Background processes started by subagents (task_id sa-*) route their
notify_on_complete / watch_pattern notifications to the parent
conversation (b95ec1cb5) because anything outliving the child needs a
durable consumer. In practice these 'npm ci finished' walls are noise
mid-conversation — the child's consolidated delegation result is the
deliverable.
- New config key delegation.surface_child_process_notifications
(default false = suppress). Flag true restores the previous behavior
exactly (delivery with subagent attribution line).
- drain_notifications drops (never requeues) completion/watch_match/
watch_disabled events whose task_id starts with 'sa-' when the flag
is false, logging at debug with session_id+task_id for diagnosis.
Requeueing would pin them forever — children never drain notifies.
- async_delegation events are NEVER suppressed (they ARE the result).
- watch_disabled emitters now carry task_id so sa- sessions' safety
events follow the same suppression as their other events.
- Config read errors fall back to the default (suppress) and never
crash the drain loop.
- Docs: delegation.md + configuration.md.
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