRONG_WORKTREE: (
+        "Create or bind a session-owned worktree under branches/, set "
+        "worktree_path (or GITEA_ACTIVE_WORKTREE), and retry."
+    ),
+    BLOCKER_FOREIGN_LEASE: (
+        "Stop. Do not stomp a foreign lease. Wait for expiry, request "
+        "takeover through the sanctioned path, or hand off to the owner."
+    ),
+    BLOCKER_TERMINAL_LOCK: (
+        "Stop. A terminal review-decision lock is active for this head. "
+        "Do not re-approve/merge; follow the #332/#620 recovery path."
+    ),
+    BLOCKER_HEAD_SHA: (
+        "Re-fetch the live PR head with gitea_view_pr, re-pin "
+        "expected_head_sha to the current head, re-validate, then retry."
+    ),
+    BLOCKER_STALE_RUNTIME: (
+        "Restart the Gitea MCP server so it reloads master's capability "
+        "gates, re-run gitea_whoami + gitea_resolve_task_capability, then retry."
+    ),
+    BLOCKER_WORKFLOW_HASH: (
+        "Reload the canonical workflow via gitea_load_review_workflow, then "
+        "rerun the full review-merge workflow from inventory (no approve/merge replay)."
+    ),
+    BLOCKER_SOURCE_CONTAMINATION: (
+        "Stop. Session is source-contaminated. Hand off to a reconciler for "
+        "audit/clear; do not clear markers by deleting session-state files."
+    ),
+    BLOCKER_MANUAL_BYPASS: (
+        "Stop. Manual state/mtime/source-file bypass is forbidden. Use "
+        "sanctioned MCP tools only; never delete or rewrite session-state "
+        "or lock files by hand."
+    ),
+}
+
+
+def is_mutation_task(task: str | None) -> bool:
+    """True when *task* is in the #604 mutation set (normalized)."""
+    name = (task or "").strip().lower().removeprefix("gitea_")
+    if not name:
+        return False
+    if name in MUTATION_TASKS:
+        return True
+    # Accept gitea_ prefixed membership for aliases already in the set.
+    return f"gitea_{name}" in MUTATION_TASKS
+
+
+def roles_compatible(active_role: str | None, required_role: str | None) -> bool:
+    """Whether *active_role* may perform a task that maps to *required_role*.
+
+    Exact match always passes. Reconcilers may run author-class mutations
+    (comment/close/cleanup) that the capability map stamps as ``author`` —
+    matching the long-standing reconciler exemption for control-checkout
+    work. No other cross-role substitutions are allowed.
+
+    Capability-authorized multi-role tasks (e.g. reviewer holding
+    ``gitea.issue.comment`` for ``comment_issue``) are handled by
+    :func:`authorization_compatible`, not by expanding this role matrix.
+    """
+    active = (active_role or "").strip().lower()
+    required = (required_role or "").strip().lower()
+    if not active or not required:
+        return True
+    if active == required:
+        return True
+    if active == "reconciler" and required in {"author", "reconciler"}:
+        return True
+    return False
+
+
+def authorization_compatible(
+    active_role: str | None,
+    required_role: str | None,
+    *,
+    required_permission: str | None = None,
+    allowed_operations: Any = None,
+) -> bool:
+    """Whether the active session may run a task given role *and* capability.
+
+    Order:
+
+    1. :func:`roles_compatible` (exact role or narrow reconciler→author).
+    2. Capability possession: when *required_permission* is non-empty and
+       present in *allowed_operations*, allow even if the nominal task role
+       differs (e.g. reviewer/merger with ``gitea.issue.comment`` on
+       ``comment_issue`` / ``mark_issue`` / ``set_issue_labels`` /
+       ``lock_issue``).
+
+    Fail closed otherwise. This is **not** a broad reviewer→author or
+    merger→author role rewrite: without the specific permission the check
+    still denies. Missing *allowed_operations* when a permission is required
+    also fails closed (callers must supply the live profile op list).
