feat(providers): convert OpenAI tool result media like user files

providers/internal/prompttest/cases.go

@@ -96,6 +96,16 @@ func Cases() []Case {
 				}},
 			},
 		},
+		{
+			Name:  "user_text_file",
+			Model: "gpt-4o",
+			Prompt: fantasy.Prompt{
+				{Role: fantasy.MessageRoleUser, Content: []fantasy.MessagePart{
+					fantasy.TextPart{Text: "Summarize the notes."},
+					fantasy.FilePart{Filename: "notes.txt", MediaType: "text/plain", Data: []byte("hello")},
+				}},
+			},
+		},
 		{
 			Name:  "user_unsupported_media",
 			Model: "gpt-4o",
@@ -307,6 +317,43 @@ func Cases() []Case {
 				}},
 			},
 		},
+		{
+			// A PDF result converts with the user file rules: a file part
+			// that keeps the tool's filename, in the deferred user message.
+			Name:  "tool_result_media_pdf",
+			Model: "gpt-4o",
+			Prompt: fantasy.Prompt{
+				{Role: fantasy.MessageRoleAssistant, Content: []fantasy.MessagePart{
+					fantasy.ToolCallPart{ToolCallID: "c1", ToolName: "read", Input: "{}"},
+				}},
+				{Role: fantasy.MessageRoleTool, Content: []fantasy.MessagePart{
+					fantasy.ToolResultPart{ToolCallID: "c1", Output: fantasy.ToolResultOutputContentMedia{
+						Data:      b64([]byte("%PDF-1.4")),
+						MediaType: "application/pdf",
+						Filename:  "report.pdf",
+					}},
+				}},
+			},
+		},
+		{
+			// Text media is the exception to the user file rules, which would
+			// send it as a bare base64 file part that providers can reject.
+			// It gets the unsupported placeholder and warning instead.
+			Name:  "tool_result_media_text",
+			Model: "gpt-4o",
+			Prompt: fantasy.Prompt{
+				{Role: fantasy.MessageRoleAssistant, Content: []fantasy.MessagePart{
+					fantasy.ToolCallPart{ToolCallID: "c1", ToolName: "read", Input: "{}"},
+				}},
+				{Role: fantasy.MessageRoleTool, Content: []fantasy.MessagePart{
+					fantasy.ToolResultPart{ToolCallID: "c1", Output: fantasy.ToolResultOutputContentMedia{
+						Data:      b64([]byte("hello")),
+						MediaType: "text/plain",
+						Filename:  "notes.txt",
+					}},
+				}},
+			},
+		},
 		{
 			// An unsupported media type still has to answer the tool_call, so
 			// the text message goes out alone with a warning naming the type.
@@ -324,6 +371,25 @@ func Cases() []Case {
 				}},
 			},
 		},
+		{
+			// Accompanying text is kept after the notice, which takes the
+			// media's place, so the model does not assume it saw the media
+			// the text describes.
+			Name:  "tool_result_media_unsupported_with_text",
+			Model: "gpt-4o",
+			Prompt: fantasy.Prompt{
+				{Role: fantasy.MessageRoleAssistant, Content: []fantasy.MessagePart{
+					fantasy.ToolCallPart{ToolCallID: "c1", ToolName: "record", Input: "{}"},
+				}},
+				{Role: fantasy.MessageRoleTool, Content: []fantasy.MessagePart{
+					fantasy.ToolResultPart{ToolCallID: "c1", Output: fantasy.ToolResultOutputContentMedia{
+						Data:      b64([]byte{1, 2, 3}),
+						MediaType: "video/mp4",
+						Text:      "Recording of the session.",
+					}},
+				}},
+			},
+		},
 		{
 			// The ordering case from the media fix: a parallel batch must keep
 			// its tool messages contiguous.

providers/internal/prompttest/testdata/tool_result_media_pdf.json

@@ -0,0 +1,37 @@
+{
+  "openai,openaicompat,openrouter,vercel": {
+    "messages": [
+      {
+        "tool_calls": [
+          {
+            "id": "c1",
+            "function": {
+              "arguments": "{}",
+              "name": "read"
+            },
+            "type": "function"
+          }
+        ],
+        "role": "assistant"
+      },
+      {
+        "content": "The tool returned application/pdf content; see the following user message.",
+        "tool_call_id": "c1",
+        "role": "tool"
+      },
+      {
+        "content": [
+          {
+            "file": {
+              "file_data": "data:application/pdf;base64,JVBERi0xLjQ=",
+              "filename": "report.pdf"
+            },
+            "type": "file"
+          }
+        ],
+        "role": "user"
+      }
+    ],
+    "warnings": []
+  }
+}

providers/internal/prompttest/testdata/tool_result_media_text.json

@@ -0,0 +1,27 @@
+{
+  "openai,openaicompat,openrouter,vercel": {
+    "messages": [
+      {
+        "tool_calls": [
+          {
+            "id": "c1",
+            "function": {
+              "arguments": "{}",
+              "name": "read"
+            },
+            "type": "function"
+          }
+        ],
+        "role": "assistant"
+      },
+      {
+        "content": "The tool returned text/plain content, which cannot be displayed.",
+        "tool_call_id": "c1",
+        "role": "tool"
+      }
+    ],
+    "warnings": [
+      "other: tool result media type text/plain not supported, sending text placeholder only"
+    ]
+  }
+}

providers/internal/prompttest/testdata/tool_result_media_unsupported_with_text.json

@@ -0,0 +1,27 @@
+{
+  "openai,openaicompat,openrouter,vercel": {
+    "messages": [
+      {
+        "tool_calls": [
+          {
+            "id": "c1",
+            "function": {
+              "arguments": "{}",
+              "name": "record"
+            },
+            "type": "function"
+          }
+        ],
+        "role": "assistant"
+      },
+      {
+        "content": "The tool returned video/mp4 content, which cannot be displayed.\n\nRecording of the session.",
+        "tool_call_id": "c1",
+        "role": "tool"
+      }
+    ],
+    "warnings": [
+      "other: tool result media type video/mp4 not supported, sending text placeholder only"
+    ]
+  }
+}

providers/internal/prompttest/testdata/user_text_file.json

@@ -0,0 +1,18 @@
+{
+  "openai,openaicompat,openrouter,vercel": {
+    "messages": [
+      {
+        "content": [
+          {
+            "text": "Summarize the notes.",
+            "type": "text"
+          }
+        ],
+        "role": "user"
+      }
+    ],
+    "warnings": [
+      "other: file part media type text/plain not supported"
+    ]
+  }
+}