BUG-048 backend invariant restoration¶

Finding¶

The implementation from three earlier fixes survived, but its rebase guidance did not:

commit 62b2103a9 paired CUDA module loads with module unloads, while the current CUDA feature guidance no longer stated that ownership rule;
commit 53c8ef155 repaired HIP and Metal dispatch allowlists, while the HIP scope summary still called its live dispatch strategy a stub and neither backend guidance retained the exact-name coupling; and
commit 4db777126 expanded vmaf_pre device parsing to all twelve VmafDnnDevice values, while its ADR-0482 rebase section was absent.

Current source inspection confirms all three implementations remain live. scripts/ci/check-dispatch-registry.sh and its red-cap test pass, but that checker covers extractor-symbol registration, not the separate HIP/Metal string allowlists. The restored guidance states that boundary explicitly. The FFmpeg patch stack is now pinned to n9.0.2, so the historical n8.1 replay command is intentionally not copied.

Resolution¶

Restore the ownership and exact-name rules in the backend-local AGENTS.md files and add a current ADR-0482 section to docs/rebase-notes.md. This is a documentation correction: no runtime source, public header, patch content, golden assertion, benchmark result, model, or training output changes.

Alternatives considered¶

Alternative	Benefit	Defect	Decision
Copy the historical text verbatim	Minimal archaeology	Restores retired paths, stale backend counts, and an obsolete FFmpeg tag	Rejected
Rely on source code alone	No documentation diff	Loses the ownership and cross-file coupling during later rebases	Rejected
Restate the invariant against current paths and gates	Accurate and actionable	Requires bounded source verification	Chosen

No ADR is needed because no architecture or policy changes; this recovers already-accepted maintenance contracts from surviving implementations.