The client-side TURN_TIMEOUT_MS was the binding constraint: turns with slow prompt processing (no first SSE frame within 120 s of visible time) errored with the 'stuck' copy even though nginx (300 s) and BOR_LLM_TIMEOUT (300 s) would have let them run. Raise the guard to 300 s so the upstream timeouts are reachable, and re-pin the tests: the unit constant pins and the fake-clock E2E timeline (295 s hidden + 290 s after the re-arm = 585 s: past the original 300 s deadline, short of the re-armed 595 s deadline). Verified: tests/unit (full, 100% pass), tests/e2e/test_hidden_tab_stream.py and tests/e2e/test_loading_feedback.py in isolation.