diff --git a/src/agent/api/mod.rs b/src/agent/api/mod.rs
index 26bb293..fac187c 100644
--- a/src/agent/api/mod.rs
+++ b/src/agent/api/mod.rs
@@ -392,15 +392,37 @@ impl SseReader {
                 }
                 Ok(Ok(None)) => return Ok(None),
                 Ok(Err(e)) => {
-                    self.save_failed_request(&format!("stream error: {}", e));
+                    let buf_preview = if self.line_buf.is_empty() {
+                        "(empty)".to_string()
+                    } else {
+                        let n = self.line_buf.len().min(500);
+                        format!("{}B: {}", self.line_buf.len(), &self.line_buf[..n])
+                    };
+                    let msg = format!(
+                        "stream error after {} chunks, {:.1}s, {} sse lines: {} | buf: {}",
+                        self.chunks_received,
+                        self.stream_start.elapsed().as_secs_f64(),
+                        self.sse_lines_parsed,
+                        e, buf_preview,
+                    );
+                    let _ = self.ui_tx.send(UiMessage::Debug(msg.clone()));
+                    self.save_failed_request(&msg);
                     return Err(e.into());
                 }
                 Err(_) => {
+                    let buf_preview = if self.line_buf.is_empty() {
+                        "(empty)".to_string()
+                    } else {
+                        let n = self.line_buf.len().min(500);
+                        format!("{}B: {}", self.line_buf.len(), &self.line_buf[..n])
+                    };
                     let msg = format!(
-                        "stream timeout: no data for {}s ({} chunks, {:.1}s elapsed)",
+                        "stream timeout: {}s, {} chunks, {} sse lines, {:.1}s elapsed | buf: {}",
                         self.chunk_timeout.as_secs(),
                         self.chunks_received,
-                        self.stream_start.elapsed().as_secs_f64()
+                        self.sse_lines_parsed,
+                        self.stream_start.elapsed().as_secs_f64(),
+                        buf_preview,
                     );
                     let _ = self.ui_tx.send(UiMessage::Debug(msg.clone()));
                     self.save_failed_request(&msg);