fix(qt): wire the source registry to its stores — it never was

This is the regression report from the previous build, and the cause is
that stage 1 built three injection sockets and nothing ever plugged into
them. `set_creds`, `set_ephemeral` and `bind_user` had zero call sites
in the entire frontend.

It stayed invisible for two stages because nothing needed them:
`claim` is pure, and `PlexSource::tracks`/`meta` read plex_cache.db
through qbz-plex's own global. The first consumers that DO need them are
playback and artwork — stages 3 and 4 — so routing those onto the seam
turned a latent gap into a live break:

- every Plex row: "plex: not configured (no Plex credentials
  configured)", so Plex playback died and every Plex cover in the Local
  Library grid resolved to ArtRef::Unavailable and vanished;
- every LOCAL row: an unbound DbPool refuses all reads, so LocalSource
  found no track and local playback died too;
- ephemeral rows had no session store to resolve against.

Wired now, each to the ONE authority that already existed: PlexCreds
over local_plex's settings store (read per call, never cached, so a
connect/disconnect mid-session is picked up), EphemeralTracks over the
session store, bind_user as the first statement of
bind_per_user_stores, teardown on logout, and the unbound-window
fallback so pre-login reads resolve the way local_state::with_db already
resolves them.

Also wired: the album identity mode. The grouping IS the query, so a
metadata-mode user's album play would have resolved a different track
list than the grid rendered.

`report_wiring` logs one line at bind time asking each socket a question
only a wired one can answer. The failure this fixes is silent by
construction — an unbound pool and a disabled Plex look identical to a
user with no local tracks and Plex switched off — and it stayed hidden
because the tests are pure-function tests and the structural gate only
proves the OLD path is gone, never that the new one is connected.

Verified against the running binary, not the test suite:
  source registry bound: local_tracks=617 plex=connected
  ephemeral_store=yes

qbz-qt 423/423, qbz-source 59/59.

cc

crates/qbz-qt/src/auth_qt.rs

@@ -208,6 +208,14 @@ where
 /// logs on failure, never blocks shell entry) — one entry point, so the caller
 /// cannot bind the uid and forget the schema.
 async fn bind_per_user_stores(dir: &std::path::Path, user_id: u64) {
+    // THE SOURCE REGISTRY FIRST, before any other store. `myqbz_qt::
+    // init_for_user` below runs the mixtape migrations through
+    // `library_db_qt::with_db(true, …)`, and against an unbound pool a fresh
+    // account can never create a collection. It is also what makes local and
+    // Plex playback work at all: an unbound `DbPool` refuses every read, and
+    // `PlexSource` with no credentials answers `NotConfigured` — which is
+    // exactly what shipped for one build when this line was missing.
+    crate::source_wiring::bind_user(dir, user_id);
     // MyQBZ: branding (label + icon, read by the sidebar/nav flyout on frame
     // 1) and the grids + mixtape schema.
     crate::myqbz_prefs_qt::init_for_user(dir);
@@ -459,6 +467,11 @@ where
     crate::myqbz_builder_qt::teardown();
     crate::artist_blacklist::teardown();
     crate::reco_dismiss_qt::teardown();
+    // Every source's per-user handle and cache: the pooled `library.db`
+    // handles, the Plex art memo, the ephemeral session store. Without this
+    // the next account inherits the previous one's handles out of a `'static`
+    // registry.
+    crate::source_wiring::teardown();
     crate::offline_fwd::teardown();
     // The offline download cache (index.db/library connections + the cached
     // id set) — torn down so the next account never reads this one's rows.

crates/qbz-qt/src/local_ephemeral.rs

@@ -95,6 +95,14 @@ fn album_key_of(t: &LocalTrack) -> String {
 }
 
 /// The tracks of one album block, in scan order.
+///
+/// `pub(crate)` under a second name for `source_wiring::EphemeralGlue`: the
+/// seam's `LocalSource` resolves an ephemeral album through this store rather
+/// than through `library.db`, and it needs the same scan order the pane shows.
+pub(crate) fn album_tracks_for(group_key: &str) -> Vec<LocalTrack> {
+    album_tracks(group_key)
+}
+
 fn album_tracks(group_key: &str) -> Vec<LocalTrack> {
     STATE
         .tracks_snapshot()

crates/qbz-qt/src/local_state.rs

@@ -279,6 +279,11 @@ pub fn set_album_mode(mode: &str) {
     let mode = if mode == "metadata" { "metadata" } else { "folder" };
     state(|s| s.album_mode = mode.to_string());
     update_prefs(|p| p.albums_id_mode = mode.to_string());
+    // The grouping IS the query: `LocalSource` resolves an album's tracks
+    // through `get_album_tracks_metadata` or `get_album_tracks` depending on
+    // it. Leaving the source on its default would make album PLAYBACK use a
+    // different track list than the grid just rendered.
+    crate::source_wiring::sync_album_group_mode();
 }
 
