The aborted hard cutover crash-looped with "Rust kernel returned null string" from
process_intent on the first live trading step. Root cause (reproduced): a non-finite
(inf/NaN) numeric field reaching the kernel — Python json.dumps emits the Infinity/NaN
token, serde_json rejects it at parse, and the FFI returned null. Magnitude is fine;
only finiteness was the problem.
Defense in depth, kernel catches it:
- Rust FFI (lib.rs): dita_kernel_process_intent_json / _on_venue_event_json now return
a clean INVALID_INTENT KernelResult on parse failure (incl. Infinity/NaN tokens) AND
on serialize failure (a non-finite produced internally) — never a null string.
- Python bridge (rust_backend.py): ExecutionKernel.process_intent validates intent
finiteness/bounds (target_size, reference_price, limit_price, leverage, exit_leg_ratios;
size>=0) BEFORE the FFI and rejects INVALID_INTENT, naming the offending field+value.
- contracts.py: add KernelDiagnosticCode.INVALID_INTENT.
- pink_direct.py: on INVALID_INTENT, log full upstream provenance (snapshot.price,
capital, leverage, sizes) so the numerical SOURCE can be located on the next live run.
- on_venue_event bridge tolerates the fallback's null slot (uses the live slot).
Verified: kernel recompiled; offline 65 + 7 new guard tests green (no regression);
direct-FFI inf payload -> INVALID_INTENT (no null crash). NOTE: this turns the cutover
crash into a clean rejection — the upstream source of the non-finite (the live run's
inf) still needs locating, now aided by the provenance log.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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