test(extension): replace model-resolution it.todo placeholders

[HaoChiBao]

Summary

• Replace it.todo placeholders in packages/extension/tests/model-resolution.test.ts with controller-level coverage for model string and object resolution paths.
• Align a misleading test name with current controller behavior (keyless models are forwarded; rejection happens later in llmService).

Test plan

• pnpm --filter @browserbasehq/stagehand-extension exec vitest run tests/model-resolution.test.ts (or equivalent package filter) passes
• Confirm no remaining it.todo in that file

---

Summary by cubic

Replaces it.todo tests in packages/extension/tests/model-resolution.test.ts with controller-level coverage for model resolution and Browserbase gateway routing, and dedupes primitive spy scaffolding via shared helpers. Increases confidence in inference selection without changing runtime behavior.

• Direct inference: uses provider auth; preferred even when a Browserbase session exists (gateway still forwarded; selection happens in llmService).
• Browserbase managed inference: keyless explicit model or no model routes via the gateway; rejects when no model and no gateway; rejects managed inference with a local browser; forwards a keyless explicit model with a local browser (later rejected by llmService); rejects a missing model with a local browser.
• Client inference: model.source: "client" uses the connected SDK callback.
• Per-call models: uses the initialized model by default; a per-call model fully overrides; initialized credentials do not inherit into per-call models.
• Aligns a misleading test name with current controller behavior.

^{Written for commit 74c6825. Summary will update on new commits.}

[cubic-dev-ai]

All reported issues were addressed across 1 file

Architecture diagram

sequenceDiagram
    participant T as Test Suite
    participant C as Stagehand Controller
    participant R as Runtime
    participant BS as Browserbase Service
    participant S as act/extract/observe Services
    participant LLM as LLM Service

    Note over T,LLM: Model Resolution and Gateway Routing Paths

    Note over T: Direct Inference with Provider Auth
    
    T->>C: init(model={name, apiKey})
    C->>R: Configure runtime
    R-->>C: Runtime ready
    T->>C: act/extract/observe
    C->>S: call service(model, gateway=undefined)
    S-->>T: Verify no gateway passed

    Note over T: Browserbase Managed Inference
    
    T->>C: init(apiKey, browser, keyless model)
    C->>R: Configure runtime
    R-->>C: Runtime ready
    T->>C: act/extract/observe
    C->>BS: Resolve gateway (apiUrl, sessionId)
    BS-->>C: Gateway config
    C->>S: call service(model, gateway)
    S-->>T: Verify gateway routing

    alt Local Browser with Keyless Model
        T->>C: init(browserCdpUrl, keyless model)
        C->>R: Configure runtime
        R-->>C: Runtime ready
        T->>C: act/extract/observe
        C->>S: Forward model (gateway=undefined)
        S->>LLM: Attempt inference
        LLM-->>S: Reject (no gateway available)
        S-->>T: Verify forwarding behavior
    else Local Browser without Model
        T->>C: init(browserCdpUrl)
        C->>R: Configure runtime
        R-->>C: Runtime ready
        T->>C: act/extract/observe
        C-->>T: Error: "An LLM was not configured"
    end

    Note over T: Client Inference Path
    
    T->>C: init(model={source: "client"})
    C->>R: Configure runtime with SDK callback
    R-->>C: Runtime ready
    T->>C: act/extract/observe
    C->>S: call service(client callback)
    S-->>T: Verify SDK callback usage

    Note over T: Per-Call Model Overrides
    
    T->>C: init(modelA)
    C->>R: Configure runtime
    R-->>C: Runtime ready
    T->>C: act(model=modelB)
    C->>S: call service(modelB)
    S-->>T: Verify override, no credential inheritance

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