should_zext_widen decides the widening direction from the narrow side's AST
node, but the return and assignment coercions passed the statement node.
A statement has no type of its own, so the literal rule and the annotated
variable rule were skipped and the value fell through to sext:
`def f() -> uint64: return 0xDEADBEEF` produced 0xFFFFFFFFDEADBEEF and the
caller compared against 0xDEADBEEF and failed.
Unwrap Return/Assign/AnnAssign/AugAssign/Expr to their value expression
before the direction rules run, so a non-negative literal wider than
INT32_MAX zero-extends (0xDEADBEEF -> 0xDEADBEEF) and a negative one keeps
its sign (-1 -> 0xFFFFFFFFFFFFFFFF).
TermiNexus
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