* perf(mobile-sync): memoize the agent-status projection per entry
buildRuntimeMobileAgentStatusProjection re-serialized every live agent on every
status ping. setAgentStatus replaces one entry and re-spreads the map, which
defeats the reference-equality skip gate, so each ping paid for every other
agent's prompt, 20-entry history, and 8 KB assistant message to discover they
had not changed.
Memoize each row's JSON by entry identity, the cachedTabsProjection pattern
already used a few functions above. Per ping: 0.18 ms -> 0.014 ms at 8 agents,
0.88 ms -> 0.063 ms at 40. The output is byte-identical — joining pre-serialized
rows matches whole-array stringify, which the new test pins against a verbatim
copy of the old implementation.
* test(perf): stop inflating the projection benchmark baseline
The pre-fix arm stringified each row and parsed it back before stringifying the
array, a per-row roundtrip the original never paid. That made the baseline
artificially slow: the reported 5.9x-14.0x is really 2.1x-5.0x.
Share one row builder between both arms, and check equivalence after a ping as
well as on the cold call — a stale-row bug can only surface once the cache is
actually exercised, which the cold-path check could never catch.
