test(openai-compatible): add Azure SSE regression test for empty choices handling

Adds regression test with Azure SSE fixture covering:
- Empty choices array with prompt_filter_results
- Extra fields (obfuscation) in delta chunks
- Post-completion content_filter_results chunks
- Verifies existing code already handles Azure format correctly

Ref #12056

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: giulio-leone

packages/openai-compatible/src/chat/__fixtures__/azure-text.chunks.txt

@@ -0,0 +1,7 @@
+{"choices":[],"created":0,"id":"","model":"","object":"","prompt_filter_results":[{"prompt_index":0,"content_filter_results":{"hate":{"filtered":false,"severity":"safe"},"jailbreak":{"filtered":false,"detected":false},"self_harm":{"filtered":false,"severity":"safe"},"sexual":{"filtered":false,"severity":"safe"},"violence":{"filtered":false,"severity":"safe"}}}]}
+{"choices":[{"content_filter_results":{},"delta":{"content":"","refusal":null,"role":"assistant"},"finish_reason":null,"index":0,"logprobs":null}],"created":1762317021,"id":"chatcmpl-test","model":"gpt-4","obfuscation":"D3WbtIxo1Q2j1Q","object":"chat.completion.chunk","system_fingerprint":null,"usage":null}
+{"choices":[{"content_filter_results":{"hate":{"filtered":false,"severity":"safe"},"self_harm":{"filtered":false,"severity":"safe"},"sexual":{"filtered":false,"severity":"safe"},"violence":{"filtered":false,"severity":"safe"}},"delta":{"content":"Hello"},"finish_reason":null,"index":0,"logprobs":null}],"created":1762317021,"id":"chatcmpl-test","model":"gpt-4","obfuscation":"NNpA6Dj2U","object":"chat.completion.chunk","system_fingerprint":null,"usage":null}
+{"choices":[{"content_filter_results":{"hate":{"filtered":false,"severity":"safe"},"self_harm":{"filtered":false,"severity":"safe"},"sexual":{"filtered":false,"severity":"safe"},"violence":{"filtered":false,"severity":"safe"}},"delta":{"content":" World"},"finish_reason":null,"index":0,"logprobs":null}],"created":1762317021,"id":"chatcmpl-test","model":"gpt-4","obfuscation":"etvV32yk5dbxb","object":"chat.completion.chunk","system_fingerprint":null,"usage":null}
+{"choices":[{"content_filter_results":{},"delta":{},"finish_reason":"stop","index":0,"logprobs":null}],"created":1762317021,"id":"chatcmpl-test","model":"gpt-4","obfuscation":"Zarov0xJhP","object":"chat.completion.chunk","system_fingerprint":null,"usage":null}
+{"choices":[{"content_filter_offsets":{"check_offset":0,"start_offset":0,"end_offset":11},"content_filter_results":{"hate":{"filtered":false,"severity":"safe"},"self_harm":{"filtered":false,"severity":"safe"},"sexual":{"filtered":false,"severity":"safe"},"violence":{"filtered":false,"severity":"safe"}},"finish_reason":null,"index":0}],"created":1762317021,"id":"chatcmpl-test","model":"gpt-4","object":"chat.completion.chunk","system_fingerprint":null}
+{"choices":[],"created":1762317021,"id":"chatcmpl-test","model":"gpt-4","obfuscation":"DjqQ9RbEQMJ3PX","object":"chat.completion.chunk","system_fingerprint":null,"usage":{"completion_tokens":5,"completion_tokens_details":{"accepted_prediction_tokens":0,"audio_tokens":0,"reasoning_tokens":0,"rejected_prediction_tokens":0},"prompt_tokens":15,"prompt_tokens_details":{"audio_tokens":0,"cached_tokens":0},"total_tokens":20}}

packages/openai-compatible/src/chat/__snapshots__/openai-compatible-chat-language-model.test.ts.snap

@@ -298,6 +298,78 @@ Finally, structure it as: <function_call>{"action": "weather", "action_input": {
 }
 `;
 
+exports[`doStream > Azure text (fixture) > should stream text content with Azure SSE format 1`] = `
+[
+  {
+    "type": "stream-start",
+    "warnings": [],
+  },
+  {
+    "id": "",
+    "modelId": "",
+    "timestamp": 1970-01-01T00:00:00.000Z,
+    "type": "response-metadata",
+  },
+  {
+    "id": "txt-0",
+    "type": "text-start",
+  },
+  {
+    "delta": "Hello",
+    "id": "txt-0",
+    "type": "text-delta",
+  },
+  {
+    "delta": " World",
+    "id": "txt-0",
+    "type": "text-delta",
+  },
+  {
+    "id": "txt-0",
+    "type": "text-end",
+  },
+  {
+    "finishReason": {
+      "raw": "stop",
+      "unified": "stop",
+    },
+    "providerMetadata": {
+      "test-provider": {
+        "acceptedPredictionTokens": 0,
+        "rejectedPredictionTokens": 0,
+      },
+    },
+    "type": "finish",
+    "usage": {
+      "inputTokens": {
+        "cacheRead": 0,
+        "cacheWrite": undefined,
+        "noCache": 15,
+        "total": 15,
+      },
+      "outputTokens": {
+        "reasoning": 0,
+        "text": 5,
+        "total": 5,
+      },
+      "raw": {
+        "completion_tokens": 5,
+        "completion_tokens_details": {
+          "accepted_prediction_tokens": 0,
+          "reasoning_tokens": 0,
+          "rejected_prediction_tokens": 0,
+        },
+        "prompt_tokens": 15,
+        "prompt_tokens_details": {
+          "cached_tokens": 0,
+        },
+        "total_tokens": 20,
+      },
+    },
+  },
+]
+`;
+
 exports[`doStream > text (fixture) > should stream text content 1`] = `
 [
   {

packages/openai-compatible/src/chat/openai-compatible-chat-language-model.test.ts

@@ -1512,6 +1512,21 @@ describe('doStream', () => {
     });
   });
 
+  describe('Azure text (fixture)', () => {
+    beforeEach(() => {
+      prepareChunksFixtureResponse('azure-text');
+    });
+
+    it('should stream text content with Azure SSE format', async () => {
+      const { stream } = await model.doStream({
+        prompt: TEST_PROMPT,
+        includeRawChunks: false,
+      });
+
+      expect(await convertReadableStreamToArray(stream)).toMatchSnapshot();
+    });
+  });
+
   describe('tool call (fixture)', () => {
     beforeEach(() => {
       prepareChunksFixtureResponse('xai-tool-call');