fix(image): fail when every generated image is rejected

The image generation API answers HTTP 200 with an empty `image_urls`
list and `success_count: 0` when all requested images are rejected by
the content policy or fail in the model. `mmx image generate` ignored
`success_count`, so it pushed the `--out` path onto `saved`, printed it
as a successful result and exited 0 without writing any file.

ERRORS.md already documents the intended behaviour for this scenario:

  | `success_count === 0` (all rejected) | `Image generation failed: all
    images were rejected (content policy or model error).` |

Reject the response before the download/write step so the documented
error and a non-zero exit code are produced instead of a phantom path.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Author: 2sumtech

src/commands/image/generate.ts

@@ -142,6 +142,16 @@ export default defineCommand({
       process.stderr.write('[Model: image-01]\n');
     }
 
+    // The API answers 200 with an empty image list when every image is rejected.
+    // Without this check the command reports the --out path as saved and exits 0
+    // even though nothing was written (see ERRORS.md, `mmx image generate`).
+    if (response.data.success_count === 0) {
+      throw new CLIError(
+        'Image generation failed: all images were rejected (content policy or model error).',
+        ExitCode.GENERAL,
+      );
+    }
+
     const saved: string[] = [];
 
     if (outPath) {

test/commands/image/generate.test.ts

@@ -1,5 +1,9 @@
 import { describe, it, expect } from 'bun:test';
+import { existsSync, rmSync } from 'fs';
+import { tmpdir } from 'os';
+import { join } from 'path';
 import { default as generateCommand } from '../../../src/commands/image/generate';
+import { createMockServer, jsonResponse } from '../../helpers/mock-server';
 
 const baseConfig = {
   apiKey: 'test-key',
@@ -91,4 +95,30 @@ describe('image generate command', () => {
     expect(parsed.request.seed).toBe(42);
     expect(parsed.request.model).toBe('image-01');
   });
+
+  it('fails when the API rejects every image instead of reporting a saved file', async () => {
+    const server = createMockServer({
+      routes: {
+        '/v1/image_generation': () => jsonResponse({
+          id: 'req-1',
+          data: { image_urls: [], task_id: 'task-1', success_count: 0, failed_count: 1 },
+          base_resp: { status_code: 0, status_msg: 'success' },
+        }),
+      },
+    });
+    const outPath = join(tmpdir(), `mmx-image-rejected-${process.pid}-${Date.now()}.jpg`);
+
+    try {
+      await expect(
+        generateCommand.execute(
+          { ...baseConfig, baseUrl: server.url, quiet: true },
+          { ...baseFlags, quiet: true, prompt: 'A cat', out: outPath },
+        ),
+      ).rejects.toThrow('Image generation failed: all images were rejected');
+      expect(existsSync(outPath)).toBe(false);
+    } finally {
+      rmSync(outPath, { force: true });
+      server.close();
+    }
+  });
 });