fix(desktop): stability batch — LCS bound / barge-in flush / refresh throttle / history bucket / fusion seed dedupe

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.

examples/desktop/src/renderer/index.html

@@ -1407,6 +1407,7 @@
   <script src="./assistant-turn.js"></script><!-- task #162 rec 22-bis: assistant-turn container (consumes the three above) -->
   <script src="./chat-side-drawer.js"></script><!-- feat/chat-triple-view: right-side turn/session detail drawer -->
   <script src="./chat-session-graph.js"></script><!-- feat/chat-triple-view: session DAG (turn nodes + fork/interrupt edges) -->
+  <script src="./chat-refresh-throttle.js"></script><!-- fix/code-bugs-batch P1-3: rAF-coalesced throttle for drawer/graph refresh -->
 
   <script src="./event-filter.js"></script>
   <script src="./capabilities.js"></script>