fix(reviewer-workflow): address review — in-process mutation authority, no /tmp lock (#199)

Addresses the sysadmin REQUEST_CHANGES on PR #203 (reviewed head
10d2644790):

1. Lock redesigned; /tmp file removed entirely. The mutation authority is
   now an in-process record (_MUTATION_AUTHORITY) plus an environment
   session lock (GITEA_SESSION_PROFILE_LOCK) exported at server launch:
   - in-process record cannot be spoofed by other local processes, cannot
     go stale across sessions, and cannot race concurrent agents;
   - the env lock is inherited by child CLI processes, so review_pr.py can
     refuse an ad-hoc GITEA_MCP_PROFILE role escalation without any shared
     file; a missing env lock (direct operator CLI use) stays allowed;
   - silent except-pass writes are gone; an unresolvable profile fails
     closed.
2. Standard reviewer workflow unbroken: verify_mutation_authority seeds
   itself from the live config-resolved context at the first mutation gate
   (approved preflight path whoami -> eligibility -> review/merge), and now
   runs as the final gate after eligibility, reusing the identity that
   eligibility proved (no extra /user call).
3. Trailing whitespace removed from review_pr.py (git diff --check clean).
4. Module-global verify_mutation_authority no-op bypass removed from
   tests/test_mcp_server.py; replaced with a tests/conftest.py autouse
   fixture that only resets per-process state (_MUTATION_AUTHORITY,
   _IDENTITY_CACHE, session lock env) between tests — the gate itself
   stays live in every test.
5. Tests rewritten for the new design: seeding on first verify, unresolved
   profile fails closed, remote/profile/identity mismatches fail closed,
   session-lock env mismatch rejected, foreign-pid authority reseeded,
   unauthorized author->reviewer pivot blocked, authorized pivot allowed;
   CLI: mismatch blocked, match allowed, no-lock allowed.
6. Rebased onto current master (c6fd0fd).

Closes #199
Refs #194

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

tests/conftest.py

@@ -0,0 +1,28 @@
+"""Shared pytest fixtures for the Gitea-Tools test suite."""
+import sys
+
+import pytest
+
+sys.path.insert(0, str(__import__("pathlib").Path(__file__).resolve().parent.parent))
+
+
+@pytest.fixture(autouse=True)
+def _reset_mutation_authority(monkeypatch):
+    """Isolate the in-process mutation authority between tests (#199).
+
+    The mutation-authority gate stays LIVE in every test — this fixture only
+    clears the per-process record and the session profile lock so one test's
+    seeded authority (or an intentionally mismatched one) cannot leak into
+    the next test. It must never replace verify_mutation_authority with a
+    no-op: individual tests that need a specific authority state set it up
+    explicitly.
+    """
+    monkeypatch.delenv("GITEA_SESSION_PROFILE_LOCK", raising=False)
+    try:
+        import mcp_server
+    except Exception:
+        yield
+        return
+    monkeypatch.setattr(mcp_server, "_MUTATION_AUTHORITY", None)
+    monkeypatch.setattr(mcp_server, "_IDENTITY_CACHE", {})
+    yield