nir c runtime profile

NIR C-runtime export profile

The Python reference interpreter implements 14 node kinds, but the nir-c-runtime C loader implements only 11: a graph using Linear, Conv1d, LIF, IF, or CubaLIF fails loading with an unsupported node kind error. This profile declares the exact supported set as data so exports can be gated spikeforge-side instead of failing at the C loader. Stage kinds with no NIR rendering at all are decided separately in plans/nir-unmappable-decisions.md.

Supported kinds

Single-sourced from SUPPORTED in c_runtime.py, which names the tracked nir-c-runtime commit (currently 7348c82) next to the constant. The validator and this table both reference it; re-audit graph.h, graph.c, ops.c, and runtime.c when the commit moves.

NIR kind	C loader support
Input	Entry node, params ignored.
Output	Pass-through readout, params ignored.
Conv2d	Dense-only weights [out, in, kh, kw]; bias optional; stride, padding, and dilation as [h, w] pairs.
Affine	Weights [out, in] with a required bias [out].
Flatten	Ignores its dims and flattens every dim, so exports must set start_dim=1, end_dim=-1.
AvgPool2d	Kernel, stride, and padding as [h, w] pairs.
SumPool2d	Kernel, stride, and padding as [h, w] pairs.
LI	tau (positive), r, v_leak.
Threshold	Scalar threshold.
Scale	Scalar scale.
Delay	Length ignored; the runtime hardcodes one step, so exports must set delay=1.

Validator

c_runtime_validate.py exposes validate_for_c_runtime, which accepts a TopologySpec, an exported NIR graph, or a summary mapping and returns a report naming every incompatible node, edge, and structural assumption. Each check mirrors one C-loader behavior: the kind table, Affine-bias and weight-layout parsing (raw or per-tensor int8/uint8 envelope), conv/pool pair shapes, the dense-only convolution, Flatten coverage, the one-step delay, positive tau, edge references, per-node inputs, single input/output, and Delay-broken cycles. check_for_c_runtime raises the typed CRuntimeUnsupportedError on the same violations for refuse-early export paths.

Profile, not a registry entry

The profile ships as a TargetSpec that classify accepts, so a capability row is one call away, but it stays out of builtin_targets(): every registered target is required to have an executable simulator backend, and none is wired for the C runtime.