refactor(datagrid): correctness, a11y, perf, tests

[datlechin]

Summary

Batch of fixes from the post-#945 datagrid audit. All Tier 1 / Tier 2 / Tier 3 items, plus 48 new tests for previously untested critical paths.

Correctness fixes

• Cell colors are appearance-aware (DataGridCellView): change-row highlights (deleted/inserted/modified) and the focus ring now re-resolve via viewDidChangeEffectiveAppearance() when the user toggles Light/Dark mid-session.
• Native focus ring (DataGridCellView): replaced the hardcoded CALayer border with focusRingMaskBounds + drawFocusRingMask() so the ring tracks the system accent color, contrast settings, and appearance automatically.
• Overlay editor discards on column resize (CellOverlayEditor): a column resize while editing a multiline cell now discards the in-progress edit instead of silently committing partial text.
• sortedIDs / cachedRowCount sync (DataGridView + coordinator): the SwiftUI bridge that writes new sortedIDs to the coordinator now also calls updateCache() immediately, removing the window where numberOfRows could disagree with the live sort permutation.

Accessibility

• VoiceOver sort state announcements (SortableHeaderCell): column headers now announce sort direction and multi-sort priority (e.g. "Column: Name, Sorted ascending, Priority 2") via accessibilityLabel() override.

Performance

• Display formats memoized (MainContentCoordinator): ValueDisplayDetector.detect now runs once per result schema instead of on every SwiftUI body evaluation. Cache keyed by (tab.id, schemaVersion, smartDetectionEnabled, overridesVersion).
• Dropped redundant acceptsMouseMovedEvents (SortableHeaderView): the window-level flag was redundant with the tracking area; removed.

Test coverage (+48 tests)

• FileColumnLayoutPersisterTests: clear-removes-file, isolation across connections, save-overwrites, columnOrder == nil round-trip, empty JSON recovery (+7).
• ColumnIdentitySchemaTests: positional schema doesn't resolve raw duplicates, name-based schema doesn't resolve col_N, reserved __rowNumber__ triggers positional, three-duplicates path (+7).
• MainContentCoordinatorTabSwitchTests: 19 tests covering filter/visibility/changeManager/selection/toolbar save+restore, switch-from-nil, switch-to-nil, unknown ids, isHandlingTabSwitch lifecycle.
• MainContentCoordinatorSortTests: 15 tests covering single/multi-column cycles, removal, replacement across columns, schemaVersion cache invariants, pagination reset.

Out of scope (future work)

• MainContentCoordinator → services split (1,502-line god class). Larger refactor, separate PR.
• Hidden columns dual persistence (FileColumnLayoutPersister widths/order vs ColumnVisibilityManager hidden state). Needs design decision on canonical store.
• Sort completion ordering (flagged by sort/cache agent): async sort completion fires dataGridDidReplaceAllRows() before SwiftUI pushes new sortedIDs, so same-row-count re-sorts may render in old order until next mutation. Separate fix.
• Sort race "stale completion" guard test: requires >1000 rows + careful task scheduling to be non-flaky.

Test plan

• Toggle Light → Dark mode while a cell with deleted/inserted/modified highlight is visible: highlight color updates immediately, no need to scroll.
• Set system accent to graphite/red, focus a cell with keyboard: focus ring renders in the accent color, not blue.
• Open multiline overlay editor on a cell, type partial text, double-click a column divider: edit is discarded, cell value unchanged.
• Sort a column then sort another: no NSTableView assertion crash on rapid sort changes.
• Sort a 100-column wide table; scroll/select repeatedly: no UI jank from displayFormats re-detection.
• VoiceOver: navigate to a sorted column header, hear "Column: <name>, Sorted ascending" (or descending, with priority for multi-sort secondary).
• xcodebuild test — all four new test files pass.
• swiftlint lint --strict — 0 violations.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Invalidate display format cache on result-set switch

The cache lookup only keys on tab.id, schemaVersion, settings, and overridesVersion, so it returns cached formats even after switchActiveResultSet(to:in:) replaces tableRows for the same tab without bumping schemaVersion (see MainContentCoordinator+TableRowsMutation.swift). In pinned multi-result workflows, switching between result sets with different columns/sample values can reuse stale detected formats, causing wrong per-column rendering (or missing formatting) until another schema-version-changing action occurs.

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