feat(recovery): stale worktree binding demotion and crash-orphan lease recovery (Closes #702)

An unhandled daemon crash skips teardown: the durable reviewer lease
comment survives, the in-memory session lease dies, and the
auto-reconnected daemon inherits a stale GITEA_ACTIVE_WORKTREE from its
parent environment (PR #701 / branches/review-pr-654 incident).

AC2 — safe clear/re-bind of stale bindings:
- new stale_binding_recovery.py: classifies the active env binding
  (corroborated / unverified_inherited / provably_stale_missing_path /
  superseded_by_session_lease) and produces a fail-closed recovery plan;
  only provably stale bindings are clear-eligible
- gitea_resolve_task_capability and daemon boot run the sanctioned
  recovery (durable audit via session state); runtime context surfaces
  the classification read-only
- namespace_workspace_binding.resolve_namespace_workspace(verify_paths=…)
  demotes env-bound worktrees whose path no longer exists; mutation and
  runtime-context resolution always verify

AC3 — recoverable lease cleanup after unexpected exit:
- durable session-lease shadow (KIND_REVIEWER_SESSION_LEASE) written on
  sanctioned record/heartbeat, removed on sanctioned clear; a crash
  leaves provable orphan evidence (owner pid + session id)
- assess_crashed_session_lease_orphan derives tri-state
  owner_process_alive: only a dead recorded owner pid proves exit; PID
  liveness is never ownership proof
- diagnose/cleanup wrappers consume the shadow instead of passing
  owner_process_alive=None
- new classification orphaned_expired_superseded_head: an expired
  superseded-head lease with no terminal review stops being a permanent
  ambiguous/wait; post-expiry it unlocks fresh acquisition, and guarded
  cleanup becomes eligible only with owner-exit evidence + clean/absent
  worktree + controller authorization + confirmation. Pre-expiry
  behavior is unchanged (fail-closed wait, no steal).

Validation: tests/test_issue_702_stale_binding_lease_recovery.py (29
tests covering lost in-session leases, old-head leases, runtime/worktree
mismatch, managed reconnect, safe expiry); full suite 2665 passed,
6 skipped, 161 subtests.

Co-Authored-By: Claude Fable 5 <[email protected]>

namespace_workspace_binding.py

@@ -56,23 +56,46 @@ def resolve_namespace_workspace(
     env: dict[str, str] | os._Environ | None = None,
     session_lease_worktree: str | None = None,
     profile_name: str | None = None,
+    demotions: list[str] | None = None,
+    verify_paths: bool = False,
 ) -> tuple[str, str]:
-    """Return ``(resolved_path, binding_source)`` for *role_kind*."""
+    """Return ``(resolved_path, binding_source)`` for *role_kind*.
+
+    With *verify_paths*, env-sourced candidates whose path no longer exists
+    are demoted (#702): a binding to a deleted worktree can never name a
+    valid task workspace, so resolution falls through to the next candidate.
+    Explicit arguments are never demoted — a caller-declared path must fail
+    loudly downstream rather than silently rebind. Demotion notes are
+    appended to *demotions* when provided. Runtime-context and mutation
+    guards resolve through :func:`resolve_namespace_mutation_context`, which
+    always verifies.
+    """
     env_map = env if env is not None else os.environ
     role = normalize_role_kind(role_kind, profile_name=profile_name)
     role_env_key = ROLE_WORKTREE_ENVS[role]
 
-    for candidate, source in (
-        (worktree_path, "worktree_path argument"),
-        (worktree, "worktree argument"),
-        (_env_value(env_map, ACTIVE_WORKTREE_ENV), f"{ACTIVE_WORKTREE_ENV} environment variable"),
-        (_env_value(env_map, role_env_key), f"{role_env_key} environment variable"),
+    for candidate, source, env_sourced in (
+        (worktree_path, "worktree_path argument", False),
+        (worktree, "worktree argument", False),
+        (_env_value(env_map, ACTIVE_WORKTREE_ENV),
+         f"{ACTIVE_WORKTREE_ENV} environment variable", True),
+        (_env_value(env_map, role_env_key),
+         f"{role_env_key} environment variable", True),
         (session_lease_worktree if role in {"reviewer", "merger"} else None,
-         "reviewer PR lease worktree"),
+         "reviewer PR lease worktree", False),
     ):
         text = (candidate or "").strip()
-        if text:
-            return os.path.realpath(os.path.abspath(text)), source
+        if not text:
+            continue
+        real = os.path.realpath(os.path.abspath(text))
+        if verify_paths and env_sourced and not os.path.isdir(real):
+            if demotions is not None:
+                demotions.append(
+                    f"{source} '{real}' demoted: path no longer exists "
+                    "(stale binding, #702)"
+                )
+            continue
+        return real, source
 
     return os.path.realpath(process_project_root), "MCP server process root (default)"
 
@@ -88,6 +111,7 @@ def resolve_namespace_mutation_context(
     profile_name: str | None = None,
 ) -> dict:
     """Shared workspace resolution for runtime_context and mutation guards."""
+    demotions: list[str] = []
     workspace, binding_source = resolve_namespace_workspace(
         role_kind=role_kind,
         worktree_path=worktree_path,
@@ -96,6 +120,8 @@ def resolve_namespace_mutation_context(
         env=env,
         session_lease_worktree=session_lease_worktree,
         profile_name=profile_name,
+        demotions=demotions,
+        verify_paths=True,
     )
     process_root = os.path.realpath(process_project_root)
     role = normalize_role_kind(role_kind, profile_name=profile_name)
@@ -111,7 +137,7 @@ def resolve_namespace_mutation_context(
         "workspace_path": workspace,
         "workspace_binding_source": binding_source,
         "workspace_role_kind": role,
-        "ignored_bindings": pollution.get("ignored_bindings") or [],
+        "ignored_bindings": demotions + (pollution.get("ignored_bindings") or []),
         "process_project_root": process_root,
         "canonical_repo_root": canonical_root,
         "roots_aligned": canonical_root == process_root,