refactor(bedrock): match :bedrock: ARN service field in is_bedrock_arn_model

Tighten the ARN detection so it pins "bedrock" to the colon-delimited service
field of the ARN rather than matching the substring anywhere. This avoids a
false positive for another service's ARN whose resource name merely contains
"bedrock" (e.g. arn:aws:sagemaker:...:endpoint/my-bedrock-transcriber).

litellm/llms/anthropic/experimental_pass_through/adapters/transformation.py

@@ -767,9 +767,11 @@ class LiteLLMAnthropicMessagesAdapter:
 
         These ARNs contain neither "anthropic" nor "claude", so is_anthropic_claude_model
         cannot identify them even though, on the /v1/messages endpoint, they point at Claude.
+        Match ":bedrock:" in the ARN service field so another service's ARN that merely names
+        bedrock in a resource (arn:aws:sagemaker:.../my-bedrock-endpoint) is not matched.
         """
         model_lower = model.lower()
-        return "arn:" in model_lower and "bedrock" in model_lower
+        return "arn:" in model_lower and ":bedrock:" in model_lower
 
     @staticmethod
     def translate_thinking_for_model(

tests/test_litellm/llms/anthropic/experimental_pass_through/adapters/test_anthropic_experimental_pass_through_adapters_transformation.py

@@ -1427,11 +1427,12 @@ def test_cache_control_not_preserved_for_non_claude_model():
         ),
         ("bedrock/amazon.titan-text-express-v1", False),
         ("arn:aws:sagemaker:us-east-1:123:endpoint/my-endpoint", False),
+        ("arn:aws:sagemaker:us-east-1:123:endpoint/my-bedrock-transcriber", False),
         (CACHE_CONTROL_NON_ANTHROPIC_MODEL, False),
     ],
 )
 def test_is_bedrock_arn_model(model, expected):
-    """is_bedrock_arn_model requires both an ARN and the bedrock service in the string."""
+    """is_bedrock_arn_model requires an ARN with bedrock in the service field, not just anywhere."""
     assert LiteLLMAnthropicMessagesAdapter.is_bedrock_arn_model(model) is expected