# 2026-03-04: Web markdown render dedup optimization

## What changed

- Updated `packages/web-reference-react/src/app/core/markdownService.ts`:
  - added hash-level cache lookup (`findCachedEntryByHash`) so markdown prepared state can be reused across different `cacheKey` values when content is identical.
  - cache reuse now requires `hash + sourceText` compatibility to avoid checksum-collision cross-contamination.
  - added explicit type guard (`hasReusableMarkdownPayload`) for safe reuse of cached `rawHtml` + `hasCodeBlocks`.

- Updated `packages/web-reference-react/src/components/MarkdownRenderer.tsx`:
  - avoid redundant `setHtml` state updates when target HTML is unchanged.
  - keep copy-button click listener stable (mounted once) and manage timeout lifecycle via ref, instead of rebinding listener on each HTML update.

- Updated tests:
  - `packages/web-reference-react/src/app/core/markdownService.test.ts` adds cross-key hash-cache reuse coverage.
  - `packages/web-reference-react/src/components/MarkdownRenderer.test.tsx` keeps worker-error fallback coverage while avoiding false coupling with cross-key cache reuse.

## Why

- Markdown rendering is a repeated hot path in transcript-heavy sessions.
- Deduplicating prepare-stage work across equal content and avoiding listener churn lowers CPU/GC pressure without changing UI behavior.
- Guard tests ensure worker path and fallback semantics remain stable.
