The kind-based solo-safe default (ChannelSnapshotJson.soloSafe is absent on a
pre-feature session, or on any channel the operator hasn't explicitly overridden) — FX
returns and matrix buses default exempt from SIP muting; everything else defaults NOT safe.
Mirrors how a scoped default (rather than an absolute one) is resolved elsewhere in this file.
The kind-based solo-safe default (ChannelSnapshotJson.soloSafe is absent on a pre-feature session, or on any channel the operator hasn't explicitly overridden) — FX returns and matrix buses default exempt from SIP muting; everything else defaults NOT safe. Mirrors how a scoped default (rather than an absolute one) is resolved elsewhere in this file.