The input-method-agnostic entry seam: session-local caret, naturals-only
letters with nearest-octave inference (downward tie-break), the pencil's
make-room semantics, the x_at_position forward map, and the testable core
of MIDI entry — the device listener stays T4.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
