`cpu_perf_headroom()` is a strict SUPERSET of `cpu_scaling_factor()`
— it folds in static cpu-freq scaling + the slow-CI bump AND the
sustained-load power-cap throttle probe. Point the timing-deadline
call sites at it so they're robust to sustained throttling too (the
gremlin behind mass `trio` deadline-miss flakes),
- `test_legacy_one_way_streaming`: `time_quad_ex` cancel-deadline +
`test_a_quadruple_example`'s `this_fast` smoke bound.
- `test_cancellation`: `test_cancel_via_SIGINT_other_task` +
`test_fast_graceful_cancel_*` deadlines.
`cpu_perf_headroom >= cpu_scaling_factor` always, so never less
headroom (CI stays green); `cpu_scaling_factor()` remains the
internal static component.
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code