diff --git a/ARCHITECTURE.md b/ARCHITECTURE.md
index b0132fe..e602f52 100644
--- a/ARCHITECTURE.md
+++ b/ARCHITECTURE.md
@@ -139,7 +139,14 @@ volume, and repeat mode.
 Selecting, deleting, or creating a tab stops playback. Tracks are de-duplicated
 by normalized source path when they are appended. Every playlist mutation is
 written in one `keystore` transaction. `playlists-for-<username>` contains the
-ordered playlist GUIDs; each GUID key contains that playlist's name and tracks.
+ordered open playlist GUIDs; `saved-playlists-for-<username>` contains the saved
+library playlist GUIDs. Each GUID key contains one playlist's name and tracks.
+Both indexes are persisted atomically; a value is deleted only when neither
+index refers to it. Closing a saved tab retains its library entry.
+`restore-playlist-context` reuses the same in-memory object for a saved playlist
+and its open tab, so track edits and renaming update both views. Old stores
+without a saved index restore their original tabs without automatically saving
+them in the library.
 Loading validates every stored track independently against all configured
 library roots, so one playlist can safely combine multiple libraries.
 `language-for-<username>` stores the user's selected interface language in the
@@ -224,7 +231,7 @@ serves static assets from [`public/`](public/) and exposes these API endpoints:
 
 | Method | Route | Responsibility |
 | --- | --- | --- |
-| `GET` | `/api/state` | Return the complete current state; also refresh network-renderer information. |
+| `GET` | `/api/state` | Return current state, omitting unchanged tracks when `playlistVersion` matches; also refresh network-renderer information. |
 | `POST` | `/api/discover` | Start asynchronous discovery and return the current state. |
 | `POST` | `/api/command/:command` | Execute a command with its JSON request body and return the updated state. |
 | `GET` | `/api/preferences` | Return the current user's durable UI preferences. |
@@ -241,13 +248,32 @@ header. Command failures are returned as HTTP 400 JSON responses with an
 
 [`public/app.js`](public/app.js) implements a framework-free client. It:
 
-- fetches a full state snapshot once per second;
+- polls status once per second, receiving tracks only when the playlist version changes;
 - temporarily suppresses polling while a browser-initiated command is active;
 - immediately renders the state returned by successful commands;
 - renders library navigation, playlists, tabs, transport status, and output
   selection;
 - implements keyboard actions and playlist drag-and-drop in the browser.
 
+[`public/playlist-library.js`](public/playlist-library.js) renders the library's
+Folders/Playlists tabs and saved playlist summaries. `playlist-save` adds an
+open tab to the library by UUID. `playlist-open` reveals its own tab, reusing an
+already open tab, and `playlist-play` also starts playback. Neither action copies
+tracks into an unrelated tab. Only summary metadata is sent in `savedPlaylists`.
+
+[`public/player-state.js`](public/player-state.js) keeps the active track array
+in memory and queues state, command and discovery requests. Each request sends
+the last received `playlistVersion` as a query parameter. A matching response
+contains `tracks: null`; the client supplies its cached tracks to the renderers.
+Requests without a version still receive the full list. Queueing prevents
+responses from being applied out of order.
+
+The player caches track JSON, count, duration and an opaque version per tab.
+`save-current-tab!` invalidates this snapshot when the track list changes.
+Renaming a tab leaves its track snapshot intact. Versions are unique across
+tabs, users and server restarts. `renderPlaylist` uses the version to decide
+when to rebuild rows instead of comparing all track metadata on every poll.
+
 [`public/translate.js`](public/translate.js) follows the key-based translation
 model used by rktplayer. It supports Dutch, English, German, French, Spanish,
 Italian, Swedish, Norwegian, Finnish and Icelandic with English fallback.
@@ -314,9 +340,9 @@ sequenceDiagram
     participant D as DLNA renderer
 
     loop Browser state polling
-        B->>H: GET /api/state
+        B->>H: GET /api/state?playlistVersion=known-version
         H->>P: player-state->jsexpr
-        P-->>H: Full state snapshot
+        P-->>H: State and version; tracks only if changed
         H-->>B: JSON response
     end
 
@@ -429,8 +455,9 @@ The main extension points are:
 - **Per-user pipelines, shared outputs:** playlist and transport state are
   isolated by username. Distinct outputs run concurrently; selecting an
   occupied output explicitly stops its previous owner and transfers it.
-- **Full-state snapshots:** a small and predictable client protocol, at the cost
-  of repeatedly transferring all tracks and browser entries.
+- **Versioned playlists:** cached tracks are transferred only when the selected
+  playlist version changes. Other status fields, including browser entries,
+  remain part of each response.
 - **One-second polling:** robust and dependency-free, but introduces periodic
   traffic and up to one second of display latency.
 - **Lazy filesystem and backend initialization:** fast startup and low idle
diff --git a/README.md b/README.md
index b219121..855f751 100644
--- a/README.md
+++ b/README.md
@@ -100,13 +100,24 @@ betrouwbare next-ondersteuning krijgen na het natuurlijke trackeinde een
 servergestuurde fallback. Een expliciet stopcommando start nooit de volgende
 track.
 
+De bibliotheek links heeft de tabs **Mappen** en **Afspeellijsten**. Met
+**Afspeellijst opslaan** boven de huidige playlist geef je de tab een naam en
+bewaar je hem in de bibliotheek. **＋** bij een bewaarde playlist opent of
+selecteert zijn eigen tab; **▶** opent die tab en speelt de playlist af.
+Een playlist die al open is, krijgt geen tweede tab. De inhoud van andere
+tabs blijft behouden. Wijzigingen in een bewaarde playlist worden automatisch
+opgeslagen, ook wanneer je de tab hernoemt. Het kruisje sluit een bewaarde tab;
+de playlist blijft beschikbaar in de bibliotheek.
+
 Playlisttabs kunnen worden toegevoegd, geselecteerd, hernoemd door dubbel te
-klikken en verwijderd. Tracks kunnen worden afgespeeld, verwijderd en met
+klikken en gesloten. Tracks kunnen worden afgespeeld, verwijderd en met
 drag-and-drop verplaatst. Tabnamen, tabvolgorde en alle tracklijsten worden na
-iedere wijziging transactioneel opgeslagen. Een verwijderde
-tab verdwijnt daarbij ook uit de keystore. Voor iedere gebruiker bevat de key
-`playlists-for-<username>` de geordende lijst met playlist-GUIDs. Onder iedere
-GUID-key staan de naam en tracks van die playlist. Tracks uit verschillende
+iedere wijziging transactioneel opgeslagen. Alleen een gesloten tab die niet
+in de bibliotheek is bewaard, verdwijnt ook uit de keystore. Voor iedere gebruiker
+bevat `playlists-for-<username>` de geordende lijst met geopende playlist-GUIDs,
+en `saved-playlists-for-<username>` de bewaarde playlists. Onder iedere
+GUID-key staan de naam en tracks van die playlist. Bestaande tabs worden niet
+automatisch aan de bibliotheek toegevoegd. Tracks uit verschillende
 geconfigureerde libraries mogen in dezelfde playlist staan; ontbrekende of
 buiten de libraries gelegen bestanden worden bij het laden overgeslagen.
 Iedere aangemelde gebruiker heeft daarbij een eigen playlistverzameling. Als
@@ -242,6 +253,8 @@ geen TLS heeft.
 
 ```console
 raco test private/users.rkt private/library.rkt private/player.rkt \
-  private-player-agent/player-agent-config.rkt
+  private/server.rkt private-player-agent/player-agent-config.rkt
+node tests/player-state.test.mjs
+node tests/playlist-library.test.mjs
 raco setup --check-pkg-deps rkt-web-player
 ```
diff --git a/private/player.rkt b/private/player.rkt
index 051601c..7ecb1a3 100644
--- a/private/player.rkt
+++ b/private/player.rkt
@@ -50,11 +50,13 @@
   #:transparent)
 
 (struct playlist-tab
-  (id [name #:mutable] [tracks #:mutable])
+  (id [name #:mutable] [tracks #:mutable] [snapshot #:auto #:mutable])
+  #:auto-value #f
   #:transparent)
 
 (struct playlist-context
-  ([tabs #:mutable] [current-index #:mutable])
+  ([tabs #:mutable] [current-index #:mutable] [saved #:auto #:mutable])
+  #:auto-value '()
   #:transparent)
 
 (struct playback-session
@@ -260,36 +262,45 @@
   (list-ref (player-tabs value)
             (player-current-tab-index value)))
 
+;;; Invalidate the browser snapshot only when the immutable track list changes.
 (define (save-current-tab! value)
-  (set-playlist-tab-tracks!
-   (current-tab value)
-   (player-tracks value)))
+  (let ((tab (current-tab value))
+        (tracks (player-tracks value)))
+    (unless (eq? tracks (playlist-tab-tracks tab))
+      (set-playlist-tab-tracks! tab tracks)
+      (set-playlist-tab-snapshot! tab #f))))
 
 (define (normal-playlist-username username)
   (let ((value (and (string? username)
                     (string-downcase (string-trim username)))))
     (if (and value (not (string=? value ""))) value "anonymous")))
 
-(define (new-playlist-context value username)
-  (define stored
-    (load-user-playlists (player-playlist-store value)
-                         username
-                         (player-libraries value)))
-  (playlist-context
-   (if (pair? stored)
-       (for/list ((tab (in-list stored)))
-         (playlist-tab (persisted-tab-id tab)
-                       (persisted-tab-name tab)
-                       (persisted-tab-tracks tab)))
-       (list (playlist-tab (uuid-string) "Default" '())))
-   0))
+;;; Restore open tabs and the library using the same object for a shared UUID.
+;;; Old stores have no saved index, so their tabs remain open and unsaved.
+(define (restore-playlist-context store username libraries)
+  (let* ((restore (λ (tab) (playlist-tab (persisted-tab-id tab)
+                                        (persisted-tab-name tab)
+                                        (persisted-tab-tracks tab))))
+         (opened (map restore (load-user-playlists store username libraries)))
+         (tabs (if (pair? opened) opened
+                   (list (playlist-tab (uuid-string) "Default" '()))))
+         (context (playlist-context tabs 0)))
+    (set-playlist-context-saved!
+     context
+     (map (λ (stored)
+            (or (findf (λ (tab) (string=? (playlist-tab-id tab) (persisted-tab-id stored)))
+                       tabs)
+                (restore stored)))
+          (load-user-playlists store username libraries #:saved? #t)))
+    context))
 
