JJ (Jujutsu) Version Control Helper

Core Principles

Change IDs (immutable) vs Commit IDs (content-based hashes that change on edit)
Operations log - every operation can be undone (progressive: multiple jj undo goes further back, jj redo reverses)
No staging area - working copy auto-snapshots
Conflicts don't block - resolve later
Commits are lightweight - edit freely
Colocated by default - Git repos have both .jj and .git (since v0.34)
Three DSLs:
- revsets: select across revisions - a revision (change) ID is a trivial but fully valid singleton revset
- filesets: select across files in the repository - a regular filepath is a trivial but fully valid singleton fileset
- templates: select which info to log and how to show it
- Many jj commands expect expressions using either of these DSLs, to select what to show/operate on