The one genuine soundness defect the unsafe-proof program surfaced (flagged
SUSPECT in program 3/N). `HelperRelay` holds an `rx: Receiver<RelayAu>`, which is
`!Sync` (std mpsc is single-consumer), so asserting `Sync` claimed more than the
fields support — an `Arc<HelperRelay>` recv'd from two threads would compile and
be UB.
It was never live-exploited, and it turns out `Sync` is also unnecessary: the
relay is a single-owner `mut relay` local in the punktfunk1 two-process mux loop
(recv_timeout/try_recv/request_keyframe all called on the owning thread; no `Arc`,
no `thread::spawn` capturing it). So the fix is simply to delete the impl — the
struct keeps its sound `unsafe impl Send` (needed for the raw `HANDLE` fields),
which is all the code uses.
Box-verified: cargo clippy -p punktfunk-host --features nvenc --target
x86_64-pc-windows-msvc -- -D warnings stays green without the Sync impl.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
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