+    """
+    if roles_compatible(active_role, required_role):
+        return True
+    perm = (required_permission or "").strip()
+    if not perm:
+        return False
+    if allowed_operations is None:
+        return False
+    try:
+        ops = {str(o).strip() for o in allowed_operations if o is not None}
+    except TypeError:
+        return False
+    return perm in ops
+
+
+def _blocker(
+    kind: str,
+    reasons: list[str],
+    *,
+    exact_next_action: str | None = None,
+    detail: dict | None = None,
+) -> dict[str, Any]:
+    if kind not in BLOCKER_KINDS:
+        raise ValueError(f"unknown anti-stomp blocker kind: {kind!r}")
+    return {
+        "kind": kind,
+        "reasons": list(reasons),
+        "exact_next_action": exact_next_action or _NEXT_ACTIONS[kind],
+        "detail": dict(detail or {}),
+    }
+
+
+def _allowed_result(checks: dict[str, Any]) -> dict[str, Any]:
+    return {
+        "allowed": True,
+        "block": False,
+        "blockers": [],
+        "reasons": [],
+        "exact_next_action": "proceed",
+        "blocker_kind": None,
+        "checks": checks,
+    }
+
+
+def _blocked_result(
+    blockers: list[dict[str, Any]],
+    checks: dict[str, Any],
+) -> dict[str, Any]:
+    primary = blockers[0]
+    all_reasons: list[str] = []
+    for b in blockers:
+        for r in b.get("reasons") or []:
+            if r not in all_reasons:
+                all_reasons.append(r)
+    return {
+        "allowed": False,
+        "block": True,
+        "blockers": blockers,
+        "reasons": all_reasons,
+        "exact_next_action": primary["exact_next_action"],
+        "blocker_kind": primary["kind"],
+        "checks": checks,
+    }
+
+
+def assess_anti_stomp_preflight(
+    *,
+    task: str | None = None,
+    # repo/org
+    remote: str | None = None,
+    resolved_org: str | None = None,
+    resolved_repo: str | None = None,
+    local_remote_url: str | None = None,
+    org_explicit: bool = False,
+    repo_explicit: bool = False,
+    check_repo: bool = True,
+    # profile/role + capability
+    profile_name: str | None = None,
+    profile_role: str | None = None,
+    required_role: str | None = None,
+    required_permission: str | None = None,
+    allowed_operations: Any = None,
+    check_role: bool = True,
+    # root checkout + worktree
+    workspace_path: str | None = None,
+    project_root: str | None = None,
+    current_branch: str | None = None,
+    root_head_sha: str | None = None,
+    root_porcelain: str | None = None,
+    remote_master_sha: str | None = None,
+    check_root_checkout: bool = True,
+    check_worktree: bool = True,
+    # stale runtime (master parity)
+    startup_head: str | None = None,
+    current_code_head: str | None = None,
+    check_stale_runtime: bool = True,
+    # lease ownership
+    lease_required: bool = False,
+    foreign_lease: bool | None = None,
+    lease_owner_session: str | None = None,
+    active_session_id: str | None = None,
+    lease_owner_identity: str | None = None,
+    active_identity: str | None = None,
+    lease_reasons: list[str] | None = None,
+    # terminal lock
+    terminal_lock_blocks: bool | None = None,
+    terminal_lock_reasons: list[str] | None = None,
+    # expected head SHA
+    require_head_sha: bool = False,
+    expected_head_sha: str | None = None,
+    live_head_sha: str | None = None,
+    # workflow hash
+    workflow_hash_valid: bool | None = None,
+    workflow_hash_reasons: list[str] | None = None,
+    # source contamination (stable-branch push / approval contamination)
+    source_contaminated: bool | None = None,
+    contamination_reasons: list[str] | None = None,
+    # manual bypass
+    manual_bypass_attempted: bool = False,
+    manual_bypass_reasons: list[str] | None = None,
+) -> dict[str, Any]:
+    """Fail-closed common anti-stomp assessment (pure).
+
+    Only checks for which facts are supplied (or which are required by the
+    mutation category) are evaluated. Unsupplied optional facts are recorded
+    as ``skipped`` so callers can see coverage without inventing defaults.
+
+    Returns a structured dict with ``allowed``/``block``, typed ``blockers``,
+    aggregated ``reasons``, ``exact_next_action``, and per-check ``checks``.
+    """
+    task_name = (task or "").strip()
+    role = (profile_role or "").strip().lower() or None
+    req_role = (required_role or "").strip().lower() or None
+    req_perm = (required_permission or "").strip() or None
+    checks: dict[str, Any] = {
+        "task": task_name or None,
+        "profile_name": profile_name,
+        "profile_role": role,
+        "required_role": req_role,
+        "required_permission": req_perm,
+    }
+    blockers: list[dict[str, Any]] = []
+
+    # ── manual bypass (always first; never skippable when attempted) ─────────
+    if manual_bypass_attempted:
+        reasons = list(manual_bypass_reasons or [
+            "manual state/mtime/source-file bypass attempt detected (fail closed)"
+        ])
+        blockers.append(_blocker(BLOCKER_MANUAL_BYPASS, reasons))
+        checks["manual_bypass"] = {"block": True, "reasons": reasons}
+    else:
+        checks["manual_bypass"] = {"block": False, "skipped": False}
+
+    # ── repo/org ─────────────────────────────────────────────────────────────
+    if check_repo and resolved_org is not None and resolved_repo is not None:
+        repo_assessment = remote_repo_guard.assess_remote_repo_match(
+            remote=remote or "",
+            resolved_org=resolved_org,
+            resolved_repo=resolved_repo,
+            local_remote_url=local_remote_url,
+            org_explicit=org_explicit,
+            repo_explicit=repo_explicit,
+        )
+        checks["repo"] = {
+            "block": bool(repo_assessment.get("block")),
+            "reasons": list(repo_assessment.get("reasons") or []),
+            "resolved_org": resolved_org,
+            "resolved_repo": resolved_repo,
+        }
+        if repo_assessment.get("block"):
+            blockers.append(
+                _blocker(
+                    BLOCKER_WRONG_REPO,
+                    list(repo_assessment.get("reasons") or ["repo/org mismatch"]),
+                    detail={
+                        "resolved_org": resolved_org,
+                        "resolved_repo": resolved_repo,
+                        "local_remote_url": local_remote_url,
+                    },
+                )
+            )
+    else:
+        checks["repo"] = {"block": False, "skipped": True}
+
+    # ── profile/role + capability ────────────────────────────────────────────
+    # Role match OR possession of the task's required permission (Blocker A).
