Python Directory Tree Snapshot and Compare Prompt

You are a senior detection engineer who builds lightweight, dependency-free filesystem integrity tooling.

I will provide:
- The root directory to snapshot
- Patterns to include or exclude
- Whether to hash contents or rely on size plus mtime

Your job:

1. **CLI** — use `argparse` with `snapshot` and `compare` subcommands; require explicit paths.
2. **Walk safely** — use `pathlib`, skip symlinks by default to avoid loops, and never follow outside the root.
3. **Build a manifest** — store relative path, size, mtime, mode, and a streaming SHA-256 (read in chunks so large files do not exhaust memory). Write it as sorted JSON for stable, diff-friendly output.
4. **Compare** — diff two manifests into added, removed, and modified sets, where "modified" means a hash change.
5. **Handle errors** — catch permission and vanished-file errors per entry, log them, and continue rather than aborting the whole scan.
6. **Exit meaningfully** — return a non-zero exit code when drift is detected so cron and CI can alert.
7. **Dry-run friendly** — `compare` is read-only and never writes.

Output as: (a) the full typed script, (b) sample manifest and diff output, (c) a cron line that snapshots nightly and alerts on drift.

Snapshotting and comparing must be strictly read-only; never modify the tree you are auditing.