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docs(web): SAFETY comment for DerivedStateActor #445

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intendednull merged 1 commit into from
Apr 27, 2026
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docs(web): SAFETY comment for DerivedStateActor #445

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11 changes: 11 additions & 0 deletions crates/web/src/state_bridge.rs
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Expand Up @@ -84,6 +84,17 @@ impl<T: Send + Sync + 'static, U: PartialEq + Clone + Send + Sync + 'static> Han
}
}

// SAFETY: All four fields are Send under the `T: Send + Sync` and `U: Send + Sync`
// bounds on the impl: `StateRef<T>` and `Arc<Mutex<Option<U>>>` propagate Send from
// their parameters, `Arc<dyn Fn(&T) -> U + Send + Sync>` is Send by its trait object
// bound, and `SendWrapper<WriteSignal<U>>` is unconditionally Send with a runtime
// panic on cross-thread access. The actor framework requires `Send` for spawning
// across its mailbox, but the actor only ever runs on a single WASM thread (Leptos
// is browser-only), so `SendWrapper`'s runtime check is never tripped. Manual impl
// guards against future field additions silently breaking auto-derive — any new
// `!Send` field must reaffirm or remove this assertion. Tracked alongside the
// `cached` Mutex follow-up in
// docs/specs/2026-04-26-state-management-model-design.md § Follow-up F2.
unsafe impl<T: Send + Sync + 'static, U: PartialEq + Clone + Send + Sync + 'static> Send
for DerivedStateActor<T, U>
{
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