On Metal, when routing is precomputed on the GPU (g_pre_idx), the moe fast
path bumps eusage/ehit/eheat for the selected experts but skips the one thing
the full CPU router does at the equivalent site: elast[layer][e] =
++eaccess_clock. So the session-local recency clock advances during prefill
(full router) but freezes the moment GPU-prerouted decode starts, and REPIN's
tier_pick_lfru() tie-breaker then runs on stale recency for the rest of the
run. Mirror the exact update the non-Metal path already does. Inside
#ifdef COLI_METAL, so CPU/CUDA are untouched; elast only feeds the LFRU
eviction heuristic, so this cannot affect output, only which experts REPIN
keeps warm.
Found and reported by @monotophic with a source-level trace repro
(ELAST_TRACE). Fix is inspection-verified against line ~3055; needs a
Metal build to exercise end-to-end.
Closes#417
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
JustVugg
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