The in-flow value line grew the card downward, dropping its vertical centre —
and the left/right handles with it, so connected pipes and links shifted. Render
the value as an out-of-flow overlay below the box; the card keeps its size and
the handles stay put.
A Stock can carry a display unit (°C, people, $, …): a new optional field, an
inspector text input, validation + round-trip in io, and a readout beside the
live value on the canvas. Equip the demonstrative samples (Water L, Balance $,
Coffee °C, Population/Epidemic people, Yeast cells). Also bumps the fill gauge
opacity for a more vivid level.
A simulation store owns one run and one playhead, so the chart and the canvas
read off the same instant. While the panel is open, Stocks show a live value and
a fill gauge, Flows and Converters their current value; a play/pause + scrubber
drives the playhead (a wall-clock-paced clock in usePlayback), and a marker
tracks it on the chart.
