Module error 

Public error type for the kernel’s execute surface.

An embedder reported the consequence of collapsing every execute failure into one untyped anyhow::Error: it could not tell a validator rejection (“you wrote a bad command”) from a genuine execution fault (“something broke while running”), so it routed both identically — surfacing a syntax hint to a model as if the shell itself had crashed. KernelError carries the distinction the kernel’s own control flow already makes, so a caller can match on it instead of parsing the message text.

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KernelError

Why a call to crate::kernel::Kernel::execute (or a sibling — execute_with_options, execute_argv, …) did not return a result.