P0-2 artifacts-board.js: guard against LCS OOM on large blob diffs; fall back to note-based render when either side exceeds bound.
P1-2 chat-side-drawer.js: flush pending turn on barge-in (user sends before assistant frame flushes), so drawer stays in sync with graph.
P1-3 chat-refresh-throttle.js (new) + renderer.js: coalesce chat + graph refreshes into per-frame flush to prevent visual jitter under high-frequency intervention/refresh events.
P1-4 artifacts.js: history entries bucket by sessionId; cross-session artifacts no longer bleed into the currently-open session's history rail.
P1-5 rubric-fusion-model.js: seedOnce idempotency guard — repeated seed calls no longer duplicate rubric fixture rows (was surfacing as double-counted evolution nodes).
test/code-bugs-batch.test.js (new, 9 assertions) covers all 5 fixes; test/artifact-evolution-board.test.js updated to align with bySession bucket shape.
9 files, +520/-43. Behavioral fixes only, no API surface change.
