Parent epic: #193

Context

The briefing generator runs daily and produces a single global briefing per user. With Emergent Lifebooks (#193 Child 1 shipped via #242), each user has 3-N detected life domains with their own wings, signals, and capability sets. A single global briefing doesn't surface the per-domain texture.

Scope

Partition the daily briefing into per-Lifebook sections, with a global "across all your domains" header that summarizes cross-cutting items, then sections per domain ordered by importance.

• Briefing generator pulls signals and decision history per wing rather than globally
• briefing-prose prompt gets a lifebook input variable so prose adapts per domain ("In Health this week, you had 2 appointments and skipped 4 walks…")
• Briefing schema grows a sections: [{ lifebookId, prose, evidence }] field; the global prose stays as the lead-in
• Falls back to single-section global briefing when no Lifebooks exist (new user)

Acceptance criteria

• Briefing generator partitions signals by wing/lifebook before invoking the prose prompt
• briefing-prose prompt accepts lifebook context; eval fixtures cover health-shaped, project-shaped, hobby-shaped sections
• Briefing API response includes sections[] with per-Lifebook prose and evidence
• Web dashboard renders the partitioned briefing (collapsible per-Lifebook sections)
• Mobile briefing screen mirrors the partitioning (ties into Capability loop #G: Mobile parity (Capabilities + Briefing + voice + push) #179)
• Falls back gracefully when user has no Lifebooks yet

Dependencies

• Epic: Emergent Lifebooks — life-management surfaces that adapt to who the user actually is #193 Child 1 (shipped feat(#193 Child 1): Emergent Lifebooks — domain extractor + dashboard surface #242) — the substrate
• Web briefing surface (shipped)
• Mobile briefing surface — partial; mobile parity tracked in Capability loop #G: Mobile parity (Capabilities + Briefing + voice + push) #179