MOCK_STALWART=0.15 (or npm run mock:legacy) switches the mock to the
generation before the registry. It is not a cut-down mock: it reproduces the
specific ways that generation differs, and every one of them is a thing the
server does not report as an error.
- urn:stalwart:jmap is not a capability it knows, and naming one it cannot
parse fails the whole request rather than the one call
- x: methods do not exist; credentials live at POST /api/account/auth
- FileNode/query masks out containers, so it returns files and never folders
- FileNode has no nodeType, and rights are only mayRead/mayWrite/mayShare
Both modes now also enforce the 2047-byte signature cap, and `using` is
validated in both — the gap that let the Identity capability bug in #12 ship.
This gives the legacy credential adapter its first automated coverage: it was
the least-tested code here, checked only by hand against the live server. The
new tests also pin the mock's own fidelity, so it cannot quietly drift back to
being 0.16-shaped in the places that matter.