fix(bedrock): wrong system prompt transformation (#10120)

* fix(bedrock): wrong system transformation

* chore: add one more test case

---------

Co-authored-by: Krish Dholakia <krrishdholakia@gmail.com>

litellm/llms/bedrock/chat/converse_transformation.py

@@ -376,25 +376,27 @@ class AmazonConverseConfig(BaseConfig):
         system_content_blocks: List[SystemContentBlock] = []
         for idx, message in enumerate(messages):
             if message["role"] == "system":
-                _system_content_block: Optional[SystemContentBlock] = None
-                _cache_point_block: Optional[SystemContentBlock] = None
-                if isinstance(message["content"], str) and len(message["content"]) > 0:
-                    _system_content_block = SystemContentBlock(text=message["content"])
-                    _cache_point_block = self._get_cache_point_block(
+                system_prompt_indices.append(idx)
+                if isinstance(message["content"], str) and message["content"]:
+                    system_content_blocks.append(
+                        SystemContentBlock(text=message["content"])
+                    )
+                    cache_block = self._get_cache_point_block(
                         message, block_type="system"
                     )
+                    if cache_block:
+                        system_content_blocks.append(cache_block)
                 elif isinstance(message["content"], list):
                     for m in message["content"]:
-                        if m.get("type", "") == "text" and len(m["text"]) > 0:
-                            _system_content_block = SystemContentBlock(text=m["text"])
-                            _cache_point_block = self._get_cache_point_block(
+                        if m.get("type") == "text" and m.get("text"):
+                            system_content_blocks.append(
+                                SystemContentBlock(text=m["text"])
+                            )
+                            cache_block = self._get_cache_point_block(
                                 m, block_type="system"
                             )
-                if _system_content_block is not None:
-                    system_content_blocks.append(_system_content_block)
-                if _cache_point_block is not None:
-                    system_content_blocks.append(_cache_point_block)
-                system_prompt_indices.append(idx)
+                            if cache_block:
+                                system_content_blocks.append(cache_block)
         if len(system_prompt_indices) > 0:
             for idx in reversed(system_prompt_indices):
                 messages.pop(idx)

tests/litellm/llms/bedrock/chat/test_converse_transformation.py

@@ -41,6 +41,85 @@ def test_transform_usage():
     assert openai_usage._cache_creation_input_tokens == usage["cacheWriteInputTokens"]
     assert openai_usage._cache_read_input_tokens == usage["cacheReadInputTokens"]
 
+def test_transform_system_message():
+    config = AmazonConverseConfig()
+
+    # Case 1:
+    # System message popped
+    # User message remains
+    messages = [
+        {"role": "system", "content": "You are a helpful assistant."},
+        {"role": "user", "content": "Hello!"},
+    ]
+    out_messages, system_blocks = config._transform_system_message(messages.copy())
+    assert len(out_messages) == 1
+    assert out_messages[0]["role"] == "user"
+    assert len(system_blocks) == 1
+    assert system_blocks[0]["text"] == "You are a helpful assistant."
+
+    # Case 2: System message with list content (type text)
+    messages = [
+        {
+            "role": "system",
+            "content": [
+                {"type": "text", "text": "System prompt 1"},
+                {"type": "text", "text": "System prompt 2"},
+            ],
+        },
+        {"role": "user", "content": "Hi!"},
+    ]
+    out_messages, system_blocks = config._transform_system_message(messages.copy())
+    assert len(out_messages) == 1
+    assert out_messages[0]["role"] == "user"
+    assert len(system_blocks) == 2
+    assert system_blocks[0]["text"] == "System prompt 1"
+    assert system_blocks[1]["text"] == "System prompt 2"
+
+    # Case 3: System message with cache_control (should add cachePoint)
+    messages = [
+        {
+            "role": "system",
+            "content": "Cache this!",
+            "cache_control": {"type": "ephemeral"},
+        },
+        {"role": "user", "content": "Hi!"},
+    ]
+    out_messages, system_blocks = config._transform_system_message(messages.copy())
+    assert len(out_messages) == 1
+    assert len(system_blocks) == 2
+    assert system_blocks[0]["text"] == "Cache this!"
+    assert "cachePoint" in system_blocks[1]
+    assert system_blocks[1]["cachePoint"]["type"] == "default"
+
+    # Case 3b: System message with two blocks, one with cache_control and one without
+    messages = [
+        {
+            "role": "system",
+            "content": [
+                {"type": "text", "text": "Cache this!", "cache_control": {"type": "ephemeral"}},
+                {"type": "text", "text": "Don't cache this!"},
+            ],
+        },
+        {"role": "user", "content": "Hi!"},
+    ]
+    out_messages, system_blocks = config._transform_system_message(messages.copy())
+    assert len(out_messages) == 1
+    assert len(system_blocks) == 3
+    assert system_blocks[0]["text"] == "Cache this!"
+    assert "cachePoint" in system_blocks[1]
+    assert system_blocks[1]["cachePoint"]["type"] == "default"
+    assert system_blocks[2]["text"] == "Don't cache this!"
+
+    # Case 4: Non-system messages are not affected
+    messages = [
+        {"role": "user", "content": "Hello!"},
+        {"role": "assistant", "content": "Hi!"},
+    ]
+    out_messages, system_blocks = config._transform_system_message(messages.copy())
+    assert len(out_messages) == 2
+    assert out_messages[0]["role"] == "user"
+    assert out_messages[1]["role"] == "assistant"
+    assert system_blocks == []
 
 def test_transform_thinking_blocks_with_redacted_content():
     thinking_blocks = [
@@ -59,3 +138,4 @@ def test_transform_thinking_blocks_with_redacted_content():
     assert len(transformed_thinking_blocks) == 2
     assert transformed_thinking_blocks[0]["type"] == "thinking"
     assert transformed_thinking_blocks[1]["type"] == "redacted_thinking"
+