Nemo Fabric Build Adapter

Build an NVIDIA NeMo Fabric Adapter

Build against the published southbound contract. Keep the adapter thin: let NeMo Fabric own planning and consumer-facing behavior, and let the adapter own only target translation and lifecycle state.

Read the Contract

Read the current adapter contract before changing code. Start with the overview, choose an integration shape, then follow the numbered descriptor, configuration, execution, results, registration, and verification stages. Read the custom-agent page when the target loads application-defined agents or workflows. Read the optional native OpenAI streaming page only when the adapter claims that capability.

Use the committed adapter-contract JSON Schemas or the schemas installed with the matching NeMo Fabric release for exact wire shapes. Do not reconstruct a schema from examples or copy field lists into adapter code.

Establish the Boundary

Establish the adapter boundary before defining its descriptor:

1. Identify the adapter implementation and its stable adapter_id.
2. Choose a harness adapter, a shared framework adapter with registered targets, or a dedicated custom-agent adapter.
3. Reuse one shared adapter across custom agents when the framework provides stable loading and invocation semantics. Use a dedicated adapter when the agent itself is the only unambiguous execution boundary.
4. List the normalized fields the target can actually enforce.
5. Separate adapter-wide harness.settings, per-target workflow.settings, and typed extensions.
6. Keep installation, environment preparation, Relay orchestration, caller scheduling, and consumer result enrichment outside the adapter.

If the requested behavior cannot be expressed by the current contract, surface the gap. Do not silently consume an unsupported northbound field or hide it in an unrelated extension.

Define the Descriptor First

Create one self-contained *.fabric-adapter.json before implementing target translation:

• Set the current contract_version, a globally stable adapter_id, adapter_kind, and runner binding.
• Declare only normalized config.accepts fields the implementation enforces.
• When accepting instructions.system, declare the exact supported config.system_instruction_modes. New descriptors must not rely on the legacy omitted-value behavior, which means replace only.
• Declare mcp.auth.oauth2 or mcp.auth.service_account only when the adapter implements the corresponding MCP authentication mode.
• Publish closed settings_schema, model_schema, tool_definition_schema, and extension_schemas where applicable. Use model_schema only for static model/provider compatibility and model settings; keep credential validity and provider availability in startup validation.
• Declare runtime requirements and telemetry outputs without secret values.
• Leave optional capability flags false unless the installed NeMo Fabric runtime exposes and tests that adapter operation. Set capabilities.streaming only when the adapter implements native OpenAI Chat Completions streaming through invoke_openai_stream. Relay-backed ATOF streaming is independent and does not require this capability.

If the adapter loads registered targets, list their types in target_types. Create one *.fabric-target.json per target. The target record owns its adapter_id, type-specific entry point, and workflow settings schema. It uses the same contract_version as the Adapter Descriptor.

Validate descriptor schemas without importing adapter code. Keep all schema references local to the descriptor document; do not rely on HTTP or file references.

Package Discovery Metadata

Install the descriptor in the standard shared-data location. For setuptools:

[tool.setuptools.data-files]
"share/nemo-fabric/adapters/acme" = ["acme.fabric-adapter.json"]
"share/nemo-fabric/targets/acme" = ["email.fabric-target.json"]

Depend on nemo-fabric-adapter-contract for typed standard-library dataclasses. Install its optional pydantic extra only for Pydantic interoperability. Add nemo-fabric-adapters-common only if the adapter chooses its lifecycle or Relay helpers. A bare adapter package should not depend on the NeMo Fabric runtime.

For a TypeScript adapter, depend on nemo-fabric-adapter-contract. Import descriptor, configuration, runtime-context, request, and result types from the package root, matching the Python package's single model namespace. TypeScript types do not validate data received from a process or network boundary; validate untrusted values against the JSON Schemas included with the package.

Map AgentConfig

Accept a validated AgentConfig and translate each declared field once at the adapter boundary:

• Resolve named model roles into target-native model clients or settings.
• Apply normalized instructions and runtime limits only when declared. Validate instructions.system.mode at the adapter startup boundary as well as during planning; replace discards the harness default, while append preserves it and adds the configured content after it.
• Convert MCP servers, tool definitions, tool policy, and skills into native target constructs.
• Resolve workflow entry points and construction settings during start in the task environment.
• Read identity, environment, artifacts, and telemetry from RuntimeContext, not from workflow settings.

Reject unsupported values with stable, safe error codes. Do not log complete configs, environment values, headers, credentials, or arbitrary user input.

Use typed extension models and publish their schemas at the exact descriptor extension point. Never treat extensions as an unchecked dictionary escape hatch.