Add adversarial tests for early cursor-line divergence cancellation

[ulugbekna]

Expand test coverage for the InlineEditsXtabEarlyCursorLineDivergenceCancellation feature across all three architectural layers (+33 tests total).

isModelCursorLineCompatible (+20 tests)

• Case sensitivity (F vs f correctly cancels — intentional for code identifiers)
• Unicode/emoji/CJK character handling
• Replacement edge cases (shorter replacement, pure deletion, different-region replacements)
• Auto-close angle brackets <>
• Non-auto-close text ((x) correctly uses startsWith, not subsequence)
• Model produced less than user typed
• Identical changes, net-zero edits
• Substring vs prefix distinction
• Whitespace edits outside model edit range
• User deletion matching model deletion

getCurrentCursorLine (+7 tests)

• Compound edits (line insertion above cursor + cursor line modification)
• Multi-line replacement of cursor line
• Empty document edge case
• Edit at document end (appending text and new lines)

Integration streaming wrapper (+6 tests)

• Feature disabled → no cancellation even with divergent typing
• Model output shorter than edit window → cursor line never reached, no false cancel
• getCurrentCursorLine returns undefined → divergence check safely skipped
• Net-zero intermediate edit → check skipped
• Partial edits yielded before cursor-line cancellation
• Auto-close pair end-to-end (() typed, model fills parens → compatible)

Findings

• No bugs discovered — the implementation correctly handles all tested adversarial cases
• The range-containment check is deliberately strict (known false positive for disjoint edits on the same line, traded for safety)
• Auto-close pair logic is correctly scoped to exactly 7 pairs

[Copilot]

Pull request overview

Adds adversarial test coverage for early cursor-line divergence cancellation in the Copilot xtab pipeline, exercising both the core compatibility logic and the integration streaming behavior.

Changes:

• Adds multiple integration tests in xtabProvider.spec.ts to validate cancellation/skip conditions and end-to-end auto-close compatibility.
• Expands unit tests in cursorLineDivergence.spec.ts for isModelCursorLineCompatible and getCurrentCursorLine across edge cases (case sensitivity, Unicode, replacements, compound edits, empty doc, end-of-doc edits).

Show a summary per file

File	Description
extensions/copilot/src/extension/xtab/test/node/xtabProvider.spec.ts	Adds integration-level streaming/cancellation tests for cursor-line divergence behavior.
extensions/copilot/src/extension/xtab/test/node/cursorLineDivergence.spec.ts	Adds unit tests covering adversarial inputs for cursor-line compatibility and cursor-line mapping under edits.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 2

[github-actions]

Screenshot Changes

Base: 689454c4 Current: 24e129b2

Changed (1)

agentSessionsViewer/ApprovalRowLongLabel/Dark

Before	After