fix(aot): strip top-level ~/^ wrappers in compiled binaries

[danieljohnmorris]

Summary

PR #275 made the in-process runners (tree, VM, Cranelift JIT) treat top-level Result returns specially: ~v from main prints v bare on stdout (exit 0), ^e prints ^e on stderr (exit 1). The AOT path (ilo compile main.ilo -o ./main && ./main) was left calling the in-program jit_prt helper from generate_main, so AOT binaries kept printing the visible wrapper and always exited 0, even for ^e. That's a real cost for shell callers piping a compiled ilo program: they have to strip a leading ~ and have no way to detect failure without parsing stdout.

This PR adds a dedicated jit_prt_main_result helper that mirrors print_value's top-level treatment and returns the desired exit code; generate_main calls it and truncates the result to i32 for main(). The in-program prnt builtin keeps using jit_prt (which always shows the wrapper), because those callers are inside a program and genuinely want to see ~v / ^e.

Repro before/after

$ cat /tmp/aot-err.ilo
m>R t t;^"err"

$ ilo compile /tmp/aot-err.ilo -o /tmp/aot-err-bin

# before
$ /tmp/aot-err-bin; echo "exit=$?"
^err
exit=0

# after
$ /tmp/aot-err-bin; echo "exit=$?"
^err          # on stderr
exit=1

And ~"hello" now prints bare hello on stdout from an AOT binary, same as the three in-process runners.

What's in the diff

• aot runtime: add jit_prt_main_result helper (src/vm/mod.rs, src/vm/jit_cranelift.rs) — new extern "C" helper that dispatches on TAG_OK / TAG_ERR and returns the exit code packed in u64; registered in the JIT symbol table so the helper resolves at link time for AOT.
• cranelift aot: route generate_main result through jit_prt_main_result (src/vm/compile_cranelift.rs) — adds prt_main: FuncId to HelperFuncs, declares the import, and switches generate_main to call it and ireduce the u64 result into the i32 main return.
• test + example: cross-engine AOT wrapper-strip coverage (tests/regression_aot_wrapper_strip.rs, examples/aot-wrapper-strip.ilo) — compiles each case to a real AOT binary and asserts byte-for-byte parity against tree, VM, and Cranelift JIT in-process; covers ~"hello", ^"err", bare 42, and ~7.

Test plan

• cargo build --release --features cranelift regenerates libilo.a with the new helper
• cargo test --release --features cranelift --test regression_aot_wrapper_strip — 4 passed
• Full cargo test --release --features cranelift — all 118 test binaries pass, no failures
• cargo fmt -- --check clean
• cargo clippy --release --features cranelift --all-targets -- -D warnings clean
• Manual smoke: AOT stdout/stderr/exit match tree/VM/Cranelift in-process byte-for-byte for all three cases

Follow-ups

• AOT arg parsing has a pre-existing oddity where a CLI int reaches num and the program prints nil instead of the parsed number (visible if you AOT-compile examples/main-err-exit-code.ilo and run ./bin 42). Unrelated to this fix; the in-process runners get it right. Will log it separately in the assessment doc.

[codecov]

Codecov Report

❌ Patch coverage is 56.52174% with 10 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/vm/mod.rs	37.50%	10 Missing ⚠️

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