diff --git a/CHANGELOG.md b/CHANGELOG.md
index b04985a..79be67f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Added
+- **Full-mix audio exposed alongside stems for the stem mixer's auto-switch.** `lib/sloppak.py::load_song` now parses the optional manifest `original_audio:` key (the single pre-separation mixdown, e.g. `original/full.ogg`) into a new `LoadedSloppak.original_audio` field, with the same path-traversal guard and permissive "missing → disabled" posture as the `drum_tab` loader. The highway WS `song_info` frame additively carries three new fields next to `stems`: `original_audio_url` (served by the existing `/api/sloppak/{filename}/file/{rel_path}` endpoint, `None` when the pack ships stems only), `has_original_audio`, and `has_stems` (mirroring the `has_drum_tab`/`has_keys` flag convention). The stems plugin consumes `original_audio_url` to play the untouched single file while every stem slider is at unity and switch to the separate stems the moment one drops below 100%. **Migration notes:** the `song_info` message shape is a stable contract — these are purely additive; all existing fields are unchanged. `audio_url` still points at stem[0] when stems exist (it is only the degraded native fallback); the one behavioural change is that a stem-less, full-mix-only sloppak now sets `audio_url` to the full mix instead of emitting `audio_error`, so it plays natively.
 - **Autoplay & auto-exit — a global "click it, it plays; finish, you're back at the menu" option (default ON).** New single Settings toggle (`autoplayExit` in `localStorage`, surfaced in both the v3 and classic settings screens; absence of the key = enabled) that closes the friction at both ends of the play loop. **Autoplay:** `playSong()` previously loaded a chart paused, requiring a Play press; a one-shot flag armed per fresh load is now consumed by the next `song:ready` (highway.js) to auto-start via the existing `togglePlay()` path (HTML5 + `_juceMode` + count-in). Arrangement switches / seeks reuse the same `song:ready` event but never arm the flag, so they don't auto-restart. **Auto-exit:** on `song:ended`, core returns to the launching menu after a short grace delay — unless a visible full-screen results/dialog overlay is on top (detected via `[role=dialog][aria-modal]` / `.fixed.inset-0` with a `getClientRects()` visibility test that works for `position:fixed`), in which case the return is deferred so that score screen's own Close button (calling `window.closeCurrentSong()`) drives the exit. A plugin can also defer explicitly via the new `window.feedBack.holdAutoExit()` (called synchronously from its own `song:ended` handler — core's listener runs first). Both paths mean **no external plugin PR is required** for a results screen to be respected. **Context-aware destination:** the player's remembered origin (`_playerOriginScreen`) now honours any real launch screen instead of clamping to library/home/favorites, and a one-shot `window.feedBack.setReturnScreen(id)` override lets the lessons catalog (`static/v3/lessons.js`) send a finished lesson back to the lessons screen — not the song library — even though the external tutorials plugin owns the `playSong` call. Also exposes a read-only `window.feedBack.autoplayExit` getter for plugins. Songs and lessons share the same `playSong` → highway path, so both inherit the behaviour. Core-only (`static/app.js`, `static/v3/lessons.js`, both `index.html`s); the end-of-song score screen itself remains a plugin. Optional polish (not required — the overlay heuristic already covers it): external scoring/note-detection plugins (e.g. SlopScale) may call `holdAutoExit()` + `closeCurrentSong()` for an exact, heuristic-free handoff.
 - **"Song Editor" promoted to a first-class v3 sidebar item.** The editor
   plugin (`id: editor`) now gets its own dedicated sidebar entry — under the
diff --git a/lib/sloppak.py b/lib/sloppak.py
index 8ee837a..d19c460 100644
--- a/lib/sloppak.py
+++ b/lib/sloppak.py
@@ -367,6 +367,14 @@ class LoadedSloppak:
     # song.arrangements (not to manifest["arrangements"]) — skipped entries are
     # absent so indexing by song.arrangements index is safe.
     arrangement_ids: list[str | None] = field(default_factory=list)
+    # Manifest-relative path to the single full-mix audio file, taken from the
+    # manifest `original_audio:` key (e.g. "original/full.ogg"). This is the
+    # pre-separation mixdown that exists alongside the per-instrument `stems`.
+    # None when the key is absent, points outside source_dir, or the file is
+    # missing on disk. Served to the front-end via the highway WS as
+    # `original_audio_url`; the stems plugin uses it to play the untouched mix
+    # when every stem slider is at unity (and the separate stems otherwise).
+    original_audio: str | None = None
 
 
 def load_song(
@@ -808,6 +816,29 @@ def load_song(
                     }
 
     _fpv = manifest.get("feedpak_version")
+    # Optional full-mix audio — manifest `original_audio:` key. The single
+    # pre-separation mixdown that ships alongside the per-instrument stems.
