Tasks: pilot-storage-backend-interface

1. Conformance harness (do FIRST, before touching production)

• 1.1 Write test/helpers/aggregation-rows-conformance.js — the shared harness + driver shape (setup, teardown, seed, listRows).
• 1.2 Write test/helpers/sqlite-aggregation-rows-driver.js calling the real SQLite path.
• 1.3 Write test/aggregation-rows-conformance.test.js (SQLite, always-run).
• 1.4 Write test/helpers/postgres-aggregation-rows-driver.js calling the real Postgres path.
• 1.5 Write test/aggregation-rows-conformance-postgres.test.js (env-gated).
• 1.6 Assert the record_json string-normalization invariant explicitly.
• 1.7 Verify BOTH conformance files green against CURRENT production code (pre-migration baseline — MUST pass before any production edit).

2. Interface + adapters

• 2.1 Define StorageBackend interface (JSDoc) with listRowsForAggregation as its sole method, including the record_json-is-string contract.
• 2.2 Implement the Postgres adapter satisfying the interface (the existing postgresQuery + stringify-normalization).
• 2.3 Implement the SQLite adapter satisfying the interface (the existing iterate(referenceQueries.recordsAggregateIterateStreamRecordsForAggregation)).
• 2.4 Wire listRowsForAggregation at records.js:2547 to dispatch through the interface; remove its isPostgresStorageBackend() branch.

3. Verification

• 3.1 SQLite conformance green post-migration.
• 3.2 Postgres conformance green post-migration (disposable pgvector).
• 3.3 Existing aggregate-route tests green, unmodified.
• 3.4 Typecheck / ultracite clean on touched files.
• 3.5 Adversarial audit of adapters + harness assertions (no behavior change, no hidden backend-specific logic absorbed).
• 3.6 Codex RI-owner direct diff/test review and sign-off.

4. Acceptance gate

• 4.1 Owner decides: continue to next seam OR close pilot as sufficient proof for the design decision.