nx_fnptr_call_gate.nx

nx_fnptr_call_gate.nx -- THE MONITOR PILLAR for indirect (function-pointer) calls. WHY THIS FILE EXISTS, AND WHY IT LIVES HERE: seq715 was a SILENT MISCOMPILE: `obj.fn_field(args)` compiled cleanly, emitted the function's ADDRESS instead of an indirect call, and DISCARDED the argument list -- so every multi-method vtable in the tree (CLAUDE rule 6 OOP) was quietly broken and the caller received a code-segment pointer that reads as a plausible integer. It failed OPEN. A monitor for exactly this already existed -- bench/nx_fn_ptr_struct_call_smoke.nx, the MONITOR pillar of the 2026-05-19 four-pillar fix -- but it lived in bench/, and nx_sov_build_run only probes runtime/_hdl_build/, runtime/, nxasm/ and runtime/wiki/. It resolved to SOURCE-NOT-FOUND, so the watchdog was never once runnable and the regression sat undetected. A guard the build cannot reach is not a guard. This gate therefore lives in runtime/_hdl_build/ where the driver WILL find it. SELF-TESTING BY CONSTRUCTION: this gate is compiled by the compiler it tests. If the indirect-call path breaks again, the gate's own calls return garbage and it goes RED. There is no separate oracle to drift out of sync. license_tier: ORIGINAL No hw writes (Rule 26).