fix(kimi): tag content parts so serde emits the type discriminant

src/providers/kimi/translate/request.rs

@@ -488,7 +488,7 @@ fn push_user_messages(out: &mut Vec<KimiMessage>, blocks: &[ContentBlock]) {
 }
 
 #[derive(Debug, Clone, Serialize)]
-#[serde(untagged)]
+#[serde(tag = "type", rename_all = "snake_case")]
 enum KimiUserContentPart {
     Text { text: String },
     ImageUrl { image_url: KimiImageUrl },
@@ -552,7 +552,7 @@ fn tool_result_content(content: &Value, is_error: Option<bool>) -> Value {
 }
 
 #[derive(Debug, Clone, Serialize)]
-#[serde(untagged)]
+#[serde(tag = "type", rename_all = "snake_case")]
 enum KimiToolResultPart {
     Text { text: String },
     ImageUrl { image_url: KimiImageUrl },
@@ -841,6 +841,64 @@ mod tests {
         }
     }
 
+    #[test]
+    fn user_content_parts_carry_a_type_discriminant() {
+        let req: MessagesRequest = serde_json::from_value(json!({
+            "model": "kimi-for-coding",
+            "messages": [{
+                "role": "user",
+                "content": [
+                    {"type": "text", "text": "describe this"},
+                    {"type": "image", "source": {"type": "base64", "media_type": "image/jpeg", "data": "xyz"}}
+                ]
+            }]
+        }))
+        .unwrap();
+        let translated = translate_request(&req, TranslateOptions { session_id: None }).unwrap();
+        match &translated.messages[0] {
+            KimiMessage::User { content, .. } => {
+                let parts = content.as_array().unwrap();
+                assert_eq!(parts[0].get("type").and_then(|v| v.as_str()), Some("text"));
+                assert_eq!(
+                    parts[1].get("type").and_then(|v| v.as_str()),
+                    Some("image_url")
+                );
+            }
+            _ => panic!("expected User message"),
+        }
+    }
+
+    #[test]
+    fn tool_result_parts_carry_a_type_discriminant() {
+        let req: MessagesRequest = serde_json::from_value(json!({
+            "model": "kimi-for-coding",
+            "messages": [{
+                "role": "user",
+                "content": [{
+                    "type": "tool_result",
+                    "tool_use_id": "toolu_1",
+                    "content": [
+                        {"type": "text", "text": "caption"},
+                        {"type": "image", "source": {"type": "base64", "media_type": "image/png", "data": "abc"}}
+                    ]
+                }]
+            }]
+        }))
+        .unwrap();
+        let translated = translate_request(&req, TranslateOptions { session_id: None }).unwrap();
+        match &translated.messages[0] {
+            KimiMessage::Tool { content, .. } => {
+                let parts = content.as_array().unwrap();
+                assert_eq!(parts[0].get("type").and_then(|v| v.as_str()), Some("text"));
+                assert_eq!(
+                    parts[1].get("type").and_then(|v| v.as_str()),
+                    Some("image_url")
+                );
+            }
+            _ => panic!("expected Tool message"),
+        }
+    }
+
     #[test]
     fn translate_text_only_user_collapses_to_string() {
         let req: MessagesRequest = serde_json::from_value(json!({