fix(api): enrich JSON parse errors with response body, provider, and model

Raw 'json_error: no field X' now includes truncated response body,
provider name, and model ID for debugging context.

rust/crates/api/src/providers/openai_compat.rs

@@ -131,7 +131,15 @@ impl OpenAiCompatClient {
         preflight_message_request(&request)?;
         let response = self.send_with_retry(&request).await?;
         let request_id = request_id_from_headers(response.headers());
-        let payload = response.json::<ChatCompletionResponse>().await?;
+        let body = response.text().await.map_err(ApiError::from)?;
+        let payload = serde_json::from_str::<ChatCompletionResponse>(&body).map_err(|error| {
+            ApiError::json_deserialize(
+                self.config.provider_name,
+                &request.model,
+                &body,
+                error,
+            )
+        })?;
         let mut normalized = normalize_response(&request.model, payload)?;
         if normalized.request_id.is_none() {
             normalized.request_id = request_id;
@@ -150,7 +158,10 @@ impl OpenAiCompatClient {
         Ok(MessageStream {
             request_id: request_id_from_headers(response.headers()),
             response,
-            parser: OpenAiSseParser::new(),
+            parser: OpenAiSseParser::with_context(
+                self.config.provider_name,
+                request.model.clone(),
+            ),
             pending: VecDeque::new(),
             done: false,
             state: StreamState::new(request.model.clone()),
@@ -282,11 +293,17 @@ impl MessageStream {
 #[derive(Debug, Default)]
 struct OpenAiSseParser {
     buffer: Vec<u8>,
+    provider: String,
+    model: String,
 }
 
 impl OpenAiSseParser {
-    fn new() -> Self {
-        Self::default()
+    fn with_context(provider: impl Into<String>, model: impl Into<String>) -> Self {
+        Self {
+            buffer: Vec::new(),
+            provider: provider.into(),
+            model: model.into(),
+        }
     }
 
     fn push(&mut self, chunk: &[u8]) -> Result<Vec<ChatCompletionChunk>, ApiError> {
@@ -294,7 +311,7 @@ impl OpenAiSseParser {
         let mut events = Vec::new();
 
         while let Some(frame) = next_sse_frame(&mut self.buffer) {
-            if let Some(event) = parse_sse_frame(&frame)? {
+            if let Some(event) = parse_sse_frame(&frame, &self.provider, &self.model)? {
                 events.push(event);
             }
         }
@@ -835,7 +852,11 @@ fn next_sse_frame(buffer: &mut Vec<u8>) -> Option<String> {
     Some(String::from_utf8_lossy(&frame[..frame_len]).into_owned())
 }
 
-fn parse_sse_frame(frame: &str) -> Result<Option<ChatCompletionChunk>, ApiError> {
+fn parse_sse_frame(
+    frame: &str,
+    provider: &str,
+    model: &str,
+) -> Result<Option<ChatCompletionChunk>, ApiError> {
     let trimmed = frame.trim();
     if trimmed.is_empty() {
         return Ok(None);
@@ -857,9 +878,9 @@ fn parse_sse_frame(frame: &str) -> Result<Option<ChatCompletionChunk>, ApiError>
     if payload == "[DONE]" {
         return Ok(None);
     }
-    serde_json::from_str(&payload)
+    serde_json::from_str::<ChatCompletionChunk>(&payload)
         .map(Some)
-        .map_err(ApiError::from)
+        .map_err(|error| ApiError::json_deserialize(provider, model, &payload, error))
 }
 
 fn read_env_non_empty(key: &str) -> Result<Option<String>, ApiError> {