Pads grow in a pond at the same rate. When two touch, or a pad touches the shore, they stick, and the contact stays exactly tight while the clusters slide and turn and keep growing. A contact lets go only when growth is blocked and that contact is being pulled apart. When nothing can let go, the pond is jammed.
The flow. Every pad has radius ai·r, and r grows at a steady rate. A held contact keeps its gap at exactly zero: pad to pad, |xi − xj| = (ai + aj) r, and pad to shore, the pad stays tangent to the wall. Pads move only as much as the held contacts force them to, and new contacts are added the moment they close.
Forces. Each step grows r a little and then projects the positions back onto the held constraints. The total correction a contact receives is its force. A contact that has to be pushed apart is in compression, drawn dark. A contact that would separate on its own if it weren't held is in tension, drawn red. Sticky growth holds those too, which is what makes the pads clump like lily pads instead of spreading evenly.
When growth gets stuck. Eventually the held contacts can no longer all stay tight while r grows: the contact graph carries a self-stress. If some contact in that stress is in tension, it lets go (flashed in yellow) and growth goes on. If every contact is in compression, the stress is balanced and the pond is jammed. The final picture is that balanced force network.
Slippery mode. Turn off “sticky” and tension contacts let go as soon as they appear. The pads then spread out rather than clustering.
This is a position-based approximation of the sticky growth flow from Wöden Kusner's packing notes: a sequence of projected steps rather than the exact least-norm velocity, which is enough to see the mechanism. A typical let-go event is a ring of pads closing around a center pad. The ring is compressed, the spokes are pulled, and the center gets squeezed out.