fix: treat model auto as runtime default - #181

Walkthrough

This PR implements handling of the "auto" model selector to resolve issue #177, where --model auto was failing. The core change normalizes "auto" (with whitespace and casing variations) to empty string, allowing fallback to runtime-specific defaults. Changes span model resolution logic, unit tests, ACP client integration tests, and a shell script symlink fix.

Changes

Model Auto-Normalization Feature

Symlink Handling Fix

Sequence Diagram: ACP Client Session Model Setup

sequenceDiagram
  participant Test
  participant Client as ACP Client
  participant Agent as Helper Agent
  
  Test->>Client: CreateSession(ClientConfig.Model="explicit-id")
  activate Client
  Client->>Client: resolveModel(normalized="explicit-id")
  Client->>Agent: SetSessionModel(model_id="explicit-id")
  activate Agent
  Agent->>Agent: Mark modelSet=true
  Agent-->>Client: SetSessionModelResponse
  deactivate Agent
  Client->>Agent: Prompt(...)
  activate Agent
  Agent->>Agent: Check modelSet==true
  Agent-->>Client: PromptResponse
  deactivate Agent
  Client-->>Test: Success
  deactivate Client

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• compozy/compozy#83: Earlier edits to the same resolveModel path in registry_launch.go that trim requested model names and resolve aliases.
• compozy/compozy#78: Prior modifications to the shared ACP test harness in internal/core/agent/client_test.go for NewSession and LoadSession expectations.
• compozy/compozy#34: Original introduction of the resolveModel path and related ACP agent client/registry tests in the "use acp instead of stream raw json" work.

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Confidence Score: 5/5

Safe to merge — the core logic change is small and well-scoped, and the tests directly exercise both the 'auto suppresses SetSessionModel' path and the 'explicit model still calls SetSessionModel' path.

The model normalisation change is a single, well-isolated function added to registry_launch.go, and the downstream conditional (requestedModel != startModel) already provides the correct gate for SetSessionModel. The new tests exercise both the happy path and the edge cases (mixed-case, trimmed whitespace). The shell script fix is a one-line additive change that cannot break working symlinks.

No files require special attention.

Important Files Changed

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["cfg.Model input (e.g. 'auto', ' AUTO ', 'composer-2')"] --> B["normalizeRequestedModel()"]
    B --> C{EqualFold 'auto'?}
    C -- yes --> D["selected = ''"]
    C -- no --> E["selected = trimmed value"]
    D --> F["selected = spec.DefaultModel"]
    E --> G["modelprovider.ResolveAlias(selected)"]
    F --> G
    G --> H["normalizeRuntimeModel()"]
    H --> I["requestedModel"]
    I --> J{requestedModel == startModel?}
    J -- yes --> K["Skip SetSessionModel"]
    J -- no --> L["Call SetSessionModel(requestedModel)"]

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