+    # Reviewer/merger may run issue-comment-class tasks when they hold
+    # gitea.issue.comment; unauthorized escalation without the permission
+    # still fails closed.
+    if check_role and req_role and role:
+        authorized = authorization_compatible(
+            role,
+            req_role,
+            required_permission=req_perm,
+            allowed_operations=allowed_operations,
+        )
+        if not authorized:
+            perm_clause = (
+                f", required_permission='{req_perm}'" if req_perm else ""
+            )
+            reasons = [
+                f"active profile role '{role}' is not authorized for task "
+                f"'{task_name or '(unknown)'}' (required_role='{req_role}'"
+                f"{perm_clause}; profile={profile_name or '(unknown)'})"
+            ]
+            checks["role"] = {
+                "block": True,
+                "reasons": reasons,
+                "required_permission": req_perm,
+                "capability_authorized": False,
+            }
+            blockers.append(
+                _blocker(
+                    BLOCKER_WRONG_ROLE,
+                    reasons,
+                    detail={
+                        "profile_name": profile_name,
+                        "profile_role": role,
+                        "required_role": req_role,
+                        "required_permission": req_perm,
+                    },
+                )
+            )
+        else:
+            checks["role"] = {
+                "block": False,
+                "reasons": [],
+                "required_permission": req_perm,
+                "capability_authorized": bool(
+                    req_perm
+                    and allowed_operations is not None
+                    and req_perm in {
+                        str(o).strip() for o in (allowed_operations or [])
+                        if o is not None
+                    }
+                    and not roles_compatible(role, req_role)
+                ),
+            }
+    else:
+        checks["role"] = {"block": False, "skipped": True}
+
+    # ── stale runtime (master parity) ────────────────────────────────────────
+    if check_stale_runtime and (
+        startup_head is not None or current_code_head is not None
+    ):
+        parity = master_parity_gate.assess_master_parity(
+            {"startup_head": startup_head},
+            current_code_head,
+        )
+        stale_reasons = master_parity_gate.parity_block_reasons(parity)
+        checks["stale_runtime"] = {
+            "block": bool(stale_reasons),
+            "reasons": list(stale_reasons),
+            "startup_head": startup_head,
+            "current_code_head": current_code_head,
+            "stale": bool(parity.get("stale")),
+        }
+        if stale_reasons:
+            blockers.append(
+                _blocker(
+                    BLOCKER_STALE_RUNTIME,
+                    list(stale_reasons),
+                    detail={
+                        "startup_head": startup_head,
+                        "current_code_head": current_code_head,
+                    },
+                )
+            )
+    else:
+        checks["stale_runtime"] = {"block": False, "skipped": True}
+
+    # ── root checkout ────────────────────────────────────────────────────────
+    if (
+        check_root_checkout
+        and workspace_path is not None
+        and project_root is not None
+        and root_porcelain is not None
+    ):
+        root_assessment = root_checkout_guard.assess_root_checkout_guard(
+            workspace_path=workspace_path,
+            canonical_repo_root=project_root,
+            current_branch=current_branch,
+            head_sha=root_head_sha,
+            porcelain_status=root_porcelain,
+            remote_master_sha=remote_master_sha,
+            resolved_role=req_role or role,
+            actual_role=role,
+        )
+        checks["root_checkout"] = {
+            "block": bool(root_assessment.get("block")),
+            "reasons": list(root_assessment.get("reasons") or []),
+        }
+        if root_assessment.get("block"):
+            blockers.append(
+                _blocker(
+                    BLOCKER_ROOT_CHECKOUT,
+                    list(root_assessment.get("reasons") or [
+                        "control checkout is not clean master"
+                    ]),
+                    detail={
+                        "workspace_path": workspace_path,
+                        "project_root": project_root,
+                        "current_branch": current_branch,
+                    },
+                )
+            )
+    else:
+        checks["root_checkout"] = {"block": False, "skipped": True}
+
+    # ── worktree under branches (author) ─────────────────────────────────────
+    worktree_role = role or req_role
+    if (
+        check_worktree
+        and workspace_path is not None
+        and project_root is not None
