P0 security batch: true global admin, quota gates on all spending paths, default quota for quota-less users, fix-review author trust + docker/owner attribution, GitHub App setup issuer binding, real cancel kill, wider shell env exclusion

- CODEX_GLOBAL_ADMINS replaces maintainer-derived global admin;
  admin endpoints (quotas, sweep, backup, push dispatch) fail-closed
  403 when unset, with audit on allow and deny.
- continue/followups/messages/retry check both caller and original
  creator quotas (USD + unpriced token cap), 402 on either overrun.
- Quota-less users now get the #86 default quota instead of unlimited;
  init_db backfills and OAuth create/bind/existing-login branches
  INSERT OR IGNORE a default row; explicit NULL row stays unlimited.
  user_quotas added to migration tables.
- /fix-review: untrusted authors rejected before dedup claim, no task;
  trusted tasks force executor=docker, created_by=project owner, owner
  quota gate, prompt is a fixed template plus a 2000-char excerpt.
- GitHub App setup state only issued by global admins, state rows bind
  issued_by (ALTER-compatible for old DBs), callback rejects issuers
  no longer in the admin list without consuming the state.
- Cancel: popen poll checks DB status every second, Docker path runs a
  cancel watchdog that kills by container name, write-back is CAS-guarded
  so late results never overwrite a new status.
- SHELL_ENV_EXCLUDE adds *_TOKEN, *_AUTH*, *_CREDENTIAL*, *API_KEY*;
  comment states the residual risk: same-UID /proc environ remains
  readable, true isolation needs UID separation or hidepid.
- Tests: new cloud/tests/test_p0_security.py (17 cases); old tests
  updated to the new semantics (admin env, default quota, trusted
  fix-review author) without weakening any gate.

cloud/tests/test_server_oauth_push.py

@@ -30,6 +30,8 @@ class OAuthPushEndpointsTestCase(unittest.TestCase):
         self.db_path = os.path.join(self.tmp.name, "control.db")
         self.auth = AuthStore(self.db_path)
         self.owner_id, self.owner_key = self.auth.create_user("owner")
+        self._old_admins = os.environ.get("CODEX_GLOBAL_ADMINS")
+        os.environ["CODEX_GLOBAL_ADMINS"] = self.owner_id
         self.outsider_id, self.outsider_key = self.auth.create_user("outsider")
         self.server = create_server(self.db_path, "127.0.0.1", 0)
         self.port = self.server.server_address[1]
@@ -49,6 +51,10 @@ class OAuthPushEndpointsTestCase(unittest.TestCase):
         except Exception:
             pass
         self.tmp.cleanup()
+        if getattr(self, "_old_admins", None) is None:
+            os.environ.pop("CODEX_GLOBAL_ADMINS", None)
+        else:
+            os.environ["CODEX_GLOBAL_ADMINS"] = self._old_admins
 
     def _req(self, method, path, body=None, key=None):
         conn = http.client.HTTPConnection("127.0.0.1", self.port, timeout=10)