test: one invariant for the importable-resource stub, drop the change-detector

Keep a single test on the seam that actually failed: an importable
``resource`` module without ``getrlimit`` (the third-party Windows stub
behind #111877/#111879) makes ``_fd_soft_limit`` return None and
``_fd_headroom_ok`` fail open, so session reads proceed.

Drop the ``resource_limits`` test from the salvaged PR: ``apply_nofile_soft_limit``
already wraps the rlimit calls in ``except Exception`` on main, so that test
was green on base and asserted nothing new.

Co-authored-by: KoNit-K <124019182+KoNit-K@users.noreply.github.com>

tests/hermes_cli/test_resource_limits.py

@@ -100,13 +100,6 @@ def test_unsupported_platform_is_a_safe_noop(monkeypatch):
     assert resource_limits.apply_nofile_soft_limit({}) is False
 
 
-def test_windows_resource_stub_without_rlimit_attributes_is_a_safe_noop(monkeypatch):
-    """Windows can import ``resource`` even when its POSIX API is absent."""
-    monkeypatch.setattr(resource_limits, "_resource", object())
-
-    assert resource_limits.apply_nofile_soft_limit({}) is False
-
-
 def test_fresh_process_import_without_posix_resource_is_a_safe_noop():
     code = textwrap.dedent(
         """

tests/hermes_state/test_session_db_read_conn_pool.py

@@ -627,14 +627,16 @@ def test_fd_headroom_guard_fails_open_where_it_cannot_measure(monkeypatch):
     assert readpool._fd_headroom_ok() is False
 
 
-def test_fd_soft_limit_ignores_windows_resource_stub(monkeypatch):
-    """A Windows resource stub has no POSIX RLIMIT attributes."""
+def test_fd_soft_limit_fails_open_for_importable_resource_stub(monkeypatch):
+    """An importable ``resource`` without ``getrlimit`` (third-party Windows stub,
+    #111877) must read as "unmeasurable", not abort every session read."""
     import sys
-    from types import SimpleNamespace
+    import types
 
-    monkeypatch.setitem(sys.modules, "resource", SimpleNamespace())
+    monkeypatch.setitem(sys.modules, "resource", types.ModuleType("resource"))
 
     assert hermes_state_readpool._fd_soft_limit() is None
+    assert hermes_state_readpool._fd_headroom_ok() is True
 
 
 @pytest.mark.requires_wal