+        and worktree_role in _BRANCHES_REQUIRED_ROLES
+    ):
+        wt = author_mutation_worktree.assess_author_mutation_worktree(
+            workspace_path=workspace_path,
+            project_root=project_root,
+            current_branch=current_branch,
+        )
+        checks["worktree"] = {
+            "block": bool(wt.get("block")),
+            "reasons": list(wt.get("reasons") or []),
+            "under_branches": wt.get("under_branches"),
+        }
+        if wt.get("block"):
+            blockers.append(
+                _blocker(
+                    BLOCKER_WRONG_WORKTREE,
+                    list(wt.get("reasons") or [
+                        "mutation worktree is not under branches/"
+                    ]),
+                    detail={
+                        "workspace_path": workspace_path,
+                        "project_root": project_root,
+                    },
+                )
+            )
+    else:
+        checks["worktree"] = {
+            "block": False,
+            "skipped": worktree_role not in _BRANCHES_REQUIRED_ROLES
+            or workspace_path is None,
+        }
+
+    # ── foreign lease ────────────────────────────────────────────────────────
+    lease_needed = lease_required or (
+        task_name.removeprefix("gitea_") in {
+            t.removeprefix("gitea_") for t in _LEASE_AWARE_TASKS
+        }
+        and foreign_lease is not None
+    )
+    if lease_needed or foreign_lease is True:
+        is_foreign = bool(foreign_lease)
+        if foreign_lease is None and lease_required:
+            # Ownership must be proven when lease_required; missing ownership
+            # facts fail closed.
+            owner_ok = (
+                (not lease_owner_session and not active_session_id)
+                or (
+                    lease_owner_session
+                    and active_session_id
+                    and lease_owner_session == active_session_id
+                )
+            )
+            identity_ok = (
+                (not lease_owner_identity and not active_identity)
+                or (
+                    lease_owner_identity
+                    and active_identity
+                    and lease_owner_identity == active_identity
+                )
+            )
+            if not owner_ok or not identity_ok:
+                is_foreign = True
+        reasons = list(lease_reasons or [])
+        if is_foreign and not reasons:
+            reasons = [
+                "active lease is owned by a foreign session or identity "
+                "(anti-stomp fail closed)"
+            ]
+        checks["lease"] = {
+            "block": is_foreign,
+            "reasons": reasons if is_foreign else [],
+            "lease_owner_session": lease_owner_session,
+            "active_session_id": active_session_id,
+        }
+        if is_foreign:
+            blockers.append(
+                _blocker(BLOCKER_FOREIGN_LEASE, reasons)
+            )
+    else:
+        checks["lease"] = {"block": False, "skipped": True}
+
+    # ── terminal lock ────────────────────────────────────────────────────────
+    if terminal_lock_blocks is not None:
+        reasons = list(terminal_lock_reasons or [])
+        if terminal_lock_blocks and not reasons:
+            reasons = [
+                "terminal review-decision lock is active for this head "
+                "(anti-stomp fail closed)"
+            ]
+        checks["terminal_lock"] = {
+            "block": bool(terminal_lock_blocks),
+            "reasons": reasons if terminal_lock_blocks else [],
+        }
+        if terminal_lock_blocks:
+            blockers.append(_blocker(BLOCKER_TERMINAL_LOCK, reasons))
+    else:
+        checks["terminal_lock"] = {"block": False, "skipped": True}
+
+    # ── expected head SHA ────────────────────────────────────────────────────
+    if require_head_sha or (
+        expected_head_sha is not None and live_head_sha is not None
+    ):
+        exp = (expected_head_sha or "").strip().lower()
+        live = (live_head_sha or "").strip().lower()
+        mismatch = False
+        reasons: list[str] = []
+        if require_head_sha and not exp:
+            mismatch = True
+            reasons.append(
+                "expected_head_sha is required before this mutation "
+                "(anti-stomp fail closed)"
+            )
+        elif exp and live and exp != live:
+            mismatch = True
+            reasons.append(
+                f"expected_head_sha '{exp}' does not match live PR head "
+                f"'{live}' (anti-stomp fail closed; stale prompt data)"
+            )
+        elif require_head_sha and exp and not live:
+            mismatch = True
+            reasons.append(
+                "live PR head SHA could not be determined to corroborate "
+                "expected_head_sha (anti-stomp fail closed)"
+            )
+        checks["head_sha"] = {
+            "block": mismatch,
+            "reasons": reasons,
+            "expected_head_sha": expected_head_sha,
