Fetch a single live HLS segment, or a track's init segment, from the in-memory live window. `seg` is `init` for the EXT-X-MAP init segment, otherwise the segment's media-sequence number; a cosmetic `.m4s` suffix is accepted (and ignored) so ffmpeg-based HLS players will fetch it. HTTP Range is honored. Segments are the verbatim signed canonical .m4s, so provenance travels with playback.

The streamer: a DID or a Bluesky handle (resolved to its DID).

Track ID (stringified u32 matching the MUXL container).

init for the track's init segment, or the segment's media-sequence number. A trailing .m4s is accepted and ignored.

Opaque playback session identifier, propagated from the media playlist that referenced this segment. Logged for view-count correlation; not used for access control.