Merge Tool Bugs We Fixed

The bugs found in the merge tool, what caused each, and why we fixed it the way we did. The user side is in Merge Tool.

The engine check compared too few merges.

• The issue: the test failed with "too few clean cases compared: 8".
• Why it happened: random edits hit one line in 12, so nearly every merge conflicted.
• The fix and why we chose it: one line in 40, 300 runs, over 50 clean comparisons required and under 5% disagreement, so the check means something.

Undo could restore the wrong chunk state.

• The issue: undoing grouped steps could bring back buttons from the wrong moment.
• Why it happened: grouped undo events carry several setChunks effects, oldest last.
• The fix and why we chose it: chunkField takes the last setChunks effect of a transaction.

Apply non-conflicting could send overlapping edits.

• The issue: after heavy manual edits, one click could produce overlapping edits, which CodeMirror rejects.
• Why it happened: a chunk grown by typing could touch the previous one.
• The fix and why we chose it: applyNonConflicting leaves such a chunk for you instead of guessing.

Word highlights on unrelated lines.

• The issue: mostly rewritten lines got scattered word highlights instead of one block.
• Why it happened: the "unrelated text" guard counted matching whitespace, and skipped base tokens were counted twice.
• The fix and why we chose it: changedSpans counts only matched words and returns null under 30% match.

Cmd+Enter added a line instead of applying.

• The issue: in the Result pane, Cmd+Enter inserted a blank line, so you had to click a side pane or Apply.
• Why it happened: CodeMirror's default keymap binds Cmd+Enter to "insert blank line". The Result is editable, so the editor used the key first, and the window handler, which skips handled keys, never saw it.
• The fix and why we chose it: applyKeymap adds a high-priority Cmd+Enter binding to all three panes and their search bars. Winning inside CodeMirror is simpler and safer than bending the window handler's "already handled" rule.

The close button dropped your work.

• The issue: the X in the title bar closed the tool at once and threw away an edited result, while Cancel and Esc asked first.
• Why it happened: the X called repoStore.closeMerge() directly; the "Discard Changes" question lived only in the editor's cancel.
• The fix and why we chose it: MergeEditor exports cancel() and the X calls it, so the X, Cancel and Esc share one path and one question. With no editor shown (loading, errors, binary files) the X closes at once, as there is nothing to lose.