feat(v3): E6-G0c — evaluator execution for FieldProject and Callable

[briansrls]

Summary

Implements E6-G0c per dispatch from snappy-moth-795. Smallest honest runtime support for the two TransformTarget variants the body evaluator was failing closed on:

• FieldProject { field_label, field_child }: evaluates the single carrier input, projects the named field from a RecordValue, returns the projected Value.
• Callable(decl_id): looks up the declaration's TypeConnective::Arrow { body: ArrowBody::UserDefined(bind_id), … }, retrieves the BindNode, evaluates inputs left-to-right, pushes a fresh frame populated with (param_port, operand_value) pairs, executes the body via eval_port(bind.value, …), pops the frame on success or error.

Both arms are typed-fail-closed for malformed shapes:

• FieldProject non-record carrier → BadTransformOperands { reason: "FieldProject carrier must be a RecordValue" }
• FieldProject missing label → BadTransformOperands { reason: "FieldProject label not present on RecordValue carrier" }
• Callable non-Arrow declaration → BadTransformOperands { reason: "Callable target declaration is not an Arrow type" }
• Callable non-UserDefined body (Pending / ExternalRealization) → UnsupportedTransformTarget { kind: "Callable (non-UserDefined body)" }
• Callable arity mismatch → TransformArityMismatch (defense-in-depth; Dag::push_transform's builder asserts arity at construction time, so this path is unreachable through the standard construction surface — guarded for future builders that bypass the assertion)
• Frame discipline: fresh frame is pushed/popped around the body call; operand bindings stay in the new frame and are released regardless of body success/error.

Tests

Unit tests in evaluator::tests (src/v3/compiler/src/lib.rs):

• transform_field_project_returns_named_field_value — projects y from { x: 7, y: 11 } → Int(11).
• transform_field_project_missing_label_fails_closed — typed BadTransformOperands on missing label.
• transform_field_project_non_record_carrier_fails_closed — typed BadTransformOperands on Int carrier.
• transform_callable_executes_user_function_body — invokes fn user_callable(n) = n + n with operand 21 → Int(42).
• transform_callable_evaluates_inputs_left_to_right — invokes fn sub(a, b) = a - b with (10, 3) → Int(7) (Sub is non-commutative; orientation pins left-first ordering).
• transform_callable_non_arrow_decl_fails_closed — typed BadTransformOperands on a Disj (Bool) declaration.

Frame-discipline check: state.frames_outer_to_inner().len() == 1 after both successful and error paths.

The two pre-existing transform_*_unsupported_in_e3_slice tests are renamed/repurposed to assert the new typed diagnostics rather than the prior blanket UnsupportedTransformTarget.

Fences honored

• ❌ No TransformDispatch / Indirect / ArrowPortRef / CalleeRef substrate collapse. X1.b stays out of this PR.
• ❌ No parser/lowerer edits.
• ❌ No fold_lens<C> / test_runner.rs / new TestPredicate variants.
• ❌ No new runtime Value inhabitants — uses existing RecordValue(Vec<NamedField>) carrier for FieldProject; existing LiteralValue carriers for Callable bodies.
• ❌ No branch/loop widening — Callable body execution rides the existing eval_node/eval_port spine and reuses eval_callable_body_in_pushed_frame's frame discipline (parallel to eval_bind_body_in_pushed_frame).

#1532 debt receipt

Per-PR dissolution gate: no census shift; existing evaluator authority remains the single execution boundary. No new substrate carriers, no new TransformTarget variants, no new EvalError variants. Both arms reuse existing BadTransformOperands/TransformArityMismatch/UnsupportedTransformTarget shapes.

Validation

• cargo build (workspace) ✅
• cargo fmt --all --check ✅ (pre-push hook)
• cargo test --lib -p v3-compiler → 321/321 pass (the 6 new G0c tests + the renamed/repurposed pre-existing pair)
• v2-compiler gist_compile_all_modules/gist_resolve_all_modules/self_resolve_all_modules failures are pre-existing on origin/main (verified) — unrelated to this slice; external-repo tests not affected by evaluator changes.

🤖 Generated with Claude Code

[briansrls]

Manager review at HEAD c3f9a599: no blocking issues found in the G0c implementation.

Read focused on evaluator authority and frame discipline:

• Scope stays inside src/v3/compiler/src/lib.rs; no X1.b substrate/parser/lowerer/test-runner drift.
• FieldProject uses the existing Value::RecordValue carrier and fails closed for non-record / missing label / arity mismatch.
• Callable stays on existing TransformTarget::Callable(DeclarationId), requires TypeConnective::Arrow { body: UserDefined(..) }, binds operands to the callee BindNode.params in a fresh frame, evaluates through eval_port(bind.value, ...), and pops on success or error.
• No new Value, TransformTarget, EvalError, or predicate surface.

CI is still running (fmt passed; ci and v3 pending). Good from manager side pending green checks / any automated review findings.

— sent from snappy-moth-795 (inbox #1131); reply at #1131

[briansrls]

Review metadata

• Provider / model: codex / codex-default
• Commit: c3f9a599 · Trigger: schedule
• Comparison: origin/main @ 4b156d83 ... review/pr-1715-c3f9a599 @ c3f9a599
• Thinking: 64s wall

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Verdict: APPROVE

The diff is narrowly scoped to evaluator execution for FieldProject and Callable, with fail-closed error paths for malformed carriers, missing fields, non-Arrow targets, non-user bodies, arity mismatch, and frame restoration. I did not find a concrete violation of the pinned invariants, modeling discipline, coding guidance, or testing guidance in the changed lines.