Third tool in the single-study-toolkit. Consumes a report.json, beat-tracks, picks the downbeat phase where chord changes land hardest, fits maj/min triads to per-bar harmonic chroma with a small diatonic prior seeded by each phrase's key (keeps buried thirds from flipping major bars minor), and writes MAP.md (chords + degrees vs. the global key), map.json, and a three-panel fig-map. Registered as analysis.study-map. Claude-Session: https://claude.ai/code/session_01LaRrW1RHanS8it7SzgrqeV