FrontlineIndependentContent

The Frontline call UI's INDEPENDENT-content decision for one render.

The Frontline screen keeps a self-contained LEGACY content model (an activeContentOwnerId inferred from isScreenSharing / world|composite camera mode / remoteContentCid, rendered via the owner's camera renderer as a single swapped video). That legacy path stays byte-identical to today and is NOT derived from this helper.

This helper layers the INDEPENDENT (dedicated content track) path on top, gated strictly on the shared resolver's ContentMode.INDEPENDENT, which is only reachable with the build flag on AND a real screen-share content track. When the resolved primary content is INDEPENDENT, the content spotlight renders the dedicated content track (not the owner camera), and the owner's CAMERA stays as its own participant tile (simultaneous camera + content) — exactly the standard CallScreen behavior, reusing the same per-owner resolver outputs.

Returns null whenever the new path must NOT engage:

• the primary content is null or LEGACY (flag off / non-capable owner / world|composite camera-as-content) ⇒ the Frontline legacy path renders unchanged;

• audio-only suppression already zeroed the scene (resolver returns no primary).