Native runtime¶

The native runtime is organised by ownership. Follow the data from the solver towards the model and change the first component that owns the required behaviour.

OpenFOAM field view
    -> adapter exchange
    -> Harbor
    -> Rune over SHM, UDS, TCP or UCX
    -> ModelHost
    -> Smedja packing and workspace
    -> BindNordic scaling and backend
    -> atomic response and field commit

Source map¶

Component	Responsibility	Primary files	Tests
Rune	Typed binary frame representation	`backend/communication/src/rune.cpp`, `rune.hpp`	`test_fjord.cpp`
Channels	Byte transport and transport-specific resources	`backend/communication/src/`	`tests/backend/communication/`
Harbor	Request publication, response sequencing and session negotiation	`harbor.cpp`, `harbor.hpp`	`test_fjord.cpp`
Adapter exchange	Tensor contracts, profiling and atomic response application	`backend/adapter/exchange.cpp`, `port.cpp`	`tests/backend/adapter/`
ModelHost	Resident programmes, readiness, admission and teardown	`backend/inference/worker.cpp`, `runner.cpp`	`test_worker.cpp`, `test_runner.cpp`
Smedja	Active-cell packing and reusable execution storage	`backend/inference/smedja.cpp`	`test_exchange.cpp`
Execution pools	Capacity, memory credits and execution contexts	`backend/inference/execution.cpp`	`test_admission.cpp`, `test_engine.cpp`
BindNordic	FNOM, scalers, tensor contracts and model kernels	`packages/bindnordic/`	`packages/bindnordic/tests/`
Connector	Adapts one native backend to the packed kernel interface	`backend/connectors/`	Backend inference tests and a packaged-runtime test

Exchange changes¶

Change Rune only when the binary frame contract changes. Change a channel only for transport-specific connection, transfer or resource behaviour. Change Harbor for request-response sequencing or capability negotiation. Change the adapter exchange for tensor-view validation, exchange profiling or atomic application semantics.

A protocol change must preserve bounded allocation, explicit byte counts, exchange identity and fail-together behaviour. Add malformed-input coverage as well as a successful round trip, and test shared-memory and stream paths when their framing differs.

Model execution changes¶

ModelHost and Smedja may schedule, admit, pack and invoke work, but they do not define a model format or apply solver semantics. FNOM parsing, scaler application and backend-specific evaluation belong in BindNordic. A new native connector adapts a BindNordic kernel to ModelHost and must not include OpenFOAM fields, scheduler choices or transport logic.

The installed plugin.h is a low-level connector ABI used by the runtime. It is not yet a complete public custom-backend workflow: FNOM format selection and launch-time plugin discovery remain closed contracts. Do not advertise an external connector as supported until artefact creation, plugin placement, ModelHost loading and packaged validation are available together.

Scaling contract¶

The packed backend receives model-space tensors after FNOM input scaling and returns model-space outputs before FNOM output scaling is reversed. OpenFOAM adapters, communication channels and external solver code must not duplicate scaler logic.