fix: drop the model roles table when the role map is cleared

Author: elkaix

packages/agent-core/src/config/toml.ts

@@ -492,7 +492,9 @@ export function configToTomlData(config: PythinkerConfig): Record<string, unknow
 
   setRecordSection(out, 'providers', config.providers, providerToToml);
   setRecordSection(out, 'models', config.models, modelToToml);
-  if (config.modelRoles !== undefined) {
+  if (config.modelRoles === undefined) {
+    delete out['model_roles'];
+  } else {
     out['model_roles'] = cloneUnknown(config.modelRoles);
   }
   setSection(out, 'thinking', config.thinking, thinkingToToml);

packages/agent-core/test/config/configs.test.ts

@@ -260,6 +260,18 @@ source = { kind = "apiJson", url = "https://registry.example/api.json", apiKey =
     expect(readConfigFile(configPath).modelRoles).toEqual({ small: '' });
   });
 
+  it('removes model roles when the role map is cleared', async () => {
+    const configPath = join(makeTempDir(), 'model-roles-removed.toml');
+    await writeFile(configPath, '[model_roles]\nsmall = "old"\n');
+    const config = readConfigFile(configPath);
+
+    await writeConfigFile(configPath, { ...config, modelRoles: undefined });
+
+    const text = await readFile(configPath, 'utf-8');
+    expect(text).not.toContain('[model_roles]');
+    expect(readConfigFile(configPath).modelRoles).toBeUndefined();
+  });
+
   it('round-trips an API key environment reference without an API key', async () => {
     const configPath = join(makeTempDir(), 'api-key-env-var.toml');
     const config = parseConfigString(