prisma-risk / tsoracle / 26380778519

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refactor(paxos-toolkit): require Send + Sync on box_err input (#387)

`box_err` is the single helper that boxes storage-side errors into
OmniPaxos's `StorageResult` (`Box<dyn Error>`). It previously bounded its
input only on `Error + 'static`, so the project-wide convention that errors
are `Box<dyn Error + Send + Sync>` was not enforced at the source.

OmniPaxos hard-codes the `StorageResult` error type at `Box<dyn Error>`
(no `Send + Sync`), and every call site funnels into it via `?`. Because
`?` desugars to `From::from`, and std provides no
`From<Box<dyn Error + Send + Sync>> for Box<dyn Error>` (the wide-to-narrow
conversion is an unsize coercion that only fires at coercion sites, never
through `?`), widening the *return* type to `Box<dyn Error + Send + Sync>`
fails to compile across the call sites and would in any case be erased back
to the bare box at the trait boundary.

Bounding the *input* `E: Error + Send + Sync + 'static` is the meaningful,
compilable change: it statically guarantees every error we box is
thread-movable at the source — a future non-`Send` `StorageError` variant
would fail to compile here — while leaving the OmniPaxos-mandated return
type untouched. A doc comment records the constraint.

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