+            "live_head_sha": live_head_sha,
+        }
+        if mismatch:
+            blockers.append(_blocker(BLOCKER_HEAD_SHA, reasons))
+    else:
+        checks["head_sha"] = {"block": False, "skipped": True}
+
+    # ── workflow hash ────────────────────────────────────────────────────────
+    if workflow_hash_valid is not None:
+        reasons = list(workflow_hash_reasons or [])
+        if not workflow_hash_valid and not reasons:
+            reasons = [
+                "workflow load proof missing or hash stale "
+                "(anti-stomp fail closed)"
+            ]
+        checks["workflow_hash"] = {
+            "block": not bool(workflow_hash_valid),
+            "reasons": reasons if not workflow_hash_valid else [],
+        }
+        if not workflow_hash_valid:
+            blockers.append(_blocker(BLOCKER_WORKFLOW_HASH, reasons))
+    else:
+        checks["workflow_hash"] = {"block": False, "skipped": True}
+
+    # ── source contamination ─────────────────────────────────────────────────
+    if source_contaminated is not None:
+        reasons = list(contamination_reasons or [])
+        if source_contaminated and not reasons:
+            reasons = [
+                "session is source-contaminated (stable-branch push or "
+                "contaminated approval path); anti-stomp fail closed"
+            ]
+        checks["source_contamination"] = {
+            "block": bool(source_contaminated),
+            "reasons": reasons if source_contaminated else [],
+        }
+        if source_contaminated:
+            blockers.append(
+                _blocker(BLOCKER_SOURCE_CONTAMINATION, reasons)
+            )
+    else:
+        checks["source_contamination"] = {"block": False, "skipped": True}
+
+    if blockers:
+        return _blocked_result(blockers, checks)
+    return _allowed_result(checks)
+
+
+def format_anti_stomp_error(assessment: dict[str, Any]) -> str:
+    """Single RuntimeError message for MCP mutation gates."""
+    kind = assessment.get("blocker_kind") or "unknown"
+    reasons = "; ".join(
+        assessment.get("reasons")
+        or ["anti-stomp preflight blocked the mutation"]
+    )
+    next_action = assessment.get("exact_next_action") or "stop and diagnose"
+    return (
+        f"Anti-stomp preflight (#604) blocked mutation "
+        f"[{kind}]: {reasons}. "
+        f"exact_next_action: {next_action}"
+    )
+
+
+def block_response(
+    assessment: dict[str, Any],
+    **extra_fields: Any,
+) -> dict[str, Any]:
+    """Structured tool-return payload for a blocked mutation."""
+    payload = {
+        "success": False,
+        "performed": False,
+        "blocked": True,
+        "anti_stomp": True,
+        "blocker_kind": assessment.get("blocker_kind"),
+        "blockers": list(assessment.get("blockers") or []),
+        "reasons": list(assessment.get("reasons") or []),
+        "exact_next_action": assessment.get("exact_next_action"),
+        "checks": assessment.get("checks") or {},
+    }
+    payload.update(extra_fields)
+    return payload
+
+
+def contamination_from_stable_marker(
+    marker: dict | None,
+    *,
+    task: str | None,
+    actual_role: str | None,
+) -> tuple[bool, list[str]]:
+    """Derive source-contamination facts from a #671 durable marker."""
+    if not marker:
+        return False, []
+    gate = stable_branch_push_guard.assess_contamination_gate(
+        marker,
+        task=task,
+        actual_role=actual_role,
+    )
+    if gate.get("block"):
+        return True, list(gate.get("reasons") or [])
+    return False, []

gitea_mcp_server.py

@@ -619,18 +619,219 @@ def _enforce_branches_only_author_mutation(worktree_path: str | None = None) ->
         )
 
 
+def _anti_stomp_in_test_mode() -> bool:
+    """Whether the #604 anti-stomp gate is skipped under pytest.
+
+    Mirrors remote-repo / stable-contamination test bypasses so the existing
+    suite (bare remotes, mocked APIs) stays green. Set
+    ``GITEA_TEST_FORCE_ANTI_STOMP=1`` to exercise the live gate under tests.
+    """
+    if not _preflight_in_test_mode():
+        return False
+    return not bool(os.environ.get("GITEA_TEST_FORCE_ANTI_STOMP"))
+
+
+def _run_anti_stomp_preflight(
+    task: str | None,
+    *,
+    remote: str | None = None,
+    worktree_path: str | None = None,
+    host: str | None = None,
+    org: str | None = None,
+    repo: str | None = None,
+    expected_head_sha: str | None = None,
+    live_head_sha: str | None = None,
+    require_head_sha: bool = False,
+    lease_required: bool = False,
+    foreign_lease: bool | None = None,
+    lease_reasons: list[str] | None = None,
+    terminal_lock_blocks: bool | None = None,
+    terminal_lock_reasons: list[str] | None = None,
+    workflow_hash_valid: bool | None = None,
+    workflow_hash_reasons: list[str] | None = None,
+    raise_on_block: bool = True,
+) -> dict | None:
+    """Shared #604 anti-stomp preflight for MCP mutation entrypoints.
