frontproxy:
- _DROP_RESP now drops date/server when relaying engine responses. The front's
  own ASGI server adds Date/Server, so keeping the engine's too produced DUPLICATE
  header lines — which nginx logged as a warning on every request, flooding the
  terminal. Now each appears once.
- Brokered route logs the engine's actual status/bytes/preview (or "NO ENGINE ->
  503") so a brokered request that "doesn't get executed" (instant tiny reply) is
  diagnosable from the log.

coderai-oci:
- Use the host-tailable file log only when it's actually writable. When the
  container runs as --user but the log dir/file was created by an earlier root
  run, it's root-owned; tee then spammed "Permission denied" and the file stayed
  empty. Now we detect that and log to stdout only with a clear note.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>