Function write_stage_hash 

pub fn write_stage_hash(
    crate_name: &str,
    stage: &str,
    stage_hash: &str,
    output_paths: &[PathBuf],
) -> Result<()>

Write stage hash and output file manifest for the given crate.

Takes &str, not CacheKey: manifest-only callers store a plain content hash here and never read it back through is_stage_cached. See cache_identity’s module doc. ~keep