 (define (playlist-context-for! value username)
   (define normalized (normal-playlist-username username))
   (hash-ref!
    (player-playlist-contexts value)
    normalized
-   (λ () (new-playlist-context value normalized))))
+   (λ () (restore-playlist-context (player-playlist-store value)
+                                   normalized (player-libraries value)))))
 
 (define (context-tracks context)
   (playlist-tab-tracks
@@ -361,7 +372,12 @@
    (for/list ((tab (in-list (player-tabs value))))
      (persisted-tab (playlist-tab-id tab)
                     (playlist-tab-name tab)
-                    (playlist-tab-tracks tab)))))
+                    (playlist-tab-tracks tab)))
+   #:saved
+   (map (λ (tab) (persisted-tab (playlist-tab-id tab)
+                                (playlist-tab-name tab)
+                                (playlist-tab-tracks tab)))
+        (playlist-context-saved context))))
 
 (define (normalize-state state)
   (cond
@@ -927,25 +943,28 @@
         trimmed)
        (persist-playlists! value)))))
 
+;;; Close a tab, retaining saved playlists in the user's library.
 (define (delete-tab! value session index)
-  (when (= (length (player-tabs value)) 1)
-    (raise-arguments-error
-     'player-command!
-     "the last playlist tab cannot be removed"))
   (unless (and (exact-nonnegative-integer? index)
                (< index (length (player-tabs value))))
     (raise-arguments-error
      'player-command!
      "playlist tab does not exist"
      "index" index))
+  (let ((context (playlist-context-for! value (player-active-playlist-user value))))
+    (when (and (= (length (player-tabs value)) 1)
+               (not (memq (current-tab value) (playlist-context-saved context))))
+      (raise-arguments-error 'player-command! "the last playlist tab cannot be removed")))
   (stop-playback! value session)
   (with-state-lock
    value
    (λ ()
      (save-current-tab! value)
-     (let* ((tabs
+     (let* ((remaining
              (append (take (player-tabs value) index)
                      (drop (player-tabs value) (+ index 1))))
+            (tabs (if (pair? remaining) remaining
+                      (list (playlist-tab (uuid-string) "Default" '()))))
             (new-index
              (min (player-current-tab-index value)
                   (- (length tabs) 1))))
@@ -958,6 +977,44 @@
        (set-playback-session-current-index! session #f)
        (persist-playlists! value)))))
 
+;;; Save an open tab in the library once; subsequent tab edits share its identity.
+(define (save-playlist! value id name)
+  (let* ((context (playlist-context-for! value (player-active-playlist-user value)))
+         (tab (findf (λ (tab) (equal? (playlist-tab-id tab) id)) (player-tabs value)))
+         (trimmed (string-trim name)))
+    (unless tab
+      (raise-arguments-error 'player-command! "playlist tab does not exist" "id" id))
+    (when (string=? trimmed "")
+      (raise-arguments-error 'player-command! "playlist name cannot be empty"))
+    (with-state-lock
+     value
+     (λ ()
+       (save-current-tab! value)
+       (set-playlist-tab-name! tab trimmed)
+       (unless (memq tab (playlist-context-saved context))
+         (set-playlist-context-saved! context
+                                      (append (playlist-context-saved context) (list tab))))
+       (persist-playlists! value)))))
+
+;;; Reveal a saved playlist as its own tab, reusing an existing tab by identity.
+;;; Opening never copies tracks into another tab; play? starts this playlist.
+(define (open-playlist! value session id play?)
+  (let* ((context (playlist-context-for! value (player-active-playlist-user value)))
+         (tab (findf (λ (tab) (equal? (playlist-tab-id tab) id))
+                     (playlist-context-saved context))))
+    (unless tab
+      (raise-arguments-error 'player-command! "saved playlist does not exist" "id" id))
+    (let ((index (index-of (player-tabs value) tab eq?)))
+      (unless index
+        (with-state-lock
+         value
+         (λ ()
+           (save-current-tab! value)
+           (set-player-tabs! value (append (player-tabs value) (list tab))))))
+      (select-tab! value session (or index (- (length (player-tabs value)) 1)))))
+  (when (and play? (pair? (player-tracks value)))
+    (play-index! value session 0)))
+
 (define (track->jsexpr item index)
   (hasheq 'index index
           'title (track-title item)
@@ -984,14 +1041,29 @@
           'name (browser-entry-name entry)
           'kind (symbol->string (browser-entry-kind entry))))
 
-;;; Include the sum of known track durations in each tab's browser summary.
-(define (tab->jsexpr tab index)
-  (hasheq 'index index
-          'id (playlist-tab-id tab)
-          'name (playlist-tab-name tab)
-          'count (length (playlist-tab-tracks tab))
-          'duration (apply + (map (λ (item) (or (track-duration item) 0))
-                                 (playlist-tab-tracks tab)))))
+;;; Cache serialized tracks and their summary until save-current-tab! invalidates
+;;; them. A fresh opaque version also prevents cache reuse across server restarts.
+(define (tab-snapshot tab)
+  (or (playlist-tab-snapshot tab)
+      (let* ((tracks (playlist-tab-tracks tab))
+             (snapshot
+              (hasheq 'version (uuid-string)
+                      'count (length tracks)
+                      'duration (apply + (map (λ (item) (or (track-duration item) 0))
+                                             tracks))
+                      'tracks (map track->jsexpr tracks (range (length tracks))))))
+        (set-playlist-tab-snapshot! tab snapshot)
+        snapshot)))
+
+;;; Return a small tab summary without rebuilding or transferring its tracks.
+(define (tab->jsexpr tab index [saved? #f])
+  (let ((snapshot (tab-snapshot tab)))
+    (hasheq 'index index
+            'id (playlist-tab-id tab)
+            'name (playlist-tab-name tab)
+            'saved saved?
+            'count (hash-ref snapshot 'count)
+            'duration (hash-ref snapshot 'duration))))
 
 (define (normal-device-id device)
   (let ((id (upnp-device-udn device)))
@@ -1121,7 +1193,12 @@
        (rename-tab! value index
                     (or (json-string data 'name #f) "")))
       ((string=? command "tab-delete")
-       (delete-tab! value session index)))))
+       (delete-tab! value session index))
+      ((string=? command "playlist-save")
+       (save-playlist! value (json-string data 'id #f) (or (json-string data 'name #f) "")))
+      ((member command '("playlist-open" "playlist-play"))
+       (open-playlist! value session (json-string data 'id #f)
+                       (string=? command "playlist-play"))))))
 
 (define (perform-command! value session command data)
   (cond
@@ -1131,7 +1208,7 @@
     ((member command '("track-remove" "track-move"
                        "playlist-clear" "tab-add"
                        "tab-select" "tab-rename"
-                       "tab-delete"))
+                       "tab-delete" "playlist-save" "playlist-open" "playlist-play"))
      (perform-playlist-command! value session command data))
     ((string=? command "play")
      (play-index!
@@ -1278,23 +1355,15 @@
          app-id))
       (string-downcase app-id)))
   (define store (open-playlist-store playlist-keystore))
-  (define stored-tabs
-    (load-user-playlists store "anonymous" libraries))
   (let* ((library (and (pair? libraries) (car libraries)))
          (browser-entries
           (if library
               (browse-library library '())
               '()))
-         (tabs
-          (if (pair? stored-tabs)
-              (for/list ((tab (in-list stored-tabs)))
-                (playlist-tab (persisted-tab-id tab)
-                              (persisted-tab-name tab)
-                              (persisted-tab-tracks tab)))
-              (list (playlist-tab (uuid-string) "Default" '()))))
+         (initial-context (restore-playlist-context store "anonymous" libraries))
+         (tabs (playlist-context-tabs initial-context))
          (selected-index 0)
-         (contexts (make-hash))
-         (initial-context (playlist-context tabs selected-index)))
+         (contexts (make-hash)))
     (hash-set! contexts "anonymous" initial-context)
     (define value
       (player libraries
@@ -1324,12 +1393,17 @@
     value))
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-; goal   : Return the complete browser-visible player state.
+; goal   : Return browser-visible state, optionally reusing known playlist tracks.
 ; pre    : Value was created with make-player.
 ; post   : Cached DLNA playback information has been incorporated.
-; result : A JSON-compatible hash.
+; result : A JSON-compatible hash with playlistVersion. tracks is null when
+;          playlist-version matches; otherwise it contains the complete list.
+; internals: tab-snapshot caches track JSON, duration and a unique version until
+;            a playlist mutation invalidates it. Comparison and state assembly
+;            share the player locks, so the version always matches the tracks.
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-(define (player-state->jsexpr value #:username [username "anonymous"])
+(define (player-state->jsexpr value #:username [username "anonymous"]
+                              #:playlist-version [playlist-version #f])
   (define normalized (normal-playlist-username username))
   (call-with-semaphore
    (player-command-lock value)
@@ -1340,7 +1414,7 @@
     (define context (playlist-context-for! value normalized))
     (define tabs (playlist-context-tabs context))
     (define tab-index (playlist-context-current-index context))
-    (define tracks (playlist-tab-tracks (list-ref tabs tab-index)))
+    (define snapshot (tab-snapshot (list-ref tabs tab-index)))
     (with-state-lock
      value
      (λ ()
@@ -1366,12 +1440,17 @@
         'tabs
         (for/list ((tab (in-list tabs))
                    (index (in-naturals)))
-          (tab->jsexpr tab index))
+          (tab->jsexpr tab index (and (memq tab (playlist-context-saved context)) #t)))
+        'savedPlaylists
+        (map (λ (tab index) (tab->jsexpr tab index #t))
+             (playlist-context-saved context)
+             (range (length (playlist-context-saved context))))
         'currentTab tab-index
+        'playlistVersion (hash-ref snapshot 'version)
         'tracks
-        (for/list ((item (in-list tracks))
-                   (index (in-naturals)))
-          (track->jsexpr item index))
+        (if (equal? playlist-version (hash-ref snapshot 'version))
+            'null
+            (hash-ref snapshot 'tracks))
         'renderers (map renderer->jsexpr
                         (player-renderers value))
         'rendererId (or (playback-session-selected-id session) 'null)
@@ -1401,14 +1480,16 @@
 ; goal   : Execute one browser player command.
 ; pre    : Command is a string and data is a JSON object hash.
 ; post   : The command has completed or a concrete exception is raised.
-; result : The updated JSON-compatible player state.
+; result : The updated JSON-compatible player state. With a matching
+;          playlist-version, tracks is null as in player-state->jsexpr.
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 (define playlist-context-commands
   '("item-play" "item-add" "track-remove" "track-move"
     "playlist-clear" "tab-add" "tab-select" "tab-rename"
-    "tab-delete" "play"))
+    "tab-delete" "playlist-save" "playlist-open" "playlist-play" "play"))
 
