fix(sloppak): the full mix is a stem — drop the invented original_audio key (#946)

* fix(sloppak): the full mix is a stem — drop the invented `original_audio` key (#933)

Core read, served, and depended on `original_audio:` — a top-level manifest key
this repo invented in #583 that the feedpak spec never defined. The format
already had a home for the pre-separation mixdown: it is a stem. feedpak 1.15.0
(feedpak-spec#53) RESERVES the id `full` for it, so read it from there.

The key existed to work around a bug in our own reader. The packer's comment
said so plainly: "we must NOT list the full mix as a playable stem — the player
sums every entry in `stems` and does not gate playback on `default`, so a listed
full mix plays on top of the stems". Faced with a reader that would double the
song, the packer put the mixdown outside `stems` and invented a key to point at
it. The fix belongs in the reader, and that is what this is.

load_song() now partitions the stem list: `full` comes out as
LoadedSloppak.full_mix, the instruments stay in .stems. Nothing that sums stems
or draws one fader per stem can see the mixdown, so retaining it is safe — which
is what lets the packer put it where the format says it goes.

- ws_highway: `song_info` gains full_mix_url / has_full_mix. The old
  original_audio_url / has_original_audio remain as deprecated aliases for one
  release so an older stems plugin keeps working (#945).
- `stems` on the wire, and stem_ids / stem_count in the library index, are now
  INSTRUMENT stems only — a separated pack that retains its mixdown no longer
  advertises a bogus "full" chip or an inflated stem count.
- enrichment: fingerprint against the mixdown wherever it lives. This widens
  coverage — _song_audio_file() previously returned None for any pack without
  the invented key, so fingerprinting silently did nothing for nearly every pack.
- sloppak: `original_audio:` is still READ as a deprecated fallback, because
  every pack in the wild carries it and would otherwise lose its pristine mix.
  tools/migrate_full_mix_stem.py rewrites those packs into the spec shape
  (original/full.ogg -> stems/full.ogg, add the `full` stem at default:off, drop
  the key); the fallback and the aliases die with #945.

The spec gate keeps the debt honest: the grandfather entry now tracks #945, and
the gate fails if it goes stale.

Verified: spec gate OK (4/4, incl. ingesting the spec's new example pack that
retains `full`); 2493 python tests, 995 js tests; migrator round-tripped over
real packs from the library and the results pass the spec's reference validator.

* fix(migrate): discover directory-form packs instead of silently skipping them

iter_packs() searched only files, so a directory-form pack (`song.sloppak/`, the
authoring shape) was walked INTO and never yielded — silently missed by a run
that's meant to be exhaustive. Discover suffix-named directories too (yielded
whole, not descended into), and route packs through migrate_pack/verify_pack.

Directory packs are REPORTED as `dir-form-unsupported`, not rewritten in place:
a single-file pack is replaced atomically (a fully-built temp archive swapped in
with one os.replace), but a populated directory can't be swapped that way, so an
interrupted in-place rewrite could leave an authoring pack half-migrated. The
status is a problem status, so it counts against the run's exit code and shows
in the summary — the operator re-packs or migrates it as a `.feedpak` instead of
it vanishing from the report. Addresses a CodeRabbit review finding.

Signed-off-by: Kris Anderson <topkoa@gmail.com>

* fix(migrate): verify requires an explicit `off` on a retained full mix

verify_zip accepted any non-truthy `default` on a multi-stem `full` (missing,
empty, boolean, `false`/`no`/`0`, malformed) as "ok". But core defaults an ABSENT
`default` to True — ON (lib/sloppak.py: `s.get("default", True)`) — and treats an
empty/unrecognized string as ON too, so a migrated-shape pack whose `full` stem
has a missing or blank default beside instrument stems would actually play the
mixdown on open and double the song. verify was certifying that as safe.

Require an explicit normalized `off` beside instrument stems: `on`-ish values are
reported `full-stem-default-on` (actively plays), everything that is not a
normalized `off` is reported `full-stem-default-not-off`. The migrator already
writes the literal `off`, so its own output is unaffected; this also certifies
the pack is in the tool's canonical, most-portable shape. The len>1 gate is kept,
so a sole `full` stem (which IS the audio) is not policed.

Adds parametrized coverage for missing / empty / boolean / off-ish / malformed
defaults, and a sole-full-stem case. Addresses a CodeRabbit review finding.

Signed-off-by: Kris Anderson <topkoa@gmail.com>

---------

Signed-off-by: Kris Anderson <topkoa@gmail.com>
Co-authored-by: Kris Anderson <topkoa@gmail.com>

lib/enrichment.py

@@ -368,10 +368,12 @@ def _acoustid_gate() -> "JSONResponse | None":
 
 def _song_audio_file(filename: str) -> "str | None":
     """Resolve a LIBRARY song (by filename/id) to a local master-audio file for
-    fingerprinting: the full-mix `original_audio` extracted from a sloppak, or a
-    loose folder's audio. None when the song can't be found or ships no full-mix
-    audio (some packs carry only stems). Mirrors serve_sloppak_file's containment
-    guards so a crafted filename can't read outside DLC_DIR / the pack."""
+    fingerprinting: a sloppak's complete mixdown, or a loose folder's audio. None
+    when the song can't be found or carries no mixdown (a pack that kept only its
+    separated stems — an acoustic fingerprint of one re-summed from them would not
+    match the recording, so we decline rather than submit a lossy reconstruction).
+    Mirrors serve_sloppak_file's containment guards so a crafted filename can't
+    read outside DLC_DIR / the pack."""
     dlc = _get_dlc_dir()
     if not dlc:
         return None
@@ -383,7 +385,20 @@ def _song_audio_file(filename: str) -> "str | None":
             canon = resolved.relative_to(dlc.resolve()).as_posix()
         except ValueError:
             return None
-        rel = (sloppak_mod.load_manifest(resolved) or {}).get("original_audio")
+        manifest = sloppak_mod.load_manifest(resolved) or {}
+        # The mixdown is the RESERVED `full` stem (spec §5.3). Unlike playback,
+        # fingerprinting wants it even when it is the pack's ONLY stem — a
+        # single-mix pack is exactly the master audio we want to fingerprint —
+        # so this asks find_full_mix() rather than partition_stems().
+        stems = manifest.get("stems") or []
+        full = sloppak_mod.find_full_mix(
+            [s for s in stems if isinstance(s, dict)]
+        )
+        rel = full.get("file") if full else None
+        # DEPRECATED fallback: packs written before the spec reserved `full` put
+        # the mixdown behind a top-level `original_audio:` key instead (#933).
+        if not isinstance(rel, str) or not rel.strip():
+            rel = manifest.get("original_audio")
         if not isinstance(rel, str) or not rel.strip():
             return None
         src = sloppak_mod.get_cached_source_dir(canon)