+
+    Gathers live workspace/parity/role/repo facts and invokes the pure
+    :func:`anti_stomp_preflight.assess_anti_stomp_preflight` assessor. On
+    block, raises ``RuntimeError`` (default) or returns a structured
+    :func:`anti_stomp_preflight.block_response` when *raise_on_block* is
+    False. Returns ``None`` when the mutation may proceed.
+    """
+    if _anti_stomp_in_test_mode():
+        return None
+
+    # Only enforce when the caller names a known mutation task. Read-only
+    # paths and legacy verify_preflight_purity calls without a task stay
+    # on the pre-#604 gate chain (whoami/capability/root/worktree).
+    if not task or not anti_stomp_preflight.is_mutation_task(task):
+        return None
+
+    profile = get_profile()
+    profile_name = profile.get("profile_name")
+    profile_role = _actual_profile_role()
+    allowed_operations = list(profile.get("allowed_operations") or [])
+    req_role = None
+    req_perm = None
+    if task:
+        try:
+            req_role = task_capability_map.required_role(task)
+        except KeyError:
+            req_role = _preflight_resolved_role
+        try:
+            req_perm = task_capability_map.required_permission(task)
+        except KeyError:
+            req_perm = None
+
+    ctx = _resolve_namespace_mutation_context(worktree_path)
+    workspace = ctx["workspace_path"]
+    canonical_root = ctx["canonical_repo_root"]
+    git_state = issue_lock_worktree.read_worktree_git_state(canonical_root)
+    remote_master_sha = root_checkout_guard.resolve_remote_master_sha(canonical_root)
+
+    # Repo/org facts (best-effort; explicit org/repo when provided).
+    resolved_org = org
+    resolved_repo = repo
+    local_remote_url = None
+    org_explicit = org is not None
+    repo_explicit = repo is not None
+    if remote:
+        try:
+            local_remote_url = _local_git_remote_url(remote)
+        except Exception:
+            local_remote_url = None
+        if resolved_org is None or resolved_repo is None:
+            try:
+                rem = _effective_remote(remote)
+                if rem in REMOTES:
+                    if resolved_org is None:
+                        resolved_org = REMOTES[rem]["org"]
+                    if resolved_repo is None:
+                        resolved_repo = REMOTES[rem]["repo"]
+            except Exception:
+                pass
+
+    parity = _current_master_parity()
+    startup_head = parity.get("startup_head")
+    current_code_head = parity.get("current_head")
+
+    # Source contamination from durable #671 marker (role-aware).
+    source_contaminated = None
+    contamination_reasons = None
+    try:
+        marker = _load_stable_contamination_marker(remote)
+        contaminated, cont_reasons = anti_stomp_preflight.contamination_from_stable_marker(
+            marker,
+            task=task,
+            actual_role=profile_role,
+        )
+        if marker is not None:
+            source_contaminated = contaminated
+            contamination_reasons = cont_reasons
+    except Exception:
+        # Fail soft on marker I/O: existing #671 enforcer still runs separately.
+        source_contaminated = None
+
+    # Workflow-hash facts when the task is review/merge oriented.
+    if workflow_hash_valid is None and task in {
+        "review_pr",
+        "submit_pr_review",
+        "approve_pr",
+        "request_changes_pr",
+        "merge_pr",
+    }:
+        try:
+            wf_reasons = _review_workflow_load_gate_reasons()
+            workflow_hash_valid = not bool(wf_reasons)
+            workflow_hash_reasons = list(wf_reasons) if wf_reasons else None
+        except Exception:
+            pass
+
+    # Mirror remote_repo_guard's pytest bypass: under the unit suite bare
+    # remote=prgs still defaults to Timesheet, and re-checking here would
+    # break happy-path reconciler/author tests that already rely on the
+    # #530 gate being opt-in via GITEA_FORCE_REMOTE_REPO_CHECK.
