# ADR-0023: Model-agnostic Node capability admission

## Status: Accepted (P0 planned)

## Context

A Node currently inventories hardware, benchmarks a generic Torch operation, loads its model, registers with the Tracker, and can be routed before its exact model/backend path has completed a bounded real forward. Optional JIT or model-kernel failures can therefore surface only after a live `/forward` request reaches the Node.

This is incompatible with a consumer-grade node experience. A Node must never advertise a Shard it cannot actually execute. The solution must not be coupled to a development model; model-specific hardcoding would recreate the support burden for every new Model Artifact.

## Decision

- Introduce a generic versioned capability report keyed by Model Artifact identity, Shard range, named recipe, backend/device identity, and local validation result.
- A recipe is data and can be one of several possible execution paths for the same Model Preset. Every recipe validates itself using a bounded real forward.
- `meshnet-node doctor` validates the selected model/shard by default. An explicit all-recipes mode supports CI and diagnosis.
- Startup fails closed for an explicitly selected Model Preset when no matching recipe validates. The Node must not become routable or accept paid work.
- Nodes register only locally validated capabilities. The Tracker routes only matching validated capabilities and uses measured performance as part of normal route selection.
- P0 carries the version of a local recipe manifest. New executable recipes arrive only through signed Node releases in a future feature. P0 does not download executable recipes, dynamically install dependencies, install OS packages/drivers, or implement an updater.
- A future Tracker-provided Model Artifact Manifest may be signed data only; it cannot instruct a Node to execute arbitrary code.

## Tracker admission and the compatibility policy for older Nodes

A Node ships its capability report with `POST /v1/nodes/register` (`capability_report`), alongside an independent declaration of the recipe it serves with (`recipe_id`, `recipe_version`). The Tracker does not re-run the forward. It decides whether the presented proof *covers what the Node advertises*, records the verdict as a sanitized state, and routes accordingly.

Registration always succeeds — a Node with a bad proof is registered and visible, it is simply not routable. "Registered but dark" is a state an operator must be able to see and diagnose, so the verdict is returned in the registration response, logged, and exposed per node on `GET /v1/network/map` under `capability` (state, detail, proven model/shard/recipe/backend/device, timestamps). The detail is credential-redacted and clipped; a raw exception or token never reaches an operator view.

Verdicts: `admitted`, `absent`, `invalid`, `failed`, `stale`, `model-mismatch`, `shard-mismatch`, `recipe-mismatch`, `catalogue-incompatible`. Only `admitted` is proof. The proof does not travel with a reassignment: if the Tracker later moves a Node to a range it never validated, the Node is re-verdicted `shard-mismatch` and stops routing until it re-registers with a proof for the range it now advertises.

Freshness is checked when the proof is *presented*, not continuously — a long-lived Node's proof does not expire out from under it while it is heartbeating; liveness is already carried by heartbeat expiry.

**Compatibility policy** (`--capability-policy`, `$MESHNET_TRACKER_CAPABILITY_POLICY`):

- **`compat` (default, transitional)** — a Node that presents *no* report at all still routes, preserving pre-capability Node behaviour during the fleet rollout. Every other verdict is refused. Presenting a broken, failed, stale or mismatched proof is a stronger negative signal than presenting none, so it is never grandfathered.
- **`enforce`** — only `admitted` routes. Absent proof is not routable, and no paid route can rest on an unproven Node.

`compat` is a deprecating default: it exists to let a mixed fleet upgrade without an outage, and `enforce` becomes the default once the deployed Nodes emit reports. The policy is a single explicit switch, checked in one gate (`_admitted_nodes`) that every route path — proxy head selection, `/v1/route`, `/v1/routes`, and bandit route enumeration — passes through. The gate only ever *removes* candidates; coverage-first selection and throughput-weighted preference among the survivors are untouched, and nothing in a report can raise a Node's routing weight (performance stays measured, per ADR-0013/ADR-0021).

The Tracker also refuses a report whose recipe catalogue predates `MIN_CATALOGUE_VERSION`: recipe ids from an older catalogue may since have been redefined, so the proof cannot be matched to a name reliably.

## Hardware claims are evidence, not a support matrix

Operator docs must distinguish three states and never collapse them: **detected hardware** (a GPU, a torch build, or an optional package is present — proves nothing), **validated recipe** (this machine ran a real forward for this model/shard/recipe/device, and there is a capability report to show for it), and **routable Node** (the Tracker admitted that proof for what the Node advertises). Each is strictly stronger than the last.

Consequently no doc promises that a model, vendor, or optional kernel works universally. A concrete model appears only as a clearly-labelled example or as environment-supplied test configuration. Hardware support is claimed per *certified lane*, where a lane is certified by an opt-in `integration` doctor run whose model identity comes from CI configuration and whose retained evidence is the capability report — see `docs/dev/certified-hardware-lanes.md`. A lane certifies hardware, not models: a new Model Artifact is unproven there until doctor has run it.

## Consequences

- First startup has a bounded validation cost before registration, but failures occur before traffic rather than under a paid request.
- The registration and routing protocols gain compatibility/capability fields and require a transition policy for older Nodes.
- Hardware support claims become evidence-based and can be tested independently of specific development models.
- The signed Node update channel is deliberately deferred until this capability contract is stable.