-(define (player-command! value command data #:username [username "anonymous"])
+(define (player-command! value command data #:username [username "anonymous"]
+                         #:playlist-version [playlist-version #f])
   (define normalized (normal-playlist-username username))
   (call-with-semaphore
    (player-command-lock value)
@@ -1426,7 +1507,8 @@
        (when (member command playlist-context-commands)
          (activate-playlist-user! value normalized session))
        (perform-command! value session command data))))
-  (player-state->jsexpr value #:username normalized))
+  (player-state->jsexpr value #:username normalized
+                        #:playlist-version playlist-version))
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ; goal   : Discover UPnP renderers and logical Sonos groups asynchronously.
@@ -1739,16 +1821,176 @@
         (λ ()
           (set-player-closed?! value #t)))))))
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Tests for module player.rkt
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
 (module+ test
-  (require rackunit
+  (require json
+           rackunit
            racket/file)
 
+  (test-case "playlist versions cache 1000 tracks and follow user mutations"
+    (let ((value (make-player '() #:playlist-keystore #f #:local-output? #f)))
+      (dynamic-wind
+        void
+        (λ ()
+          (let* ((session (playback-session-for! value "anonymous"))
+                 (tracks
+                  (build-list
+                   1000
+                   (λ (index)
+                     (track (build-path (find-system-path 'temp-dir)
+                                        (format "playlist-test-~a.flac" index))
+                            (format "Track ~a" index) "Artist" "Album" 60 "audio/flac")))))
+            (replace-tracks! value session tracks)
+            (let* ((full (player-state->jsexpr value))
+                   (version (hash-ref full 'playlistVersion))
+                   (compact (player-state->jsexpr value #:playlist-version version))
+                   (repeated (player-state->jsexpr value)))
+              (check-equal? (length (hash-ref full 'tracks)) 1000)
+              (check-equal? (hash-ref (car (hash-ref full 'tabs)) 'duration) 60000)
+              (check-eq? (hash-ref compact 'tracks) 'null)
+              (check-eq? (hash-ref full 'tracks) (hash-ref repeated 'tracks))
+              (check-true (< (bytes-length (jsexpr->bytes compact))
+                             (/ (bytes-length (jsexpr->bytes full)) 20)))
+              (check-eq?
+               (hash-ref (player-command! value "repeat" (hasheq 'mode "all")
+                                          #:playlist-version version) 'tracks)
+               'null)
+              (check-eq?
+               (hash-ref (player-command! value "tab-rename" (hasheq 'index 0 'name "Music")
+                                          #:playlist-version version) 'tracks)
+               'null)
+              (let* ((moved (player-command! value "track-move" (hasheq 'from 0 'to 1)
+                                             #:playlist-version version))
+                     (moved-version (hash-ref moved 'playlistVersion))
+                     (other-browser (player-state->jsexpr value #:playlist-version version)))
+                (check-not-equal? moved-version version)
+                (check-equal? (hash-ref (car (hash-ref moved 'tracks)) 'title) "Track 1")
+                (check-equal? (hash-ref other-browser 'playlistVersion) moved-version)
+                (check-equal? (hash-ref other-browser 'tracks) (hash-ref moved 'tracks))
+                (let* ((removed (player-command! value "track-remove" (hasheq 'index 0)
+                                                 #:playlist-version moved-version))
+                       (removed-version (hash-ref removed 'playlistVersion))
+                       (new-tab (player-command! value "tab-add" (hasheq)
+                                                 #:playlist-version removed-version))
+                       (selected (player-command! value "tab-select" (hasheq 'index 0)
+                                                  #:playlist-version (hash-ref new-tab 'playlistVersion))))
+                  (check-equal? (length (hash-ref removed 'tracks)) 999)
+                  (check-not-equal? removed-version moved-version)
+                  (check-equal? (hash-ref new-tab 'tracks) '())
+                  (check-equal? (hash-ref selected 'playlistVersion) removed-version)
+                  (check-equal? (length (hash-ref selected 'tracks)) 999)
+                  (let ((other-user (player-state->jsexpr value #:username "another-user"
+                                                          #:playlist-version removed-version))
+                        (cleared (player-command! value "playlist-clear" (hasheq)
+                                                   #:playlist-version removed-version)))
+                    (check-equal? (hash-ref other-user 'tracks) '())
+                    (check-not-equal? (hash-ref other-user 'playlistVersion) removed-version)
+                    (check-equal? (hash-ref cleared 'tracks) '())
+                    (check-not-equal? (hash-ref cleared 'playlistVersion) removed-version)
+                    (append-tracks! value session (list (car tracks)))
+                    (let* ((added (player-state->jsexpr value
+                                                      #:playlist-version (hash-ref cleared 'playlistVersion)))
+                           (added-version (hash-ref added 'playlistVersion)))
+                      (check-equal? (length (hash-ref added 'tracks)) 1)
+                      (check-equal? (hash-ref (car (hash-ref added 'tabs)) 'duration) 60)
+                      (append-tracks! value session (list (car tracks)))
+                      (check-eq? (hash-ref (player-state->jsexpr value #:playlist-version added-version)
+                                           'tracks)
+                                 'null))))))))
+        (λ () (player-close! value)))))
+
   (check-equal? (error->jsexpr #f) 'null)
   (check-equal?
    (error->jsexpr 'dlna-renderer-unreachable)
    "dlna-renderer-unreachable")
   (check-equal? (error->jsexpr "technical error") "technical error")
 
+  (test-case "saved playlists reopen as shared tabs and survive closing and restart"
+    (let ((root (make-temporary-file "saved-playlists-~a" 'directory)))
+      (dynamic-wind
+        (λ ()
+          (call-with-output-file (build-path root "one.flac") void)
+          (call-with-output-file (build-path root "two.flac") void))
+        (λ ()
+          (let* ((libraries (make-music-libraries (list root)))
+                 (store-file (build-path root "playlists.keystore"))
+                 (agent-id (make-string 64 #\b))
+                 (value (make-player libraries #:playlist-keystore store-file
+                                     #:local-output? #f #:allowed-agent-ids (list agent-id)))
+                 (session (playback-session-for! value "anonymous"))
+                 (first (track (build-path root "one.flac") "One" "Artist" "Album" 60 "audio/flac"))
+                 (second (track (build-path root "two.flac") "Two" "Artist" "Album" 120 "audio/flac")))
+            (dynamic-wind
+              void
+              (λ ()
+                (replace-tracks! value session (list first second))
+                (let* ((initial (player-state->jsexpr value))
+                       (id (hash-ref (car (hash-ref initial 'tabs)) 'id))
+                       (version (hash-ref initial 'playlistVersion))
+                       (saved (player-command! value "playlist-save" (hasheq 'id id 'name "Favorites")
+                                                #:playlist-version version)))
+                  (check-equal? (hash-ref initial 'savedPlaylists) '())
+                  (check-eq? (hash-ref saved 'tracks) 'null)
+                  (check-true (hash-ref (car (hash-ref saved 'tabs)) 'saved))
+                  (check-equal? (hash-ref (car (hash-ref saved 'savedPlaylists)) 'id) id)
+                  (check-equal? (hash-ref (car (hash-ref saved 'savedPlaylists)) 'duration) 180)
+                  (check-equal?
+                   (length (hash-ref (player-command! value "playlist-save" (hasheq 'id id 'name "Favorites"))
+                                     'savedPlaylists)) 1)
+                  (player-command! value "tab-add" (hasheq))
+                  (replace-tracks! value session (list first))
+                  (let ((opened (player-command! value "playlist-open" (hasheq 'id id))))
+                    (check-equal? (length (hash-ref opened 'tabs)) 2)
+                    (check-equal? (hash-ref opened 'currentTab) 0)
+                    (check-equal? (map track-title (playlist-tab-tracks (list-ref (player-tabs value) 1))) '("One"))
+                    (check-equal? (length (hash-ref (player-command! value "playlist-open" (hasheq 'id id)) 'tabs)) 2))
+                  (player-command! value "tab-rename" (hasheq 'index 0 'name "Renamed"))
+                  (let ((edited (player-command! value "track-remove" (hasheq 'index 0))))
+                    (check-equal? (hash-ref (car (hash-ref edited 'savedPlaylists)) 'name) "Renamed")
+                    (check-equal? (hash-ref (car (hash-ref edited 'savedPlaylists)) 'count) 1)
+                    (check-equal? (hash-ref (car (hash-ref edited 'savedPlaylists)) 'duration) 120))
+                  (player-command! value "tab-delete" (hasheq 'index 0))
+                  (let ((opened (player-command! value "playlist-open" (hasheq 'id id))))
+                    (check-equal? (length (hash-ref opened 'tabs)) 2)
+                    (check-equal? (hash-ref opened 'currentTab) 1)
+                    (check-equal? (map (λ (track) (hash-ref track 'title)) (hash-ref opened 'tracks)) '("Two")))
+                  (player-agent-register! value (hasheq 'appId agent-id 'name "Test agent"))
+                  (player-command! value "renderer" (hasheq 'id (agent-renderer-id agent-id)))
+                  (let ((playing (player-command! value "playlist-play" (hasheq 'id id))))
+                    (check-equal? (hash-ref playing 'currentIndex) 0)
+                    (check-equal? (length (hash-ref playing 'tabs)) 2)
+                    (check-equal?
+                     (hash-ref (hash-ref (player-agent-poll! value (hasheq 'appId agent-id)) 'command) 'action)
+                     "play"))
+                  (player-command! value "tab-delete" (hasheq 'index 1))
+                  (check-equal? (hash-ref (player-state->jsexpr value #:username "other") 'savedPlaylists) '())
+                  (check-exn exn:fail?
+                             (λ () (player-command! value "playlist-open" (hasheq 'id id) #:username "other")))
+                  (player-close! value)
+                  (let ((restored (make-player libraries #:playlist-keystore store-file #:local-output? #f)))
+                    (dynamic-wind
+                      void
+                      (λ ()
+                        (let ((state (player-state->jsexpr restored)))
+                          (check-equal? (length (hash-ref state 'tabs)) 1)
+                          (check-equal? (hash-ref (car (hash-ref state 'savedPlaylists)) 'id) id))
+                        (player-command! restored "playlist-open" (hasheq 'id id))
+                        (let ((renamed (player-command! restored "tab-rename" (hasheq 'index 1 'name "Restored"))))
+                          (check-equal? (hash-ref (car (hash-ref renamed 'savedPlaylists)) 'name) "Restored")
+                          (check-equal? (map (λ (track) (hash-ref track 'title)) (hash-ref renamed 'tracks)) '("Two")))
+                        (player-command! restored "tab-delete" (hasheq 'index 0))
+                        (let ((closed (player-command! restored "tab-delete" (hasheq 'index 0))))
+                          (check-equal? (length (hash-ref closed 'tabs)) 1)
+                          (check-false (hash-ref (car (hash-ref closed 'tabs)) 'saved))
+                          (check-equal? (hash-ref closed 'tracks) '())
+                          (check-equal? (hash-ref (car (hash-ref closed 'savedPlaylists)) 'id) id)))
+                      (λ () (player-close! restored))))))
+              (λ () (player-close! value)))))
+        (λ () (delete-directory/files root)))))
+
   (define root
     (make-temporary-file "rkt-web-player-~a" 'directory))
 
