Independent Nox loop-return review

Reviewed src/ir/tree/lower/nox/loops.rs, statement dispatch and scope restoration in nox.rs, aggregate layout/type lookup, and the new tests/nox_surface.rs regressions. This was source review; the separately reported lower/surface and Triton parity runs belong to the implementation owner, not this review.

One actionable correctness issue was found in Scope::seal_frames_above: absorbed branch fallthrough erased local names while retaining their parallel tys entries. An outer aggregate value could consequently be read using a shadowing inner aggregate's layout. For example, outer Pair { a:11, b:22 } and inner Reverse { b:99, a:88 } named x could make a subsequent outer x.a select field1 instead of field0. This affects continuations inside a return-aware loop as well as existing absorbed branches. The implementation owner was asked to seal type frames too and add an execution regression with different aggregate field order. The owner reproduced the bug in actual Nox execution inside a returning loop: expected11, actual999 after the wrong x.a == 22 branch (/tmp/nox-loop-type-shadow-before.log). The fix now clears sealed type frames, stops type lookup at the same nearest lexical binding as value lookup, and clears stale same-frame types on bind. The finding is now resolved: the named actual regression returning_loop_seals_shadowed_aggregate_type_with_its_name ... ok appears in /tmp/trident-nox-return-workspace-neural-final.log, inspected independently. It exercises debug/release and return/fallthrough inputs0,1,9. The owner reports 858 workspace tests (including39 Nox surface tests) passing and two genuine Joy public/private proof tests passing; those runs were not executed by this reviewer. Earlier scalar-shadow tests did not cover the defect.

The new loop continuation design otherwise preserves the reviewed semantics:

• return compiles directly to the function result. Only fallthrough calls the continuation that drops iteration-local subject bindings and starts later iterations/the post-loop continuation. Nested loops share that function result continuation; no synthetic scalar flag truncates aggregate returns.
• The post-loop continuation is compiled against the outer scope; that scope is restored before compiling iteration bodies. The analogous non-returning loop restoration fixes following bindings shifting body variable axes.
• Dynamic end guards are evaluated lazily against the current outer subject. Inactive bodies do not evaluate assertions, secret calls or state lookups. Static empty/reversed ranges and zero dynamic bounds preserve fallthrough.
• The actual shared iteration bound is4096, not256. Each returning-loop index addition is checked; emitted continuation trees are additionally limited to 2,000,000 nodes. Subject depth checks remain active. These are bounds, not a claim that every syntactically bounded nested loop fits the formula budget.
• Struct/tuple results retain the ordinary aggregate noun representation. Existing new tests cover nested helper returns, unit returns, shadowing, post-loop locals and unreachable secret/state effects in debug and release.
• match is still explicitly unsupported by Nox lowering; recursive return discovery does not falsely make match lowering available.

No additional actionable issue was identified in this bounded review. This is not a proof of all compiler behavior or a new heavy proof/test-suite execution.