The queue-level dispatch of issue events had no test at all; a revert of
the reopened mapping in WorkerPool._dispatch would silently reintroduce
the routing gap #5891 fixes. Mirrors the existing PR-review dispatch
test convention.
Ran deferred-submission promotion on an independent timer in addition to the empty-queue path, so a sustained ordinary queue can no longer starve a rate-limited submitter after their rolling window frees. Added ROBOMP_DEFERRED_PROMOTION_SCAN_SECONDS to tune or disable the sweep.
Fixes#5882
Stored a bounded per-login overflow backlog and promoted deferred events oldest-first as rolling-window capacity became available. Surfaced the deferred state through the dashboard contract and documented admission behavior.
Fixes#5882
can1357