diff --git a/private/playlists.rkt b/private/playlists.rkt
index dafdecd..abd6365 100644
--- a/private/playlists.rkt
+++ b/private/playlists.rkt
@@ -30,9 +30,9 @@
 ;; Supporting functions
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
-;;; Produces the keystore key containing one user's ordered playlist ids.
-(define (user-playlists-key username)
-  (format "playlists-for-~a" username))
+;;; Keep open tabs and saved library playlists in separate ordered UUID indexes.
+(define (user-playlists-key username [saved? #f])
+  (format "~aplaylists-for-~a" (if saved? "saved-" "") username))
 
 ;;; Produces the keystore key containing one user's language preference.
 (define (user-language-key username)
@@ -135,7 +135,7 @@
   (void))
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-; goal   : Restore one user's ordered playlist tabs.
+; goal   : Restore one user's open tabs, or saved library playlists with saved?.
 ; pre    : Store is #f or open, username is normalized, and libraries are valid.
 ; post   : Store contents remain unchanged and unsafe track paths are omitted.
 ; result : Valid persisted-tab values in their saved order.
@@ -144,17 +144,16 @@
 ;            validates each referenced tab and delegates track safety checks to
 ;            datum->track.
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-(define/contract (load-user-playlists store username libraries)
-  (-> (or/c keystore? #f)
-      string?
-      (listof music-library?)
-      (listof persisted-tab?))
+(define/contract (load-user-playlists store username libraries #:saved? [saved? #f])
+  (->* ((or/c keystore? #f) string? (listof music-library?))
+       (#:saved? boolean?)
+       (listof persisted-tab?))
   (if (eq? store #f)
       '()
       (ks-with-lock
        store
        (λ ()
-         (let ((ids (ks-get store (user-playlists-key username) '())))
+         (let ((ids (ks-get store (user-playlists-key username saved?) '())))
            (if (list? ids)
                (filter-map
                 (λ (id)
@@ -163,29 +162,40 @@
                '()))))))
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-; goal   : Persist one user's complete ordered collection of playlist tabs.
+; goal   : Persist one user's open tabs and saved library playlists atomically.
 ; pre    : Store is #f or open, username is normalized, and tabs are valid.
-; post   : The UUID index and tab data match tabs; omitted old tabs are removed.
+; post   : Both UUID indexes match tabs/saved. Closing a saved tab retains its
+;          data; playlists absent from both indexes are removed.
 ; result : Void.
 ; internals: ks-with-lock prevents another operation from entering this update.
 ;            ks-transaction removes stale ids from user-playlists-key, stores
-;            every tab using track->datum, and atomically replaces the index.
+;            each distinct playlist using track->datum, and replaces both indexes.
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-(define/contract (save-user-playlists! store username tabs)
-  (-> (or/c keystore? #f) string? (listof persisted-tab?) void?)
+(define/contract (save-user-playlists! store username tabs #:saved [saved '()])
+  (->* ((or/c keystore? #f) string? (listof persisted-tab?))
+       (#:saved (listof persisted-tab?))
+       void?)
   (when store
     (ks-with-lock
      store
      (λ ()
        (let* ((index-key (user-playlists-key username))
-              (old-ids (ks-get store index-key '()))
+              (saved-key (user-playlists-key username #t))
+              (old-open (ks-get store index-key '()))
+              (old-saved (ks-get store saved-key '()))
+              (old-ids (append (if (list? old-open) old-open '())
+                               (if (list? old-saved) old-saved '())))
               (ids (map persisted-tab-id tabs))
+              (saved-ids (map persisted-tab-id saved))
+              (all-tabs (remove-duplicates (append tabs saved)
+                                           string=? #:key persisted-tab-id))
               (stale-ids
                (filter
                 (λ (id)
                   (and (string? id)
-                       (not (member id ids string=?))))
-                (if (list? old-ids) old-ids '()))))
+                       (not (member id ids string=?))
+                       (not (member id saved-ids string=?))))
+                (remove-duplicates old-ids))))
          (ks-transaction
           store
           (for-each (λ (id) (ks-drop! store id)) stale-ids)
@@ -197,8 +207,9 @@
               (hasheq 'name (persisted-tab-name tab)
                       'tracks (map track->datum
                                    (persisted-tab-tracks tab)))))
-           tabs)
-          (ks-set! store index-key ids))
+           all-tabs)
+          (ks-set! store index-key ids)
+          (ks-set! store saved-key saved-ids))
          (void)))))
   (void))
 
diff --git a/private/server.rkt b/private/server.rkt
index e07d23f..69821f2 100644
--- a/private/server.rkt
+++ b/private/server.rkt
@@ -101,12 +101,18 @@
 (define (request-username auth request)
   (or (auth-request-user auth request) "anonymous"))
 
-;;; Returns the player state belonging to the requesting user.
+;;; Read the opaque version of the playlist already held by this browser.
+(define (request-playlist-version request)
+  (let ((entry (assq 'playlistVersion (url-query (request-uri request)))))
+    (and entry (cdr entry))))
+
+;;; Returns user state, including tracks only when this browser needs them.
 (define (state-handler player auth request)
   (json-response
    (player-state->jsexpr
     player
-    #:username (request-username auth request))))
+    #:username (request-username auth request)
+    #:playlist-version (request-playlist-version request))))
 
 ;;; Starts renderer discovery and returns the updated player state.
 (define (discover-handler player auth request)
@@ -114,7 +120,8 @@
   (json-response
    (player-state->jsexpr
     player
-    #:username (request-username auth request))))
+    #:username (request-username auth request)
+    #:playlist-version (request-playlist-version request))))
 
 ;;; Applies one player command for the requesting user.
 (define (command-handler player auth request command)
@@ -125,7 +132,8 @@
       player
       command
       (request-jsexpr request)
-      #:username (request-username auth request)))))
+      #:username (request-username auth request)
+      #:playlist-version (request-playlist-version request)))))
 
 ;;; Returns the persisted interface preferences for the requesting user.
 (define (preferences-handler player auth request)
@@ -405,6 +413,31 @@
   (check-equal?
    (request-jsexpr (test-request #"POST" "/api/preferences"))
    (hasheq))
+  (test-case "HTTP state and commands accept the browser's playlist version"
+    (let* ((value (make-player '() #:playlist-keystore #f #:local-output? #f))
+           (auth (make-auth-manager '()))
+           (dispatch (make-dispatch value auth)))
+      (dynamic-wind
+        void
+        (λ ()
+          (let* ((full (response-jsexpr (dispatch (test-request #"GET" "/api/state"))))
+                 (version (hash-ref full 'playlistVersion))
+                 (compact
+                  (response-jsexpr
+                   (dispatch (test-request #"GET" (string-append "/api/state?playlistVersion=" version))))))
+            (check-equal? (hash-ref full 'tracks) '())
+            (check-eq? (hash-ref compact 'tracks) 'null)
+            (check-equal? (hash-ref compact 'playlistVersion) version)
+            (let ((renamed
+                   (response-jsexpr
+                    (dispatch
+                     (test-request #"POST"
+                                   (string-append "/api/command/tab-rename?playlistVersion=" version)
+                                   #:headers (list (header #"Content-Type" #"application/json"))
+                                   #:body #"{\"index\":0,\"name\":\"Music\"}")))))
+              (check-eq? (hash-ref renamed 'tracks) 'null)
+              (check-equal? (hash-ref (car (hash-ref renamed 'tabs)) 'name) "Music"))))
+        (λ () (player-close! value)))))
   (check-equal?
    (request-jsexpr
     (test-request #"POST"
diff --git a/public/app.js b/public/app.js
index 311dd9f..42c2e8a 100644
--- a/public/app.js
+++ b/public/app.js
@@ -1,7 +1,8 @@
 /*
  * Browser client for the web player.
  *
- * refresh and command obtain complete player-state snapshots from the server.
+ * PlayerStateClient merges status updates with the cached playlist; tracks are
+ * transferred only when their version changes. State requests share a queue.
  * render stores that snapshot and passes it to the selector, library, playlist,
  * and playback renderers. Collection renderers retain a DOM signature so the
  * one-second polling loop only rebuilds lists whose contents changed.
@@ -11,6 +12,9 @@
  * returned state has been rendered.
  */
 
