fix(web): keep oversized diff lines from locking the UI

[notkadez]

What Changed

Adds a render-safety guard to the web diff panel so files with pathologically long diff lines are skipped instead of being passed into the browser diff renderer.

This includes:

• a shared canRenderFileDiff helper in diffRendering
• a MAX_RENDERABLE_DIFF_LINE_LENGTH limit for oversized added/deleted lines
• updated DiffPanel sorting and rendering behavior
• user-facing fallback copy for files that are too large to render safely
• unit coverage for both accepted and rejected line lengths

Renderable diffs continue to display normally. Files that exceed the line-length threshold still appear in the diff list, but their diff body is collapsed and replaced with guidance to open the file directly.

Why

A single extremely long added or deleted line can make browser-side diff rendering expensive enough to freeze or severely degrade the UI, even when the rest of the patch is small.

This keeps the diff panel reliable under pathological inputs without rejecting or hiding the entire patch. Safe files remain visible, oversized files remain represented, and users can still inspect the full change in their editor when needed.

The implementation is intentionally localized: shared diff-rendering logic owns the renderability decision, and DiffPanel uses that result only to avoid the unsafe render path.

UI Changes

For files that are too large to render safely, the diff panel now shows:

• the file header in a collapsed state
• fallback text: This file is too large to display. Open the file to inspect the change.

There are no layout or interaction changes for normal-sized diffs.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

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Note

Low Risk
Localized UI guard with a clear fallback; normal diffs are unchanged aside from sort order prioritizing renderable files.

Overview
Adds a 500k character per-line guard in shared diff rendering via canRenderFileDiff and MAX_RENDERABLE_DIFF_LINE_LENGTH, so pathologically long added/deleted lines are not treated as safe to render in the browser.

DiffPanel now annotates each file with that result: renderable files sort first, oversized entries stay in the list but are forced collapsed, their expand/collapse control is disabled, and a short message tells users to open the file in the editor instead of viewing the inline diff.

Unit tests cover acceptance at the limit and rejection when a line exceeds it.

^{Reviewed by Cursor Bugbot for commit 5c66665. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Prevent oversized diff lines from locking the UI in DiffPanel

• Adds canRenderFileDiff in diffRendering.ts that returns false if any line in a file diff exceeds 500,000 characters.
• Non-renderable files are sorted after renderable ones, shown collapsed by default, and have the collapse toggle disabled.
• A message is shown below the diff view indicating the file is too large to display.

^{Macroscope summarized 5c66665.}

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[macroscopeapp]

Approvability

Verdict: Approved

Straightforward bug fix that prevents UI lockup on oversized diff lines by collapsing non-renderable files and showing an informative message. The change is self-contained, includes unit tests, and poses minimal runtime risk.

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[gameroman]

Not sure about this, but everything else looks good

[cursor]

Cursor Bugbot has reviewed your changes and found 2 potential issues.

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit 57d9293. Configure here.}

Dismissing prior approval to re-evaluate 376e79b

Dismissing prior approval to re-evaluate 5c66665