test(#5121): make auth-failure tests host-independent

The 4 terminal-auth-failure tests assert an unrecoverable 401 surfaces an
apperror / persisted _error turn. The settlement path first attempts the
#1401 credential self-heal, which reads ~/.hermes/auth.json. On a host with
populated credentials, self-heal can succeed and retry the mock agent,
swallowing the error the test expects -- so the result depended on host
credentials (green on CI / Windows with no creds, red on a live agent box).

Add an autouse fixture that forces _attempt_credential_self_heal to a no-op
so every host exercises the unrecoverable-failure path. The one test that
verifies a successful retry already patches the symbol in its own body, so it
is unaffected.

Co-authored-by: rodboev <rodboev@users.noreply.github.com>

tests/test_issue5121_provider_auth_terminal_error.py

@@ -55,6 +55,26 @@ def _isolate_agent_locks():
     config.SESSION_AGENT_LOCKS.clear()
 
 
+@pytest.fixture(autouse=True)
+def _neutralize_credential_self_heal(monkeypatch):
+    """Make the 401 self-heal path a deterministic no-op by default.
+
+    The terminal-auth-failure tests assert that an unrecoverable 401 surfaces
+    an ``apperror`` / persisted ``_error`` turn. The streaming settlement path
+    first tries ``_attempt_credential_self_heal`` (#1401), which calls
+    ``read_auth_json()``. On a host with a populated ``~/.hermes/auth.json``
+    (e.g. a developer's real Hermes box) self-heal can succeed and silently
+    retry the mock agent, swallowing the error the test expects — so the
+    outcome would depend on host credentials. CI / Windows boxes have no such
+    credentials, which is why the tests pass there but fail on a live agent
+    host. Force self-heal off by default so every host exercises the
+    unrecoverable-failure path; the one test that intentionally verifies a
+    successful retry patches this symbol explicitly inside its own body.
+    """
+    monkeypatch.setattr(streaming, "_attempt_credential_self_heal", lambda *a, **k: None)
+    yield
+
+
 @pytest.fixture(autouse=True)
 def _mock_hermes_modules(monkeypatch):
     fake_runtime_module = types.ModuleType("hermes_cli.runtime_provider")