StreamSourceSequenceSettings.onStreamsChanged property

Active-pin sibling of onPreloaded: fires when the currently- active pin’s seen-stream-key set changes — typically the first time each stream emits a frame on the active pin after a paused-then-resumed upstream. Distinct from onAdvance (source change only) and onPreloaded (held pins only).

The most common scenario this signals is a passthrough preload that goes directly active (no holding window) because it was the only source in the sequence — when the client later resumes the paused upstream, this callback fires as each stream’s first frame arrives. Without it, downstream switches that gate on the active pin’s stream complement have no event to react to.

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