fix(ci): unblock libvmafx_tad link error + orphan test_ansnr_simd

[lusoris]

Summary

• Root cause A (TAD link error): enable_rust_features defaulted to true in core/meson_options.txt. GitHub Ubuntu runners have cargo but lack cbindgen (a build dependency of the TAD crate's build.rs). The cargo build step silently produced no .a, but the linker still received libvmafx_tad.a as a link_arg propagated transitively from the libvmaf library's rust_tad_dep dependency. Result: 44 link failures on every non-Rust CI job (PR fix(ci): post-rename path refs (unblocks merge train) #46 and all queued PRs refactor(core): C++23 pilot — mem.c → mem.cpp (ADR-0720) #41, refactor(core): C++23 pilot Wave 1 — opt.c → opt.cpp (ADR-0721) #43–refactor(core): cpp23 Wave 2 — project-wide cpp_std=c++23 + dict.c → dict.cpp #48).
• Root cause B (test_ansnr_simd): PR feat(core): drop legacy ansnr feature (pre-VMAF, never Netflix-adopted) #38 (feat/drop-ansnr-20260528) deleted core/test/test_ansnr_simd.c but did not remove the executable() + test() declarations from core/test/meson.build. Meson halted with ERROR: File test_ansnr_simd.c does not exist on all CPU arches, blocking the build before the TAD link step.

Fix path chosen: default enable_rust_features=false (safest — no CI image changes needed) + remove orphan ansnr test declarations.

Changes

• core/meson_options.txt: enable_rust_features default true → false. Opt in via -Denable_rust_features=true when a full Rust + cbindgen toolchain is present.
• core/test/meson.build: removed orphan test_ansnr_simd executable() + test() blocks.
• changelog.d/fixed/ci-libvmafx-tad-link.md: fragment per ADR-0221.
• docs/state.md: recently-closed row for T-CI-LIBVMAFX-TAD-LINK-2026-05-28.
• docs/rebase-notes.md: note for future Rust-extractor PRs.

Test plan

• meson setup build core -Denable_cuda=false -Denable_sycl=false — completes without error (enable_rust_features not in output = false default)
• ninja -C build — 724/724 targets, test_context links cleanly
• meson test -C build --suite=fast — 49/49 pass
• CI: all standard build matrix legs should proceed past the link step

Reproducer

/usr/bin/ld: cannot find /home/runner/work/vmafx/vmafx/core/build/src/libvmafx_tad.a: No such file or directory

Reproduced by: meson setup core/build -Denable_rust_features=true on a host with cargo but no cbindgen, then ninja -C core/build.

Deep-dive deliverables checklist

• research digest: no digest needed: pre-existing master bug fix
• decision matrix: no alternatives needed: only-one-way fix
• AGENTS.md invariant: no rebase-sensitive invariants beyond rebase-notes.md entry
• reproducer: exact error string above + fix command
• changelog fragment: changelog.d/fixed/ci-libvmafx-tad-link.md
• rebase-notes.md: entry added for enable_rust_features default change

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no user-discoverable surface change — no per-surface docs required (ADR-0100 §exclusions: internal refactors + bug fixes with no user-visible delta)

🤖 Generated with Claude Code

[lusoris]

Superseded — rust default flip landed via PR #46 (commit 3cdc9f2).