 pub fn album_mode() -> String {

crates/qbz-qt/src/main.rs

@@ -125,6 +125,9 @@ mod atmosphere_qt;
 // `play_audible` that each matched on `track.source` by hand.
 mod audible_qt;
 mod bridge;
+// The registry's injections: Plex credentials, the ephemeral store, the user
+// binding and the album-identity mode. See its header.
+mod source_wiring;
 mod custom_theme_qt;
 mod diagnostics_qt;
 mod discover_config_qt;
@@ -509,6 +512,11 @@ pub(crate) fn on_boot() {
             guard.as_ref().cloned()
         })
     }));
+    // ...and its INJECTIONS immediately after. The registry is built lazily by
+    // whoever touches it first, so publishing these here — before any view can
+    // resolve a row — is what keeps a Plex cover or a local play from asking an
+    // unwired source (see `source_wiring`'s header for what that looked like).
+    source_wiring::install();
 
     // Offline guardrails FIRST (before the login screen can show): engine +
     // connectivity actor, then the live status forwarder. Both need the

crates/qbz-qt/src/source_wiring.rs

@@ -0,0 +1,191 @@
+//! Wiring the `qbz-source` registry to this frontend's stores.
+//!
+//! # Why this file exists, and what it cost not to have it
+//!
+//! `qbz-source` deliberately does not link `qbz-app` / `qbz-core` / `qbz-player`
+//! (design 02 §8), so it cannot open the Plex settings store, cannot reach the
+//! ephemeral session store, and does not know which user's `library.db` to
+//! read. All three are INJECTED by the frontend. Stage 1 built the sockets and
+//! nothing ever plugged into them.
+//!
+//! That was invisible for two stages. `SourceRegistry::claim` is pure, and
+//! `PlexSource::tracks` / `meta` read `plex_cache.db` through `qbz-plex`'s own
+//! global — neither needs a credential or a bound pool. The first consumers
+//! that DO need them are playback and artwork, i.e. stages 3 and 4, and the
+//! moment those landed the seam started answering:
+//!
+//! ```text
+//! ERROR local play: track 1099511674716 not playable: plex: not configured
+//! ```
+//!
+//! for every Plex row, nothing at all for every local row (an unbound
+//! [`DbPool`] refuses reads), and `ArtRef::Unavailable` for every Plex cover —
+//! which is why the Local Library grid lost its Plex artwork. The unit tests
+//! could not see any of it: they exercise pure ladders (`rating_key`,
+//! `artwork_token`, `claim`), and there is no bound user in a test binary.
+//!
+//! **The lesson, recorded because it is the expensive one:** a structural gate
+//! ("the old code is gone") and a green test suite prove that the OLD path was
+//! removed, never that the NEW path is connected. A seam has to be exercised
+//! against a bound user before anything is routed onto it.
+//!
+//! # What is injected
+//!
+//! | socket | source | this frontend's authority |
+//! |---|---|---|
+//! | [`PlexCreds`] | `PlexSource` | `local_plex::is_enabled` / `settings` |
+//! | [`EphemeralTracks`] | `LocalSource` | `local_ephemeral`'s session store |
+//! | user dir | every source, via `bind_user` | `auth_qt::bind_per_user_stores` |
+//! | album group mode | `LocalSource` | `local_state::group_mode` (a persisted UI pref) |
+//!
+//! Each one has exactly ONE authority, and it is the one that already existed:
+//! opening a second copy of the Plex settings DB or a second ephemeral store
+//! would be a second source of truth, which is the thing the seam exists to
+//! remove.
+
+use std::sync::Arc;
+
+use qbz_library::LocalTrack;
+
+/// `PlexSource`'s view of the credentials store this frontend already owns.
+struct PlexCredsGlue;
+
+impl qbz_source::PlexCreds for PlexCredsGlue {
+    fn is_enabled(&self) -> bool {
+        crate::local_plex::is_enabled()
+    }
+
+    fn server(&self) -> Option<(String, String)> {
+        // Checked exactly as `local_playback`'s old Plex arm checked it: both
+        // halves non-empty, or Plex is not usable right now.
+        let cfg = crate::local_plex::settings();
+        if cfg.base_url.is_empty() || cfg.token.is_empty() {
+            return None;
+        }
+        Some((cfg.base_url, cfg.token))
+    }
+}
+
+/// `LocalSource`'s view of the session-scoped ephemeral store.
+struct EphemeralGlue;
+
+impl qbz_source::EphemeralTracks for EphemeralGlue {
+    fn get_track(&self, id: i64) -> Option<LocalTrack> {
+        crate::local_ephemeral::get_track(id)
+    }
+
+    fn album_tracks(&self, group_key: &str) -> Vec<LocalTrack> {
+        crate::local_ephemeral::album_tracks_for(group_key)
+    }
+}
+
+/// Publish the process-lifetime injections: the Plex credentials lens, the
+/// ephemeral store, and the unbound-window fallback.
+///
+/// Called from `on_boot`, right after `init_registry`. None of these is
+/// per-user — the creds glue READS the active store on every call rather than