+    # Same permissive, path-traversal-guarded posture as drum_tab above: a
+    # missing/escaping/absent file simply leaves the full mix unavailable (the
+    # player falls back to the separate stems) rather than aborting the load.
+    # We store the manifest-relative string so server.py can build its URL the
+    # same way it builds stem URLs (via the /api/sloppak/.../file/ endpoint).
+    original_audio_data: str | None = None
+    original_audio_rel = manifest.get("original_audio")
+    if isinstance(original_audio_rel, str) and original_audio_rel.strip():
+        rel = original_audio_rel.strip()
+        try:
+            oa_path = (source_dir / rel).resolve()
+            oa_path.relative_to(source_dir.resolve())
+        except ValueError:
+            log.warning("sloppak: original_audio path %r escapes source_dir — skipped", rel)
+            oa_path = None
+        except OSError as e:
+            log.warning("sloppak: original_audio path resolution failed (%s) — skipped", e)
+            oa_path = None
+        if oa_path is not None and oa_path.is_file():
+            original_audio_data = rel
+
     return LoadedSloppak(
         song=song,
         stems=stems,
@@ -821,6 +852,7 @@ def load_song(
         keys=keys_data,
         notation_by_id=notation_by_id_data,
         arrangement_ids=arrangement_ids_acc,
+        original_audio=original_audio_data,
     )
 
 
diff --git a/server.py b/server.py
index 2d3c266..d6b99f9 100644
--- a/server.py
+++ b/server.py
@@ -6923,6 +6923,11 @@ async def highway_ws(websocket: WebSocket, filename: str, arrangement: int = -1,
         audio_url = None
         audio_error: str | None = None  # Surfaced in song_info when audio_url is None
         stems_payload: list[dict] = []
+        # URL of the single full-mix audio (sloppak `original_audio:`), when the
+        # pack ships one. The stems plugin uses this to play the untouched mix
+        # while every stem slider is at unity; None otherwise (separate stems
+        # only, loose folder, or archive).
+        original_audio_url: str | None = None
         if is_loose:
             # Loose folder filenames are relative paths (artist/album/song).
             # Hash the *canonical* dlc-relative path (so two URL spellings
@@ -6961,8 +6966,22 @@ async def highway_ws(websocket: WebSocket, filename: str, arrangement: int = -1,
             for s in loaded_slop.stems:
                 url = f"/api/sloppak/{q_fn}/file/{quote(s['file'])}"
                 stems_payload.append({"id": s["id"], "url": url, "default": s["default"]})
+            # Full-mix URL (served by the same /api/sloppak/.../file/ endpoint).
+            if loaded_slop is not None and loaded_slop.original_audio:
+                original_audio_url = (
+                    f"/api/sloppak/{q_fn}/file/{quote(loaded_slop.original_audio)}"
+                )
             if stems_payload:
+                # Stems present: keep the core <audio> pointed at stem[0]. This
+                # URL is only ever heard in the degraded path (stems plugin
+                # refuses takeover / decode fails); the full-mix↔stems switch is
+                # driven client-side by `original_audio_url`, not `audio_url`.
                 audio_url = stems_payload[0]["url"]
+            elif original_audio_url:
+                # Stem-less full-mix pack: nothing to separate, so play the full
+                # mix natively through the core <audio>. The stems plugin's
+                # onSongReady returns early on an empty stems list (no graph).
+                audio_url = original_audio_url
             else:
                 audio_error = "This sloppak has no playable stems."
         else:
@@ -7098,6 +7117,15 @@ async def highway_ws(websocket: WebSocket, filename: str, arrangement: int = -1,
             "offset": _sanitized_song_offset(song) if is_loose else 0.0,
             "format": "sloppak" if is_slop else ("loose" if is_loose else "archive"),
             "stems": stems_payload,
+            # Full-mix audio (sloppak `original_audio:`) served alongside the
+            # separate `stems`. The stems plugin plays this single file while
+            # every stem slider is at unity and switches to the separate stems
+            # the moment one drops below 100%. None when the pack ships stems
+            # only. `has_*` flags mirror the has_drum_tab/has_keys convention so
+            # a client can branch without re-deriving from the URLs.