+import { PlayerStateClient } from "./player-state.js";
+import { PlaylistLibrary } from "./playlist-library.js";
+
 ///////////////////////////////////////////////////////////////////////////////
 // Browser elements and state
 ///////////////////////////////////////////////////////////////////////////////
@@ -44,6 +48,7 @@ const elements = {
   tabAdd: document.querySelector("#tab-add"),
   count: document.querySelector("#track-count"),
   playlistClear: document.querySelector("#playlist-clear"),
+  playlistSave: document.querySelector("#playlist-save"),
   playlistEmpty: document.querySelector("#playlist-empty"),
   playlist: document.querySelector("#playlist"),
   bits: document.querySelector("#audio-bits"),
@@ -67,6 +72,9 @@ let state = null;
 let seekBusy = false;
 let draggedTrack = null;
 let commandBusy = false;
+let refreshBusy = false;
+const playerState = new PlayerStateClient(api);
+const playlistLibrary = new PlaylistLibrary(document.querySelector("#library-pane"), command, formatPlayingTime);
 
 // Represents an unsuccessful API response, including its HTTP status and code.
 class ApiError extends Error {
@@ -193,7 +201,7 @@ async function command(name, data = {}, pendingMessage = "") {
 
   commandBusy = true;
   try {
-    render(await api(`/api/command/${name}`, data));
+    render(await playerState.request(`/api/command/${name}`, data));
   } catch (error) {
     setStatus(errorMessage(error));
   } finally {
@@ -376,6 +384,14 @@ function renameTab(tab) {
   }
 }
 
+// Give this tab a library name while retaining its identity and current tracks.
+function savePlaylist() {
+  if (!state) return;
+  const tab = state.tabs[state.currentTab];
+  const name = window.prompt(t("playlistName"), tab.name === "Default" ? t("defaultPlaylist") : tab.name);
+  if (name !== null) command("playlist-save", { id: tab.id, name });
+}
+
 // Builds one playlist tab, including its count and optional delete control.
 function createTab(tab, canDelete) {
   const button = document.createElement("button");
@@ -396,11 +412,11 @@ function createTab(tab, canDelete) {
   button.addEventListener("click", () => command("tab-select", { index: tab.index }));
   button.addEventListener("dblclick", () => renameTab(tab));
 
-  if (canDelete) {
+  if (canDelete || tab.saved) {
     const remove = document.createElement("span");
     remove.className = "tab-delete";
     remove.textContent = "×";
-    remove.title = t("removePlaylist");
+    remove.title = t(tab.saved ? "closePlaylist" : "removePlaylist");
     remove.addEventListener("click", (event) => {
       event.stopPropagation();
       command("tab-delete", { index: tab.index });
@@ -414,7 +430,7 @@ function createTab(tab, canDelete) {
 // Rebuilds changed tabs and marks the server-selected tab as active.
 function renderTabs(nextState) {
   const signature = nextState.tabs
-    .map((tab) => `${tab.index}:${tab.name}:${tab.count}`)
+    .map((tab) => `${tab.index}:${tab.name}:${tab.count}:${tab.saved}`)
     .join("|");
   if (elements.tabs.dataset.signature !== signature) {
     const canDelete = nextState.tabs.length > 1;
@@ -510,17 +526,19 @@ function createPlaylistRow(track) {
 
 // Rebuilds changed tracks and updates the active row and playlist summary.
 function renderPlaylist(nextState) {
-  const signature = nextState.tracks
-    .map((track) => `${track.index}:${track.title}:${track.artist}:${track.album}:${track.duration}`)
-    .join("|");
+  const signature = nextState.playlistVersion;
   if (elements.playlist.dataset.signature !== signature) {
     const rows = nextState.tracks.map(createPlaylistRow);
     elements.playlist.replaceChildren(...rows);
     elements.playlist.dataset.signature = signature;
   }
 
-  for (const row of elements.playlist.children) {
-    row.classList.toggle("current", Number(row.dataset.index) === nextState.currentIndex);
+  const previousRow = elements.playlist.querySelector(".current");
+  const currentRow = Number.isInteger(nextState.currentIndex)
+    ? elements.playlist.children[nextState.currentIndex] : null;
+  if (previousRow !== currentRow) {
+    previousRow?.classList.remove("current");
+    currentRow?.classList.add("current");
   }
 
   elements.playlistEmpty.hidden = nextState.tracks.length > 0;
@@ -528,6 +546,8 @@ function renderPlaylist(nextState) {
   const tab = nextState.tabs[nextState.currentTab];
   elements.count.textContent = `${nextState.tracks.length} ${t(trackLabel)}, ${formatPlayingTime(tab.duration)}`;
   elements.playlistClear.disabled = nextState.tracks.length === 0;
+  elements.playlistSave.disabled = tab.saved;
+  elements.playlistSave.textContent = t(tab.saved ? "playlistSaved" : "savePlaylist");
 }
 
 ///////////////////////////////////////////////////////////////////////////////
@@ -645,6 +665,7 @@ function render(nextState) {
   state = nextState;
   renderSelectors(nextState);
   renderBrowser(nextState);
+  playlistLibrary.render(nextState.savedPlaylists);
   renderTabs(nextState);
   renderPlaylist(nextState);
   renderPlayer(nextState);
@@ -726,7 +747,7 @@ function handleTranslationChange() {
 // Starts renderer discovery and renders the state returned by the server.
 async function discoverRenderers() {
   try {
-    render(await api("/api/discover", {}));
+    render(await playerState.request("/api/discover", {}));
   } catch (error) {
     setStatus(errorMessage(error));
   }
@@ -768,14 +789,15 @@ function seek() {
   command("seek", { percentage: Number(elements.seek.value) });
 }
 
-// Polls a complete state snapshot unless a browser command is still active.
+// Polls status and changed tracks, without overlapping polls or busy commands.
 async function refresh() {
-  if (commandBusy) {
+  if (commandBusy || refreshBusy) {
     return;
   }
 
+  refreshBusy = true;
   try {
-    render(await api("/api/state"));
+    render(await playerState.request("/api/state"));
     hideLogin();
   } catch (error) {
     if (error.code === "authentication-required") {
@@ -783,6 +805,8 @@ async function refresh() {
     } else {
       setStatus(t("noConnection", { message: errorMessage(error) }));
     }
+  } finally {
+    refreshBusy = false;
   }
 }
 
@@ -859,6 +883,7 @@ elements.library.addEventListener("change", () => {
 elements.libraryUp.addEventListener("click", () => command("up"));
 elements.tabAdd.addEventListener("click", () => command("tab-add"));
 elements.playlistClear.addEventListener("click", () => command("playlist-clear"));
+elements.playlistSave.addEventListener("click", savePlaylist);
 elements.loginForm.addEventListener("submit", login);
 elements.logout.addEventListener("click", logout);
 
diff --git a/public/index.html b/public/index.html
index 47a4596..0911f1c 100644
--- a/public/index.html
+++ b/public/index.html
@@ -56,20 +56,33 @@
 
       <section class="workspace">
         <aside class="left-pane">
-          <section class="library-pane panel">
-            <div class="panel-header library-header">
-              <div>
-                <span class="panel-kicker" data-i18n="musicLibrary">MUSIC LIBRARY</span>
-                <select id="library" data-i18n-aria="musicLibrary" aria-label="Music library"></select>
+          <section id="library-pane" class="library-pane panel">
+            <div class="library-tabs" role="tablist" data-i18n-aria="musicLibrary" aria-label="Music library">
+              <button id="folders-tab" class="library-tab active" type="button" role="tab" aria-selected="true" aria-controls="folders-panel" data-i18n="folders">Folders</button>
+              <button id="saved-playlists-tab" class="library-tab" type="button" role="tab" aria-selected="false" aria-controls="saved-playlists-panel" tabindex="-1" data-i18n="playlists">Playlists</button>
+            </div>
+            <div id="folders-panel" class="library-folders" role="tabpanel" aria-labelledby="folders-tab">
+              <div class="panel-header library-header">
+                <div>
+                  <span class="panel-kicker" data-i18n="musicLibrary">MUSIC LIBRARY</span>
+                  <select id="library" data-i18n-aria="musicLibrary" aria-label="Music library"></select>
+                </div>
+                <button id="library-up" class="square-button" type="button" data-i18n-title="upFolder" title="Up one folder" aria-label="Up one folder">↑</button>
               </div>
-              <button id="library-up" class="square-button" type="button" data-i18n-title="upFolder" title="Up one folder" aria-label="Up one folder">↑</button>
+              <nav id="breadcrumb" class="breadcrumb" data-i18n-aria="currentFolder" aria-label="Current folder"></nav>
+              <div id="library-empty" class="empty-state" hidden>
+                <p data-i18n="noLibraryConfigured">No library configured.</p>
+                <code>[libraries] muziek=D:\Muziek</code>
+              </div>
+              <ul id="library-entries" class="library-list" data-i18n-aria="folderContents" aria-label="Folder contents"></ul>
             </div>
-            <nav id="breadcrumb" class="breadcrumb" data-i18n-aria="currentFolder" aria-label="Current folder"></nav>
-            <div id="library-empty" class="empty-state" hidden>
-              <p data-i18n="noLibraryConfigured">No library configured.</p>
-              <code>[libraries] muziek=D:\Muziek</code>
+            <div id="saved-playlists-panel" class="library-saved" role="tabpanel" aria-labelledby="saved-playlists-tab" hidden>
+              <div id="saved-playlists-empty" class="empty-state">
+                <p data-i18n="noSavedPlaylists">No saved playlists yet.</p>
+                <span data-i18n="savePlaylistHint">Save a playlist tab to find it here.</span>
+              </div>
+              <ul id="saved-playlists" class="library-list" data-i18n-aria="playlists" aria-label="Playlists"></ul>
             </div>
-            <ul id="library-entries" class="library-list" data-i18n-aria="folderContents" aria-label="Folder contents"></ul>
           </section>
 
