B-WUHV-editor-600kb-source-open-perf
State: promoted/task
Measured by the markdown-ui playground perf suite (production build, nuxi preview; Apple M2 Max x12 under load 93-132): sourceOpen600kbMs 1387-1417 ms across three runs vs the 500 ms PLAN budget - stable 2.8x, not load noise (the other budgets scale with load; this one does not). Suspects to profile in the engine: full-document StateFields (blockWidgetField, docBytesField, table/HTML widget scans) walking the whole doc at init even in source mode; the 600 KB fixture sitting exactly at the large-file threshold (which side of the guard does it land on?); lineSeparatorFor / TextEncoder byte scans; an eager full Lezer parse instead of CodeMirror’s incremental viewport parse. Evidence: PR 3 handoff evidence/perf (playground-perf*.json, run*.log).