core/docs/adr/ADR-0263-ratified-ledger-bridge.md

ADR-0263 — The ratified-ledger bridge

• Status: Proposed
• Date: 2026-07-24
• Arc: generalization Phase 3.3 (docs/plans/generalization-arc-2026-07-24.md §2)
• Governs: core/ratified_ledger.py and the three adapters over it — generate/determine/estimation_license.py, chat/deduction_serve_license.py, chat/curriculum_serve_license.py — plus the sealed-artifact writer in evals/deduction_serve/practice/runner.py.

1. Context

Three capabilities had independently converged on the same four-step pattern: sealed practice writes a per-class tally table → the table is committed as a ratified artifact → serving verifies its content_sha256 on load → a per-class gate decides SERVE against fixed ceilings.

Three near-identical implementations is the point at which a shared component is an extraction rather than a guess. It matters now because the generalization plan puts a per-subject arena behind every new subject: without a bridge, each subject copies fifty lines of verification, and the copies drift.

2. Decision

core/ratified_ledger.py owns the mechanics — seal_artifact, write_sealed_ledger, load_sealed_ledger, serve_license, tally_dict — and states the four rules once:

1. The engine reads; only sealed practice writes.
2. Tamper-evidence is structural — a load that cannot reproduce content_sha256 REFUSES. A hand-edited ledger is not a slightly-wrong ledger; it is an unratified one.
3. Ceilings are not negotiable at the call site (ADR-0175 invariant #4).
4. Absent evidence is never a license — a missing class yields None, and every caller's None branch serves the disclosed surface.

Each capability keeps a thin adapter that names its artifact, keeps its memoization, and preserves its public API. One genuine difference is now declared rather than implied: load_sealed_ledger(..., missing_ok=True) distinguishes a ledger a capability ships with (absence = broken deployment, refuse) from one whose practice volume is still being built (absence = no class has earned anything, serve disclosed). Curriculum serving is the second kind today (ADR-0262 §5.1).

3. Why this is safe

The extraction's safety property is byte-identity: seal_artifact and write_sealed_ledger reproduce exactly what the bespoke sealers wrote, so re-sealing through the bridge leaves every committed artifact and every lane pin unmoved. That is asserted, not assumed — test_committed_deduction_ledger_reseals_byte_identically re-derives the committed 25-band ledger through the bridge and compares the bytes.

4. What this unblocks

A new subject arena now needs a gold corpus and a band key. It does not need to re-implement ratification — which is what the plan meant by "so each subject arena plugs in without bespoke wiring", and why §3 sequenced this ahead of the second subject.

5. Scope-outs

• The estimation adapter keeps its predicate → converse-class naming. That mapping is genuinely local to estimation; the bridge gates a class name and does not know how one is derived.
• No ledger migration. All three artifacts already share the schema shape; nothing is rewritten, versioned, or moved.
• core/learning_arena's practice engine is untouched. The bridge covers the consumption half (seal → serve); the production half (run practice, tally) is already shared.

6. Verification

tests/test_ratified_ledger_bridge.py — 8 tests: round-trip, hand-edit rejection, required-vs-optional absence, absent class never licensed, the Wilson volume floor, a single wrong costing the license, committed-ledger byte-identity, and a guard that all three adapters read through the bridge (they no longer import a hashing module of their own). Plus the existing consumers unchanged: core test --suite deductive 252 passed; the estimation and license test set 355 passed.