The models service starts a conversation with start({agent, cwd, ownership?}, context). The agent field names a built-in definition or a project overlay. The service stores that name in models.profile. discover(cwd) exposes the same live definition resolver to subagents. configure(tx, id, {agent, inheritedTools, excludeTools?, model?, thinking?}) configures an existing child in its creation transaction. It retains the parent's tool scope, explicit overrides, and exclusions for subsequent run boundaries. It applies the definition during creation and before each new run. Definitions without an explicit model follow their family, then the default family.

Each resolution reads /src/sausage/agents/models.json and the definition files through host.fs. A file edit applies at the next run boundary without a restart. The project definitions live under <repo>/.sausage/agents/. The existing T37 parser controls validation, overlays, model suffixes, and tool denials.

The optional models.pin service supplies pin(tx, conversationId) for an external model override. Without that provider, the definition or default family selects the model. No login fallback runs.

Existing registered models retain their transport. New model references reuse a template from their own registered provider and retain its proxy auth resolver. They never inherit another provider's transport. Unknown providers fail instead of silently using OpenAI. Models absent from the catalog receive zero prices, not the template's prices. The extension never reads a credential or registers a direct provider SDK.

Host proxy transports and prices

host/js/proxy-models.ts reads the authenticated /v1/models catalog once at host startup. OpenAI models use pi-ai's Responses transport. Anthropic models use its Messages transport. The catalog endpoint determines each model's base URL. For Anthropic, effort capabilities select adaptive thinking and its advertised effort levels. Both providers use the existing llm-proxy key and usage tag. No provider login or direct endpoint fallback runs.

If the catalog fails or exceeds five seconds, a small table supplies these defaults:

Provider/model	API	Proxy path
`openai/gpt-6.1-sol`	Responses	`/v1/responses`
`anthropic/claude-opus-5-5`	Messages, adaptive thinking	`/apis/anthropic/v1/messages`

Catalog prices use USD per million tokens, with conversion from unit_tokens when necessary. The host uses the first advertised route's quote, including cache reads and cache writes. These costs are estimates, not billing totals. Another proxy route can charge different prices. Unavailable prices remain zero. Catalog changes apply after a host restart. World family edits still apply at the next run boundary without a restart. host/tests/proxy_models.rs tests the real transports against a local fake proxy.

host/tests/core_ext.rs tests these services through the snapshot loader.