The synchronous handler.merge() call blocked the uvicorn event loop for
the entire merge duration (38s for a 19-member helm virtual repo), stalling
all other requests on the same worker during that window.
Wrapping the call in asyncio.to_thread() releases the event loop while the
CPU-bound YAML parse/merge/dump runs in the default thread pool, allowing
health checks and other requests to be served concurrently.
Measured impact (19-member helm-all, single worker):
Before: first concurrent /health stalled for 37721ms
After: all concurrent /health requests served in <65ms
The change is at the generic handler dispatch site, so it applies to all
current and future _VirtualHandler implementations without modification.
Also fix base_url/package keys merged onto a single line in
examples/single-file/remotes.yaml, which prevented docker-compose startup.
unkinben