fix(responses): route URL-shaped file_id to file_url in input_file

When a Chat Completion request carries a `file` block whose `file_id` is
actually an http(s) URL, the Responses API rejects it: providers (OpenAI,
Azure) require `file_id` to be an uploaded file identifier such as
`file-abc123`. The Responses API does, however, natively accept a `file_url`
field on `input_file` for URL inputs.

Detect URL-shaped `file_id` values during the
`/chat/completions -> /responses` transformation and route them to
`file_url`, dropping the original `file_id`. Also include `file_url` in the
set of keys forwarded from the Chat Completion `file` block so callers can
pass it through directly.

Adds tests for URL-shaped `file_id` -> `file_url` mapping and for native
`file_url` passthrough alongside the existing file_data / file_id tests.

litellm/completion_extras/litellm_responses_transformation/transformation.py

@@ -783,15 +783,29 @@ class LiteLLMResponsesTransformationHandler(CompletionTransformationBridge):
                                 f"Chat provider:   image -> {converted}"
                             )
                         elif item_type == "file":
-                            # Map Chat Completion file to Responses API input_file
-                            # {"type": "file", "file": {"file_data": "...", "filename": "..."}}
-                            # -> {"type": "input_file", "file_data": "...", "filename": "..."}
+                            # Map Chat Completion file to Responses API input_file.
+                            # {"type": "file", "file": {"file_id" | "file_data" | "filename" | "file_url": ...}}
+                            # -> {"type": "input_file", "file_id" | "file_data" | "filename" | "file_url": ...}
+                            # If `file_id` is an http(s) URL, route it to `file_url` instead — providers
+                            # require `file_id` to be an uploaded file identifier (e.g. "file-abc123") and
+                            # reject URLs there.
                             file_data = item.get("file", {})
                             converted = {"type": "input_file"}
                             if isinstance(file_data, dict):
-                                for key in ["file_id", "file_data", "filename"]:
+                                for key in (
+                                    "file_id",
+                                    "file_data",
+                                    "filename",
+                                    "file_url",
+                                ):
                                     if key in file_data:
                                         converted[key] = file_data[key]
+                                file_id = converted.get("file_id")
+                                if isinstance(file_id, str) and file_id.startswith(
+                                    ("https://", "http://")
+                                ):
+                                    converted.setdefault("file_url", file_id)
+                                    converted.pop("file_id", None)
                             result.append(converted)
                             verbose_logger.debug(
                                 f"Chat provider:   file -> {converted}"

tests/test_litellm/completion_extras/litellm_responses_transformation/test_completion_extras_litellm_responses_transformation_transformation.py

@@ -2188,6 +2188,87 @@ def test_convert_chat_completion_file_type_with_file_id():
     assert "file_data" not in content[1]
 
 
+@pytest.mark.parametrize(
+    "url",
+    [
+        "https://pdfobject.com/pdf/sample.pdf",
+        "http://example.com/report.pdf",
+    ],
+)
+def test_convert_chat_completion_file_type_with_url_file_id_routes_to_file_url(url):
+    """
+    Chat Completion clients sometimes pass a URL in `file_id`. The Responses API
+    requires `file_id` to be an uploaded file identifier (e.g. "file-abc123") and
+    rejects URLs there, but it natively accepts `file_url`. The transformation
+    should route URL-shaped `file_id` values to `file_url` and drop `file_id`.
+    """
+    from litellm.completion_extras.litellm_responses_transformation.transformation import (
+        LiteLLMResponsesTransformationHandler,
+    )
+
+    handler = LiteLLMResponsesTransformationHandler()
+
+    messages = [
+        {
+            "role": "user",
+            "content": [
+                {"type": "text", "text": "Summarize this PDF."},
+                {
+                    "type": "file",
+                    "file": {"file_id": url},
+                },
+            ],
+        }
+    ]
+
+    (
+        input_items,
+        _,
+    ) = handler.convert_chat_completion_messages_to_responses_api(messages)
+
+    file_item = input_items[0]["content"][1]
+    assert file_item["type"] == "input_file"
+    assert file_item["file_url"] == url
+    assert "file_id" not in file_item
+
+
+def test_convert_chat_completion_file_type_passes_through_file_url():
+    """
+    When the caller already provides `file_url` directly (Responses-API-shaped
+    payload nested inside a Chat Completion `file` block), the transformation
+    should pass it through unchanged.
+    """
+    from litellm.completion_extras.litellm_responses_transformation.transformation import (
+        LiteLLMResponsesTransformationHandler,
+    )
+
+    handler = LiteLLMResponsesTransformationHandler()
+
+    url = "https://example.com/report.pdf"
+    messages = [
+        {
+            "role": "user",
+            "content": [
+                {
+                    "type": "file",
+                    "file": {"file_url": url, "filename": "report.pdf"},
+                },
+            ],
+        }
+    ]
+
+    (
+        input_items,
+        _,
+    ) = handler.convert_chat_completion_messages_to_responses_api(messages)
+
+    file_item = input_items[0]["content"][0]
+    assert file_item["type"] == "input_file"
+    assert file_item["file_url"] == url
+    assert file_item["filename"] == "report.pdf"
+    assert "file_id" not in file_item
+
+
 # =============================================================================
 # Tests for reasoning_items round-trip (encrypted_content preservation)
 # =============================================================================