Ja.

STDIO-PROTOCOL.md

@@ -69,3 +69,18 @@ A normal shutdown sends `CMD_QUIT`, waits for its result, closes the child's
 stdin, and waits for the child process. If the Racket process terminates
 unexpectedly, the operating system closes the pipe; EOF on stdin makes the Qt
 backend close all windows and quit.
+
+## Structured stderr logging
+
+The backend writes diagnostic logging to stderr, never to stdout. Log entries
+created through `utils.h` are emitted as one line beginning with `json:` followed
+by a compact JSON object:
+
+```text
+json:{"topic":"webview-backend","level":"debug","elapsed":1.234,"message":"..."}
+```
+
+Newlines and other control characters in the message are JSON escaped, so one
+C++ log call always produces one physical stderr line. Consumers should also
+accept unstructured stderr lines because Qt, Qt WebEngine, or another library
+may write diagnostics directly.