Authoritative engineering contract for #33. Source: docs/handoff.md §Slice 7, §Semantic retrieval and the OOM constraint.

Proposal

Vectors by evidence, never by default: demand history decides eligibility, budgets bound compilation, a bounded candidate set is re-ranked last, and the switch turns everything off.

Specification Delta

• ADD per-level retrieval miss attribution and demand history (rebuildable data).
• ADD declared eligibility + eviction policy with hard budgets.
• ADD selected-material embedding + bounded re-rank as the fifth, default-off stage.
• EXIT: observed benefit, hard budget, complete off switch.

Design

Retrieval order (entity → graph → exact/BM25 → Datalog → optional semantic) is normative; the estate's 25 OOM failures are the constraint this Session answers to.

Tasks

#25 · #26 · #27