For a loop chord in the detected key, suggest up to 4 alternatives:
relative/diatonic-third sub, borrowed-minor iv colour, extension
colour, and the secondary dominant of the next chord — each with a
one-line teaching why, ranked softest to boldest. Worked through the
Am-C-F case under both the A-minor and C-major readings; circle-of-
fifths tie-in kept honest (relative + secondary-dominant are circle
moves, borrowed + extension are not). Mounts as a compact TryThis card
above RelatedProgressions in App's relatedSlot (file-disjoint). Critic
returned once (chordRootPC circular-import trap, sharp-spelled b6, one
wrong mediant claim — all copy/plumbing, rules verified correct),
fixed, re-gate waived (gate-prescribed fixes verified directly).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
vadimwit