The alpha.1 handover refused 27 extensions so DSH's own document preview
could own them, but nine of those have NO host renderer at all: `avif` and
`ods` sit in `document/unviewable.ts`'s "known binary, no renderer" list
and get the unsupported empty state directly, while `xlsb` / `xlt` /
`xltx` / `xltm` / `ots` / `dot` / `dotx` fall through to the plain-text
body, fail the binary check and land on the same dead end.
Before that handover these files reached the plugin's `code` catch-all and
rendered the binary-download pane, so refusing them was a user-visible
regression we introduced ourselves — and rc.1 did not restore it. They are
claimed again (`fods` stays handed over: the host shows that flat XML as
plain text, which beats a download pane).
`canOpen` had zero test coverage, which is exactly why the regression went
unnoticed, so `tests/native-surface.spec.ts` now pins both directions:
every format the host renders must be refused, every format it cannot
render must be claimed. Reverting to the old list makes it fail with
`macro.xlsb: expected false to be true`.
Menghuan1918
1d01ad942c