fix(observability): preserve inbound trace context

apps/admin-api/tests/integration/openapi_source/telemetry.rs

@@ -154,17 +154,19 @@ impl<'a> MakeWriter<'a> for SharedLogWriter {
     fn make_writer(&'a self) -> Self::Writer {
         SharedLogGuard {
             buffer: Arc::clone(&self.buffer),
+            pending: Vec::new(),
         }
     }
 }
 
 struct SharedLogGuard {
     buffer: Arc<Mutex<Vec<u8>>>,
+    pending: Vec<u8>,
 }
 
 impl io::Write for SharedLogGuard {
     fn write(&mut self, bytes: &[u8]) -> io::Result<usize> {
-        self.buffer.lock().unwrap().extend_from_slice(bytes);
+        self.pending.extend_from_slice(bytes);
         Ok(bytes.len())
     }
 
@@ -173,6 +175,24 @@ impl io::Write for SharedLogGuard {
     }
 }
 
+impl Drop for SharedLogGuard {
+    fn drop(&mut self) {
+        self.buffer.lock().unwrap().extend_from_slice(&self.pending);
+    }
+}
+
+#[test]
+fn shared_log_writer_publishes_complete_records_only() {
+    let writer = SharedLogWriter::default();
+    let mut guard = writer.make_writer();
+    io::Write::write_all(&mut guard, b"message").unwrap();
+    assert!(writer.output().is_empty());
+
+    io::Write::write_all(&mut guard, b" stage=\"fetch\"\n").unwrap();
+    drop(guard);
+    assert_eq!(writer.output(), "message stage=\"fetch\"\n");
+}
+
 #[derive(Clone, Debug)]
 struct CapturingExporter(Arc<Mutex<Vec<SpanData>>>);