Accept feedpak name/extension as additive alias for sloppak

Phase 1 of deprecating the format name sloppak -> feedpak. Purely additive
and fully back-compat: nothing sloppak stops working, and no on-disk/runtime
artifacts (cache dir, config, SLOPSMITH_* env) are touched.

- lib/sloppak.py: detection accepts both `.feedpak` and `.sloppak`
  (new PACK_SUFFIXES / is_pack / is_feedpak; is_sloppak kept as a deprecated
  alias that now matches both). Read the optional top-level `feedpak_version`
  manifest key onto LoadedSloppak and into extract_meta(). Add LoadedFeedpak
  class alias and a deprecation note in the module docstring.
- lib/feedpak.py (new): canonical module name; re-exports the sloppak public
  API unchanged so new code can `import feedpak`.
- server.py: accept `.feedpak` uploads (_ALLOWED_SONG_EXTS + message); add a
  `get_feedpak_cache_dir` plugin-context key alongside the legacy
  `get_sloppak_cache_dir` (same dir); tolerate a `feedpak` value in the
  library format filter.
- static/: accept `.feedpak` in the upload picker (index.html accept=, app.js
  client-side filter).
- tests/test_feedpak_alias.py: both extensions detected + loaded via both
  module names, feedpak_version read, legacy aliases intact.

The emitted `format` library tag stays "sloppak" for both extensions this
phase (flipping it to "feedpak" with badge/gating updates is a deliberate
frontend-touching follow-up). Format spec: got-feedback/feedback-feedpak-spec.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Signed-off-by: Kris Anderson <topkoa@gmail.com>

tests/test_feedpak_alias.py

@@ -0,0 +1,107 @@
+"""Coverage for the additive sloppak → feedpak rename (back-compat foundation).
+
+The format was renamed `sloppak` → `feedpak`. This phase is purely additive: both
+the `.feedpak` and legacy `.sloppak` extensions must load, the new `feedpak`
+module must re-export the loader, the `feedpak_version` manifest key must be read,
+and every legacy `sloppak`-named symbol must keep working. Nothing sloppak breaks.
+"""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+
+import pytest
+import yaml
+
+import sloppak as sloppak_mod
+import feedpak as feedpak_mod
+
+
+def _build(root: Path, suffix: str, manifest_extras: dict | None = None) -> Path:
+    """Build a minimal directory-form pack with the given extension."""
+    pak = root / f"{root.name}{suffix}"
+    pak.mkdir()
+    arr_dir = pak / "arrangements"
+    arr_dir.mkdir()
+    (arr_dir / "lead.json").write_text(json.dumps({
+        "name": "Lead", "tuning": [0, 0, 0, 0, 0, 0], "capo": 0,
+        "notes": [], "chords": [], "anchors": [], "handshapes": [], "templates": [],
+    }))
+    manifest = {
+        "title": "Test", "artist": "Tester", "album": "", "year": 2026,
+        "duration": 10.0,
+        "arrangements": [{"id": "lead", "name": "Lead", "file": "arrangements/lead.json"}],
+        "stems": [{"id": "full", "file": "stems/full.ogg", "default": True}],
+    }
+    manifest.update(manifest_extras or {})
+    (pak / "manifest.yaml").write_text(yaml.safe_dump(manifest, sort_keys=False))
+    return pak
+
+
+def _load(mod, pak: Path, tmp_path: Path):
+    cache = tmp_path / "cache"
+    cache.mkdir()
+    return mod.load_song(pak.name, pak.parent, cache)
+
+
+# ── Both extensions are detected ──────────────────────────────────────────────
+
+@pytest.mark.parametrize("suffix", [".feedpak", ".sloppak"])
+def test_detection_accepts_both_extensions(tmp_path: Path, suffix: str):
+    pak = tmp_path / f"song{suffix}"
+    assert sloppak_mod.is_pack(pak)
+    assert sloppak_mod.is_feedpak(pak)
+    assert sloppak_mod.is_sloppak(pak)  # deprecated alias still accepts .feedpak
+
+
+def test_detection_rejects_other_extensions(tmp_path: Path):
+    assert not sloppak_mod.is_pack(tmp_path / "song.zip")
+    assert not sloppak_mod.is_pack(tmp_path / "song.mp3")
+
+
+# ── Both extensions load, via both module names ───────────────────────────────
+
+@pytest.mark.parametrize("suffix", [".feedpak", ".sloppak"])
+def test_load_via_sloppak_module(tmp_path: Path, suffix: str):
+    pak = _build(tmp_path, suffix)
+    loaded = _load(sloppak_mod, pak, tmp_path)
+    assert loaded.song.title == "Test"
+    assert loaded.stems[0]["id"] == "full"
+
+
+@pytest.mark.parametrize("suffix", [".feedpak", ".sloppak"])
+def test_load_via_feedpak_module(tmp_path: Path, suffix: str):
+    """The canonical `feedpak` module re-exports the loader and loads both forms."""
+    pak = _build(tmp_path, suffix)
+    loaded = _load(feedpak_mod, pak, tmp_path)
+    assert loaded.song.title == "Test"
+
+
+def test_feedpak_module_reexports_match_sloppak():
+    for name in ("load_song", "load_manifest", "extract_meta", "resolve_source_dir",
+                 "is_pack", "is_feedpak", "is_sloppak", "read_feedpak_version"):
+        assert getattr(feedpak_mod, name) is getattr(sloppak_mod, name)
+    assert feedpak_mod.LoadedFeedpak is sloppak_mod.LoadedSloppak
+
+
+# ── feedpak_version is read ───────────────────────────────────────────────────
+
+def test_feedpak_version_read_when_present(tmp_path: Path):
+    pak = _build(tmp_path, ".feedpak", {"feedpak_version": "1.0.0"})
+    loaded = _load(feedpak_mod, pak, tmp_path)
+    assert loaded.feedpak_version == "1.0.0"
+    assert feedpak_mod.extract_meta(pak)["feedpak_version"] == "1.0.0"
+
+
+def test_feedpak_version_none_when_absent(tmp_path: Path):
+    pak = _build(tmp_path, ".feedpak")
+    loaded = _load(feedpak_mod, pak, tmp_path)
+    assert loaded.feedpak_version is None
+    assert feedpak_mod.extract_meta(pak)["feedpak_version"] is None
+
+
+def test_feedpak_version_ignores_non_string(tmp_path: Path):
+    pak = _build(tmp_path, ".feedpak", {"feedpak_version": 1})
+    loaded = _load(feedpak_mod, pak, tmp_path)
+    assert loaded.feedpak_version is None