Pick the code from the right range (diagnostics); never reuse
a retired one.
Register it in stitchcraft-core’s diagnostics table with severity, title and the long
explanation: what it means, why it matters for the sew-out, how to fix it, an example.
Emit it where the problem is detected, with the element, a location when there is one, a
specific message (“0.18 mm tall; rows are 0.25 mm apart”) and a fix hint or applicable fix.
Trigger it in a test named diag_sc_w0305_<what>, in the crate that emits it: produce the code
from real input through the public API and assert the whole text a user reads (d.to_string() and
the fix). cargo xtask conformance --check fails until such a test exists.
Regenerate docs:cargo xtask docs adds the explanation page; consider a shot showing the
problem and the fix.