CI exposed a latent validator defect masked locally: the desktop runner's
Gitea-registered name is 'rune-desktop' (label 'rune-ci-desktop'), but
validate_placement required the LABEL string inside runner_name — so every
CI-executed stage was PLACEMENT_REJECTED while local runs passed (local:
prefix path).
Fix: desktop identity = label in name/labels, OR the registered rune-desktop
runner name, OR verified local execution. Pi rejection semantics unchanged
(regression-tested: rune-pi/rune-infra-pi still rejected via name, hostname,
and labels).
Found via RP11 PR CI — exactly what RP12's post-cleanup re-run is designed
to catch, caught one run early.