Client apps: optional live-offset override in settings

[jonathaneoliver]

Background

All three client apps currently let the manifest's EXT-X-SERVER-CONTROL HOLD-BACK (HLS) or its DASH equivalent decide where the player joins live:

• Android (Compose / Media3) — MediaItem.LiveConfiguration.setTargetOffsetMs(C.TIME_UNSET) in PlayerViewModel.loadStream().
• Apple (AVPlayer) — item.automaticallyPreservesTimeOffsetFromLive = true in PlaybackViewModel.swift.
• Roku — defers to the OS player; no equivalent override surfaced.

Both clients report liveOffset for metrics, but neither lets the user pin the player to a specific offset.

Ask

Add an optional Live Offset Override under Settings → Advanced (next to the existing 4K / Local Proxy / Auto-Recovery / Go Live toggles), with two states:

1. Off (default) — current behavior, manifest decides.
2. On — exposes a numeric input or stepper (e.g. 1–60 s in 1 s steps) and pins the player to that offset.

Behavior when on:

• Android: setTargetOffsetMs(<seconds>*1000) plus setMinOffsetMs / setMaxOffsetMs so ABR / rate-adjustment doesn't drift away.
• Apple: item.automaticallyPreservesTimeOffsetFromLive = false and seek to currentDate - <offset> after the manifest is parsed.

Why

• Reproducible bug repros: pin every device to the same offset to compare ABR / stall behavior under identical conditions.
• Test the server's HOLD-BACK math: pinning a known-good offset eliminates client-side variance.
• Verify recovery — see whether the player snaps back to the configured offset after a stall, or drifts.

Out of scope

• Changing the server's HOLD-BACK is a separate problem (already configurable via go-live env).
• Overriding MIN-OFFSET / MAX-OFFSET independently — start with the simple single-value override.

Touch points

• android/InfiniteStreamPlayer/app/src/main/java/com/infinitestream/player/state/PlayerState.kt — add field on UiState
• .../PlayerViewModel.kt — persist + apply in loadStream()
• .../ui/screen/SettingsOverlay.kt — Advanced picker row
• apple/InfiniteStreamPlayer/.../PlaybackViewModel.swift — same pattern
• Possibly the dashboard, if we want a per-session override there too — separate issue if so.