feedBack/docs/plugin-v3-ui.md

Building plugins for the v3 UI (fee[dB]ack v0.3.0)

v0.3.0 ("fee[dB]ack") ships a redesigned UI. It is the only UI — the classic v2 shell and its FEEDBACK_UI / /v2 opt-outs have been removed, so there is no longer a second shell to support.

The good news: v3 reuses the same engine the classic UI did — same server.py, app.js, highway.js, playSong, showScreen, capability registry, library providers, and the window.feedBackViz_<id> / setRenderer visualization contract. So your plugin's backend, capabilities, library providers, nav/screen, visualization renderers, diagnostics, and settings export all work unchanged. v3 surfaces your nav entry in the new sidebar (via shell.js renderPluginNav) and your screen mounts exactly as before.

The one thing that changed is the player chrome — and only if your plugin injects controls into it.

What changed in the player

In v2, #player-controls was a wide, always-visible bottom bar. In v3 it became a minimal, auto-hiding centered transport (it fades ~2.5 s after the pointer goes still during playback), flanked by a hover-reveal left icon rail with popovers.

So the legacy way of injecting a control breaks in v3 two ways:

1. Auto-hide — a button you append to #player-controls vanishes with the transport after a couple seconds.
2. Dead anchors — legacy code commonly inserts before a <span class="text-gray-700"> separator or the button:last-child (the ✕ Close button). Neither exists in the v3 transport, so your control lands at the wrong end or is unreachable.

The contract: detect v3, mount into the plugin-control slot

The host exposes:

• window.feedBack.uiVersion === 'v3' — detect v3 (absent / not 'v3' in v2).
• window.feedBack.ui.playerControlSlot() — returns a stable, always-reachable container (the "Plugins" rail popover). In v3, append your control(s) here instead of #player-controls.

Canonical pattern for any control you inject into the player:

function playerSlot() {
  return (window.feedBack && window.feedBack.uiVersion === 'v3'
    && window.feedBack.ui && typeof window.feedBack.ui.playerControlSlot === 'function')
    ? window.feedBack.ui.playerControlSlot() : null;
}

function injectMyButton() {
  const slot = playerSlot();
  const controls = slot || document.getElementById('player-controls');   // v3 slot, else v2 bar
  if (!controls) return;
  if (myBtn && controls.contains(myBtn)) return;                          // guard the ACTUAL container
  // Legacy inserts before a separator / the ✕ Close button; the v3 slot has no
  // such anchor, so just append there.
  const anchor = slot ? null : controls.querySelector('span.text-gray-700, button:last-child');
  myBtn = document.createElement('button');
  /* ... */
  if (anchor) controls.insertBefore(myBtn, anchor); else controls.appendChild(myBtn);
}

Rules:

• Gate v3 behavior on uiVersion so v2 is byte-for-byte unchanged.
• Never insertBefore the legacy span.text-gray-700 separator or button:last-child — they don't exist in the v3 transport. Append instead.
• Guard idempotency against the actual container (controls.contains(myBtn)), not a hard-coded #player-controls — otherwise re-injection logic breaks in v3.
• Dropdowns/panels your control opens: position them via the trigger's getBoundingClientRect() (portal to document.body or #player), not relative to #player-controls — the trigger now lives in the rail popover.
• Overlays/HUDs/canvases you attach to #player keep working; just keep their z-index under the chrome layers: transport/HUD z-20, rail z-30, popovers z-40.

Pedalboard metadata (icon, description, category)

The v3 Plugins page renders each plugin as a guitar pedal grouped onto category pedalboards. To make your pedal look good, declare three optional, additive manifest fields (all surfaced in /api/plugins):

{
  "id": "my_plugin",
  "name": "My Plugin",
  "description": "One short sentence shown under the pedal name.",
  "category": "audio",
  "icon": "assets/thumb.png"
}

• description — one short sentence (clamped to ~2 lines on the pedal).
• category — which board the pedal sits on. Suggested: audio | creation | practice | game | tools. Unknown/absent → a curated default then "other".
• icon — assets-relative thumbnail (~square, ~256×256 PNG/SVG), served via the existing sandboxed /api/plugins/<id>/assets/... route (same containment rule as styles). Shortcut: if you omit icon but ship assets/thumb.png, the loader auto-detects it — no manifest edit needed. Plugins with no thumbnail get a default pedal graphic.

