Function repo_file_decision

atomic-agent/src/integrations/install.rs:520–548

Decide what to do with a [[repo-file]] destination. Unlike [[file]] and [[skill]], a repo-file that exists but isn't ours can be *merged* — the canonical content is appended with a separator, preserving the user's existing content. If the file already contains the Atomic marker, it's treated as a refresh (replace the whole file).

(
    dst: &Path,
    previous: Option<&Receipt>,
    force: bool,
)

/// existing content. If the file already contains the Atomic marker, it's
/// treated as a refresh (replace the whole file).
fn repo_file_decision(
    dst: &Path,
    previous: Option<&Receipt>,
    force: bool,
) -> AgentResult<Decision> {
    if !dst.exists() {
        return Ok(Decision::Install);
    }
    let recorded = previous.and_then(|r| r.recorded_hash(dst));
    match recorded {
        // Ours and untouched since install → safe to refresh.
        Some(hash) if hash == hash_file(dst)? => Ok(Decision::Refresh),
        // Ours but the user changed it → hands off unless forced.
        Some(_) if !force => Ok(Decision::Skip(SkipReason::UserModified)),
        // Not ours. If it already has the Atomic marker, treat as refresh
        // (replace the whole file — it's Atomic content, just not from this
        // receipt). Otherwise merge (append with separator).
        None if !force => {
            let existing = std::fs::read_to_string(dst).unwrap_or_default();
            if existing.contains(ATOMIC_MARKER) {
                Ok(Decision::Refresh)
            } else {
                Ok(Decision::Merge)
            }
        }
        // --force: clobber everything.
        _ => Ok(Decision::Refresh),
    }
}

/// Expand a leading `~` in a destination path.
fn expand_dst(dst: &str) -> AgentResult<PathBuf> {