mutation-model: indirect-ownership self-test pins a test that stopped reaching scroll-edge-state

## Purpose

`mutation-model` — the mutation harness self-test inside `pnpm check:affected` — fails on a clean `origin/main` checkout, so any contributor whose diff selects that check sees a red local gate for a reason unrelated to their work. It hit #2533 and #2521 during wave 1 of #2531.

## Reproduce

```sh
pnpm install --frozen-lockfile
pnpm mutation:test
# or, as check:affected selects it:
pnpm check:affected --run # → check:affected: mutation-model failed.
```

```text
ℹ pass 39
ℹ fail 1
✖ a kernel is owned by tests that reach it indirectly
AssertionError [ERR_ASSERTION]: The expression evaluated to a falsy value:
at scripts/mutation/ownership.test.ts:40:10
```

The other 39 assertions in that file pass, including `ownership is complete: every test reaching a kernel owns it`.

## Root cause

`scripts/mutation/ownership.test.ts:40-44` pins `src/commands/interaction/runtime/gestures.test.ts` as an *indirect* owner of the `scroll-edge-state` kernel. That kernel is `packages/capture-kit/src/snapshot/scroll-edge-state.ts` plus `packages/capture-kit/src/snapshot/scroll-edge-state/selection.ts`.

`gestures.test.ts` no longer imports anything on the scroll path: its resolved import graph is 257 modules and contains neither kernel source, so `ownersOf` returns `kernel-errors`, `interaction-settle`, `selectors`, `target-annotation-serde`, `snapshot-occlusion` and no `scroll-edge-state`. Scroll moved out of the interaction command family — `src/daemon/scroll-runtime.ts` was added by `bcca714a07` ("refactor: move gesture family to platform runtime", #1952) and the snapshot zone relocation landed in `1f9d940bff` (#2385) — and the ownership assertion was never moved with it.

The kernel itself is not uncovered: it has 82 owning test files, including the mirrored `packages/capture-kit/src/snapshot/__tests__/scroll-edge-state-*.test.ts` set, and the `ownership is complete: every test reaching a kernel owns it` test passes. Only this hand-pinned pair is stale.

## Required behavior

- The indirect-reachability assertion keeps its purpose — proving the deriver credits a test that exercises a kernel without importing it by name — while naming a pair that is true today.
- Verified live replacement pair: `src/daemon/__tests__/scroll-runtime.test.ts`. It never contains the string `scroll-edge-state`, reaches both kernel sources through `src/daemon/scroll-runtime.ts`, and `ownershipDeriver(...).ownersOf` includes `scroll-edge-state`. `src/daemon/scroll-until.test.ts` is a second verified candidate.
- Give the assertion a failure message in the style of its sibling at `:37-38`, so the next relocation reports which pair went stale instead of printing a bare falsy expression.

## Observable completion conditions

- `pnpm mutation:test` passes on a clean tree with no other assertion weakened.
- `pnpm check:affected --run` reports no `mutation-model` failure on a docs- or config-only diff.
- The replacement assertion still fails when the deriver stops crediting indirect reach, i.e. it is not converted into a direct-import assertion.

## Dependencies and blast radius

- No CI job runs `mutation:test` or `check:affected`: `mutation-affected.yml` triggers on `scripts/mutation/**`, `scripts/lib/**`, `stryker.config.json`, or its own workflow file, and `mutation-weekly.yml` is a Sunday schedule plus `workflow_dispatch`. This issue therefore gates local contribution, not PRs, and no PR label or re-run depends on it.
- Contained in `scripts/mutation/**`; no runtime or kernel source changes are implied.

Start in scripts/mutation/ownership.test.ts, especially the indirect-ownership assertion around lines 40-44 and its sibling failure message at lines 37-38. Run pnpm mutation:test, inspect the verified scroll-runtime test candidates and ownershipDeriver().ownersOf, then run pnpm check:affected --run. Done means the indirect reachability check remains meaningful, reports a useful stale-pair message, and both commands pass.

Written by the indexing model from the issue text.