fix(lang): surface orig in errors and flag the original audio track over the API

Error messages named the resolved language for a user who only ever defaulted to orig. Audio tracks now carry is_original, resolved through Tracks.by_language so it agrees with the downloader.

tests/lang_selection/test_as_requested.py

@@ -0,0 +1,24 @@
+from __future__ import annotations
+
+from typing import Optional
+
+import pytest
+
+from unshackle.core.utilities import as_requested
+
+
+@pytest.mark.parametrize(
+    "tokens,orig_token,expected",
+    [
+        # the user passed no -l, so orig resolved to en behind their back; report orig
+        (["en"], "en", "orig"),
+        (["en", "ja"], "en", "orig, ja"),
+        # the user named en, so report en
+        (["en"], None, "en"),
+        (["ja"], "en", "ja"),
+        (["en", "ja"], None, "en, ja"),
+        ([], "en", ""),
+    ],
+)
+def test_as_requested(tokens: list[str], orig_token: Optional[str], expected: str) -> None:
+    assert as_requested(tokens, orig_token) == expected

tests/lang_selection/test_original_audio_ids.py

@@ -0,0 +1,43 @@
+from __future__ import annotations
+
+from typing import Optional
+
+import pytest
+
+from unshackle.core.api.handlers import original_audio_ids
+
+
+class FakeTrack:
+    def __init__(self, language: str) -> None:
+        self.id = language
+        self.language = language
+
+
+class FakeTitle:
+    def __init__(self, language: Optional[str]) -> None:
+        self.language = language
+
+
+@pytest.mark.parametrize(
+    "title_language,track_languages,expected",
+    [
+        # paradigm collapse: CLDR calls these the same language, RFC 4647 picks the specific one
+        (["en"], ["en", "en-US"], ["en"]),
+        (["en"], ["en-US", "en-GB"], ["en-US"]),
+        (["pt"], ["pt-BR", "pt-PT"], ["pt-BR"]),
+        (["es"], ["es-ES", "es-419"], ["es-ES"]),
+        # non-paradigm regionals: exact mode drops them, so the fuzzy fallback catches
+        # them and the flag still matches what a default 'orig' download selects
+        (["es"], ["es-419"], ["es-419"]),
+        (["fr"], ["fr-CA"], ["fr-CA"]),
+        # alias
+        (["zh"], ["cmn"], ["cmn"]),
+        # nothing in the original language, and no language on the title at all
+        (["en"], ["ja", "de"], []),
+        ([None], ["en"], []),
+    ],
+)
+def test_original_audio_ids(title_language: list, track_languages: list[str], expected: list[str]) -> None:
+    tracks = [FakeTrack(t) for t in track_languages]
+    ids = original_audio_ids(tracks, FakeTitle(title_language[0]))
+    assert [t for t in track_languages if t in ids] == expected