[beinan]

A hot table discovered early in a stats scan currently waits for every remaining table to finish before the merge sweep can see its pending WAL. On one production master, completed scans averaged about 92 minutes; this is a discovery delay independent of the separate legacy-worker admission blocker.

Consume each completed observation immediately and submit eligible targets to the existing durable merge queue. Incremental observations also qualify because they recount pending WAL. Preserve automatic-merge disablement, canonical deduplication, target encoding and all existing execution/ownership rules. Each scan can admit at most 256 new tasks and spend at most 10 seconds on queue admission, with a 2-second individual bound. An ambiguous queue error stops early admission for that round while observation and snapshot publication continue.

Validation: formatting and diff checks pass. Three real isolated-etcd regressions cover enqueue before a blocked observation completes, disablement/threshold/deduplication/budgets, and queue failure preserving the entire scan result. The final committed source passed all 18 scanner tests, including the three isolated-etcd regressions (0 failed or ignored); its commit and diff fingerprint stayed unchanged throughout the run. CI is running.

This adds no executor pool or rollout mode. It does not resolve historical unfenced requests, authorize replacement of an old writer, or bypass core_not_ready in the external recovery controller. It is separate from the already-building #454/#456 release.