The compile-time feature kernel-step-trace gates inclusion of the ring
code. NEW: --kernel-step-trace <PATH> CLI flag on alpha_train gates
RUNTIME activation:
- Path provided -> ring allocated, drain spawns, JSONL records written
to <PATH> (truncated). One record per kernel emission.
- Path omitted -> ring not allocated, drain not spawned, zero overhead
even with the feature compiled in.
JSONL schema: {"step": u32, "kid": u8, "kname": str, "rt": u8,
"rt_name": str, "payload": {field: f32, ...}}. The payload field names
come from the existing per-(kid, rt) decoders in gpu_log.rs (ported to
serde_json::json! in decode_to_json).
Trainer ring fields are now Option<_>; populated only when the runtime
trace path is Some. Tick kernel, step-counter shadow, smoothness
controller pointer-passing, and Drop all become path-conditional.
The tracing::info!-based drain variant is removed (file-writer is
strictly more useful; tests migrated to assert JSONL file contents).
Argo template:
- New parameter kernel-step-trace-enable (build-time feature opt-in)
- New parameter kernel-step-trace-path (runtime CLI value)
- ensure-binary cache-busts when feature toggles
- training step passes --kernel-step-trace flag conditionally
Per feedback_no_feature_flags: compile-time gate retained because the
ring carries real memory cost (~2 MiB pinned) and per-step write overhead;
the specific name kernel-step-trace narrows scope to this mechanism.
Runtime gate is Option<PathBuf>, not a boolean enable_*.
2d5a66f6e4