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ISA spec does not match actual VM implementation #5

@SuperInstance

Description

@SuperInstance

Problem

The canonical ISA spec (derived from isa_unified.py) defines opcode values and encoding formats that differ from what the Python VM actually executes:

Instruction Spec (isa_unified) VM (opcodes.py)
HALT 0x00 0x80
NOP 0x01 0x00
MOV 0x3A 0x01
IADD 0x20 0x08
MOVI Format D, 3B (imm8) Format D, 4B (i16)

Impact

This is the #1 convergence blocker. No runtime can be simultaneously compliant with both the spec and the Python VM.

Proposed Fix

Since flux-conformance (88 test vectors, 100% pass) validates against opcodes.py, designate that as canonical and update the spec accordingly.

Discovered By

Super Z — flux-conformance suite (session 9, 2026-04-12)

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