           <section class="now-playing-pane panel">
@@ -99,7 +112,10 @@
               <span class="panel-kicker" data-i18n="playlist">PLAYLIST</span>
               <strong id="track-count">0 tracks</strong>
             </div>
-            <button id="playlist-clear" class="text-button" type="button" data-i18n="clearList">CLEAR LIST</button>
+            <div class="playlist-actions">
+              <button id="playlist-save" class="text-button" type="button" data-i18n="savePlaylist">SAVE PLAYLIST</button>
+              <button id="playlist-clear" class="text-button" type="button" data-i18n="clearList">CLEAR LIST</button>
+            </div>
           </div>
 
           <div id="playlist-empty" class="empty-state playlist-empty">
@@ -151,6 +167,6 @@
     </section>
 
     <script src="/translate.js" defer></script>
-    <script src="/app.js" defer></script>
+    <script src="/app.js" type="module"></script>
   </body>
 </html>
diff --git a/public/package.json b/public/package.json
new file mode 100644
index 0000000..e986b24
--- /dev/null
+++ b/public/package.json
@@ -0,0 +1,4 @@
+{
+  "private": true,
+  "type": "module"
+}
diff --git a/public/player-state.js b/public/player-state.js
new file mode 100644
index 0000000..a71661c
--- /dev/null
+++ b/public/player-state.js
@@ -0,0 +1,40 @@
+/*
+ * Keeps the active playlist in memory between player-state requests.
+ * State, command and discovery requests share a queue so responses cannot
+ * overwrite newer state or reuse tracks from a different playlist version.
+ */
+export class PlayerStateClient {
+  #sendRequest;
+  #snapshot = null;
+  #pending = Promise.resolve();
+
+  // sendRequest performs the application's JSON GET/POST transport.
+  constructor(sendRequest) {
+    this.#sendRequest = sendRequest;
+  }
+
+  // Queues a state-producing request and returns a complete browser snapshot.
+  // A failed request does not prevent subsequent requests from being sent.
+  request(path, body) {
+    const result = this.#pending.then(() => this.#read(path, body));
+    this.#pending = result.catch(() => {});
+    return result;
+  }
+
+  // Sends the cached version and restores omitted tracks from that exact version.
+  async #read(path, body) {
+    if (this.#snapshot) {
+      path += `?playlistVersion=${encodeURIComponent(this.#snapshot.playlistVersion)}`;
+    }
+    const nextState = await this.#sendRequest(path, body);
+    if (nextState.tracks === null) {
+      if (!this.#snapshot || nextState.playlistVersion !== this.#snapshot.playlistVersion) {
+        this.#snapshot = null;
+        throw new Error("Playlist cache does not match the server version.");
+      }
+      nextState.tracks = this.#snapshot.tracks;
+    }
+    this.#snapshot = nextState;
+    return nextState;
+  }
+}
diff --git a/public/playlist-library.js b/public/playlist-library.js
new file mode 100644
index 0000000..2a5b3ff
--- /dev/null
+++ b/public/playlist-library.js
@@ -0,0 +1,124 @@
+/*
+ * Library view for the Folders and Playlists tabs. Saved playlists are server
+ * objects: actions address their UUID and reveal their existing playlist tab.
+ * Only the selected library view and highlighted row are local UI state.
+ */
+export class PlaylistLibrary {
+  #tabs;
+  #panels;
+  #list;
+  #empty;
+  #command;
+  #formatDuration;
+  #selectedId = null;
+  #signature = null;
+
+  // root owns both library panels; command sends server actions and renders state.
+  constructor(root, command, formatDuration) {
+    this.#tabs = [root.querySelector("#folders-tab"), root.querySelector("#saved-playlists-tab")];
+    this.#panels = [root.querySelector("#folders-panel"), root.querySelector("#saved-playlists-panel")];
+    this.#list = root.querySelector("#saved-playlists");
+    this.#empty = root.querySelector("#saved-playlists-empty");
+    this.#command = command;
+    this.#formatDuration = formatDuration;
+    this.#tabs.forEach((tab, index) => {
+      tab.addEventListener("click", () => this.show(index));
+      tab.addEventListener("keydown", (event) => {
+        if (["ArrowLeft", "ArrowRight", "Home", "End"].includes(event.key)) {
+          event.preventDefault();
+          const next = event.key === "Home" ? 0 : event.key === "End" ? 1 : 1 - index;
+          this.show(next);
+          this.#tabs[next].focus();
+        }
+      });
+    });
+  }
+
+  // Switch the library panel without changing the selected playlist or playback.
+  show(index) {
+    this.#tabs.forEach((tab, current) => {
+      const active = current === index;
+      tab.classList.toggle("active", active);
+      tab.setAttribute("aria-selected", String(active));
+      tab.tabIndex = active ? 0 : -1;
+      this.#panels[current].hidden = !active;
+    });
+  }
+
+  // Refresh saved playlist summaries only when metadata or language changes.
+  render(playlists) {
+    const signature = JSON.stringify([window.RktTranslate.language(), playlists]);
+    if (signature === this.#signature) return;
+    if (!playlists.some((playlist) => playlist.id === this.#selectedId)) this.#selectedId = null;
+    this.#list.replaceChildren(...playlists.map((playlist) => this.#createEntry(playlist)));
+    this.#empty.hidden = playlists.length > 0;
+    this.#signature = signature;
+    this.#select(this.#selectedId);
+  }
+
+  #select(id) {
+    this.#selectedId = id;
+    for (const row of this.#list.children) {
+      const selected = row.dataset.id === id;
+      row.classList.toggle("selected", selected);
+      row.setAttribute("aria-current", selected ? "true" : "false");
+    }
+  }
+
+  // Each action reveals this playlist by UUID; repeated opening is idempotent.
+  #action(label, title, playlist, play) {
+    const button = document.createElement("button");
+    button.type = "button";
+    button.className = "entry-action";
+    button.textContent = label;
+    button.title = title;
+    button.setAttribute("aria-label", title);
+    button.disabled = play && playlist.count === 0;
+    button.addEventListener("click", (event) => {
+      event.stopPropagation();
+      this.#select(playlist.id);
+      this.#command(play ? "playlist-play" : "playlist-open", { id: playlist.id });
+    });
+    return button;
+  }
+
+  #createEntry(playlist) {
+    const { t } = window.RktTranslate;
+    const row = document.createElement("li");
+    row.className = "library-entry";
+    row.dataset.id = playlist.id;
+    row.tabIndex = 0;
+    const icon = document.createElement("span");
+    icon.className = "entry-icon";
+    icon.textContent = "♫";
+    const name = document.createElement("span");
+    name.className = "entry-name";
+    name.textContent = playlist.name;
+    name.title = playlist.name;
+    const details = document.createElement("small");
+    details.className = "entry-details";
+    details.textContent = `${playlist.count} ${t(playlist.count === 1 ? "oneTrack" : "manyTracks")}, ${this.#formatDuration(playlist.duration)}`;
+    name.append(details);
+    const actions = document.createElement("span");
+    actions.className = "entry-actions";
+    actions.append(
+      this.#action("▶", t("playNow", { name: playlist.name }), playlist, true),
+      this.#action("＋", t("openPlaylistNamed", { name: playlist.name }), playlist, false),
+    );
+    row.append(icon, name, actions);
+    row.addEventListener("click", () => this.#select(playlist.id));
+    row.addEventListener("dblclick", (event) => {
+      if (event.target.closest("button")) return;
+      this.#command("playlist-open", { id: playlist.id });
+    });
+    row.addEventListener("keydown", (event) => {
+      if (event.target !== row) return;
+      if (["Enter", "+", " "].includes(event.key)) {
+        event.preventDefault();
+        this.#select(playlist.id);
+        if (event.key !== " ") this.#command("playlist-open", { id: playlist.id });
+      }
+    });
+    return row;
+  }
+}
diff --git a/public/styles.css b/public/styles.css
index 07771db..281b8d1 100644
--- a/public/styles.css
+++ b/public/styles.css
@@ -332,10 +332,61 @@ input[type="range"] {
 
 .library-pane {
   display: grid;
-  grid-template-rows: auto auto minmax(0, 1fr);
+  grid-template-rows: auto minmax(0, 1fr);
   border-bottom: 0;
 }
 
+.library-tabs {
+  display: flex;
+  border-bottom: 1px solid var(--line-soft);
+}
+
+.library-tab {
+  flex: 1;
+  min-height: 36px;
+  border: 0;
+  background: transparent;
+  color: var(--muted);
+  font-size: 12px;
+}
+
+.library-tab.active {
+  color: var(--accent);
+  box-shadow: inset 0 -2px var(--accent);
+}
+
+.library-folders {
+  display: grid;
+  grid-template-rows: auto auto minmax(0, 1fr);
+  min-height: 0;
+}
+
+.library-saved {
+  display: grid;
+  min-height: 0;
+}
+
+.library-folders[hidden],
+.library-saved[hidden] {
+  display: none;
+}
+
+.library-saved > .library-list,
+.library-saved > .empty-state {
+  grid-area: 1 / 1;
+}
+
+.library-entry.selected {
+  background: var(--panel-raised);
+}
+
+.entry-details {
+  display: block;
+  margin-top: 3px;
+  color: var(--muted);
+  font-size: 10px;
+}
+
 .panel-header {
   min-height: 55px;
   padding: 8px 10px;
@@ -601,6 +652,8 @@ input[type="range"] {
 
 .playlist-toolbar {
   justify-content: space-between;
+  flex-wrap: wrap;
+  gap: 8px;
   min-height: 53px;
   padding: 8px 12px;
   border-bottom: 1px solid var(--line-soft);
@@ -611,6 +664,12 @@ input[type="range"] {
   gap: 4px;
 }
 
+.playlist-toolbar > .playlist-actions {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 6px;
+}
+
 .playlist-toolbar strong {
   font-size: 14px;
 }
@@ -739,7 +798,7 @@ input[type="range"] {
   align-self: center;
 }
 
