[ADR-043] Embedding Model Registry and Vector Engine Migration

[ohdearquant]

Summary

Add vector/embedding engine migration steps and registry-backed table naming after storage and retrieval contracts are settled.

Source ADRs

• F227 ADR-043 (CRIT): MIGRATIONS contains only V1 through V4 and stops at dedupe_graph_edge_triples. (from audit-rest/r5/ADR-043.md)
• F228 ADR-043 (CRIT): Vector tables are created as vec_<model_key> with only subject_id, namespace, kind, and embedding columns. (from audit-rest/r5/ADR-043.md)

Files affected

• crates/khive-db/src/migrations.rs (506 sampled LOC)
• crates/khive-db/src/backend.rs (627 sampled LOC)
• crates/khive-storage/src/types.rs (436 sampled LOC)
• crates/khive-storage/src/vectors.rs (446 sampled LOC)

Acceptance criteria

• All source findings listed above are addressed exactly once in this cluster.
• Public types, handlers, schema, and docs touched by the affected files agree on the ADR contract.
• Regression tests cover happy path and edge cases for the changed public APIs or schema behavior.
• cargo test -p khive-db -p khive-storage passes.
• cargo clippy --workspace -- -D warnings passes.
• make ci passes.

Dependencies

• Depends on: #[ADR-001] Entity Kind and Type Contract
• Depends on: #[ADR-002] Edge Ontology, Lifecycle, and Bulk Link Semantics
• Depends on: #[ADR-004] Note Kind, Storage, and Curation Operations
• Depends on: #[ADR-005] Storage Capabilities, Sparse Store, and Vector Contract
• Depends on: #[ADR-004] Event Observable and Provenance Model
• Depends on: #[ADR-003] Runtime Backend and Substrate Coordinator
• Depends on: #[ADR-004] HandlerDef Pack Contract
• Depends on: #[ADR-004] GTD Pack Schema Plan and Lifecycle Audit
• Blocks: #[ADR-025] Event-Sourced Proposals
• Blocks: #[ADR-015] Schema Migration Ledger

LOC estimate

~100 lines added/30 removed; 4 existing affected file(s) sampled at 2015 current LOC via wc -l, plus 0 new/planned path(s).

Risk notes

• Same-file dependencies must merge first; dependency list includes the exact overlapping paths.
• Contains CRIT findings; do not defer without owner approval.

Auto-generated by ADR alignment triage

[ohdearquant]

Landed in main via PR #349 (integration of cluster c20 — original cluster PR was #374). Tracker complete.