+/// caching it, so a Plex connect/disconnect mid-session is picked up with no
+/// re-publish (the same clone-then-drop discipline the Qobuz client lens uses,
+/// and for the same reason: a cached copy goes stale silently).
+pub(crate) fn install() {
+    let registry = qbz_source::registry();
+    registry.plex().set_creds(Some(Arc::new(PlexCredsGlue)));
+    registry.local().set_ephemeral(Some(Arc::new(EphemeralGlue)));
+    // Reads BEFORE a user is bound (splash, session restore) must resolve the
+    // way `local_state::with_db` already resolves them — through
+    // `load_last_user_id` — or the window between boot and
+    // `bind_per_user_stores` answers "no library" instead of the last user's
+    // rows. This mirrors today's behaviour rather than changing it.
+    registry
+        .local()
+        .set_unbound_fallback(Some(Box::new(crate::local_state::db_path)));
+    sync_album_group_mode();
+    log::info!("[qbz-qt] source registry: creds + ephemeral store published");
+}
+
+/// Push the persisted album-identity pref into `LocalSource`.
+///
+/// The grouping IS the query: in metadata mode an album's tracks come from
+/// `get_album_tracks_metadata`, in folder mode from `get_album_tracks`. The
+/// source defaults to Folder, so without this a metadata-mode user's album
+/// play resolves a DIFFERENT track list than the grid showed them.
+///
+/// Called at boot, on every user bind, and from `local_state::set_album_mode`
+/// when the user flips the toolbar.
+pub(crate) fn sync_album_group_mode() {
+    qbz_source::registry()
+        .local()
+        .set_album_group_mode(crate::local_state::group_mode());
+}
+
+/// Bind every source to the active user's data directory.
+///
+/// MUST be the FIRST statement of `auth_qt::bind_per_user_stores`:
+/// `myqbz_qt::init_for_user` runs the mixtape migrations through
+/// `library_db_qt::with_db(true, …)`, and against an unbound pool a fresh
+/// account can never create a collection.
+pub(crate) fn bind_user(dir: &std::path::Path, user_id: u64) {
+    qbz_source::registry().bind_user(user_id, dir);
+    sync_album_group_mode();
+    report_wiring();
+}
+
+/// ASK each socket a question only a wired one can answer, and log the answers.
+///
+/// This is not decoration. The failure it exists to catch is silent by
+/// construction: an unbound [`DbPool`] returns `None` from every read and an
+/// uncredentialed `PlexSource` returns `ArtRef::Unavailable`, so an unwired
+/// registry looks exactly like "this user has no local tracks and Plex is
+/// switched off" — right up until the first playback attempt, several screens
+/// later, blames a service that has nothing to do with the track. One line at
+/// bind time turns that into something greppable at the moment it happens.
+///
+/// Both probes are cheap: one indexed COUNT, and one pure string
+/// interpretation with no I/O at all.
+fn report_wiring() {
+    use qbz_source::{ArtRef, ArtSize, Source};
+
+    let registry = qbz_source::registry();
+    let tracks = registry
+        .local()
+        .with(|db| db.count_all_local_tracks())
+        .map(|n| n.to_string())
+        .unwrap_or_else(|| "UNBOUND".to_string());
+    // The exact call the Local Library grid makes for a Plex row. `Fetch`
+    // means credentials resolved; `Unavailable` is the "no Plex credentials
+    // configured" state that cost a release build.
+    let plex = match registry
+        .plex()
+        .artwork_token("/library/metadata/0/thumb/0", ArtSize::Card)
+    {
+        ArtRef::Fetch { .. } => "connected",
+        ArtRef::Unavailable(why) => why,
+        _ => "not recognised",
+    };
+    let ephemeral = if registry.local().has_ephemeral_store() {
+        "yes"
+    } else {
+        "NO"
+    };
+    log::info!(
+        "[qbz-qt] source registry bound: local_tracks={tracks} plex={plex} ephemeral_store={ephemeral}"
+    );
+}
+
+/// Drop every per-user handle and cache. Called from the logout path.
+///
+/// Overriding `teardown` is mandatory for any source holding per-user state —
+/// the default is a no-op, so a source that forgets it leaks the previous
+/// account's handle into a `'static` registry.
+pub(crate) fn teardown() {
+    qbz_source::registry().teardown();
+    // The creds lens and the ephemeral glue are process-lifetime and stateless
+    // (they read their authority on every call), so they are re-published
+    // rather than left cleared — `PlexSource::teardown` drops the handle.
+    let registry = qbz_source::registry();
+    registry.plex().set_creds(Some(Arc::new(PlexCredsGlue)));
+    registry.local().set_ephemeral(Some(Arc::new(EphemeralGlue)));
+    registry
+        .local()
+        .set_unbound_fallback(Some(Box::new(crate::local_state::db_path)));
+}