1. DEFENSIVE (backend_metal.mm, coli_metal_register): re-registering a live
base overwrote s.buf and resset_add'ed the new wrapper without removing
the OLD one from the residency set -- ARC drops our reference but the set
retains the object and keeps its pages resident: a leak and a
set/g_slabs divergence. The found branch now stashes the replaced
wrapper under g_slab_mtx and, after dropping the lock (round-1 invariant:
no Metal call under the slab lock), resset_remove(old)s it before
resset_add(b); identical old==b early-outs both set operations.
Invariant defended, stated in the comment: residency-set membership
mirrors g_slabs exactly. No in-tree caller re-registers a live base
today (audited) -- closed defensively.
2. DOC (SUMMARY.md): the moe_submit lifecycle bullet still said
resset_flush commits "under g_slab_mtx" -- stale text from before the
round-1 mutex split; the code takes g_resset_mtx and never touches the
slab lock there. Parenthetical corrected; register bullet updated to
describe the re-register hygiene from item 1.
monotophic
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