Get an HLS CMAF playlist for a live stream. Returns a master playlist when `track` is omitted, or a single-track media playlist when `track` is supplied. The playlist references each segment + per-track init segment via getLiveSegment. Segments come from an in-memory sliding window fed as the stream is ingested (or replicated to this node), so a playlist is only available while the stream is live here.

The streamer to play back: a DID (did:plc/did:web/did:key) or a Bluesky handle, which is resolved to its DID.

Track ID (stringified u32 matching the MUXL container) for a single-track media playlist. Omit for the master playlist.

Opaque playback session identifier. Omit on the master playlist request; the server generates one and threads it through the sub-playlist + segment URLs it returns, for view-count correlation.