Bind production answer semantics to the joined R1A/R1C contract

[douglasmonsky]

What changed

Implements the exact 18-path CK-08R1B selected successor cohort from the merged join authority. Production structural derivations now consume the committed answer-semantics-v1 contract and answer-truth-requalification-v2 schema with complete session hierarchy, measurement masks, tool start/terminal coordinates, exact comparison boundaries, and fail-closed null/missing behavior.

The bounded consumer seams:

• admit the contract-selected fields in the plan operand/query compiler and synthetic database adapter;
• materialize complete synthetic coordinates and hierarchy;
• requalify the independent 80-case evaluator seam and regenerate the tiny-v2 oracle bundle from independent facts;
• update only the authorized Candidate A compare-session budget.

No public API, projection, cursor, EvidenceService, grading source in production, live data, real Codex data, or successor packet was changed.

Validation

• 208 focused contract/compiler/adapter/structural/evaluator/fixture tests passed.
• 45 replay/oracle/reconciliation tests passed.
• Synthetic 80-case production-vs-independent replay: rows, typed grades, ordered rows, provenance, and null semantics all 80/80 equal.
• Deterministic fixture regeneration exactly matches committed tiny-v2 artifacts and all five source JSONL digests.
• python3 scripts/bootstrap_dev_environment.py --check
• just vp, just v, just vc green (1,433 passed, 1 skipped in the full local profile; package/dist checks green).
• GitNexus impact and detect_changes completed; staged secret/privacy scan clean.
• Authority patch digest: d3ba81015172cd6e0be2dbaa3beb0aa321cc0232c7820d7ce7cba5630c0674d2.