- Windows (`_WIN32`): replace full-duration waitable-timer sleep in `PreciseSleepHundredNanos` and the repeated `PreciseSleepUs` call loop in `PreciseSleepUntil` with a hybrid sleep-then-spin helper (`PreciseSleepFromCounterWithTimer`) that sleeps on the thread-local high-resolution waitable timer up to a 250 us spin tail, falls back to `std::this_thread::sleep_for` if timer setup/wait fails, and finishes the remaining window using `QueryPerformanceCounter` + `YieldProcessor()` (thresholded to 200 ns and ceiling-rounded via `PreciseHundredNanosToQpcTicks` for non-10MHz QPC frequencies).
- Linux & POSIX (`!_WIN32 && !__EMSCRIPTEN__`): replace repeated `nanosleep` loop in `PreciseSleepUs` and `PreciseSleepUntil` with `PreciseSleepFromNanos` using `clock_gettime(CLOCK_MONOTONIC)`. On Linux (`__linux__`), cache `PR_SET_TIMERSLACK` (`1 ns`) once per thread (`thread_local`) and sleep via `clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME)` up to a 15 us spin tail (falling back to a conservative 100 us tail if `prctl` fails; 100 us `nanosleep` tail on other POSIX platforms) before finishing with `_mm_pause()` on x86 or `std::atomic_signal_fence` on non-x86.
- Tests: expand `core/libs/tests/PreciseWait.cpp` to assert that the 31-sample median of `PreciseSleepUs(50)` stays below 90 us (which fails on `main` at ~118 us on Linux and ~518 us on Windows) and verify ceiling QPC tick conversion and timer fallbacks.
hamb3r