feat(jit): Cranelift lazy-stdin dispatch for for-line iterator (ILO-342)

[danieljohnmorris]

Summary

• Implements Cranelift JIT support for for-line "stdin" lazy iterator (ILO-70 / feat: for-line stdin lazy line iterator (ILO-70) #601)
• Both JIT backends (jit_cranelift.rs and compile_cranelift.rs) now dispatch OP_FOREACHPREP / OP_FOREACHNEXT to jit_foreachprep_lazy / jit_foreachnext_lazy trampolines when the HeapObj discriminant at ptr+0 equals 8 (LazyStdinLines); the existing plain-List fast path (discriminant == 1) is unchanged
• Foreach cache vars expanded from 4 → 5 per loop to carry an is_lazy flag so FOREACHNEXT knows which path to take without re-reading the discriminant each iteration
• Two new extern "C" helpers in vm/mod.rs: jit_foreachprep_lazy and jit_foreachnext_lazy — both call handle.next_line() via the Arc<Mutex<...>> and return a heap-string NanVal or TAG_NIL on EOF/error
• StdinLinesHandle::from_lines test helper added (#[cfg(test)]) for in-memory iterator injection

Test plan

• cranelift_foreachprep_lazy_stdin_count — 3-line handle yields count 3
• cranelift_foreachprep_lazy_stdin_empty — empty handle skips loop body, returns 0
• cranelift_foreachprep_lazy_stdin_collects_text — actual line text ("hi" + "world" → len sum 7) flows through the lazy dispatch path
• probe_heapobj_lazy_discriminant — runtime-confirms discriminant values (List=1, LazyStdinLines=8) match JIT constants
• Full cargo build --features cranelift — clean (only pre-existing unrelated warnings)

🤖 Generated with Claude Code

[danieljohnmorris]

needs manual rebase (conflicts in: src/builtins.rs)

[danieljohnmorris]

needs manual — rebase conflict in non-doc file(s)

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
688	1	687	0

View the full list of 1 ❄️ flaky test(s)

ilo::interpreter::tests::interpret_braced_guard_in_loop_no_early_return

Flake rate in main: 66.67% (Passed 1 times, Failed 2 times)

Stack Traces | 0.012s run time

thread 'interpreter::tests::interpret_braced_guard_in_loop_no_early_return' (32989) panicked at src/interpreter/mod.rs:10350:9:
parse errors: [ParseError { code: "ILO-P003", position: 27, span: Span { start: 35, end: 36 }, message: "expected `{`, got `;`", hint: Some("ilo bodies are single-line, `;`-separated — not python/swift-style indented. Use either the brace-block form `name p:t>r;{body1;body2}` or the single-line form `name p:t>r;body1;body2`. For statements that require a block (`@k xs{...}`, `wh cond{...}`, `?subj{...}`), the `{...}` must be on the same line as the head.") }]
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

To view more test analytics, go to the Test Analytics Dashboard
_{📋 Got 3 mins? Take this short survey to help us improve Test Analytics.}