nx_fnident_probe.nx

nx_fnident_probe.nx -- MINIMAL ISOLATION for seq1337 (nx_cc hangs on a local named `fn`). The gate-file repro renamed TWO identifiers at once (fn + en), so which one hangs was UNPROVEN. This probe changes exactly ONE thing from a trivially-compiling program: a local named `fn`. If /api/build hangs on this and the `en` sibling builds, `fn` is the token, isolated. license_tier: ORIGINAL expect_exit: 0 No hw writes (Rule 26).