+    check_repo = True
+    if "pytest" in sys.modules and not os.environ.get(
+        "GITEA_FORCE_REMOTE_REPO_CHECK"
+    ):
+        check_repo = False
+
+    assessment = anti_stomp_preflight.assess_anti_stomp_preflight(
+        task=task,
+        remote=remote,
+        resolved_org=resolved_org,
+        resolved_repo=resolved_repo,
+        local_remote_url=local_remote_url,
+        org_explicit=org_explicit,
+        repo_explicit=repo_explicit,
+        check_repo=check_repo,
+        profile_name=profile_name,
+        profile_role=profile_role,
+        required_role=req_role or _preflight_resolved_role,
+        required_permission=req_perm,
+        allowed_operations=allowed_operations,
+        workspace_path=workspace,
+        project_root=canonical_root,
+        current_branch=git_state.get("current_branch"),
+        root_head_sha=git_state.get("head_sha"),
+        root_porcelain=git_state.get("porcelain_status") or "",
+        remote_master_sha=remote_master_sha,
+        startup_head=startup_head,
+        current_code_head=current_code_head,
+        lease_required=lease_required,
+        foreign_lease=foreign_lease,
+        lease_reasons=lease_reasons,
+        terminal_lock_blocks=terminal_lock_blocks,
+        terminal_lock_reasons=terminal_lock_reasons,
+        require_head_sha=require_head_sha,
+        expected_head_sha=expected_head_sha,
+        live_head_sha=live_head_sha,
+        workflow_hash_valid=workflow_hash_valid,
+        workflow_hash_reasons=workflow_hash_reasons,
+        source_contaminated=source_contaminated,
+        contamination_reasons=contamination_reasons,
+        manual_bypass_attempted=False,
+    )
+    if not assessment.get("block"):
+        return None
+    if raise_on_block:
+        raise RuntimeError(anti_stomp_preflight.format_anti_stomp_error(assessment))
+    return anti_stomp_preflight.block_response(assessment)
+
+
 def verify_preflight_purity(
     remote: str | None = None,
     worktree_path: str | None = None,
     task: str | None = None,
+    *,
+    expected_head_sha: str | None = None,
+    live_head_sha: str | None = None,
+    require_head_sha: bool = False,
+    lease_required: bool = False,
+    foreign_lease: bool | None = None,
+    lease_reasons: list[str] | None = None,
+    terminal_lock_blocks: bool | None = None,
+    terminal_lock_reasons: list[str] | None = None,
+    workflow_hash_valid: bool | None = None,
+    workflow_hash_reasons: list[str] | None = None,
+    org: str | None = None,
+    repo: str | None = None,
 ):
-    """Verify that identity and capability were verified prior to session edits."""
+    """Verify that identity and capability were verified prior to session edits.
+
+    Also runs the shared #604 anti-stomp preflight for mutation tasks (typed
+    blocker + exact next action). Extended lease/head/terminal facts may be
+    supplied by review/merge callers.
+    """
     global _preflight_reviewer_violation_files
 
     in_test = _preflight_in_test_mode()
     if in_test and not (
         os.environ.get("GITEA_TEST_FORCE_DIRTY")
         or os.environ.get("GITEA_TEST_PORCELAIN") is not None
+        or os.environ.get("GITEA_TEST_FORCE_ANTI_STOMP")
     ):
         return
 
@@ -717,6 +918,30 @@ def verify_preflight_purity(
 
     _enforce_root_checkout_guard(worktree_path)
     _enforce_branches_only_author_mutation(worktree_path)
+
+    # #604: common anti-stomp preflight (typed blocker + exact next action).
+    # Runs after the legacy enforcers so existing happy paths stay green and
+    # the shared module remains the single fail-closed composition point for
+    # repo/role/worktree/lease/terminal-lock/head/stale/workflow/contamination.
+    _run_anti_stomp_preflight(
+        task,
+        remote=remote,
+        worktree_path=worktree_path,
+        org=org,
+        repo=repo,
+        expected_head_sha=expected_head_sha,
+        live_head_sha=live_head_sha,
+        require_head_sha=require_head_sha,
+        lease_required=lease_required,
+        foreign_lease=foreign_lease,
+        lease_reasons=lease_reasons,
+        terminal_lock_blocks=terminal_lock_blocks,
+        terminal_lock_reasons=terminal_lock_reasons,
+        workflow_hash_valid=workflow_hash_valid,
+        workflow_hash_reasons=workflow_hash_reasons,
+        raise_on_block=True,
+    )
+
     _clear_preflight_capability_state()
 
 
@@ -930,6 +1155,7 @@ import author_mutation_worktree  # noqa: E402
 import root_checkout_guard  # noqa: E402
 import stable_branch_push_guard  # noqa: E402
 import remote_repo_guard  # noqa: E402
+import anti_stomp_preflight  # noqa: E402
 import issue_claim_heartbeat  # noqa: E402
 import issue_work_duplicate_gate  # noqa: E402
 import issue_workflow_labels  # noqa: E402
@@ -3833,6 +4059,30 @@ def _evaluate_pr_review_submission(
         result["pr_work_lease"] = lease_block
         return result
 
+    if live:
+        # #604: common anti-stomp with live head + lease proof (typed blocker).
