test(inbox): bind side-effecting pop() before assert

CodeQL flagged the bare `assert state.pop(...) is None` — under
`python -O` asserts are stripped, which would skip the call entirely
and the test would silently pass without exercising the code. Bind
the result first so the call always runs.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

workspace/tests/test_inbox.py

@@ -182,7 +182,10 @@ def test_pop_removes_specific_message(state: inbox.InboxState):
 
 def test_pop_missing_id_returns_none(state: inbox.InboxState):
     state.record(_msg("a"))
-    assert state.pop("does-not-exist") is None
+    # Bind the result before asserting so the call still runs under
+    # ``python -O`` (which strips bare assert statements).
+    result = state.pop("does-not-exist")
+    assert result is None
     # Original message still present
     assert len(state.peek(10)) == 1