feat(core): subagents inherit the parent session's model and thinking level (#38)

Co-authored-by: Alice <alice@prismshadow.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

packages/core/src/state/default-config.ts

@@ -253,7 +253,7 @@ function defaultBuiltinTools(): ToolDefinitionConfig[] {
           model_id: {
             type: "string",
             description:
-              "Which model the subagent should use, as the upstream model id. Must be given together with provider — a model is always referenced by the pair. Omit both to use the Project default model.",
+              "Which model the subagent should use, as the upstream model id. Must be given together with provider — a model is always referenced by the pair. Omit both to inherit the parent session's model.",
           },
           provider: {
             type: "string",