test(conftest): reset module-level state + unset platform allowlists (#13400)

Three fixes that close the remaining structural sources of CI flakes
after PR #13363.

## 1. Per-test reset of module-level singletons and ContextVars

Python modules are singletons per process, and pytest-xdist workers are
long-lived. Module-level dicts/sets and ContextVars persist across tests
on the same worker. A test that sets state in `tools.approval._session_approved`
and doesn't explicitly clear it leaks that state to every subsequent test
on the same worker.

New `_reset_module_state` autouse fixture in `tests/conftest.py` clears:
  - tools.approval: _session_approved, _session_yolo, _permanent_approved,
    _pending, _gateway_queues, _gateway_notify_cbs, _approval_session_key
  - tools.interrupt: _interrupted_threads
  - gateway.session_context: 10 session/cron ContextVars (reset to _UNSET)
  - tools.env_passthrough: _allowed_env_vars_var (reset to empty set)
  - tools.credential_files: _registered_files_var (reset to empty dict)
  - tools.file_tools: _read_tracker, _file_ops_cache

This was the single biggest remaining class of CI flakes.
`test_command_guards::test_warn_session_approved` and
`test_combined_cli_session_approves_both` were failing 12/15 recent main
runs specifically because `_session_approved` carried approvals from a
prior test's session into these tests' `"default"` session lookup.

## 2. Unset platform allowlist env vars in hermetic fixture

`TELEGRAM_ALLOWED_USERS`, `DISCORD_ALLOWED_USERS`, and 20 other
`*_ALLOWED_USERS` / `*_ALLOW_ALL_USERS` vars are now unset per-test in
the same place credential env vars already are. These aren't credentials
but they change gateway auth behavior; if set from any source (user
shell, leaky test, CI env) they flake button-authorization tests.

Fixes three `test_telegram_approval_buttons` tests that were failing
across recent runs of the full gateway directory.

## 3. Two specific tests with module-level captured state

- `test_signal::TestSignalPhoneRedaction`: `agent.redact._REDACT_ENABLED`
  is captured at module import from `HERMES_REDACT_SECRETS`, not read
  per-call. `monkeypatch.delenv` at test time is too late. Added
  `monkeypatch.setattr("agent.redact._REDACT_ENABLED", True)` per
  skill xdist-cross-test-pollution Pattern 5.

- `test_internal_event_bypass_pairing::test_non_internal_event_without_user_triggers_pairing`:
  `gateway.pairing.PAIRING_DIR` is captured at module import from
  HERMES_HOME, so per-test HERMES_HOME redirection in conftest doesn't
  retroactively move it. Test now monkeypatches PAIRING_DIR directly to
  its tmp_path, preventing rate-limit state from prior xdist workers
  from letting the pairing send-call be suppressed.

## Validation

- tests/tools/: 3494 pass (0 fail) including test_command_guards
- tests/gateway/: 3504 pass (0 fail) across repeat runs
- tests/agent/ + tests/hermes_cli/ + tests/run_agent/ + tests/tools/:
  8371 pass, 37 skipped, 0 fail — full suite across directories

No production code changed.

tests/conftest.py

@@ -186,6 +186,31 @@ _HERMES_BEHAVIORAL_VARS = frozenset({
     "HERMES_HOME_MODE",
     "BROWSER_CDP_URL",
     "CAMOFOX_URL",
+    # Platform allowlists — not credentials, but if set from any source
+    # (user shell, earlier leaky test, CI env), they change gateway auth
+    # behavior and flake button-authorization tests.
+    "TELEGRAM_ALLOWED_USERS",
+    "DISCORD_ALLOWED_USERS",
+    "WHATSAPP_ALLOWED_USERS",
+    "SLACK_ALLOWED_USERS",
+    "SIGNAL_ALLOWED_USERS",
+    "SIGNAL_GROUP_ALLOWED_USERS",
+    "EMAIL_ALLOWED_USERS",
+    "SMS_ALLOWED_USERS",
+    "MATTERMOST_ALLOWED_USERS",
+    "MATRIX_ALLOWED_USERS",
+    "DINGTALK_ALLOWED_USERS",
+    "FEISHU_ALLOWED_USERS",
+    "WECOM_ALLOWED_USERS",
+    "GATEWAY_ALLOWED_USERS",
+    "GATEWAY_ALLOW_ALL_USERS",
+    "TELEGRAM_ALLOW_ALL_USERS",
+    "DISCORD_ALLOW_ALL_USERS",
+    "WHATSAPP_ALLOW_ALL_USERS",
+    "SLACK_ALLOW_ALL_USERS",
+    "SIGNAL_ALLOW_ALL_USERS",
+    "EMAIL_ALLOW_ALL_USERS",
+    "SMS_ALLOW_ALL_USERS",
 })
 