+            "original_audio_url": original_audio_url,
+            "has_original_audio": bool(original_audio_url),
+            "has_stems": bool(stems_payload),
             # Surface a drum_tab presence flag so the visualization picker
             # can auto-activate the drums plugin even when the chosen
             # arrangement isn't named "Drums" (drum_tab.json lives next
diff --git a/tests/test_sloppak_original_audio_load.py b/tests/test_sloppak_original_audio_load.py
new file mode 100644
index 0000000..e3a30cb
--- /dev/null
+++ b/tests/test_sloppak_original_audio_load.py
@@ -0,0 +1,119 @@
+"""End-to-end test for the sloppak loader recognising an `original_audio:`
+manifest key (the single full-mix file shipped alongside the separate stems)
+and surfacing the manifest-relative path on the LoadedSloppak."""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+
+import yaml
+
+import sloppak as sloppak_mod
+
+
+def _write_dir_sloppak(root: Path, manifest_extras: dict, *, write_full_mix: bool) -> Path:
+    """Build a minimal directory-form sloppak that load_song will accept.
+
+    Uses the tmp_path leaf name to make the sloppak filename unique per test,
+    avoiding the module-level ``resolve_source_dir`` cache being poisoned by a
+    previous test that happened to share the same "song.sloppak" filename.
+    """
+    pak = root / f"{root.name}.sloppak"
+    pak.mkdir()
+    arr_dir = pak / "arrangements"
+    arr_dir.mkdir()
+
+    arr = {
+        "name": "Lead",
+        "tuning": [0, 0, 0, 0, 0, 0],
+        "capo": 0,
+        "notes": [],
+        "chords": [],
+        "anchors": [],
+        "handshapes": [],
+        "templates": [],
+        "beats": [],
+        "sections": [],
+    }
+    (arr_dir / "lead.json").write_text(json.dumps(arr))
+
+    manifest = {
+        "title": "Test",
+        "artist": "Tester",
+        "album": "",
+        "year": 2026,
+        "duration": 10.0,
+        "arrangements": [{"id": "lead", "name": "Lead", "file": "arrangements/lead.json"}],
+        "stems": [{"id": "guitar", "file": "stems/guitar.ogg", "default": True}],
+    }
+    manifest.update(manifest_extras)
+    (pak / "manifest.yaml").write_text(yaml.safe_dump(manifest, sort_keys=False))
+
+    if write_full_mix:
+        orig_dir = pak / "original"
+        orig_dir.mkdir()
+        # The loader only checks presence (is_file); contents are irrelevant.
+        (orig_dir / "full.ogg").write_bytes(b"OggS-not-real")
+
+    return pak
+
+
+def _load(pak_path: Path, tmp_path: Path):
+    dlc_root = pak_path.parent
+    cache = tmp_path / "cache"
+    cache.mkdir()
+    return sloppak_mod.load_song(pak_path.name, dlc_root, cache)
+
+
+# ── Happy path ───────────────────────────────────────────────────────────────
+
+def test_load_song_attaches_original_audio_when_manifest_opts_in(tmp_path: Path):
+    pak = _write_dir_sloppak(
+        tmp_path, {"original_audio": "original/full.ogg"}, write_full_mix=True
+    )
+    loaded = _load(pak, tmp_path)
+    # Stored as the manifest-relative string so server.py can build the URL the
+    # same way it builds stem URLs.
+    assert loaded.original_audio == "original/full.ogg"
+
+
+# ── Absent / degraded branches ───────────────────────────────────────────────
+
+def test_load_song_original_audio_none_when_manifest_silent(tmp_path: Path):
+    pak = _write_dir_sloppak(tmp_path, {}, write_full_mix=True)
+    loaded = _load(pak, tmp_path)
+    assert loaded.original_audio is None
+
+
+def test_load_song_original_audio_none_when_file_missing(tmp_path: Path):
+    # Manifest points at a full mix that isn't on disk — disabled silently.
+    pak = _write_dir_sloppak(
+        tmp_path, {"original_audio": "original/full.ogg"}, write_full_mix=False
+    )
+    loaded = _load(pak, tmp_path)
+    assert loaded.original_audio is None
+
+
+def test_load_song_original_audio_none_when_value_blank(tmp_path: Path):
+    pak = _write_dir_sloppak(tmp_path, {"original_audio": "   "}, write_full_mix=True)
+    loaded = _load(pak, tmp_path)
+    assert loaded.original_audio is None
+
+
+# ── Security / path-traversal branches ──────────────────────────────────────
+
+def test_load_song_original_audio_none_when_path_escapes_sloppak(tmp_path: Path):
+    pak = _write_dir_sloppak(
+        tmp_path, {"original_audio": "../outside.ogg"}, write_full_mix=True
+    )
+    loaded = _load(pak, tmp_path)
+    assert loaded.original_audio is None
+
+
+def test_load_song_original_audio_none_when_path_is_absolute(tmp_path: Path):
+    pak = _write_dir_sloppak(
+        tmp_path, {"original_audio": "/etc/passwd"}, write_full_mix=True
+    )
+    loaded = _load(pak, tmp_path)
+    assert loaded.original_audio is None