fix(conversion): improve stream failures and diagnostic exports

crates/aether-ai/serving/src/failure_diagnostic.rs

@@ -34,6 +34,7 @@ pub struct CandidateFailureDiagnostic {
     client_api_format: Option<String>,
     provider_api_format: Option<String>,
     safe_to_show: bool,
+    details: Option<Value>,
 }
 
 impl CandidateFailureDiagnostic {
@@ -50,6 +51,7 @@ impl CandidateFailureDiagnostic {
             client_api_format: None,
             provider_api_format: None,
             safe_to_show: true,
+            details: None,
         }
     }
 
@@ -58,6 +60,11 @@ impl CandidateFailureDiagnostic {
         self
     }
 
+    pub fn details(mut self, details: Value) -> Self {
+        self.details = Some(details);
+        self
+    }
+
     pub fn formats(
         mut self,
         client_api_format: impl Into<String>,
@@ -219,6 +226,10 @@ impl CandidateFailureDiagnostic {
             "client_api_format": self.client_api_format,
             "provider_api_format": self.provider_api_format,
             "safe_to_show": self.safe_to_show,
+            "details": self.details,
+            "stage": "request",
+            "source_format": self.client_api_format,
+            "target_format": self.provider_api_format,
         })
     }
 }

crates/aether-ai/serving/src/request_body_diagnostics.rs

@@ -224,6 +224,7 @@ fn diagnostic_from_format_error(
         format_error_path(error),
         format_error_message(error, client_api_format, provider_api_format),
     )
+    .details(error.diagnostic())
 }
 
 fn format_error_path(error: &FormatError) -> String {
@@ -982,6 +983,23 @@ mod tests {
             "request_conversion"
         );
         assert_eq!(diagnostic["failure_diagnostic"]["path"], "$.n");
+        assert_eq!(diagnostic["failure_diagnostic"]["stage"], "request");
+        assert_eq!(
+            diagnostic["failure_diagnostic"]["details"]["code"],
+            "lossy_conversion_blocked"
+        );
+        assert_eq!(
+            diagnostic["failure_diagnostic"]["details"]["path_source"],
+            "structured"
+        );
+        assert_eq!(
+            diagnostic["failure_diagnostic"]["source_format"],
+            "openai:chat"
+        );
+        assert_eq!(
+            diagnostic["failure_diagnostic"]["target_format"],
+            "openai:responses"
+        );
         assert_eq!(diagnostic["request_conversion_error"]["path"], "$.n");
         assert!(diagnostic["failure_diagnostic"]["message"]
             .as_str()