Spec: ../F1-keys.md · Pure declarative: signature ↔ key, both directions, both clefs, both modes. Every frame runs on any device; minors and bass clef are drill-scope toggles (02).
sig→key · the KeyPicker mode named in the prompt · clef part of the atom
KEYS · 3/7Rehearsalaway · no device
Which major key is this?
E major 1.2s · Good
Major mode, treble clef. The full 12-key wheel: chance is honestly 1/12, distractor design doesn't exist, and the circle-of-fifths layout quietly reteaches neighborhood every rep. One reusable widget for the whole app. Knowledge frames keep the portrait phone.
KEYS · 4/7Rehearsalaway · no device
Which minor key is this?
C minor 1.8s · Good
Minor mode. Only the prompted mode's ring shows before the answer — a full-size ring of minors, no major labels to lean on. The relative pairing (c ↔ E♭) is revealed with the confirmation. Minors are a drill-scope toggle, not a schema change.
KEYS · 5/7Rehearsalaway · no device
Which major key is this?
D major 1.5s · Good
Bass clef. The same signature sits differently on the bass staff — reading it there is its own visual memory, so clef is part of the atom's identity in both directions. A drill-scope toggle like minors.
key→sig · the SignaturePicker engraved glyphs, not counts
KEYS · 6/7Rehearsalaway · no device
B major
Tap its signature
5♯ — F♯ C♯ G♯ D♯ A♯ 1.9s · Good
key→sig on the engraved grid. All twelve signatures as real glyphs — the answer is visual matching, which builds the memory that reading actually uses; the grid doubles as a reference chart. Ordered by count (sharps, then flats); rendered in the configured clef; minor prompts ("g♯ minor") answer on the same grid. Confirmation spells the accidentals in order.