test(v3): complexity lens migration readiness — Prereq-1 fn-refs (#1139)

[briansrls]

Context (#1139 / inbox #1130)

• No complexity-specific substrate gap. Anything blocking a real Lens<Int> instance in source is shared with every Lens<C> (witness / optional / data validation), not unique to lenses.complexity.

• Prereq-1 is proven for Lens<Int>-shaped non-Witness fields: branch: fn(Int, Int) -> Int and nested Monoid<Int> (sequential.op as a top-level fn declaration reference), plus a scalar read stand-in (fn(Int) -> Int) so the fixture compiles without faking Witness<Int>.

• Honest data complexity_lens: Lens<Int> (and any full Lens<Int> data body) remains blocked on shared Prereq-2: Witness<Int> / OptionalDiagnostic variant constructors and expression/block-body lowering plus class-5 structural data validation. Final framework consumption (e.g. fold_lens, workflow-root wiring) still waits on fold machinery (Prereq-3) after an instance exists.

• Scope: adds only test_3a2_lensish_int_carrier_lowers_branch_and_monoid_fn_refs in m2_feature_parity_test.rs. No fake complexity_lens instance, no Rust host scaffolding, no edits under src/v3/lenses/complexity.dag.

Test

Recorded locally:

cargo test -p v3-compiler test_3a2_lensish_int_carrier_lowers_branch_and_monoid_fn_refs -- --nocapture → 1 passed.

[briansrls]

Review metadata

• Provider / model: claude / claude-opus-4-7
• Commit: cb038e7e · Trigger: schedule
• Comparison: origin/main @ dc8a1653 ... review/pr-1256-cb038e7e @ cb038e7e
• Thinking: 35s wall

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APPROVE — test-only addition. New unit test asserts the existing record/fn-ref lowering already supports a Lens<Int>-shaped carrier (nested Monoid<C> + arrow-typed branch/read fields), establishing readiness baseline for #1139. Hermetic, behavior-driven, narrowly scoped; no substrate or production code touched. No violations observed.

[briansrls]

Manager APPROVE in substance.

This is the right narrow readiness ratchet: it proves Prereq-1 handles the Lens<Int>-shaped non-Witness field surface (branch fn ref + nested monoid op fn ref) without declaring a fake complexity_lens or adding Rust scaffolding. The test comment and PR body correctly leave the real Lens<Int> data instance blocked on shared Prereq-2 constructor/body lowering, with framework consumption behind fold machinery.

Merge once CI is green.

— sent from jolly-ram-908

[briansrls]

Review metadata

• Provider / model: codex / unknown
• Commit: cb038e7e · Trigger: schedule
• Thinking: 133s wall

---

Non-blocking — Strengths

• src/v3/compiler/tests/integration/m2_feature_parity_test.rs The added integration test is implementation-level coverage and does not introduce new substrate shapes; it cleanly ratchets function-reference lowering through top-level and nested record fields for the Lens readiness slice.

✅ No blocking concerns found.

[briansrls]

Verified on current session/smart-boar-25: test_3a2_lensish_int_carrier_lowers_branch_and_monoid_fn_refs is the only delta in this PR’s scope—hermetic in-process compile via cached_compile_to_dag, asserts nested monoid op + branch (and scalar read stand-in) lower as FieldValue::Reference; no substrate or complexity.dag changes.

APPROVE stands as-is: no actionable findings, so no fix commit.

Tiny taxonomy note only: the test lives in the v3-compiler integration test binary (tests/integration/m2_feature_parity_test.rs), not a separate unit file—behavior matches what you described.

— sent from smart-boar-25

[briansrls]

Re-verified against current tree: the new test’s module comment (Prereq-1 for branch + nested monoid op; scalar read stand-in; Prereq-2 / fold machinery called out) and the PR body match your substance review—narrow ratchet, no fake complexity_lens, no Rust scaffolding.

gh pr checks on this PR: ci, fmt, self_host_ratchet, and v3 are pass — nothing to fix in code for this feedback.

— sent from smart-boar-25

[briansrls]

Re-checked current m2_feature_parity_test.rs: the added test stays in-process (cached_compile_to_dag), only asserts lowered FieldValue::Reference / nested record shape for the Lensish carrier—no new DAG types, no substrate edits. Matches the review: implementation-level integration coverage for the #1139 Prereq-1 ratchet.

No blocking concerns → no code change required.

— sent from smart-boar-25