arch 0001 core boundary

ARCH-0001 core boundary

Status: accepted — implemented. Date: 2026-09-11 · Issue: ARCH-0001 Phased repo split: core library, deploy targets, dashboard Owner: Capsize Games (maintainer) · Depends on: plans/arch-0001-target-topology.md

Decision

The spikeforge distribution MUST install and import without any of the following distributions present. This list is the enforced core boundary and is frozen for protocol_version 1.0.

fastapi
pydantic
uvicorn
huggingface_hub
nir
nirtorch
onnx
onnxruntime
norse
lava
lava-nc
tonic
tensorboard
wandb

The list mixes distribution names and import roots deliberately. Where they differ: distribution lava-nc is imported as lava; huggingface_hub, pydantic, fastapi, uvicorn, nir, nirtorch, onnx, onnxruntime, tonic, tensorboard, and wandb use the same token for both.

The boundary rule

Three tiers define what "forbidden" means. A core module violates the boundary if it breaks tier 1 or tier 2; tier 3 is explicitly permitted.

1. Tier 1 — never a required dependency. None of the forbidden distributions may appear in the core distribution's [project].dependencies. They may appear only in the core's optional extras (plans/arch-0001-packaging-versioning.md).
2. Tier 2 — never imported at import time. No core module may perform a top-level import fastapi, from pydantic import ..., and so on. A core module that needs an optional SDK must import it inside a function, through one of the existing lazy modules, and degrade honestly when it is absent.
3. Tier 3 — lazy access is allowed. The core-owned lazy modules (nir_bridge/api.py, onnx_bridge/api.py, events/tonic_api.py, tracking/tensorboard_sink.py, tracking/wandb_sink.py, tracking/sink_probe.py) may import a forbidden SDK inside a function and report availability rather than raise. These modules are the only sanctioned exception sites and are enumerated in the static scan's allow-list. The backend and hub probes (spikeforge_targets/probe.py, spikeforge_targets/backends/api.py, spikeforge_hub/probe.py) moved out of core with their distributions and are no longer core exception sites.

The server distribution is exempt by construction: fastapi, pydantic, and uvicorn are its base dependencies (plans/arch-0001-target-topology.md). That is why core no longer packages server/ — the pre-split tree did, via setup.py, which was the single largest boundary violation in the tree; the core distribution now excludes server/ in its package discovery.

CI enforcement

Enforcement has two independent mechanisms; both must pass.

1. Extend the blocked-deps runtime gate

The existing blocker at scripts/blocked_deps/sitecustomize.py makes a listed package unimportable at runtime so graceful-degradation paths are exercised even when the optional extras are installed. Its BLOCKED set today covers the SDKs but not fastapi, pydantic, or uvicorn, which were only ever exercised because server/ shipped in the same distribution. Extend it:

BLOCKED = frozenset(
    {
        # server stack — must be absent from a headless core install
        "fastapi",
        "pydantic",
        "uvicorn",
        # data/event SDKs
        "onnx",
        "onnxruntime",
        "onnxscript",
        "tonic",
        # logging/tracking SDKs
        "tensorboard",
        "wandb",
        # model hub
        "huggingface_hub",
        # deploy backends
        "norse",
        "lava",
        "lava-nc",
        "spinnaker2",
        "sinabs",
        "rockpool",
    }
)

The blocked-deps CI job then proves every available: false and typed unavailable path — including "the server stack is not installed" — in one run.

2. Static import scan

Add scripts/check_core_boundary.py, run in a new core-boundary job. It walks the core distribution's packages (everything in include = ["spikeforge*"], exclude = ["server*", "spikeforge_targets*", "spikeforge_hub*"]), parses each module's AST, and fails if any module-level import names a forbidden root. Function-local imports are permitted only inside the enumerated shim allow-list; a function-local import of a forbidden SDK anywhere else is a failure too, so the boundary cannot be widened silently.

check_core_boundary.py
  forbidden = {fastapi, pydantic, uvicorn, huggingface_hub, nir, nirtorch,
               onnx, onnxruntime, norse, lava, tonic, tensorboard, wandb}
  scan roots = spikeforge/**  and  main.py, main_encodings.py
  exclude    = server*, tests*, spikeforge_targets*, spikeforge_hub*
  rule       = no module-level import of a forbidden root, anywhere
  rule       = no function-level import of a forbidden root outside
               {"spikeforge.nir_bridge.api",
                "spikeforge.onnx_bridge.api",
                "spikeforge.events.tonic_api",
                "spikeforge.tracking.tensorboard_sink",
                "spikeforge.tracking.wandb_sink",
                "spikeforge.tracking.sink_probe"}

3. Headless install proof

Add a headless verification step that builds the distribution with no extras and asserts the boundary from the outside:

python -m build packages/spikeforge            # no extras requested
python -m venv /tmp/headless && . /tmp/headless/bin/activate
pip install dist/spikeforge-*.whl
python - <<'PY'
import importlib.util as u
for mod in ("fastapi", "pydantic", "uvicorn", "huggingface_hub",
            "nir", "nirtorch", "onnx", "onnxruntime",
            "norse", "lava", "tonic", "tensorboard", "wandb"):
    assert u.find_spec(mod) is None, f"core install leaked forbidden dep: {mod}"
import spikeforge  # must import cleanly with the forbidden set absent
PY

The wheel must not contain server/ either, verified by listing the archive and asserting no server/ entry is present.

Corrections and findings

• The old blocked-deps gate had a blind spot. sitecustomize.py blocked the SDKs but not fastapi/pydantic/uvicorn, so it could not catch a core-code import of the server stack. BLOCKED now includes the server stack.
• The web extra was the wrong home for the server stack. The old setup.py extras declared web = [fastapi, uvicorn, websockets, pydantic]; those are now the base dependencies of the spikeforge-server distribution and web is gone from core (plans/arch-0001-packaging-versioning.md).
• nir stays core-optional, not core-required. nir_bridge stays in the core distribution and satisfies the boundary because its SDK imports are lazy. huggingface_hub and the backend SDKs moved out of core with spikeforge-hub and spikeforge-targets respectively. They are forbidden only as required deps of core.

Related decisions

• plans/arch-0001-target-topology.md — which distribution owns which root.
• plans/arch-0001-packaging-versioning.md — extras placement that keeps core headless.
• plans/arch-0001-migration-plan.md — when the server leaves core.
• plans/arch-0001-risk-register.md — the boundary-drift risk and its owner.