drogna

A demonstration harness. Every number in it is invented.

The check worked, and the drawing still had to go

The background

Every architecture diagram starts accurate. Then something lands, the picture does not change, and nothing says so. Code that drifts from its callers fails a test; a drawing that drifts just lies quietly, to exactly the readers who trusted it most. So — can a diagram be made to fail?

The requirement

The first tab a visitor opens was a numbered list of what had been built: a changelog, written for someone who already knew what the thing was. It had to become a picture of the shape, grown one part at a time under the arrow keys, and stay true with nobody maintaining it.

The options considered

It can. Four passes drew the declared parts, labelled from configuration and wired from the real topology, and a build check failed on any part the picture had not decided about. It fired the week it was written — a merge added a component, the build named it, and a caption about that component's neighbour turned out to have gone false earlier still.

Then the picture was made abstract: six roles, not one component named. All of that retired with it. The check was never wrong; it was propping up a claim the page should not have been making — these are all the parts — which another tab already answers properly. A drawing that names nothing cannot go stale, because it never said it was the list. The repair was a smaller claim, not a stronger check.

The demo

A recording of the Intro tab. Across the top the shell header shows the simulated time 2026-01-01T00:00:00Z and the words 'rate 0', with the Intro tab selected below it. Under the heading a paragraph ends 'The movement below is an illustration on a fixed cycle'. The drawing beneath is a row of four labelled boxes with wide gaps between them: Measurements ('what was found, and where'), Divergence ('measured against believed'), Model run ('assimilate, re-forecast') and The forecast ('what is believed'). Each gap is a rounded track with an arrowhead at its right end and a caption above and below it — the first is labelled SensorThings and carries five small teal squares strung out along it, the next MQTT divergence, the next 'a new field'. A wider track labelled MQTT run published runs the full width below the row, and under that a second lane holds one box, A client ('this page, or anything'). Throughout the recording the teal squares slide steadily left to right along the SensorThings track and wrap round to the start, and single marks appear on the other tracks and cross them; the header still reads rate 0. Partway through, two more tracks — OGC API-EDR request and CoverageJSON response, the second travelling right to left — and a final box, What came back ('a slice, and a trajectory'), fade into the lower lane beside A client.

The clock is pinned at zero throughout and the messages move regardless: an illustration on a fixed cycle, not a readout. Open it, press the right arrow six times, and click something crossing a gap to read it.