fix(undo): drop a document's undo stack when its file is rewritten while switched away#78
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…ile switched away Per-document undo (#77) makes a document's undo stack survive switching away and back. But the stack records absolute text ranges, so if the document's file is rewritten externally while backgrounded — e.g. renaming a node rewrites the [[label]] in every file that links it — switch-back reloads the changed text and Cmd+Z replays stale ranges, corrupting the text (or silently no-op'ing when a range is out of bounds). Snapshot each document's content (storage form) on switch-away and, on switch-back, drop its undo stack when the reloaded text differs. Snapshots are pruned alongside the per-document undo managers. Also corrects the now-stale `documentId` doc comment. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Problem
Per-document undo (#77) makes a document's undo stack survive switching away and back. But AppKit's text undo records absolute character ranges, so if a document's file is rewritten externally while it's switched away, switch-back reloads the changed text and Cmd+Z replays stale ranges against it.
Concrete repro in the embedder (wiki-link notes): edit note A (which links
[[B]]) → switch to B → rename B (after the debounce the rename rewrites A's file on disk, changing the[[label]]length) → switch back to A → Cmd+Z corrupts A's text (misplaced edit), or silently no-ops when the stale range is now out of bounds.Before #77 this couldn't happen — undo was wiped on every switch, so switch-back Cmd+Z was an empty no-op. Surviving undo is the feature; this PR makes it safe.
Fix
undoContentSnapshots, fromlastSyncedText).invalidateUndoIfContentDiverged(for:incomingText:)drops that document's undo stack when the reloaded text differs from the snapshot (timing-independent; the SwiftUI two-phase switch is covered by the existinglastSyncedText == textearly-return, so the switch branch runs once with the real reloaded text).documentIddoc comment ("Changing this invalidates undo history" → undo now survives switches).Net: +/- across 3 source files + a focused test. No public API change.
Test
swift test— 131 pass (128 existing + 3 new inPerDocumentUndoTests): stable manager per document / distinct across / original returned on switch-back; undo dropped only on diverged content; no snapshot never clears. Also verified end-to-end in a Debug build (rename-linked-node repro no longer corrupts; normal Cmd+Z-survives-switch still works).🤖 Generated with Claude Code