D123 - An opcode with no shape row is an error

Status: assumed Date: 2026-09-26

Builder::check verifies that every emitted opcode has a row in the shape table before it checks anything about identifiers.

Why: skipping an unknown opcode also skips recording its result, so the next instruction using that result is reported as referring to nothing - a false failure naming the wrong instruction. A check that degrades on unknown input has to be asked what it does with the parts that depend on the unknown.

Rejected:

• Skipping unknown opcodes: misattributed failures downstream.
• Guessing an unknown opcode's shape: reads literals as identifiers.