A Table Is the Universal Renderer

Context

ADR 013 promised a host could install the gem and navigate its own dashboards the same day, which is why the engine serves an index and a frame page of its own. ADR 011 established that those pages render in the engine’s minimal layout, which loads none of the host’s assets because the engine cannot know their names or bundler. ADR 014 then had a frame render its panes inline so that the page is correct before any JavaScript.

Correct, but not complete. A chart pane is a canvas the Stimulus chart controller fills in, and the engine’s own pages deliberately load no Stimulus and no Chart.js. So a frame with two chart panes served by the engine shows two empty holes the height of a chart. The claim that those pages are a correct static dashboard was not true.

The engine could not fix this by loading a chart runtime: emitting a working module graph needs the host’s importmap or bundle, which is exactly what ADR 011 said the engine cannot assume.

Decision

Where no chart runtime exists, a chart pane renders as a table.

The engine’s own frame page passes charts: false to janela_frame, and a pane whose renderer is bar or line renders its table instead. A host’s own page renders charts normally, because a host that registered the Stimulus controllers has the runtime.

This is not JavaScript detection and it is not a fallback that guesses. The engine’s pages deterministically have no chart renderer, so they deterministically use the one that needs nothing.

A renderer is a viewing choice, not part of the pane. ADR 009 already decided this when it made a snapshot store results rather than markup, and this follows from it: the row records that a pane is best seen as a bar chart, and a surface that cannot draw one shows the same numbers another way. Nothing about the data changes.

A table is the renderer that always works, needing no JavaScript, no canvas and no measurement, which is why it is the one to fall back to rather than an error or an empty space.

Consequences

• The engine’s own pages are now what ADR 013 promised: a host mounts the engine and reads a real dashboard the same day, with no JavaScript wiring at all.
• The same frame can look different in two places: a bar chart on a host’s page and a table on the engine’s. That is the cost, it will surprise someone, and the README says so plainly rather than leaving them to discover it.
• Cross-filtering is still absent from the engine’s pages, because that genuinely needs Stimulus. They are for reading, and a host that wants interaction renders the frame in its own page, which is one helper call.
• charts: is a rendering option rather than a stored column, so no migration and nothing for an analyst to get wrong.
• If the engine ever gains a way to know a host’s asset setup, this decision is worth revisiting, because the better answer is a chart that draws everywhere.