Function compute_body_hash 

pub fn compute_body_hash(arity: u16, locals_count: u16, code: &[Op]) -> BodyHash

Hash a function body so that two structurally-identical bodies — the fn(x) -> x + 1 literal repeated at two source locations, two flow trampolines built from the same shape, etc. — yield the same hash.

Inputs: the bytecode Op sequence, the arity, the locals count. Capture types are intentionally not hashed: capture values already participate in Value::Closure’s equality through the captures field, so two closures with different capture values already compare non-equal regardless of the hash. Capture types without values don’t add equality information that captures don’t already provide (a value of type Int and a value of type Str can’t both be 42).

Constants pool indices referenced from the body are not resolved before hashing — within a single compile the pool is shared, so two equivalent literals produce identical Op sequences. Cross-compile canonicality is deliberately out of scope (#222).