feat(verify): cross-compat integration suite (C5)

[hyperpolymath]

Summary

• Adds crates/typed-wasm-verify/tests/cross_compat.rs — a 10-fixture integration test suite.
• Each fixture models a representative AffineScript source program through the wasm shape that affinescript's codegen would emit.
• Each fixture's doc comment includes the conceptual AffineScript source, a hand-trace of the OCaml verifier (tw_verify.ml / tw_interface.ml) over the wasm structure, and the expected verdict.
• 50/50 tests pass (40 unit + 10 new integration).

Why this design

Original C5 scope was "drive affinescript build to produce real OCaml-emitted .wasm files, compare verdicts byte-for-byte." That requires a built affinescript binary in PATH (dune build of hyperpolymath/affinescript), which isn't currently wired into typed-wasm CI.

This PR delivers the regression-net value now using wasm-encoder fixtures that emit the same byte shape affinescript produces:

• Same affinescript.ownership custom-section payload (via the C2 encoder)
• Same function-index conventions (imports first in declaration order, locals after)
• Same control-flow patterns (Block / Loop / If / Else / End delimiters)

When the OCaml-emitter integration lands (call it C5.1), these synthetic fixtures stay — they cover codegen-bug edge cases that may not appear in any source program — and OCaml-emitted .wasm files get vendored alongside.

Fixture inventory

#	Test	Expected verdict
1	Clean Linear consumer (drop s)	pass
2	Duplicated Linear (s + s)	LinearUsedMultiple{count:2}
3	Dropped Linear in else (if(t) drop s)	LinearDroppedOnSomePath
4	Aliased ExclBorrow (b.len() + b.len())	ExclBorrowAliased{count:2}
5	Multi-fn: one clean, one buggy	single error on fn 1
6	Cross-mod: clean Linear call	pass
7	Cross-mod: Linear called twice	LinearImportCalledMultiple{count:2}
8	Cross-mod: 3 fns, only last misuses	single error on caller_fn_idx=3
9	extract_exports of 3 different shapes	correct param_kinds
10	Realistic multi-fn clean module	pass

Test infrastructure

The test file includes an internal ModuleBuilder that constructs affinescript-shaped modules with multiple functions, imports, exports, and the ownership section. Keeps each fixture ~30 lines, so the conceptual-source → wasm-bytes mapping stays legible.

Build status

$ cargo test -p typed-wasm-verify
... unit tests ...
running 40 tests
test result: ok. 40 passed; 0 failed; 0 ignored

     Running tests/cross_compat.rs
running 10 tests
test fixture_aliased_excl_borrow ... ok
test fixture_dropped_linear_in_else ... ok
test fixture_clean_linear_consumer ... ok
test fixture_duplicated_linear ... ok
test fixture_extract_exports_three_shapes ... ok
test fixture_multi_function_one_buggy ... ok
test fixture_xmod_clean_linear_call ... ok
test fixture_realistic_clean_module ... ok
test fixture_xmod_linear_called_twice ... ok
test fixture_xmod_mixed_correctness ... ok
test result: ok. 10 passed; 0 failed; 0 ignored

Stacking

Stacked on #22 (C4 cross-module verifier). Merge order: #22 → this.

Follow-up

• C5.1 (future): vendor real OCaml-emitted .wasm files alongside these synthetic ones once affinescript build is part of CI; assert byte-for-byte parity in section payloads and verdict-for-verdict parity in verifier output.
• C6 (#41): ephapax-wasm emits the affinescript.ownership custom section from linear-typed bindings.
• C7 (#42): ephapax-cli gets --verify-ownership flag.

Closes #40 once merged.