CODE-076: mounts() memo keyed on a fresh negative token never hits

Now: OPEN
Sev: LOW
Rep: ///bee
Ask: gritzko
Rev: ///bee#8cb69a0
See: CODE-044
See: BEE-048

Input

Context

index/mount.js:182:pN-197 keys subsOf's memo on cache.rev(root) (the CODE-044 fix), but rev() returns a FRESH negative token whenever the tree is big or blind, so on such a tree the memo can never hit and every mounts() pays a full openRepo + readCommit + tree walk per root (measured 147 ms cold vs 0 ms memoized with no watcher). Needs a >32768-dir tree or a failed arm (CODE-058). Found in the 2026-09-18 index review.

Goals

Treat a token as "don't cache and don't invalidate", or key on (rev, tokenCount).

WIP

TODOs

[v] repro: big tree, mounts() cost per call
[v] token-aware memo

Design decisions

"Don't cache and don't invalidate" it is. A token is not a rev, it is the NO-WATCHER case said of one root: fsw witnesses nothing there and, S.big and S.blind holding for the run, never will. So it is never a key (the walk is stored under the null the watcher-less run already uses) and never a reason to drop what stands.
(rev, tokenCount) was the other half of the goal; it keeps the memo missing on exactly the trees the ticket is about, since the count moves with every blind query. Only by reading a token as "unchanged" would it hit — which is the same staleness by another name.
CODE-044's bar is untouched: a WITNESSED root keeps its rev key, so a mount that comes or goes under a resident server is still seen without a restart. The price is paid where there is no witness to buy freshness with: on a big or blind root the sub map now holds for the process, as it always has for a one-shot CLI run (wtstat.js:40:sb's law).

Blockers and bummers

A root blind by BEE-048 (its refs/ fan past GITDIRS) has a LIVE worktree spot — armTree succeeded, only the git side did not — and a mount coming or going is a worktree event. rev() rightly hides that behind a token, so mount.js cannot use it; a cache.js that told the two blindnesses apart would keep both the speed and the freshness here. Wants a ticket of its own (BEE-048 scope).