fix(core): handle non-string model flags in resolution (#26069)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

packages/cli/src/config/config.test.ts

@@ -804,6 +804,100 @@ describe('loadCliConfig', () => {
     vi.restoreAllMocks();
   });
 
+  describe('Model resolution', () => {
+    it('should handle multiple --model flags by taking the last one', async () => {
+      const argv = {
+        query: undefined,
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        model: ['gemini-1.5-pro', 'gemini-2.0-flash'] as any,
+        sandbox: undefined,
+        debug: false,
+        prompt: undefined,
+        promptInteractive: undefined,
+        yolo: undefined,
+        approvalMode: undefined,
+        policy: undefined,
+        adminPolicy: undefined,
+        allowedMcpServerNames: undefined,
+        allowedTools: undefined,
+        extensions: undefined,
+        listExtensions: false,
+        listSessions: false,
+        deleteSession: undefined,
+        screenReader: undefined,
+        isCommand: false,
+        rawOutput: false,
+        acceptRawOutputRisk: false,
+        startupMessages: [],
+        resume: undefined,
+        includeDirectories: [],
+        useWriteTodos: false,
+        outputFormat: undefined,
+        fakeResponses: undefined,
+        recordResponses: undefined,
+        skipTrust: false,
+      };
+
+      const settings = createTestMergedSettings();
+      const config = await loadCliConfig(
+        settings,
+        'test-session',
+        argv as unknown as CliArgs,
+        {
+          cwd: process.cwd(),
+        },
+      );
+
+      expect(config.getModel()).toBe('gemini-2.0-flash');
+    });
+
+    it('should handle non-string model flags by coercing to string', async () => {
+      const argv = {
+        query: undefined,
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        model: true as any,
+        sandbox: undefined,
+        debug: false,
+        prompt: undefined,
+        promptInteractive: undefined,
+        yolo: undefined,
+        approvalMode: undefined,
+        policy: undefined,
+        adminPolicy: undefined,
+        allowedMcpServerNames: undefined,
+        allowedTools: undefined,
+        extensions: undefined,
+        listExtensions: false,
+        listSessions: false,
+        deleteSession: undefined,
+        screenReader: undefined,
+        isCommand: false,
+        rawOutput: false,
+        acceptRawOutputRisk: false,
+        startupMessages: [],
+        resume: undefined,
+        includeDirectories: [],
+        useWriteTodos: false,
+        outputFormat: undefined,
+        fakeResponses: undefined,
+        recordResponses: undefined,
+        skipTrust: false,
+      };
+
+      const settings = createTestMergedSettings();
+      const config = await loadCliConfig(
+        settings,
+        'test-session',
+        argv as unknown as CliArgs,
+        {
+          cwd: process.cwd(),
+        },
+      );
+
+      expect(config.getModel()).toBe('true');
+    });
+  });
+
   describe('Proxy configuration', () => {
     const originalProxyEnv: { [key: string]: string | undefined } = {};
     const proxyEnvVars = [

packages/cli/src/config/config.ts

@@ -841,9 +841,16 @@ export async function loadCliConfig(
   );
 
   const defaultModel = PREVIEW_GEMINI_MODEL_AUTO;
-  const specifiedModel =
+  const rawModel =
     argv.model || process.env['GEMINI_MODEL'] || settings.model?.name;
 
+  // Ensure specifiedModel is a string (e.g. if yargs parsed multiple --model as an array)
+  const specifiedModel = Array.isArray(rawModel)
+    ? String(rawModel.at(-1) ?? '').trim() || ''
+    : rawModel === undefined
+      ? undefined
+      : String(rawModel ?? '').trim() || '';
+
   const resolvedModel =
     specifiedModel === GEMINI_MODEL_ALIAS_AUTO
       ? defaultModel