feat: add recommendation domain foundations

backend/tests/test_profile.py

@@ -0,0 +1,46 @@
+"""Tests for compact taste profile construction."""
+
+from app.domain.models import TasteProfile, Track
+from app.domain.profile import compress_taste_profile
+
+
+def test_profile_compression_includes_bounded_signals_and_known_ids() -> None:
+    short_track = _track("short", "Quick Song", "Quick Artist")
+    long_track = _track("long", "Lasting Song", "Lasting Artist")
+    saved_track = _track("saved", "Saved Song", "Saved Artist")
+    profile = TasteProfile(
+        short_term_artists=("Current Artist",),
+        long_term_artists=("Enduring Artist",),
+        short_term_tracks=(short_track,),
+        long_term_tracks=(long_track,),
+        saved_tracks=(saved_track,),
+    )
+
+    compressed = compress_taste_profile(profile)
+
+    assert compressed.text.splitlines() == [
+        "Short-term top artists: Current Artist",
+        "Long-term top artists: Enduring Artist",
+        "Short-term top tracks: Quick Song by Quick Artist",
+        "Long-term top tracks: Lasting Song by Lasting Artist",
+        "Saved-track sample: Saved Song by Saved Artist",
+    ]
+    assert compressed.known_track_ids == frozenset({"short", "long", "saved"})
+
+
+def test_empty_profile_sections_are_explicit() -> None:
+    profile = TasteProfile((), (), (), (), ())
+
+    assert compress_taste_profile(profile).text.count(": none") == 5
+
+
+def _track(track_id: str, title: str, artist: str) -> Track:
+    return Track(
+        id=track_id,
+        uri=f"spotify:track:{track_id}",
+        title=title,
+        artists=(artist,),
+        album_name="Album",
+        album_art_url=None,
+        external_url=None,
+    )