[antono3]

Summary

• Use an overflow-checked int byte count for vmemset, accepted by both supported V and current V master.
• Preserve normal H.264 alignment padding; reject lengths beyond max_int before narrowing.
• Add regressions for boundary/overflow lengths and zeroing only the intended buffer region.

Verification

• Reproduced the old isize argument error with V master 4394f53933a3939edf0c7afe14c8f4d84d97509e; the patched frontend check passes.
• All four V test files pass with supported stable V 0.5.2 and TinyCC.
• Fresh VPM dependency graph resolves all seven expected tags; clean native ImGui 0.4.0-standard rebuild and player build pass.
• Hardware Vulkan Video playback with the Dear ImGui overlay was visually checked on GTX 1060; Escape exits cleanly.
• Current-V full C compilation is advisory and evaluated separately; supported compiler/dependency pins are unchanged.

[antono3]

Additional current-master diagnostics: with V 4394f539 the padding patch passes frontend checking and full TinyCC compilation against the released dependency graph. The resulting current-V binary still faults during Vulkan instance initialization, independently of padding execution. The supported stable-V binary plays the sample with the real ImGui 1.93 overlay and exits cleanly. This PR fixes the reproduced length-signature incompatibility only; it does not claim full moving-master runtime support or change supported toolchain pins.