U3: both array shapes read fine but every write failed BadInternalError.
String[] now encodes each element at its register width (StringLength chars,
2 per register); BitInRegister[] reads the span once, flips the addressed bit
of each register and writes the span back with FC16 (per-register RMW locks
taken in ascending order). A length mismatch is BadOutOfRange and sends
nothing. DriverArrayWriteSupport (outside this lane) still advertises these
nodes read-only - recorded as follow-up F1 in the parity test.
Refs #741
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT
Joseph Doherty