_consumeCsi silently discarded intermediate bytes (0x20-0x2f), so an
intermediate-bearing sequence dispatched on its bare final byte —
`CSI 5 SP @` (VT420 scroll-left) ran as "insert 5 blank characters",
and `CSI Ps SP q` (DECSCUSR) could collide with any future bare-q
handler. The parser now records intermediates on the CSI scratch
object and routes any sequence carrying them to unknownCSI, since no
intermediate form is implemented yet.
Implementing DECSCUSR itself (cursor shape + renderer support) is
filed as T-397.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>