fix(primitives): eslint/tsconfig migration, asChild refactor, type fixes

- Migrate to eslint flat config + composite tsconfig.
- Complete the asChild→as="template" refactor (remove asChild prop + :as-child
  bindings across components, matching Primitive's slot model).
- Fix test type errors and source type-safety (useGraceArea hull/point math,
  FocusScope/util ref typing).

Note: ~53 vue-tsc errors remain (HTML attr/event passthrough typing on
transparent wrapper components + a couple of duplicate-export naming
collisions) — not gated by CI (build/lint/test green); pending a
component-attribute-typing design decision.

vue/primitives/src/toast/__test__/Toast.regression.test.ts

@@ -0,0 +1,103 @@
+// Regression tests for confirmed bugs from Phase 1 audit:
+//   1. ToastRoot tabindex must be -1 (programmatic only), not 0 (conflicts with roving focus).
+//   2. ToastViewport hotkey must validate against empty array (otherwise vacuous-truth
+//      focuses the viewport on every keystroke).
+//   3. ToastRoot must restart the auto-dismiss timer when `duration` changes reactively.
+
+import { mount } from '@vue/test-utils';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { defineComponent, h, nextTick, ref } from 'vue';
+import { ToastProvider, ToastRoot, ToastViewport } from '../index';
+
+function createHarness(props: {
+  duration?: number;
+  hotkey?: string[];
+} = {}) {
+  return defineComponent({
+    components: { ToastProvider, ToastViewport, ToastRoot },
+    setup() {
+      const duration = ref(props.duration);
+      return { duration, hotkey: props.hotkey };
+    },
+    render() {
+      return h(ToastProvider, {}, {
+        default: () => [
+          h(ToastViewport, { hotkey: this.hotkey ?? ['F8'] }),
+          h(ToastRoot, { duration: this.duration }, { default: () => 'Toast body' }),
+        ],
+      });
+    },
+  });
+}
+
+describe('toast — bug regression', () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it('ToastRoot has tabindex="-1" (programmatic focus only)', () => {
+    const wrapper = mount(createHarness({ duration: Infinity }), { attachTo: document.body });
+    const toast = wrapper.find('[role="status"]');
+    expect(toast.exists()).toBe(true);
+    expect(toast.attributes('tabindex')).toBe('-1');
+    wrapper.unmount();
+  });
+
+  it('ToastViewport ignores empty hotkey array (does not focus on every keypress)', async () => {
+    const wrapper = mount(createHarness({ duration: Infinity, hotkey: [] }), { attachTo: document.body });
+    const viewport = wrapper.find('[role="region"]').element as HTMLElement;
+    const focusSpy = vi.spyOn(viewport, 'focus');
+
+    document.dispatchEvent(new KeyboardEvent('keydown', { key: 'a' }));
+    document.dispatchEvent(new KeyboardEvent('keydown', { key: 'F8' }));
+    document.dispatchEvent(new KeyboardEvent('keydown', { key: 'Enter' }));
+
+    expect(focusSpy).not.toHaveBeenCalled();
+    wrapper.unmount();
+  });
+
+  it('ToastViewport responds to F8 when hotkey=["F8"]', () => {
+    const wrapper = mount(createHarness({ duration: Infinity }), { attachTo: document.body });
+    const viewport = wrapper.find('[role="region"]').element as HTMLElement;
+    const focusSpy = vi.spyOn(viewport, 'focus');
+
+    document.dispatchEvent(new KeyboardEvent('keydown', { key: 'F8' }));
+
+    expect(focusSpy).toHaveBeenCalledOnce();
+    wrapper.unmount();
+  });
+
+  it('ToastRoot restarts auto-dismiss timer when duration prop changes reactively', async () => {
+    const Harness = createHarness({ duration: 1000 });
+    const wrapper = mount(Harness, { attachTo: document.body });
+
+    // Bump duration to 5000ms BEFORE original 1000ms elapses.
+    vi.advanceTimersByTime(500);
+    wrapper.vm.duration = 5000;
+    await nextTick();
+
+    // Original 1000ms total would have fired by 1100ms — but the watcher restarted the
+    // timer with the new duration. Toast must still be open.
+    vi.advanceTimersByTime(600); // 1100ms elapsed total
+    await nextTick();
+    expect(wrapper.find('[role="status"]').exists()).toBe(true);
+
+    // Now advance the full new duration (5000ms) — toast should close.
+    vi.advanceTimersByTime(5000);
+    await nextTick();
+    await nextTick();
+    expect(wrapper.find('[role="status"]').exists()).toBe(false);
+    wrapper.unmount();
+  });
+
+  it('ToastRoot timer does not fire when duration=Infinity', () => {
+    const wrapper = mount(createHarness({ duration: Infinity }), { attachTo: document.body });
+    vi.advanceTimersByTime(60_000);
+    expect(wrapper.find('[role="status"]').exists()).toBe(true);
+    wrapper.unmount();
+  });
+});