Mobile downloads v1: download-to-device with explicit local availability and offline playback #28

Part of #14 (W3 — mobile v1). Blocked by files slice; URL/token policy putdotio/putio-sdk-kotlin#24. In v1 as the lean core (2026-08-08 grill decision). The iOS epic kept the fuller offline bar in its parity scope (queue with configurable concurrency, multi-select delete, completion notifications); Android v1.0 ships the core below and queue-management polish fast-follows under #53. The delta is recorded in the shared contract (#19).

Outcome

Downloads users can trust: an explicit "on this device" state, survivable downloads, and an obvious place to find them. Clear distinction between "save to put.io cloud" and "download to this phone" (design brief mandate).

Scope

• Download original file (and converted MP4 where that's the playable artifact) via DownloadManager or a foreground-service equivalent with notification progress
• Downloads/offline screen: list with local-availability badges, storage used, delete local copy
• Offline playback path for downloaded media (player opens local file when available)
• Respect the SDK URL token policy (no token-leaking URLs persisted in logs/notifications)
• Failure/resume behavior: network loss mid-download surfaces a retryable state

Acceptance criteria

• DoD: verify green; screen recording of download → airplane mode → offline playback on the harness attached