testserver: roll task outcomes up into the run state

[radakam]

Changes

The fake workspace reported every run as TERMINATED SUCCESS, overwriting the FAILED state it had just recorded for a task it executed locally. A run now reports the terminal state its tasks add up to.

Tasks whose code the fake workspace does not have are left successful. An immutable deployment, for example, uploads the bundle as a snapshot zip that the fake workspace never unpacks, so there is nothing to execute; that gap is in the fake workspace, not in the job under test.

With that, job_runs/failed_run drops the runs/get and runs/get-output stubs from its test.toml and fails for real, on a task that exits non-zero.

Why

Follow-up to #5882, where a stub stood in for a failing run because the fake workspace could not produce one. Splitting it out keeps the behaviour change for existing tests out of that PR.

The stub could not know the test server's address, so it could not report a run page URL; the golden now covers the run URL and the progress lines too.

Tests

libs/testserver unit tests for the rollup, for completing the tasks that jobs/runs/submit leaves running, and for a task whose code is missing not failing its run. job_runs/failed_run covers the end-to-end path. The rest of the acceptance suite passes unchanged.

[github-actions]

Approval status: pending

/acceptance/bundle/ - needs approval

4 files changed
Suggested: @denik
Also eligible: @pietern, @anton-107, @andrewnester, @janniklasrose, @lennartkats-db, @shreyas-goenka

General files (require maintainer)

Files: libs/testserver/jobs.go, libs/testserver/jobs_test.go
Based on git history:

• @denik -- recent work in libs/testserver/

_{Any maintainer (@andrewnester, @anton-107, @denik, @pietern, @shreyas-goenka, @simonfaltum, @renaudhartert-db, @janniklasrose, @lennartkats-db) can approve all areas.
See OWNERS for ownership rules.}