-.library-pane > .empty-state {
+.library-folders > .empty-state {
   grid-row: 3;
   z-index: 2;
 }
diff --git a/public/translate.js b/public/translate.js
index 355021c..a00b69d 100644
--- a/public/translate.js
+++ b/public/translate.js
@@ -3,6 +3,13 @@
 
   const translations = {
     en: {
+      folders: "Folders",
+      savePlaylist: "SAVE PLAYLIST",
+      playlistSaved: "SAVED",
+      noSavedPlaylists: "No saved playlists yet.",
+      savePlaylistHint: "Save a playlist tab to find it here.",
+      openPlaylistNamed: "Open {name} as a tab",
+      closePlaylist: "Close tab",
       playingTime: "{duration} playing time",
       output: "OUTPUT", searchPlayers: "Search for network players", logout: "LOG OUT",
       rendererLocal: "LOCAL", defaultPlaylist: "Default",
@@ -34,6 +41,13 @@
       "dlna-renderer-unreachable": "The DLNA renderer is unreachable.",
     },
     nl: {
+      folders: "Mappen",
+      savePlaylist: "AFSPEELLIJST OPSLAAN",
+      playlistSaved: "OPGESLAGEN",
+      noSavedPlaylists: "Nog geen opgeslagen afspeellijsten.",
+      savePlaylistHint: "Sla een playlisttab op om hem hier terug te vinden.",
+      openPlaylistNamed: "{name} als tab openen",
+      closePlaylist: "Tab sluiten",
       playingTime: "{duration} speeltijd",
       output: "UITVOER", searchPlayers: "Netwerkspelers zoeken", logout: "UITLOGGEN",
       rendererLocal: "LOKAAL", defaultPlaylist: "Standaard",
@@ -65,6 +79,13 @@
       "dlna-renderer-unreachable": "De DLNA-renderer is niet bereikbaar.",
     },
     de: {
+      folders: "Ordner",
+      savePlaylist: "WIEDERGABELISTE SPEICHERN",
+      playlistSaved: "GESPEICHERT",
+      noSavedPlaylists: "Noch keine gespeicherten Wiedergabelisten.",
+      savePlaylistHint: "Speichern Sie eine Wiedergabeliste, um sie hier zu finden.",
+      openPlaylistNamed: "{name} als Tab öffnen",
+      closePlaylist: "Tab schließen",
       playingTime: "{duration} Spielzeit",
       output: "AUSGABE", searchPlayers: "Netzwerkplayer suchen", logout: "ABMELDEN",
       rendererLocal: "LOKAL", defaultPlaylist: "Standard",
@@ -96,6 +117,13 @@
       "dlna-renderer-unreachable": "Der DLNA-Renderer ist nicht erreichbar.",
     },
     fr: {
+      folders: "Dossiers",
+      savePlaylist: "ENREGISTRER LA LISTE",
+      playlistSaved: "ENREGISTRÉE",
+      noSavedPlaylists: "Aucune liste de lecture enregistrée.",
+      savePlaylistHint: "Enregistrez une liste de lecture pour la retrouver ici.",
+      openPlaylistNamed: "Ouvrir {name} dans un onglet",
+      closePlaylist: "Fermer l’onglet",
       playingTime: "{duration} de lecture",
       output: "SORTIE", searchPlayers: "Rechercher les lecteurs réseau", logout: "DÉCONNEXION",
       rendererLocal: "LOCAL", defaultPlaylist: "Par défaut",
@@ -127,6 +155,13 @@
       "dlna-renderer-unreachable": "Le lecteur DLNA est inaccessible.",
     },
     es: {
+      folders: "Carpetas",
+      savePlaylist: "GUARDAR LISTA",
+      playlistSaved: "GUARDADA",
+      noSavedPlaylists: "Todavía no hay listas guardadas.",
+      savePlaylistHint: "Guarda una lista de reproducción para encontrarla aquí.",
+      openPlaylistNamed: "Abrir {name} en una pestaña",
+      closePlaylist: "Cerrar pestaña",
       playingTime: "{duration} de reproducción",
       output: "SALIDA", searchPlayers: "Buscar reproductores de red", logout: "CERRAR SESIÓN",
       rendererLocal: "LOCAL", defaultPlaylist: "Predeterminada",
@@ -158,6 +193,13 @@
       "dlna-renderer-unreachable": "No se puede acceder al renderizador DLNA.",
     },
     it: {
+      folders: "Cartelle",
+      savePlaylist: "SALVA PLAYLIST",
+      playlistSaved: "SALVATA",
+      noSavedPlaylists: "Nessuna playlist salvata.",
+      savePlaylistHint: "Salva una playlist per ritrovarla qui.",
+      openPlaylistNamed: "Apri {name} in una scheda",
+      closePlaylist: "Chiudi scheda",
       playingTime: "{duration} di riproduzione",
       output: "USCITA", searchPlayers: "Cerca lettori di rete", logout: "ESCI",
       rendererLocal: "LOCALE", defaultPlaylist: "Predefinita",
@@ -189,6 +231,13 @@
       "dlna-renderer-unreachable": "Il renderer DLNA non è raggiungibile.",
     },
     sv: {
+      folders: "Mappar",
+      savePlaylist: "SPARA SPELLISTA",
+      playlistSaved: "SPARAD",
+      noSavedPlaylists: "Inga sparade spellistor ännu.",
+      savePlaylistHint: "Spara en spellista för att hitta den här.",
+      openPlaylistNamed: "Öppna {name} som en flik",
+      closePlaylist: "Stäng fliken",
       playingTime: "{duration} speltid",
       output: "UTGÅNG", searchPlayers: "Sök efter nätverksspelare", logout: "LOGGA UT",
       rendererLocal: "LOKAL", defaultPlaylist: "Standard",
@@ -220,6 +269,13 @@
       "dlna-renderer-unreachable": "DLNA-renderaren kan inte nås.",
     },
     no: {
+      folders: "Mapper",
+      savePlaylist: "LAGRE SPILLELISTE",
+      playlistSaved: "LAGRET",
+      noSavedPlaylists: "Ingen lagrede spillelister ennå.",
+      savePlaylistHint: "Lagre en spilleliste for å finne den her.",
+      openPlaylistNamed: "Åpne {name} som en fane",
+      closePlaylist: "Lukk fanen",
       playingTime: "{duration} spilletid",
       output: "UTGANG", searchPlayers: "Søk etter nettverksspillere", logout: "LOGG UT",
       rendererLocal: "LOKAL", defaultPlaylist: "Standard",
@@ -251,6 +307,13 @@
       "dlna-renderer-unreachable": "DLNA-gjengiveren kan ikke nås.",
     },
     fi: {
+      folders: "Kansiot",
+      savePlaylist: "TALLENNA SOITTOLISTA",
+      playlistSaved: "TALLENNETTU",
+      noSavedPlaylists: "Ei vielä tallennettuja soittolistoja.",
+      savePlaylistHint: "Tallenna soittolista, niin löydät sen täältä.",
+      openPlaylistNamed: "Avaa {name} välilehtenä",
+      closePlaylist: "Sulje välilehti",
       playingTime: "Toistoaika: {duration}",
       output: "ULOSTULO", searchPlayers: "Etsi verkkosoittimia", logout: "KIRJAUDU ULOS",
       rendererLocal: "PAIKALLINEN", defaultPlaylist: "Oletus",
@@ -282,6 +345,13 @@
       "dlna-renderer-unreachable": "DLNA-toistimeen ei saada yhteyttä.",
     },
     is: {
+      folders: "Möppur",
+      savePlaylist: "VISTA SPILUNARLISTA",
+      playlistSaved: "VISTAÐ",
+      noSavedPlaylists: "Engir vistaðir spilunarlistar enn.",
+      savePlaylistHint: "Vistaðu spilunarlista til að finna hann hér.",
+      openPlaylistNamed: "Opna {name} í flipa",
+      closePlaylist: "Loka flipa",
       playingTime: "Spilunartími: {duration}",
       output: "ÚTTAK", searchPlayers: "Leita að netspilurum", logout: "SKRÁ ÚT",
       rendererLocal: "STAÐBUNDIÐ", defaultPlaylist: "Sjálfgefið",
diff --git a/scribblings/rkt-web-player.scrbl b/scribblings/rkt-web-player.scrbl
index df0d195..d629859 100644
--- a/scribblings/rkt-web-player.scrbl
+++ b/scribblings/rkt-web-player.scrbl
@@ -50,13 +50,62 @@ The central server is the heart of the application. Its main features are:
      allowlist for playback agents.}
 ]
 
-The browser is a thin remote control, not a second player. It polls a complete
-JSON state snapshot once per second and sends commands to the central server;
+The browser is a thin remote control, not a second player. It polls player
+status once per second and sends commands to the central server;
 playlists, preferences and playback state are kept there. The server exposes
 the browser application under the root URL and its JSON API under @tt{/api}.
 The API includes state, discovery, playback commands, preferences, artwork and
 the agent registration, polling and media routes.
 
