Add `recommended_pause_ms` field to DirectAppendAdmissionReqOutput so D
can advise callers when its transfer queue is heavy or KV pool is near
capacity. The hint is computed from transfer_queue_depth,
retracted_queue_depth, and post-trim token_usage; thresholds are simple
heuristics (>0.90 usage, >=8 queue depth, retracted>0).
Default behavior is unchanged for callers that ignore the field.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
ca4b64c79a