feat(player): 7-way content-dial resolution (design §6)

player/content.py

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+"""Resolve the 7-way content dial into an audio source + video on/off (§6).
+
+The single source of truth for design §6's table: which audio source plays and
+whether the projector shows video, for each dial position.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+# The four distinct audio sources. "white_noise" is generated at runtime;
+# "music" is the public-domain classical pool; "audio_track" is the clip's own
+# field audio; "none" is silence.
+AUDIO_SOURCES = frozenset({"none", "white_noise", "music", "audio_track"})
+
+
+@dataclass(frozen=True)
+class ContentResolution:
+    audio_source: str
+    video: bool
+
+
+# Design §6, one row per dial position.
+_TABLE = {
+    "off": ContentResolution("none", False),
+    "white_noise": ContentResolution("white_noise", False),
+    "music": ContentResolution("music", False),
+    "audio_track": ContentResolution("audio_track", False),
+    "video": ContentResolution("none", True),
+    "music_video": ContentResolution("music", True),
+    "audio_video": ContentResolution("audio_track", True),
+}
+
+
+def resolve_content(position: str) -> ContentResolution:
+    """Map a content-dial position to its audio source and video flag (§6)."""
+    try:
+        return _TABLE[position]
+    except KeyError:
+        raise ValueError(
+            f"unknown content position {position!r}; expected one of {sorted(_TABLE)}"
+        ) from None