Phase C cleanup follow-up to the routes/federation split (#9). Behavior-
preserving; full server suite (790 tests) green.
A) rateLimits.ts: the four near-identical sliding-window limiters
(accept/relay/lookup/ensure) and their duplicated prune loops collapse
into one createLimiter(windowMs, max) factory. Per-call and periodic-
sweep semantics are preserved exactly, including that lookup buckets are
pruned per-call but never swept (unchanged from before). 177 -> 101 lines.
B) Extract sendSignedJson(reply, payload, hmacSecret) — the single
definition of how this instance signs an S2S JSON response — and use it
in the /epoch and /verify-attach-proof|reattach handlers, replacing two
copies of the build-headers-and-send boilerplate.
TheZwiss
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