perf(editor): reduce live preview typing latency

[murongg]

Summary

• keep unchanged Mermaid and table previews mounted while editing elsewhere in the document
• incrementally map live-preview, block-control, math, footnote, raw HTML, heading, and code-highlight state for safe non-structural edits
• preserve automatic syntax highlighting for code blocks without a recognized language while caching unchanged highlight results
• persist the first dirty draft immediately, then coalesce continuous workspace writes; defer document summaries from 64 KB

Why

Issue #636 reports severe typing lag in Markdown documents. Profiling also reproduced the problem in small documents when expensive preview blocks were located after the caret. The input path was rebuilding preview state and, on desktop, queueing a settings-store read/write/save for every character.

Validation

• pnpm --filter @markra/editor exec vitest run --environment jsdom --globals --maxWorkers=1 --no-file-parallelism — 35 files, 430 tests passed after the compatibility adjustment
• pnpm --filter @markra/app exec vitest run --environment jsdom --globals --maxWorkers=1 --no-file-parallelism — 130 files, 1486 tests passed
• pnpm --filter @markra/editor build && pnpm --filter @markra/editor typecheck:test — passed after the compatibility adjustment
• pnpm --filter @markra/app build && pnpm --filter @markra/app typecheck:test — passed
• desktop runtime check with the supplied small Mermaid document: a 20-character batch took 48.4 ms above the diagram, 50.9 ms below it, and 51.3 ms with the diagram removed

Risk

• incremental mapping is restricted to edits that cannot create Markdown structure; structural edits and custom renderer nodes fall back to rebuilding decorations
• code blocks without a recognized language retain the existing automatic language detection behavior
• the first dirty draft is still persisted immediately, limiting the coalescing window to later continuous input

Closes #636

[vercel]

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Project	Deployment	Actions	Updated (UTC)
markra-web	Ready	Preview	Aug 3, 2026 6:37am