A workflow can override the spindle's default Buildkite organisation via `tack.buildkite.org`, but `BuildkiteBuildRef` didn't carry the org field. Spawn used the override for `CreateBuild` and then dropped it, so `Logs` always recomputed org := p.defaultOrg and any cross-org workflow's /logs request 404'd against the wrong organisation. Extend TestBuildkiteSpawnWorkflowConfig to assert the org survives the round-trip via LookupBuildkiteBuildByTuple.