 
@@ -258,6 +283,107 @@ def _isolate_hermes_home(_hermetic_environment):
     return None
 
 
+# ── Module-level state reset ───────────────────────────────────────────────
+#
+# Python modules are singletons per process, and pytest-xdist workers are
+# long-lived. Module-level dicts/sets (tool registries, approval state,
+# interrupt flags) and ContextVars persist across tests in the same worker,
+# causing tests that pass alone to fail when run with siblings.
+#
+# Each entry in this fixture clears state that belongs to a specific module.
+# New state buckets go here too — this is the single gate that prevents
+# "works alone, flakes in CI" bugs from state leakage.
+#
+# The skill `test-suite-cascade-diagnosis` documents the concrete patterns
+# this closes; the running example was `test_command_guards` failing 12/15
+# CI runs because ``tools.approval._session_approved`` carried approvals
+# from one test's session into another's.
+
+@pytest.fixture(autouse=True)
+def _reset_module_state():
+    """Clear module-level mutable state and ContextVars between tests.
+
+    Keeps state from leaking across tests on the same xdist worker. Modules
+    that don't exist yet (test collection before production import) are
+    skipped silently — production import later creates fresh empty state.
+    """
+    # --- tools.approval — the single biggest source of cross-test pollution ---
+    try:
+        from tools import approval as _approval_mod
+        _approval_mod._session_approved.clear()
+        _approval_mod._session_yolo.clear()
+        _approval_mod._permanent_approved.clear()
+        _approval_mod._pending.clear()
+        _approval_mod._gateway_queues.clear()
+        _approval_mod._gateway_notify_cbs.clear()
+        # ContextVar: reset to empty string so get_current_session_key()
+        # falls through to the env var / default path, matching a fresh
+        # process.
+        _approval_mod._approval_session_key.set("")
+    except Exception:
+        pass
+
+    # --- tools.interrupt — per-thread interrupt flag set ---
+    try:
+        from tools import interrupt as _interrupt_mod
+        with _interrupt_mod._lock:
+            _interrupt_mod._interrupted_threads.clear()
+    except Exception:
+        pass
+
+    # --- gateway.session_context — 9 ContextVars that represent
+    #     the active gateway session. If set in one test and not reset,
+    #     the next test's get_session_env() reads stale values.
+    try:
+        from gateway import session_context as _sc_mod
+        for _cv in (
+            _sc_mod._SESSION_PLATFORM,
+            _sc_mod._SESSION_CHAT_ID,
+            _sc_mod._SESSION_CHAT_NAME,
+            _sc_mod._SESSION_THREAD_ID,
+            _sc_mod._SESSION_USER_ID,
+            _sc_mod._SESSION_USER_NAME,
+            _sc_mod._SESSION_KEY,
+            _sc_mod._CRON_AUTO_DELIVER_PLATFORM,
+            _sc_mod._CRON_AUTO_DELIVER_CHAT_ID,
+            _sc_mod._CRON_AUTO_DELIVER_THREAD_ID,
+        ):
+            _cv.set(_sc_mod._UNSET)
+    except Exception:
+        pass
+
+    # --- tools.env_passthrough — ContextVar<set[str]> with no default ---
+    # LookupError is normal if the test never set it. Setting it to an
+    # empty set unconditionally normalizes the starting state.
+    try:
+        from tools import env_passthrough as _envp_mod
+        _envp_mod._allowed_env_vars_var.set(set())
+    except Exception:
+        pass
+
+    # --- tools.credential_files — ContextVar<dict> ---
+    try:
+        from tools import credential_files as _credf_mod
+        _credf_mod._registered_files_var.set({})
+    except Exception:
+        pass
+
+    # --- tools.file_tools — per-task read history + file-ops cache ---
+    # _read_tracker accumulates per-task_id read history for loop detection,
+    # capped by _READ_HISTORY_CAP. If entries from a prior test persist, the
+    # cap is hit faster than expected and capacity-related tests flake.
+    try:
+        from tools import file_tools as _ft_mod
+        with _ft_mod._read_tracker_lock:
+            _ft_mod._read_tracker.clear()
+        with _ft_mod._file_ops_lock:
+            _ft_mod._file_ops_cache.clear()
+    except Exception:
+        pass
+
+    yield
+
+
 @pytest.fixture()
 def tmp_dir(tmp_path):
     """Provide a temporary directory that is cleaned up automatically."""