Adding a New Runtime to Fracta

type Host struct{}

func (Host) WriteWorkspace(workdir string, allowedTools []string, cfg host.WorkspaceConfig) error {
    // Write host-specific config files into the workspace.
    // For a Batch host, this can be a no-op (return nil).
    return nil
}

func (Host) Bootstrap(task, baseBranch, contract string) host.BootstrapResult {
    // Return the task file name and initial prompt.
    // FileName can be "" if the host doesn't use file-based contracts.
    return host.BootstrapResult{
        FileName:      "",                    // or "TASK.md", etc.
        InitialPrompt: "Execute: " + task,
    }
}

func (Host) BuildBatchCommand(prompt, model, resumeToken string) host.CommandSpec {
    return host.CommandSpec{
        Command: "your-cli",
        Args:    []string{"--prompt", prompt},
    }
}

func (Host) ParseBatchOutput(stdout []byte, waitErr error) (host.Result, error) {
    // Parse your CLI's output into a host.Result.
    return host.Result{Output: string(stdout)}, nil
}

func (Host) StartStream(workdir, model, logPath string) (host.StreamSession, error) {
    // Return ErrStreamNotSupported for Batch-only hosts.
    return nil, host.ErrStreamNotSupported
}

func (Host) Capabilities() host.Capabilities {
    return host.Capabilities{
        Stream:          false,
        AgentMCP:        false,
        ToolPermissions: false,
        ResumeToken:     false,
    }
}

func buildRuntimeRegistry() *host.MapRegistry {
    reg := host.NewMapRegistry("claude") // default runtime
    reg.Register("claude", claude.Host{})
    reg.Register("myruntime", myruntime.Host{})
    return reg
}

agents:
  agent_runtimes:
    myruntime:
      adapter: myruntime
      model: my-default-model
      model_tiers:
        heavy: my-large-model
        medium: my-default-model
        light: my-small-model
      env:                        # local execution env
        MY_API_KEY: "${MY_API_KEY}"
      kubernetes:                 # K8s execution env
        env:
          - name: MY_API_KEY
            secret_ref:
              name: myruntime-secret
              key: api-key

fracta spawn --task my-task --runtime myruntime

{"task": "my-task", "runtime": "myruntime"}