feat(genome): demand-aligned-recall PR-3d — WorkingSetCandidateSource (genome stack payoff)

[joelteply]

Summary

The architectural payoff of the genome stack. A persona's page_in calls populate the working set (my #1355); this source reads that same working set to surface "what's already hot" candidates that LocalDemandAlignedRecall (#1372 + #1374) ranks via the scoring function (#1371).

End-to-end loop now closed:

page_in(persona, page)
  → WorkingSet.pages updated
  → bus publishes PageFault (via #1362)
recall(query, ctx)
  → WorkingSetCandidateSource::fetch
    → working_set_snapshot
      → CandidateArtifact per resident page
        → LocalDemandAlignedRecall::rank
          → RankedPool

What lands

• WorkingSetCandidateSource holding Arc<LocalWorkingSetManager>
• CandidateSource::fetch impl that:
  • reads persona's working_set_snapshot
  • returns empty Vec on unregistered persona (legitimate cold-start signal, not error)
  • translates each ResidentPage → CandidateArtifact with ResidencyHint::Hot { role } (resident = hot by definition)
  • preserves PageKind for downstream sub-pool partitioning
  • sets NEUTRAL_FACTOR_STUB (0.5) for semantic / outcome_history / provenance_trust factors (dedicated integrations land in separate PRs)
• NEUTRAL_FACTOR_STUB public constant making the contract visible

Design choices

• Snapshot via working_set_snapshot helper rather than holding RwLock across the await. Same pattern as feat(genome): working-set-manager PR-5 — LocalWorkingSetManager auto-publishes via bus hook (+MessageBus borrow fix) #1362's bus_arc hook.
• Object-safe: works through Arc<dyn CandidateSource> per PR-3c's contract.
• All resident pages map to Hot residency. A separate genome-catalog walker PR will add Local{role=Bench/Cold/Frozen} for candidates outside the working set.
• Stub-0.5 factors documented inline + via constant. When embedding/sentinel/trust integrations land, they replace stubs without re-touching this file.

What is deliberately deferred

• Genome catalog walker (Bench/Cold/Frozen tier sources)
• Federation peer source
• Embedding integration (semantic factor)
• Sentinel outcome lookup (outcome_history factor)
• Trust registry lookup (provenance_trust factor)

Test plan

• cargo test --lib --features metal,accelerate genome::recall_source_working_set — 7/7 pass:
  • fetch_unregistered_persona_returns_empty_not_error
  • fetch_registered_empty_working_set_returns_empty
  • fetch_after_page_in_returns_resident_pages_as_hot_candidates — the payoff test
  • translation_preserves_page_kind_for_sub_pool_partitioning
  • translation_uses_neutral_factor_stubs_for_non_tier_factors — pins the contract
  • source_is_object_safe_for_arc_dyn_dispatch
  • end_to_end_page_in_then_recall_returns_ranked_pool — full pipeline through LocalDemandAlignedRecall::recall
• No regressions across other 2822 lib tests
• Pre-push gate clean

Stack

• feat(genome): working-set-manager PR-1 — typed data layer for cache hierarchy + paging #1346 / feat(genome): working-set-manager PR-2 — WorkingSetManager + TierStore traits (+sentinel cleanup) #1353 / feat(genome): working-set-manager PR-3 — LocalWorkingSetManager per-process impl #1355 / feat(genome): working-set-manager PR-4 — canonical ArtifactKeys + bus publishing helpers #1358 / feat(genome): working-set-manager PR-5 — LocalWorkingSetManager auto-publishes via bus hook (+MessageBus borrow fix) #1362 — my working-set-manager
• feat(genome): demand-aligned-recall PR-1 — typed data layer (Part 7) #1366 — DAR PR-1: pure types
• feat(genome): demand-aligned-recall PR-2 — DemandAlignedRecall trait + composite types #1367 + fix(genome): align recall generated type names #1370 — DAR PR-2: trait + composite types
• feat(genome): demand-aligned-recall PR-3a — scoring function + per-factor curves #1371 — DAR PR-3a: scoring function + per-factor curves
• feat(genome): demand-aligned-recall PR-3b — LocalDemandAlignedRecall ranking engine #1372 — DAR PR-3b: LocalDemandAlignedRecall ranking engine
• feat(genome): demand-aligned-recall PR-3c — trait impl + CandidateSource seam #1374 — DAR PR-3c: trait impl + CandidateSource seam
• This PR — DAR PR-3d: WorkingSetCandidateSource (closes the loop)

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