jj v0.46, second read: the on-ramp widened, the undo grew guardrails

And the lie this piece refuses: that a version number is news. Most point releases are plumbing. v0.46.0 is not — it changes the switching calculus, and the fortnight's demand data explains why that matters more than the changelog admits.

THE FORTNIGHT RECORD

Numbers first, because they are the only part of this piece nobody can argue with.

Stars are vanity, cadence is signal: two releases inside six weeks with breaking changes properly listed is a project that ships and tells you what it broke. The 1,260 open issues read the same way — a moving tool, not a finished one.

Our own ledger carries the second signal. The single biggest impression family on the git cluster this month is still undo a commit but keep the changes — impressions up 100% week over week, and almost zero clicks, because the honest git answer runs three commands deep and readers can tell. The demand for undo did not wait for jj. It never does.

JUJUTSU VS GIT: THE UNDO TABLE

The first read explained the model — the working copy is a commit, every operation writes to the operation log, conflicts are first-class. What it skipped, and what the search data says people actually need at 6am, is the phrase-level table: the job, typed the way searchers type it, in both dialects.

In git, undo is archaeology — dig through the reflog, find the shard, rebuild. In jj, the tape was never buried: undo is an operation on the log of operations. Excavation versus a rewind button.

Picture it: git gives you the flight recorder — mounted behind the plane, readable after the crash. jj mounted it on the dashboard and wired it to a rewind button.

V0.46.0: THE TWO CHANGES THAT MATTER

Workspaces that colocate through real git worktrees. jj workspace add --colocate (or the git.colocate setting) puts a jj workspace beside a plain git checkout without taking the clone over. Read that as the on-ramp widening: a team can run one jj workspace next to a git checkout on the same machine, the same repository, and compare — which is exactly the trial the first read's verdict asked for. It leans on git worktree add --orphan, which is why the minimum git rises to 2.42.0.

Undo that knows its boundaries. jj undo and jj redo now refuse to touch operations from another workspace unless you pass --allow-cross-workspace. A tool whose entire pitch is "undo is safe" tightening the guards around undo is the culture test passing. The rest of the notes read the same way: jj bisect run checks its good and bad endpoints before walking, and jj split stops juggling editor sessions.

TRY THE RECORDER WITHOUT RISKING ANYTHING

A throwaway clone, three commands, and the ledger is real on your box — not just in the docs.

# in a throwaway clone — git keeps working exactly as before
jj git init --colocate

# a .jj directory now sits beside .git; the recorder is running:
jj op log

# the door out, whenever you want it:
rm -rf .jj

verify: jj op log in that clone lists your operations with timestamps — one line per command means the ledger is real.

THE HONEST LEDGER: WHAT BREAKS

Muscle memory, first. The index dance — git add -p, partial staging — maps to jj's squash and split, which solve the same problem with different hands. For the first week you will type git verbs and be annoyed.

Team optics, second. Colocated repositories look like plain git to hosting and to teammates — but a jj user's working-copy commits only become visible when pushed, and "where is my half-finished work" gets a different answer than git people expect. Small teams shrug; monorepos with deep tooling should wait. v0.46's cross-workspace undo refusal is one more boundary to learn — deliberately, and honestly, the right call.

And the receipt still missing: benchmarks. Two reads in, the claim remains unmade. We cannot tell you jj's rebase beats git's on a 10,000-commit repository, because we have not run it — that number does not exist until the bench does, and a second read does not turn a record-read into a bench.

VERDICT, REVISED: WHO MOVES THIS WEEK

The first read said: trial it. Two weeks and one release later, the calculus moved in exactly one direction — v0.46's worktree colocation lowered the cost of the trial itself, and the demand data hardened. The undo family our board tracks did not cool by a single impression; the tool that answers it in one command shipped twice. When a gap that wide keeps widening, someone is going to close it. jj is closing it at the model level, not the mnemonic level — the full comparison sits beside the classic decision it disturbs: revert vs reset, which now has a third answer, and the third answer is a button.

Two questions before that bench: has a reflog rescue ever failed you at the worst possible moment — and if you run jj in anger this month, what breaks first? Tell us what to test.

end of the second read · nothing fetched · everything local