Harden mouse input routing contracts with deterministic coverage

[RtlZeroMemory]

Summary

• audited mouse click, wheel, drag, and mixed input routing paths across router, focus, split pane, keybinding, and hit-testing integrations
• fixed a mixed-input bug where active keybinding chords were not cleared on mouse click (mouseKind down/up)
• added deterministic mouse hardening suites:
  • packages/core/src/runtime/__tests__/mouse.click.test.ts (23 tests)
  • packages/core/src/runtime/__tests__/mouse.scroll.test.ts (13 tests)
  • packages/core/src/runtime/__tests__/mouse.drag.test.ts (16 tests)
  • packages/core/src/runtime/__tests__/mouse.mixed.test.ts (14 tests)
• added app-level regression coverage for chord reset on click in packages/core/src/keybindings/__tests__/keybinding.conflicts.test.ts
• documented mouse invariants and mixed input behavior in:
  • docs/guide/mouse-support.md
  • docs/guide/input-and-focus.md

Why

This hardening pass pins existing mouse contracts (no feature expansion) and closes routing/test gaps so regressions in click activation, scroll clamping/routing, split-pane drag constraints, hit-testing precedence, and mouse+keyboard interaction are caught deterministically.

Validation

• npm run build
• npm run typecheck
• npm run lint
• node scripts/run-tests.mjs

All commands pass locally.

• Full test suite: 2254 passed, 0 failed.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Reset pending chord only on mouse-down

Including mouseKind === 4 here can cancel a chord that started after the click began: if a user presses and holds mouse, types the first key of a multi-key binding, then releases mouse, this branch clears pendingKeys on mouse-up and the next key no longer matches. The fix for stale pre-click chords only needs to clear on down (or otherwise distinguish up events that belong to a click that happened before the chord started).

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[RtlZeroMemory]

Addressed in cb49e31.

Changes:

• Reset pending chord state only on mouseKind === 3 (mouse-down) in createApp.
• Added regression test mouse up does not clear chord started after mouse down in packages/core/src/keybindings/__tests__/keybinding.conflicts.test.ts.

Validation:

• npm -w @rezi-ui/core run build
• node --test --test-concurrency=1 packages/core/dist/keybindings/__tests__/keybinding.conflicts.test.js
• npm run lint

All pass.