Why: The first material reply could stream an unsupported numeric relationship before the sourced background card had any verified finding.
Evidence: Task 2 red/green SQLite run tests cover parent provider suppression, queue/reuse, completed source binding, focus retention, squad entry, failed/unknown state, and attempt ordering; full Backend vet/Go/race SELF receipt /tmp/fast-slow-u3-r05-task2-backend-final-v2.json exited 0.
Impact: Prestarted material sends receive one server-owned status message with zero parent model calls; small-text and explicit completed follow-up paths retain their existing runner. No public contract or model budget increases.
Refs: U3 r0.5 approved design and plan; Backend PR #193
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