test(evaluator): R3 diagnostics_empty_after_bootstrap ratchet for method-template-contracts

[briansrls]

Summary

Per Director / Debt-Paydown dispatch: smallest ratchet that pays down the missing diagnostics_empty_after_bootstrap debt row for the method-template-contract bootstrap fixture authorities.

Adds one combined-axis test in src/v3/compiler/tests/integration/method_template_contract_test.rs::bootstrap_method_template_contracts_lower_to_list_with_empty_diagnostics. The test asserts, for the full bootstrap Dag:

1. dag.diagnostics().is_empty() (checked first so structural assertions cannot pass over a noisy Dag — exactly the failure mode ROADMAP.md:504 names).
2. Each of rust_method_template_contracts / python_method_template_contracts / go_method_template_contracts is present.
3. Each lowers to ValueBody::List(_) (not Map, not the no-body fallback).

Debt receipt — Disposition #1 / Debt paid

Per Debt-Paydown Mgr clarification: this is a Disposition #1 (Debt paid) target from docs/debt/r3-debt-paydown-ledger-2026-05-02.md (#1531), complementary to (not overlapping with) Grounding method-template migration. Any blocker / closure update routes through zesty-dove-500 #1526.

Citations (in dispatch authority order):

• docs/debt/r3-debt-paydown-ledger-2026-05-02.md:82 (docs(r3-debt-paydown): initial debt-row inventory ledger 2026-05-02 #1531) — primary ledger row: "Missing diagnostics-empty bootstrap gate" / "Open" / diagnostics_empty_after_bootstrap ratchet for new bootstrap authorities. This PR closes the method-template-contract authority slice of that row.
• ROADMAP.md:502 — "go_method_template_contracts live diagnostic mismatch": Dissolution = "structural gate that all 3 method-template-contract data declarations both lower to ValueBody::List AND leave dag.diagnostics() empty."
• ROADMAP.md:504 — "diagnostics empty acceptance gate" missing for new bootstrap fixtures: Dissolution = "every new bootstrap fixture authority gets a diagnostics_empty_after_bootstrap ratchet test".
• ROADMAP.md:576 (table row 6) — diagnostics_empty_after_bootstrap for new bootstrap fixture authorities, especially method-template-contract data.

This PR closes the method-template-contract slice of the ledger row. Other new bootstrap fixture authorities can adopt the same pattern as they land; the broader ledger row stays open until each authority has its receipt. Blockers / closure updates route through zesty-dove-500 #1526.

Constraints upheld

• No broad bootstrap regeneration.
• No unrelated snapshot churn.
• No suppression of diagnostics — the gate fails closed if the Dag carries any.
• No parser / substrate changes.
• The bootstrap is already diagnostic-clean today; the gate ratchets the property forward, it does not require landing a fix.
• Complementary to Grounding method-template migration (not overlapping).

Test plan

• cargo test -p v3-compiler --test integration method_template_contract_test::bootstrap_method_template_contracts_lower_to_list_with_empty_diagnostics — 1 passed locally.
• CI v3 + ci.

🤖 Generated with Claude Code

[briansrls]

Review metadata

• Provider / model: cursor / composer-2
• Commit: 21a23b7b · Trigger: schedule
• Comparison: origin/main @ 0ad95356 ... review/pr-1537-21a23b7b @ 21a23b7b
• Thinking: 47s wall

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Findings

None. This diff only adds an integration test plus comments in method_template_contract_test.rs; it does not touch substrate types, DAG modeling, or compiler boundaries, so INVARIANTS.md / docs/modeling-discipline.md do not apply in a meaningful way. CODING.md applies to compiler sources; the new code matches existing patterns in the same file (generated_full_bootstrap_dag(), reuse of assert_per_target_list_dag_method_unique). TESTING.md: the test is behavior-driven (diagnostics empty + structural shape), uses the same integration entry point as method_template_contract_per_target_dag_method_unique immediately above, and the bundled assertions are explicitly justified as one combined R3 ratchet rather than unrelated multi-claim noise.

Verdict

APPROVE — Small, targeted regression/ratchet test with clear documentation of overlap with neighboring tests and why the combined gate matters; no rubric violations grounded in this diff.