route I/O JIT helpers through JIT_RUNTIME_ERROR (batch 7)

[danieljohnmorris]

Summary

Group E of the JIT-helper permissive-nil sweep (batches 1-6 in #264, #259, #282, #285). Routes the type-error paths in jit_rd, jit_rdl, jit_wr, jit_wrl, jit_jpar, jit_rdjl, jit_dtfmt, jit_dtparse through JIT_RUNTIME_ERROR so cranelift surfaces a VmError::Type diagnostic on the same inputs where tree and VM raise. jit_rdjl additionally routes its fs::read_to_string failure through the same channel to match OP_RDJL in the VM. The Result-typed heap_err returns in jit_rd/jit_rdl/jit_wr/jit_wrl for actual filesystem failures are preserved unchanged because the VM produces the same heap_err there too.

Manifesto-aligned: agents calling rd path with a value they expected to be a string (but wasn't, through dynamic dispatch) previously got nil on Cranelift and a typed error on tree/VM. They now get the same diagnostic everywhere, with no token cost in the source program.

Repro

Before, on Cranelift:

jit_rd(non-string) -> TAG_NIL
jit_dtfmt(text, fmt) -> TAG_NIL
jit_wrl(path, non-list) -> TAG_NIL
jit_rdjl("missing-file") -> TAG_NIL

After:

jit_rd(non-string) -> sets VmError::Type("rd requires a string path"), TAG_NIL
jit_dtfmt(text, fmt) -> sets VmError::Type("dtfmt requires a number (epoch)"), TAG_NIL
jit_wrl(path, non-list) -> sets VmError::Type("wrl arg 2 must be a list"), TAG_NIL
jit_rdjl("missing-file") -> sets VmError::Type("rdjl failed to read file"), TAG_NIL

JIT_RUNTIME_ERROR is then picked up by the entry-point post-call check (PR #254) and surfaced as VmRuntimeError with a caret matching tree/VM.

What's in the diff (per commit)

• 12a92e7 route I/O JIT helpers through JIT_RUNTIME_ERROR. All eight helpers grow a span_bits: u64 immediate; call sites in src/vm/jit_cranelift.rs (in-process JIT) and src/vm/compile_cranelift.rs (AOT) pack chunk.spans[ip] and pass it through. declare_helper arities updated in both modules. The existing jit_jpar unit tests are updated for the new signature, and 11 new unit tests cover every type-error path for the eight helpers.
• ea6295c add cross-engine regression suite for batch-7 helpers. 7 CLI tests pin happy-path parity for wr/rd, wrl/rdl, jpar, rdjl, dtfmt, dtparse across tree, VM, Cranelift, plus a stale-error-leak guard.
• 181eff5 add example pinning batch-7 helper happy paths through examples_engines. Five functions in examples/jit-io-roundtrip.ilo run on every engine via the tests/examples_engines.rs harness.

Test plan

• cargo build --release --features cranelift clean
• cargo fmt --check clean
• cargo clippy --release --features cranelift --all-targets clean
• cargo test --release --features cranelift 4992 passing across 123 binaries (zero failures)
• New regression_jit_nil_sweep_batch7 suite passes on all engines (7/7)
• New examples/jit-io-roundtrip.ilo runs clean on tree, VM, Cranelift
• No em dashes in new code; commit messages follow the project's human-voice style

Follow-ups

Groups F+ (network helpers jit_get/jit_post/jit_geth/jit_posth/jit_getmany, jit_env, the remaining map/record nil-returners) are not in this batch. The Cranelift CLI div-by-zero behaviour for the always-num inline path noted in batch 3 is still tracked separately.

[codecov]

Codecov Report

❌ Patch coverage is 83.87097% with 30 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	87.30%	16 Missing ⚠️
src/vm/compile_cranelift.rs	76.66%	7 Missing ⚠️
src/vm/jit_cranelift.rs	76.66%	7 Missing ⚠️

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