test(cuda): kernel parity coverage round 4 — last 5 uncovered kernels

[lusoris]

CUDA kernel coverage round 4 — last 5 uncovered kernels. Final coverage: 19/19 CUDA kernels (100%) post-merge of PRs #351 + #374 + #442 + this PR.

Tests added (5 new files):

• core/test/test_cuda_float_adm_parity.c
• core/test/test_cuda_float_motion_parity.c
• core/test/test_cuda_float_ssim_parity.c
• core/test/test_cuda_speed_chroma_smoke.c
• core/test/test_cuda_speed_temporal_smoke.c

Critical finding: round-3 claimed 18 CUDA kernels — actual count is 19. ssim_cuda.c and integer_ssim_cuda.c are distinct TUs.

Pre-existing host CUDA build issue flagged: cuda_helper.cuh missing for float_motion_score.cu — tracked separately.

no state delta: coverage closure per CLAUDE.md §12 r8; T-CUDA-KERNEL-PARITY-ROUND4-2026-05-31 row added.

ADR-0108 deliverables checklist

• Research digest — docs/research/0956-cuda-kernel-coverage-round4-2026-05-31.md.
• Decision matrix — no alternatives: closeout via established parity-test pattern.
• AGENTS.md invariant note — no rebase-sensitive invariants: pure test additions.
• Reproducer / smoke-test command — meson test -C core/build-cuda --suite=fast | grep cuda_float — skip-clean on no-device, pass with real CUDA.
• CHANGELOG fragment — changelog.d/added/0956-cuda-kernel-coverage-round4.md.
• Rebase note — docs/rebase-notes.md — additive test files.

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