SEMI E5 allows identifier fields (DATAID, RPTID, VID, CEID, ALID,
EXID, OBJID, …) to be encoded as U1, U2, U4, or U8. Our parsers
route through any_unsigned_first<T> in messages_helpers.hpp. The
existing per-message round-trip tests prove the U4 path; this
commit adds the cross-width matrix that the interop incident with
secsgem-py demanded:
- as_u4_scalar accepts U1/U2/U4/U8 inputs for the same value
- as_u8_scalar accepts every narrower width
- as_u1_scalar accepts wider widths when the value fits
- as_u1_scalar / as_u2_scalar REJECT out-of-range values rather
than silently truncating
- codec round-trip preserves the format byte AND the value
- signed counterparts (as_i4_scalar) follow the same rule for I1/I2
If a future code-gen change hard-codes a single width on any
identifier field, the rejection case here breaks loudly.
Closes#12 in the test-gap backlog (renumbered: this is gap entry
"identifier wildcard matrix").
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
