refactor(TreeList): let useTreeFocus own roving tabindex

[cixzhang]

Summary

Make useTreeFocus own roving-tabindex management internally so TreeList no longer has to hand-roll it. This mirrors the useListFocus pattern (hasRovingTabIndex + handleFocus), where the hook stamps tabindex 0/-1 on the items directly, repairs the tab stop on mount/layout, and moves the stop alongside keyboard navigation.

Previously useTreeFocus only provided handleKeyDown; TreeList stamped tabindex on treeitem <li> elements itself via an activeId state, a resolvedActiveId derivation, and an isTabbable prop threaded through TreeListItem.

Changes

packages/core/src/hooks/useTreeFocus.ts

• New hasRovingTabIndex?: boolean option (default false).
• When enabled, focusItem stamps tabindex=0 on the focused treeitem and -1 on all others via setAttribute.
• New syncTabStops utility + useIsomorphicLayoutEffect that repairs the stop on mount/commit: it preserves an existing tabindex="0" seed, otherwise promotes the first enabled treeitem.
• New handleFocus return (always returned; a no-op unless hasRovingTabIndex is on) that keeps the stop in sync after clicks/programmatic focus.
• When false, behavior is unchanged — the hook only moves focus and never touches tabindex.

packages/core/src/TreeList/TreeList.tsx

• Passes hasRovingTabIndex: true and wires handleFocus on the role="tree" onFocus.
• Removes the activeId state, the resolvedActiveId useMemo derivation, the onActiveChange wiring, and renames the seed helper to findInitialTabbableId.
• Still seeds the initially-tabbable treeitem in render (selected item or first enabled); the hook's repair pass preserves that seed.

packages/core/src/TreeList/TreeListItem.tsx

• isTabbable is now documented as the initial mount seed; the hook takes over dynamically.

Verification

• typecheck (core + docs): pass
• eslint: clean
• vitest run packages/core/src/TreeList packages/core/src/hooks/useTreeFocus: 57/57 pass (arrow nav, expand/collapse, Home/End, typeahead, aria-level/posinset/setsize, roving-tabindex seeding + movement all preserved)

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Project	Deployment	Actions	Updated (UTC)
astryx	Ready	Preview, Comment	Jul 3, 2026 5:43am

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Package	Size (ESM)	Size (CJS)	Gzipped
@astryxdesign/core	N/A	4.6KB	0B

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[josephfarina]

Heads up: the test check is red, but the only failures are the two Table render-performance benchmarks in Table.perf.test.tsx (100 rows: 202ms vs 200ms budget, 500 rows: 551ms vs 500ms budget). Those are timing-sensitive budget assertions that flake under CI load and are unrelated to this TreeList/useTreeFocus change — TreeList.test.tsx and useTreeFocus.test.tsx both pass clean locally (57/57). Approving; just wanted it on your radar in case the perf budgets need a nudge.