Audio can drive emphasis in a composition but cannot move focus on the beat in the current rig

In the 4-bin browser rig, audio can drive compositional emphasis: a band amplitude can push a focal region’s brightness or scale, using the audio-reactive-map pattern. This creates a reactive sense of depth and weight responding to music energy. However, moving focus ‘on the beat’ — i.e. changing which region is the focal point in response to a precise beat event — is not yet possible. The tempo-locked-change concept is not-yet-possible in this rig because Hydra and GLSL have no tempo or beat-phase signal; the only current proxy is a band’s amplitude envelope.

Examples

Bass amplitude drives a central shape’s scale (+10-30%) on loud hits — this is realizable. Switching the focal point to a new region exactly on beat 1 — this is not-yet-possible.

Assessment

Explain why scaling a shape with a.fft[0] is realizable but moving the focal point on the beat is not, citing what signal is missing in the rig.