fix(diffs): Refresh reshaped split edits safely

[necolas]

Fixes split-diff edit-mode rerendering issues surfaced by the Codex review on this branch.

Reproduction

1. Open a split editable diff (e.g. /playground with Edit mode).
2. Edit an added line back to the old-side text so its hunk disappears or changes shape.

Before this change the editor stayed on the split fast-refresh path, which only patches row attributes — leaving stale added/deleted rows in the DOM.

Changes

• Detect when recomputing content hunks changes the rendered hunk shape, and use a full refresh (clearing the render cache) for that case instead of the in-place fast patch.
• Reset the editor's caret/selection geometry caches when a split content edit rebuilds rows, so the caret doesn't measure a detached row and jump.
• fastRefreshDiffView self-escalates to a full rebuild when a column's rendered row count diverges, instead of silently leaving stale rows.
• Guard the async editor-sync continuation so a highlighter promise from an older render can't resync a detached or replaced editor.
• Document getDiffRenderShapeKey (the fast-vs-full gate) and add regression coverage: split reshape that removes a hunk, a same-split-count reshape, and fast-path reachability.

Scope note
Rebased to drop the "preserve editor history across layout toggles" commit — that workaround is being handled via the cacheKey approach in #878. This PR is now only the split-reshape / async-sync correctness fix.

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Project	Deployment	Actions	Updated (UTC)
pierre-docs-diffs	Ready	Preview	Jun 30, 2026 6:51pm
pierre-docs-diffshub	Ready	Preview	Jun 30, 2026 6:51pm
pierre-docs-trees	Ready	Preview	Jun 30, 2026 6:51pm
pierrejs-diff-demo	Ready	Preview	Jun 30, 2026 6:51pm

[chatgpt-codex-connector]

💡 Codex Review

pierre/packages/diffs/src/components/FileDiff.ts

Line 1093 in 4c61db5

this.fastRefreshDiffView();

Use a full refresh when split edits reshape hunks

In split edit mode, when a user edits an added line back to the old-side text (or otherwise causes hunks to merge/split), recomputeContentHunks can replace the hunk structure, but this path still schedules fastRefreshDiffView(). That fast path only patches data-line-type and skips when the new AST child count differs, so the stale deletion/addition rows remain visible until some later full rerender. Use the full refresh path when the recompute changes the hunk shape/row count.

---

pierre/packages/diffs/src/components/FileDiff.ts

Lines 1007 to 1008 in 4c61db5

	void this.hunksRenderer.initializeHighlighter().then((highlighter) => {
	editor.__syncRenderView(

Guard async editor sync against stale renders

If an editable diff changes files or unmounts while initializeHighlighter() is still pending, this captured continuation can still call __syncRenderView with the old fileDiff/container after a newer render has attached the same editor. In that race the editor document can be reset to stale contents, or a cleaned editor can be touched after unmount. Check that this.editor, this.fileDiff, and this.fileContainer still match the captured values before syncing.

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[necolas]

Still working on this...

[ije]

LGTM

[ije]

@necolas #878 will ensure the cacheKey with the file name if it's not provided. we better should not add workarounds for the layout/options update. in further update, we need to cache TextDocuments using the cacheKey. so when switching file the undo stack remains.

i also updated the playground/home apps in #878, please take a look