AI coding agents make changes at scale. A single session can touch dozens of files — refactoring functions, updating dependencies, modifying configuration. When something goes wrong, you need a reliable way to undo everything without manually tracking what changed.

nono's snapshot system captures the filesystem state before every agent session and lets you restore it with a single command.

How snapshots work

When nono starts an agent session, it walks every file in the sandbox scope and stores a content-addressed copy. Each file is hashed with SHA-256, and the hash is used as the storage key. This means:

Identical files share storage (deduplication)
The snapshot database grows only by unique content
Verification is built in — corrupted files produce different hashes

After the session ends, a second snapshot captures the final state. The diff between the two snapshots tells you exactly what changed.

Listing sessions

bash

nono sessions list

This shows all recorded sessions with their IDs, timestamps, and number of files changed.

Reviewing changes

Before deciding to undo, review what the agent changed:

bash

nono diff <session-id>

This produces a unified diff showing:

New files (added by the agent)
Modified files (with line-level changes)
Deleted files

Tip

Pipe the diff output to your preferred review tool. For example, nono diff latest | delta for side-by-side rendering with syntax highlighting.

Undoing a session

To restore all files to their pre-session state:

bash

nono undo <session-id>

This is an atomic operation — either all files are restored or none are. The undo itself is recorded as a new snapshot, so you can undo the undo if needed.

Selective restoration

Sometimes you want to keep some of the agent's changes but revert others. nono supports file-level selective restoration:

bash

nono undo <session-id> --files src/auth/middleware.ts package.json

This restores only the specified files, leaving all other agent changes in place.

Practical workflows

Experiment-and-compare

Run multiple agent sessions with different prompts or configurations, then compare the results:

bash

# Session 1: conservative approach
nono run --allow ~/projects/myapp -- claude "refactor auth module"
nono diff latest > approach-1.diff

# Undo and try again
nono undo latest

# Session 2: aggressive approach
nono run --allow ~/projects/myapp -- claude "rewrite auth module from scratch"
nono diff latest > approach-2.diff

Compare the two diffs and keep the better result.

CI integration

In CI pipelines, capture a snapshot before the agent runs and automatically revert if tests fail:

bash

nono run --allow . -- claude "fix failing tests"

if ! npm test; then
  echo "Agent changes broke tests, reverting"
  nono undo latest
  exit 1
fi

Warning

Snapshots are local to the machine where nono runs. They are not synchronized across CI workers or team members. For shared state, commit the agent's changes to a branch and use standard git workflows.

Storage management

Snapshots accumulate over time. To see storage usage:

bash

nono sessions stats

To prune old snapshots:

bash

nono sessions prune --older-than 30d

This removes snapshots older than 30 days while preserving the content-addressed store entries that are still referenced by newer snapshots.

Next steps

Read the Undo & Rollback infrastructure page for technical details on the snapshot format
Read the Audit Trail page to understand how snapshots integrate with the cryptographic audit log
Check the full documentation for the complete snapshot CLI reference