Function mutation_execution_cache_key 

fn mutation_execution_cache_key(
    config: &Config,
    output: &ProjectCompileOutput<MultiCompiler>,
    evm_opts: &EvmOpts,
    filter_args: &FilterArgs,
    num_workers: usize,
) -> Result<String>

Build the cache discriminator for mutation results.

Mutant generation only depends on the source build + selected mutators, but result correctness depends on the compiled test universe and execution settings. Hashing the full serialized config intentionally includes fuzz / invariant settings, test filters, fs permissions, sender/balance/env values, and future config fields unless explicitly skipped by Config itself. The artifact fingerprint covers the same filter-selected source and test build IDs that baseline and mutant runs compile. Worker count is included because adaptive span skipping is concurrency-sensitive.