+@subsection{Playlist synchronization}
+
+State responses include an opaque @tt{playlistVersion} for the selected
+playlist. The browser sends its last received version as the
+@tt{playlistVersion} query parameter on @tt{/api/state}, @tt{/api/discover}
+and @tt{/api/command/}@italic{command}. When that version still matches,
+@tt{tracks} is JSON @tt{null}; otherwise the response includes the complete
+track array. Requests without a version continue to receive all tracks.
+The version and track data are returned together in one consistent snapshot.
+
+The server caches serialized tracks, count and total duration per playlist.
+Changing the track list invalidates that snapshot and generates a fresh version
+when it is next requested. Renaming a tab or updating playback position does
+not invalidate the tracks. Versions are renewed after a server restart and
+are distinct between playlists and users. Changes from another browser are
+picked up by the next poll.
+
+The browser keeps the active playlist in memory and serializes state-producing
+requests through @tt{PlayerStateClient}, so a delayed response cannot replace
+newer state. Unchanged playlist rows are reused; changing the interface language
+still rebuilds their translated labels.
+
+@subsection{Saved playlists in the library}
+
+The library has @italic{Folders} and @italic{Playlists} tabs. The playlist
+toolbar's @italic{Save playlist} button names and saves the current tab in
+the user's library. The library row's @tt{＋} button opens that playlist as
+its own tab, or selects its existing tab. @tt{▶} does the same and starts
+playback. These actions never append tracks to or replace another tab.
+
+A saved playlist and its open tab share one UUID and one track list. Track
+edits and renaming therefore update the saved playlist automatically. Closing
+the tab keeps it in the library. Closing the last saved tab leaves a new empty
+default tab. Existing tabs remain open and appear in the library only after
+the user explicitly saves them.
+
+The keystore retains @tt{playlists-for-}@italic{username} for the ordered open
+tabs and adds @tt{saved-playlists-for-}@italic{username} for library playlists.
+Each UUID has one stored value, shared by both indexes. The private storage
+procedure @tt{load-user-playlists} reads the open index by default and the saved
+index with @tt{#:saved? #t}. @tt{save-user-playlists!} accepts the saved collection
+through @tt{#:saved} and updates both indexes atomically. Values absent from
+both indexes are removed. Legacy stores without a saved index need no migration.
+
+Browser state includes @tt{savedPlaylists} summaries without track arrays and
+a @tt{saved} flag on each tab. @tt{playlist-save} takes an open tab's @tt{id}
+and a @tt{name}; @tt{playlist-open} and @tt{playlist-play} take a saved playlist's
+@tt{id}. All three commands operate within the requesting user's collection.
+
 @subsection{Player agents}
 
 A player agent is an additional renderer implemented by this package. It runs
diff --git a/tests/player-state.test.mjs b/tests/player-state.test.mjs
new file mode 100644
index 0000000..6fdf7ac
--- /dev/null
+++ b/tests/player-state.test.mjs
@@ -0,0 +1,87 @@
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import { PlayerStateClient } from "../public/player-state.js";
+
+test("polls reuse tracks and accept edits from another browser", async () => {
+  const tracks = [{ title: "First" }];
+  const changedTracks = [{ title: "Second" }];
+  const responses = [
+    { playlistVersion: "first", tracks, position: 0 },
+    { playlistVersion: "first", tracks: null, position: 1 },
+    { playlistVersion: "changed", tracks: changedTracks, position: 2 },
+    { playlistVersion: "changed", tracks: null, position: 3 },
+  ];
+  const paths = [];
+  const client = new PlayerStateClient(async (path) => {
+    paths.push(path);
+    return responses.shift();
+  });
+  assert.equal((await client.request("/api/state")).tracks, tracks);
+  const unchanged = await client.request("/api/state");
+  assert.equal(unchanged.tracks, tracks);
+  assert.equal(unchanged.position, 1);
+  assert.equal((await client.request("/api/state")).tracks, changedTracks);
+  assert.equal((await client.request("/api/state")).tracks, changedTracks);
+  assert.deepEqual(paths, [
+    "/api/state", "/api/state?playlistVersion=first",
+    "/api/state?playlistVersion=first", "/api/state?playlistVersion=changed",
+  ]);
+});
+
+test("commands and discovery wait for polling and use its latest version", async () => {
+  let finishPoll;
+  const paths = [];
+  const commandBody = { index: 1 };
+  const client = new PlayerStateClient((path, body) => {
+    paths.push(path);
+    if (paths.length === 1) {
+      return new Promise((resolve) => { finishPoll = resolve; });
+    }
+    if (paths.length === 2) {
+      assert.equal(body, commandBody);
+      return { playlistVersion: "other-tab", tracks: [] };
+    }
+    return { playlistVersion: "other-tab", tracks: null };
+  });
+  const poll = client.request("/api/state");
+  const command = client.request("/api/command/tab-select", commandBody);
+  const discovery = client.request("/api/discover", {});
+  await Promise.resolve();
+  assert.deepEqual(paths, ["/api/state"]);
+  finishPoll({ playlistVersion: "original-tab", tracks: [{ title: "First" }] });
+  await poll;
+  assert.deepEqual((await command).tracks, []);
+  assert.deepEqual((await discovery).tracks, []);
+  assert.deepEqual(paths, [
+    "/api/state",
+    "/api/command/tab-select?playlistVersion=original-tab",
+    "/api/discover?playlistVersion=other-tab",
+  ]);
+});
+
+test("a failed request leaves the queue usable", async () => {
+  let calls = 0;
+  const client = new PlayerStateClient(async () => {
+    if (++calls === 1) throw new Error("Offline");
+    return { playlistVersion: "recovered", tracks: [] };
+  });
+  await assert.rejects(client.request("/api/state"), /Offline/);
+  assert.deepEqual((await client.request("/api/state")).tracks, []);
+});
+
+test("mismatched omitted tracks force a full refresh instead of stale reuse", async () => {
+  const paths = [];
+  const responses = [
+    { playlistVersion: "before", tracks: [{ title: "Before" }] },
+    { playlistVersion: "after", tracks: null },
+    { playlistVersion: "after", tracks: [] },
+  ];
+  const client = new PlayerStateClient(async (path) => {
+    paths.push(path);
+    return responses.shift();
+  });
+  await client.request("/api/state");
+  await assert.rejects(client.request("/api/state"), /Playlist cache/);
+  assert.deepEqual((await client.request("/api/state")).tracks, []);
+  assert.equal(paths[2], "/api/state");
+});
diff --git a/tests/playlist-library.test.mjs b/tests/playlist-library.test.mjs
new file mode 100644
index 0000000..84b3391
--- /dev/null
+++ b/tests/playlist-library.test.mjs
@@ -0,0 +1,96 @@
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import { PlaylistLibrary } from "../public/playlist-library.js";
+
+// Minimal DOM elements let the view's actions run without a browser dependency.
+class Element {
+  constructor() {
+    this.children = [];
+    this.dataset = {};
+    this.attributes = {};
+    this.listeners = {};
+    this.classes = new Set();
+    this.classList = { toggle: (name, active) => active ? this.classes.add(name) : this.classes.delete(name) };
+  }
+  append(...children) { this.children.push(...children); }
+  replaceChildren(...children) { this.children = children; }
+  setAttribute(name, value) { this.attributes[name] = value; }
+  addEventListener(name, callback) { this.listeners[name] = callback; }
+  fire(name, values = {}) { this.listeners[name]({ target: this, stopPropagation() {}, preventDefault() {}, ...values }); }
+  focus() {}
+  closest() { return null; }
+}
+
+class Fixture {
+  constructor() {
+    this.nodes = new Map();
+    this.commands = [];
+    this.language = "en";
+    globalThis.window = { RktTranslate: {
+      language: () => this.language,
+      t: (key, values = {}) => `${key} ${values.name || ""}`,
+    } };
+    globalThis.document = { createElement: () => new Element() };
+    this.view = new PlaylistLibrary({ querySelector: (selector) => this.node(selector) },
+      (name, data) => this.commands.push({ name, data }), duration => `${duration} seconds`);
+  }
+  node(selector) {
+    if (!this.nodes.has(selector)) this.nodes.set(selector, new Element());
+    return this.nodes.get(selector);
+  }
+}
+
+test("library tabs change only the visible panel", () => {
+  const fixture = new Fixture();
+  fixture.node("#saved-playlists-tab").fire("click");
+  assert.equal(fixture.node("#folders-panel").hidden, true);
+  assert.equal(fixture.node("#saved-playlists-panel").hidden, false);
+  assert.equal(fixture.node("#saved-playlists-tab").attributes["aria-selected"], "true");
+  fixture.node("#saved-playlists-tab").fire("keydown", { key: "ArrowLeft" });
+  assert.equal(fixture.node("#folders-panel").hidden, false);
+  assert.deepEqual(fixture.commands, []);
+});
+
+test("plus and play address the saved playlist UUID and never use item-add/play", () => {
+  const fixture = new Fixture();
+  fixture.view.render([{ id: "saved-id", name: "Music", count: 2, duration: 120 }]);
+  const row = fixture.node("#saved-playlists").children[0];
+  row.fire("click");
+  assert.deepEqual(fixture.commands, []);
+  assert.ok(row.classes.has("selected"));
+  row.children[2].children[1].fire("click");
+  row.children[2].children[0].fire("click");
+  assert.deepEqual(fixture.commands, [
+    { name: "playlist-open", data: { id: "saved-id" } },
+    { name: "playlist-play", data: { id: "saved-id" } },
+  ]);
+  assert.equal(fixture.node("#saved-playlists-empty").hidden, true);
+});
+
+test("unchanged summaries reuse rows while metadata and language changes refresh them", () => {
+  const fixture = new Fixture();
+  const playlists = [{ id: "one", name: "Music", count: 0, duration: 0 }];
+  fixture.view.render(playlists);
+  const row = fixture.node("#saved-playlists").children[0];
+  assert.equal(row.children[2].children[0].disabled, true);
+  assert.equal(row.children[2].children[1].disabled, false);
+  fixture.view.render(playlists);
+  assert.equal(fixture.node("#saved-playlists").children[0], row);
+  fixture.language = "nl";
+  fixture.view.render(playlists);
+  assert.notEqual(fixture.node("#saved-playlists").children[0], row);
+  fixture.view.render([{ ...playlists[0], name: "Renamed" }]);
+  assert.equal(fixture.node("#saved-playlists").children[0].children[1].textContent, "Renamed");
+  fixture.view.render([]);
+  assert.equal(fixture.node("#saved-playlists-empty").hidden, false);
+});
+
+test("keyboard opening does not intercept a nested action button", () => {
+  const fixture = new Fixture();
+  fixture.view.render([{ id: "one", name: "Music", count: 1, duration: 60 }]);
+  const row = fixture.node("#saved-playlists").children[0];
+  row.fire("keydown", { key: "Enter", target: row.children[2].children[0] });
+  assert.deepEqual(fixture.commands, []);
+  row.fire("keydown", { key: "Enter" });
+  assert.deepEqual(fixture.commands, [{ name: "playlist-open", data: { id: "one" } }]);
+});