The job registry gains admission classes. A records job is refused
while any records or guarded job runs, a guarded job while a records
job runs, and read jobs share only the one-job-per-kind rule.
record_changing=True stays as the spelling of records. Job summaries
add cancellable and admission, and a non-cancellable job ignores
cancel.
JobRegistry.hold() registers a running, non-cancellable job for a
legacy-page operation and ends it when the request does. The legacy
restore, maintenance, prompt cleanup, duplicate image delete, LoRA
import and batch auto-tag routes hold as records; thumbnail generation
(both routes) and thumbnail clear hold as guarded. A maintenance run
of only read checks holds as read. So a restore during a scan, or a
scan during a legacy restore, is refused with the running job named
instead of interleaving; this closes the gap noted on #269.
Refusals keep each route's shape: the JSON routes return the legacy
409 "<title> already running", and the thumbnail and LoRA streams
send their existing error event.
Vito Sansevero
ebebf0d69c