Follow-up: 7 unresolved review threads from #14900 (missing node packs)

Follow-up to #14900 (`fix(errors): keep missing node packs across prompt submissions`), which merged on 2026-08-16 with **7 review threads still unresolved**. None were addressed before merge, so they are tracked here rather than lost with the PR.

One is a real correctness concern; the rest are non-blocking suggestions and nitpicks. Ordered accordingly.

## Blocking-severity

- [ ] `src/scripts/app.test.ts` — **test isolation leak**
https://github.com/Comfy-Org/ComfyUI_frontend/pull/14900#discussion_r3742148347
`Reflect.set(singletonApp, 'rootGraphInternal', graph)` mutates the live exported `app` singleton. `vi.resetAllMocks()` does not undo `Reflect.set`, so the patched graph can leak into tests that run after this block. The same pattern appears more than once.

## Non-blocking suggestions

- [ ] `src/scripts/app.test.ts:1063` — missing negative-path coverage
https://github.com/Comfy-Org/ComfyUI_frontend/pull/14900#discussion_r3742148350
No test asserts that missing-node state is **not** cleared when `importA1111` returns `'not-a1111'` or a core-node result.

- [ ] `src/scripts/app.ts` — `beforeLoadNewGraph()` throw path
https://github.com/Comfy-Org/ComfyUI_frontend/pull/14900#discussion_r3742148355
If `useWorkflowService().beforeLoadNewGraph()` throws (thumbnail capture, draft persist), the following `setMissingNodeTypes([])` is skipped and stale rows persist for the new graph.

- [ ] `src/scripts/app.ts:2439` — duplicated clearing logic
https://github.com/Comfy-Org/ComfyUI_frontend/pull/14900#discussion_r3742148358
`clean()` and the A1111 callback both call `setMissingNodeTypes([])` directly. A thin `clearGraphErrors` on the store would give this one home.

## Nitpicks

- [ ] `src/scripts/app.ts` — justification comment on a single-line fix, contrary to AGENTS.md
https://github.com/Comfy-Org/ComfyUI_frontend/pull/14900#discussion_r3742148354

- [ ] `src/stores/executionErrorStore.ts:124` — `hasMissingError` delegation note
https://github.com/Comfy-Org/ComfyUI_frontend/pull/14900#discussion_r3742148359

- [ ] `browser_tests/tests/propertiesPanel/errorsTabMissingNodes.spec.ts` — redundant comment; `waitForResponse` + `await prompted` is self-documenting
https://github.com/Comfy-Org/ComfyUI_frontend/pull/14900#discussion_r3742148361

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Close individual boxes as they are addressed. If a thread is judged not worth acting on, say so in a comment and tick it — the goal is that none of these silently disappear, not that all seven get changed.