test: flaky Overflow indicator tests fail intermittently on CI with 'Maximum recursive updates exceeded'

[johnleider]

Symptom

Two tests in `packages/0/src/components/Overflow/index.test.ts` fail intermittently on CI with:

```
Unknown Error: Maximum recursive updates exceeded in component .
This means you have a reactive effect that is mutating its own dependencies
and thus recursively triggering itself.
```

Affected tests (both under `describe('indicator')`):

• `should render when overflowing and expose count + hidden`
• `should not count disabled items as hidden`

A `[Vue warn]: Unhandled error during execution of app errorHandler` appears in stderr immediately before the recursion error.

Reproduction

Not reproducible locally:

• `pnpm test:run packages/0/src/components/Overflow` — 16/16 pass
• `pnpm test:coverage packages/0/src/components/Overflow` — 16/16 pass
• `pnpm test:coverage` (full suite) — 5952/5952 pass, run 3x consecutively, all green

Fails in GitHub Actions CI under `Run tests with coverage` (`vitest run --coverage`). Confirmed pre-existing on master:

• Run 26584691208 on master commit `437585f9` failed with this exact error
• Same tests pass on neighboring master commits (`8c9c14ae`, `d8c7af09`)
• Same tests fail again on PR refactor: attach structured cause to v0 throws #247 across two CI runs, before and after rebasing onto current master

Likely causes (untriaged)

• A reactive effect in `OverflowRoot` or `createOverflow` that converges in two ticks under normal timing but loops under CI's coverage instrumentation when scheduling differs.
• Interaction with the test's `vi.stubGlobal('ResizeObserver', TestResizeObserver)` and the module-level `resizeObserverCallback` reference — if a re-mount captures a new callback while the old one is still scheduled, the reactive chain could re-enter.
• The `triggerResize(120)` → `measure()` x3 → `nextTick()` flow may race against `OverflowRoot`'s own resize observer setup.

Environment

• vitest `pool: 'vmThreads'`, coverage `provider: 'v8'`
• happy-dom
• Node 26+

Next steps

• Reproduce by running the full coverage suite under GHA matrix locally (act).
• Inspect `OverflowRoot.vue` and `createOverflow` for a watcher that mutates a ref it observes.
• Consider isolating the resize-observer mock per-test instead of module-level so re-mounts can't share callbacks.

Filed from PR #247 review — the PR's only changes are to `createContext` / `useDate` throws and palette/adapter throws (V0Error class adoption) and do not touch Overflow source.