Playlist mode — queue heterogeneous items in an active session

[Dandiggas]

Problem

Practice sessions aren't single-item. A real session jumps between an MP3, a YouTube reference, sheet music, maybe a second tune. Today the session UI assumes one media source (either YouTube OR uploaded audio) and switching mid-session means starting over.

Expected behaviour

A Playlist tab inside the active session lets users queue heterogeneous items:

• MP3 / uploaded audio
• YouTube URL
• Sheet music (PDF or image)
• (Open to other types later — Spotify, local video, etc.)

Behaviour:

• Items can be added, removed, and reordered during the session without stopping the timer.
• Clicking an item immediately swaps the active media source to that item (YouTube player mounts, audio player loads, sheet-music viewer opens, etc.).
• The previously-playing item pauses cleanly; scrub position on the previous item is optionally remembered so jumping back resumes where you were.
• Playlist persists with the instrument project (alongside BPM, notes, song title), so reopening the project restores the queue.

Open design questions (for brainstorming)

• Where does the Playlist tab live? Sidebar in the session view? A toggle that replaces the main media panel with a list?
• Auto-advance when a track finishes, or pure click-through?
• How do sheet-music items behave inside the same surface as a media player (different interaction model)?
• Does the playlist live on the project or per-session? Per-project is more useful; per-session is simpler.

Implementation notes

• Existing session already supports two distinct media modes (youtube / audio) via mediaSource state. Playlist generalizes this into a list of typed entries.
• Unified item shape probably: { id, type: 'youtube' | 'audio' | 'sheet', source: string, title?: string }.
• Persist under the instrument project in localStorage alongside existing fields; schema migration needed for existing projects (empty playlist = fine default).
• Scope: this is a bigger feature than the metronome volume control — expect brainstorm → spec → plan → subagent-driven execution.

[Dandiggas]

Adding sharper product context from real-world use.

The playlist feature is not just a nice queue UI — it is probably the core workflow for the app.

User story:

I sit down to practise. I need to quickly upload an MP3, slow it down, loop a section, and work out the part. I should not have to fight the session setup flow first.

Implications for playlist mode:

• Playlist should be available as part of the main workspace, not hidden behind a completed setup flow.
• MP3 upload should be quick-addable directly into the playlist.
• YouTube / MP3 / sheet music should be switchable without restarting the timer/session.
• Clicking a playlist item should immediately make it the active practice item.
• The active item should expose the right controls immediately: slowdown, AB loop, scrub, etc.
• Playlist should persist with the instrument/project/workspace so reopening The Shed restores the queue.
• It should still work if the user does not care about timer/session metadata yet.

This links to the broader product decision: The Shed may need to be a practice workspace that happens to track time, rather than a timer-first practice tracker.