E2E resolve job fails every engine when one platform key is missing

### System details

RStudio Edition : N/A -- scheduled E2E rotation workflow
RStudio Version : N/A
OS Version : N/A
R Version : N/A

### Steps to reproduce the problem

1. Open the `resolve` job in `.github/workflows/os-test-e2e-rstudio-scheduled.yml`.
2. Note the ten `emit ... || exit 1` calls, which all run on a version-pinned dispatch no matter which engines `pick` selected.
3. Dispatch the workflow with a `version` while any one of those keys is missing from https://dailies.rstudio.com/rstudio/latest/index.json.
- `resolve` fails, and every engine depends on it, so none runs -- including macOS and Windows, whose keys were fine.

### Describe the problem in detail

One missing Linux platform blocks the whole dispatch, including engines that never needed that key. Nothing is failing today, as all ten keys are present as of 2026-08-05.

Each `emit` being fatal is deliberate and the code says why: a non-fatal `emit` leaves an empty installer URL, which tells engines to self-resolve the latest daily and silently ignores the version pin. That part would ideally stay as it is.

### Describe the behavior you expected

Resolving only the keys the selected engines need, so a missing platform fails just those engines. Every `emit` stays fatal.

See #18452, which added `resolute-amd64` to the existing set.