Projects the effective config's realtime.session tuning section onto the FLAT Config-bag keys
the realtime drivers consume (effortLevel, parallelToolCalls, mcpTools,
inputTranscriptionModel). Returns null when the section is absent or contributes nothing —
callers then skip the merge entirely, preserving the prior bag byte-for-byte.
Projects the effective config's
realtime.sessiontuning section onto the FLAT Config-bag keys the realtime drivers consume (effortLevel,parallelToolCalls,mcpTools,inputTranscriptionModel). Returnsnullwhen the section is absent or contributes nothing — callers then skip the merge entirely, preserving the prior bag byte-for-byte.