+        anti_task = {
+            "approve": "approve_pr",
+            "request_changes": "request_changes_pr",
+            "comment": "submit_pr_review",
+        }.get(action, "submit_pr_review")
+        try:
+            _run_anti_stomp_preflight(
+                anti_task,
+                remote=remote,
+                worktree_path=worktree_path,
+                org=org,
+                repo=repo,
+                expected_head_sha=pinned_sha,
+                live_head_sha=actual_sha,
+                require_head_sha=True,
+                foreign_lease=False,
+                terminal_lock_blocks=False,
+            )
+        except RuntimeError as exc:
+            reasons.append(str(exc))
+            return result
+
     if (body or "").strip():
         gate = _canonical_comment_gate(body, context="pr_review")
         if gate["blocked"]:
@@ -4787,7 +5037,12 @@ def gitea_edit_pr(
         raise ValueError("At least one field to edit (title, body, state, base) must be provided.")
 
     closing = payload.get("state") == "closed"
-    verify_preflight_purity(remote, task="close_pr" if closing else None)
+    # Closing uses close_pr; non-closing title/body/base edits use edit_pr so
+    # the shared #604 anti-stomp inventory stays consistent with wiring.
+    if closing:
+        verify_preflight_purity(remote, task="close_pr")
+    else:
+        verify_preflight_purity(remote, task="edit_pr")
 
     # PR closure is a first-class capability, distinct from retitling or
     # rebasing edits (#216). Gate BEFORE auth/API setup so a blocked close
@@ -5269,6 +5524,25 @@ def gitea_merge_pr(
         reasons.extend(lease_block.get("reasons") or [])
         result["pr_work_lease"] = lease_block
         return result
+
+    # #604: common anti-stomp with live head + lease proof (typed blocker).
+    try:
+        _run_anti_stomp_preflight(
+            "merge_pr",
+            remote=remote,
+            worktree_path=worktree_path,
+            org=org,
+            repo=repo,
+            expected_head_sha=expected_head_sha,
+            live_head_sha=actual_sha,
+            require_head_sha=True,
+            foreign_lease=False,
+            terminal_lock_blocks=False,
+        )
+    except RuntimeError as exc:
+        reasons.append(str(exc))
+        return result
+
     if expected_head_sha and actual_sha and expected_head_sha != actual_sha:
         reasons.append(
             "expected head SHA does not match current PR head (fail closed)"
@@ -7388,7 +7662,11 @@ def gitea_acquire_reviewer_pr_lease(
             "permission_report": _permission_block_report("gitea.pr.comment"),
         }
 
-    _verify_role_mutation_workspace(remote, worktree=worktree, task="review_pr")
+    # task=acquire_reviewer_pr_lease so verify_preflight_purity runs shared #604
+    # anti-stomp for the declared lease-acquire mutation inventory entry.
+    _verify_role_mutation_workspace(
+        remote, worktree=worktree, task="acquire_reviewer_pr_lease"
+    )
     h, o, r = _resolve(remote, host, org, repo)
     auth = _auth(h)
     profile = get_profile()
@@ -7529,6 +7807,7 @@ def gitea_adopt_merger_pr_lease(
             "permission_report": _permission_block_report("gitea.pr.merge"),
         }
 
+    # task=adopt_merger_pr_lease so verify_preflight_purity runs shared #604 anti-stomp.
     _verify_role_mutation_workspace(
         remote, worktree=worktree, task="adopt_merger_pr_lease"
     )

task_capability_map.py

@@ -60,6 +60,15 @@ TASK_CAPABILITY_MAP: dict[str, dict[str, str]] = {
         "permission": "gitea.pr.close",
         "role": "author",
     },
+    # Non-closing PR metadata edits (title/body/base). Closing uses close_pr.
+    "edit_pr": {
+        "permission": "gitea.pr.create",
+        "role": "author",
+    },
+    "gitea_edit_pr": {
+        "permission": "gitea.pr.create",
+        "role": "author",
+    },
     "address_pr_change_requests": {
         "permission": "gitea.branch.push",
         "role": "author",
@@ -68,10 +77,22 @@ TASK_CAPABILITY_MAP: dict[str, dict[str, str]] = {
         "permission": "gitea.pr.review",
         "role": "reviewer",
     },
+    "submit_pr_review": {
+        "permission": "gitea.pr.review",
+        "role": "reviewer",
+    },
     "merge_pr": {
         "permission": "gitea.pr.merge",
         "role": "merger",
     },
+    "acquire_reviewer_pr_lease": {
+        "permission": "gitea.pr.comment",
+        "role": "reviewer",
+    },
+    "gitea_acquire_reviewer_pr_lease": {
+        "permission": "gitea.pr.comment",
+        "role": "reviewer",
+    },
     "adopt_merger_pr_lease": {
         "permission": "gitea.pr.comment",
         "role": "reviewer",