test: authenticate first-use ISA authority

[zhoubot]

Summary

• authenticate the compiled LinxISA catalog containing the first-use exception contract
• add a negative mutation test for the exact first-use cause value
• preserve PTO 0.58.1 lock/release hashes and codec counts/tables

Verification

• generator checks 8/8
• clean CMake/Ninja build
• CTest 12/12
• generated codec tables unchanged

[zhoubot]

Hosted st rerun is stuck in Install toolchain and has not reached configure/tests. The exact-head sanitizers job checked out LinxISA authority e8aa0e2179184df6b3d410163baaa566b92d392e and passed the complete 12-test CTest set, including system and codec freshness. UT, Debug/Release, format, lint, docs also pass; local ordinary build/CTest is 12/12. Merging with administrator authorization records st as an infrastructure-pending lane, not a pass.