[Bug] Markdown typing shaking

[ShivLee]

Before Submitting

• I searched existing issues and did not find a duplicate.
• I can reproduce this issue on the latest release (or latest main build).
• I included reproducible details (environment, steps, expected and actual behavior, and evidence), not only a code-level suggestion.

Bug Summary

Issue: When editing in Markdown, once the text fills the entire screen — whether in Chinese or English — the whole interface starts

badly while typing, almost like a rippling water effect (see Figure 1). The editor view moves up and down quite dramatically and feels very unstable.

What I’ve checked: This issue first appeared after upgrading to the latest 0.6.50 version. However, even after rolling back to 0.6.49, the problem still persists.

Device: MacBook Pro M5

Operating System

macOS

VMark Version

0.6.50

Install Method

DMG / Installer Download

Steps to Reproduce

In the vMark editor, I automatically upgraded to version 0.6.50.
After noticing that the Markdown editor view was shaking up and down while typing, I uninstalled version 0.6.50 and downloaded version 0.6.49 from GitHub to reinstall it.

Expected Behavior

This causes the entire Markdown editor to remain stable while typing, instead of automatically shifting up and down.

Actual Behavior

1. In version 0.6.14, I was able to write up to 50,000 characters in a single document without the input area shifting up and down. The interface remained stable and did not jump at all.

2. After upgrading to the latest 0.6.50 version, the input area starts jumping up and down before I even reach 1,000 characters — basically as soon as the screen is filled. The entire Markdown editor becomes very unstable and difficult to use.

Logs, Screenshots, or Repro

No response

Additional Context

No response

[xiaolai]

Thanks for the detailed repro — the "rippling" description was the key clue.

Root cause (a regression, as you suspected, introduced during the large-file perf work before 0.6.49): the WYSIWYG editor toggles content-visibility: auto on and off via a .cv-idle class — applied at rest, stripped during typing, re-applied 500ms after the last keystroke. On small docs, the contain-intrinsic-size: auto 2.5em fallback that backs that optimization doesn't match the real block heights for off-screen content (until each block has been rendered at least once). Every 500ms idle window reapplied the class, the estimated total doc height jumped to a different value than the real height, and the viewport rippled up/down. Short docs saw the worst of it because almost every block was "off-screen but never rendered", so the height delta was large.

Fix (shipping in v0.6.53): gate the entire cv-idle mechanism behind a 50K-char threshold. Below that, the optimization is skipped entirely — small docs never needed it and were paying pure layout-shift cost. Large docs keep the optimization and its debounced toggle unchanged. Regression test included so this can't silently come back.

Please try v0.6.53 once the build is up and confirm the shaking is gone. If you still see it on docs around or above 50K chars, reopen with the doc size and I'll tighten the threshold.