v0.2.1 — fix UB in submitter_free_mask when max_submitter_queues == 64 Critical UB in `Core.init` when `max_submitter_queues == 64` (the documented maximum the `Config.normalized` clamp produces). The `(1 << n) - 1` mask-construction idiom evaluated `1 << 64` on a `u64`, which panics in `Debug`/`ReleaseSafe` and silently produces a zero free-mask in `ReleaseFast`/`ReleaseSmall` (every `registerSubmitter` call returns `error.NoSubmitterSlots`). Fixed by special-casing `n == 64` to `std.math.maxInt(u64)`. Defense-in-depth `Config.validate` now rejects `max_submitter_queues > 64` with `error.SubmitterCapExceedsBitmap`. Three regression tests added: 64-slot success, 1-slot boundary, validate rejection. Verified green under Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Pipeline 2479802566 (main @ 01b5a80) — 22 succeeded, 0 hard failures across Linux unit/integration/stress/fuzz/TSan, all 4 Linux unit optimize variants, macOS build/unit/stress, cross-target smoke (x86_64-linux, aarch64-macos, x86_64-windows-gnu), zig-format, secret_detection, gitlab-advanced-sast, security-gitleaks, sbom-generate, sbom-scan, bench-micro, benchmark-regression. See docs/BUG_2026-04-25_submitter_free_mask_shift_ub.md for the full bug analysis.