All three are backward-compatible: omit them and the plugin still loads and shows a default pedal.

The compatibility shim (don't rely on it)

So un-updated plugins still function, the host runs a MutationObserver that re-homes any non-native #player-controls child into the slot. It's a safety net — but it breaks plugins that guard re-injection with #player-controls.contains(myBtn) (once the host moves the node out, the check goes false and the plugin re-injects every song). Mount into the slot yourself (the pattern above) to be correct; treat the shim as a fallback only.

Styling

v3 uses fb-* design tokens (fb-card, fb-text, fb-textDim, fb-primary, fb-border); v2 uses dark-* / accent. Legacy classes still render acceptably in v3's dark theme, so a plugin that only uses core-guaranteed utilities is functional in both. For polish, ship your own stylesheet via the styles capability (plugin-styles.md) declaring the tokens you use — but the host slot already provides a styled container, so simple controls need nothing special.

Enabling / disabling plugins (Pedalboard footswitch)

The v3 Pedalboard Plugins page renders each plugin as a guitar pedal whose "footswitch" turns the plugin on or off. The backend contract:

• enabled field on every /api/plugins entry — a boolean, default true. Absent (older entries, stubbed test rows) is treated as enabled. The frontend hides the nav and shows the footswitch unlit when enabled is false.
• POST /api/plugins/{plugin_id}/enabled — body {"enabled": <bool>}, returns {"id": "<id>", "enabled": <bool>}.
  • 400 if the body is missing/invalid or enabled isn't a real boolean (0/1/strings are rejected).
  • 400 if you try to disable an always-on plugin — capability_inspector and any app_tour_* may never be disabled (disabling would brick the app or the capability-graph review surface). Bundled plugins are otherwise disable-able.
  • 404 for an unknown plugin id (not loaded and not pending).

Persistence

The choice is persisted under CONFIG_DIR/plugin_state.json as {"<plugin_id>": {"enabled": false}, ...}. Only non-default (enabled:false) entries are stored — re-enabling drops the key entirely, so the file stays small and "absent ⇒ enabled" is the invariant. A missing or corrupt state file is tolerated (logged, falls back to {}) and never crashes startup.

Restart semantics

• Toggling persists immediately and flips the in-memory enabled flag, so the very next /api/plugins (and thus the nav, the Pedalboard, and the capability pipeline) reflects the change at once — no restart needed for the UI to update.
• A plugin disabled at runtime keeps its already-mounted routes/screen until the next restart; full hot-unload is out of scope. The frontend treats enabled:false as "off" regardless.
• At startup, the loader skips disabled plugins entirely — it does not install requirements, run routes.setup(), or register their screen, nav, or capabilities. They still appear in /api/plugins as a disabled entry (status: "disabled", enabled: false) so the UI can show an "off" pedal you can switch back on. Re-enabling a plugin that was skipped at startup updates the flag immediately but the plugin only actually mounts on the next restart.

Capability pipeline

A disabled plugin is excluded from the capability pipeline: its capabilities, standards, capability_validation_warnings, capability_unsupported_versions, and compatibility_shims are emptied in the /api/plugins response whenever enabled is false (covering both startup-skipped and runtime-toggled-off plugins). Because the browser capability registry registers any entry that carries a capability declaration regardless of status, suppressing the metadata here is what actually keeps a disabled plugin out of the capability graph.

Checklist

• Backend / capabilities / library provider / nav + screen / visualization renderer — no change needed (they work in v3 as-is).
• If you inject a control into the player: detect v3 and mount into window.feedBack.ui.playerControlSlot(); drop the dead separator / button:last-child anchor; guard contains() against the actual container.
• Dropdowns positioned via getBoundingClientRect(), not #player-controls.
• #player overlays keep z-index ≤ the chrome layers (transport/HUD 20, rail 30, popovers 40).
• Verify at / — it and /v3 serve the same (and only) v3 shell.