fix: keep markdown preview in sync on local edits

[peter-gy]

Summary

Fixes the below-illustrated markdown preview sync bug where the preview could miss the last typed character or stay stale after local edits.

last-char-md-sync.mp4.mov

Details

• Kept the local markdown autorun fix in the frontend editor path.
• Marked Loro's initial reconciliation dispatch as RTC sync, the same way later sync updates are marked.
• Markdown autorun now:
  • runs for local edit transactions (input, delete, undo, redo)
  • ignores formatting-only changes
  • ignores RTC sync transactions, including init sync
• Testing:
  • markdown autorun gating
  • RTC init-sync annotation

[vercel]

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Mar 23, 2026 3:14pm

[Copilot]

Pull request overview

Fixes a markdown preview sync issue by ensuring markdown autorun triggers on true local edit transactions while ignoring RTC sync (including initial reconciliation) and formatting-only changes, keeping preview updates consistent.

Changes:

• Annotate Loro’s initial reconciliation dispatch with the existing RTC sync annotation.
• Refactor markdown autorun gating into a reusable helper that filters by local user events, focus fallback, formatting changes, and RTC sync annotations.
• Add Vitest coverage for both RTC init-sync annotation and markdown autorun gating behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
frontend/src/core/codemirror/rtc/loro/sync.ts	Marks the initial reconciliation dispatch as RTC sync via loroSyncAnnotation.
frontend/src/core/codemirror/rtc/loro/tests/sync.test.ts	Adds a test asserting init reconciliation dispatch is annotated as RTC sync.
frontend/src/core/codemirror/cells/extensions.ts	Implements shouldAutorunMarkdownUpdate and updates markdown autorun to use it (including RTC sync/formatting filters).
frontend/src/core/codemirror/cells/tests/extensions.test.ts	Adds focused tests for markdown autorun gating logic (local events, formatting, RTC sync, predicate, focus fallback).

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[github-actions]

🚀 Development release published. You may be able to view the changes at https://marimo.app?v=0.21.2-dev39