fix image model alias compatibility

tests/unit/generator-api.test.ts

@@ -118,7 +118,7 @@ describe('generator-api gateway routing', () => {
     expect(result).toEqual({ success: true, imageUrl: 'compat-template-image' })
   })
 
-  it('normalizes legacy openai-compatible gemini image model ids before template gateway call', async () => {
+  it('prefers the resolved openai-compatible image model id before trying aliases', async () => {
     resolveModelSelectionMock.mockResolvedValueOnce({
       provider: 'openai-compatible:oa-1',
       modelId: 'gemini-3.1-flash-image',
@@ -137,6 +137,35 @@ describe('generator-api gateway routing', () => {
     await generateImage('user-1', 'openai-compatible:oa-1::gemini-3.1-flash-image', 'draw hero')
 
     expect(generateImageViaOpenAICompatTemplateMock).toHaveBeenCalledWith(expect.objectContaining({
+      modelId: 'gemini-3.1-flash-image',
+    }))
+  })
+
+  it('retries openai-compatible image generation with a compatible alias after a model-id rejection', async () => {
+    resolveModelSelectionMock.mockResolvedValueOnce({
+      provider: 'openai-compatible:oa-1',
+      modelId: 'gemini-3.1-flash-image',
+      modelKey: 'openai-compatible:oa-1::gemini-3.1-flash-image',
+      mediaType: 'image',
+      compatMediaTemplate: {
+        version: 1,
+        mediaType: 'image',
+        mode: 'sync',
+        create: { method: 'POST', path: '/v1/images/generations' },
+        response: { outputUrlPath: '$.data[0].url' },
+      },
+    })
+    resolveModelGatewayRouteMock.mockReturnValueOnce('openai-compat')
+    generateImageViaOpenAICompatTemplateMock
+      .mockRejectedValueOnce(new Error('Template request failed with status 400: invalid model'))
+      .mockResolvedValueOnce({ success: true, imageUrl: 'compat-template-image' })
+
+    await generateImage('user-1', 'openai-compatible:oa-1::gemini-3.1-flash-image', 'draw hero')
+
+    expect(generateImageViaOpenAICompatTemplateMock).toHaveBeenNthCalledWith(1, expect.objectContaining({
+      modelId: 'gemini-3.1-flash-image',
+    }))
+    expect(generateImageViaOpenAICompatTemplateMock).toHaveBeenNthCalledWith(2, expect.objectContaining({
       modelId: 'gemini-3.1-flash-image-preview',
     }))
   })