D133 - A consumer's strict decoder found a defective fixture the checker had passed. Both are fixed

Status: derived - from orbistoun's read/call consumer, built against the spec.

docs/examples/protocol/06-read.txt carried a bytes record with 65 hex digits for a read of 0x20 (32 bytes = 64 digits) - one nibble too many to be a whole number of bytes. It survived because two things did not check it: the fixture was hand-written, and scripts/protocol.py validated a bytes record's structure but never its hex run. A consumer whose decoder refuses the impossible - rather than dropping or inventing a nibble, both invisible - is what surfaced it.

Fixed on both sides, because a defect a downstream reader catches is a defect the gate should have caught:

• The fixture now reads back 0x20 as two 16-byte records at offsets 0 and 16, each a valid 32-digit run - which also corrects a second error, that the single record ignored the server's 16-byte-per-record chunking. The fixture now matches what the live server emits.
• protocol.py now checks every bytes record's run is even-length and actually hex, and the self-test mutates a run to odd length and requires the checker to catch it. The invariant lives in the gate now, not only in the one consumer strict enough to notice.

The lesson is the same one that keeps recurring here: a parser that copes with the impossible hides it, and a strict one that refuses it is doing the contract a favour. The consumer was right to refuse and pin it; the fix is upstream, where the fixture is.