startMcpTransport loads optional observation providers once per process
and passes them to every server instance the SDK constructs. Each
instance's closeProviders also closed the shared browser scenario
provider, so when the SDK discarded a server/discover probe instance for a
legacy initialize, every later capture_browser_scenario call failed with
"Browser scenario provider is closing." Server instances no longer close
the caller-supplied provider; the transport returns
closeOptionalProviders and process shutdown closes it once.
Fixes#2195
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>