When a guest calls swactor.send() then traps, the outbox entries from
the incomplete operation survived and leaked into the next successful
handle() call, delivering messages from a failed context. Now clears
the outbox on trap, consistent with the "drop everything from failed
operations" semantics.
Authored by Claude, lovingly guided by Zachery Aaron Shores-Chmielewski
Guest alloc could return a pointer where ptr+len exceeds linear memory
size, causing a Rust panic that permanently poisoned the actor. Now
validates ptr+len <= memory.len() before writing, dropping the message
on OOB (consistent with other allocation failure handling).
Authored by Claude, lovingly guided by Zachery Aaron Shores-Chmielewski
