Defer recentOutput line reconstruction from every text_delta to the
progress emit boundary. appendRecentOutputTail only extends the capped
raw tail and marks dirty; refreshRecentOutput runs the exact old
split/filter/slice(-8)/reverse algorithm as the first step of every
emitProgressNow snapshot (onProgress + event bus), including coalesced
and finalize/error/cancel flushes. Reset publishes [] immediately;
replace marks dirty; past snapshot arrays stay immutable via spread.
Before (base pool median-of-5):
w8_d3 61.55 cpu_ms/1k_events
w32_d3 44.16 cpu_ms/1k_events
After (stable final run on E+G, 7 episodes, trimmed CV gate pass):
w8_d3 55.78 cpu_ms/1k_events (1.103×) trimmed CV 15.1%
w32_d3 40.72 cpu_ms/1k_events (1.084×) trimmed CV 11.1%
Checksums match prior exactness baseline; retained_after_release_kb
1284 / 2864 (no regression vs prior concur).
Op: GConcurEmitBoundary emit-boundary dirty flag
Restores: none
metaphorics
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