Fail-closed medium auto-detect (§5). Routes pasted/dropped data to an engine,
but NEVER upgrades an ambiguous artifact onto the identical path: anything
markup-shaped that isn't a recognized entviz SVG, a bare URL (fetch-vs-value is
the user's call), or an unrecognized data URL returns ambiguous for the caller
to reject or route to the least-authoritative (raster) engine.
Fail-closed medium auto-detect (§5). Routes pasted/dropped data to an engine, but NEVER upgrades an ambiguous artifact onto the
identicalpath: anything markup-shaped that isn't a recognized entviz SVG, a bare URL (fetch-vs-value is the user's call), or an unrecognized data URL returnsambiguousfor the caller to reject or route to the least-authoritative (raster) engine.