id: design: rendering pipeline & conformance suite (from #5679) #5855

Summary

Follow-on design ticket from #5679 — its decomposition sketch names this as a separate design, and the parent's acceptance requires these tickets to be filed and linked. Filed in the 2026-11-04 gap pass (WS-F) so the design work exists and can be prioritised on its own merits; implementation timing is a separate decision, possibly months out.

What this design must settle

Compile/runtime split, per-target expected-output tests, and author tooling/linting for the markup and styling model.

Context from the parent

The parent design fixes the semantic markup + style-assertion model by which programs-as-websites render across web, native, and custom targets. The parent issue carries the surrounding decisions this ticket must not re-decide; where this ticket's answer would change a parent decision, record that explicitly rather than silently forking it.

Decision record expected

Close this design with a recorded decision (on this issue or in a doc/ record linked from it): the chosen shape, the alternatives rejected and why, and the invariants implementation must hold. If the design splits further, file the splits and link them here rather than growing this issue.

Relations

Parent: #5679. Programme: epic #2056. Filed by WS-F (2026-11-04 ID design gap & expansion pass).