Duplicate change id's after rebase

[avsaase]

Hi, new to jj. Overall I'm loving it but I ran into a problem when rebasing a bookmark onto the main branch in my git colocated repo. On the remote we use squash merge on our PR's.

Our CI requires that all branches are up to date with main so this morning I tried to rebase my changes with

jj gitch fetch
jj rebase -b SED-1514-cbc-config -d main
jj git push

The rebase itself and pushing to the remote works fine but now my jj log has question marks at the end of the change id's that where rebased:

@  vrrxsprz [email protected] 2025-07-10 10:16:03 d2deb92e
│  Refactor telemetry-api error handling
│ ○  nmvkwzml?? [email protected] 2025-07-09 16:14:50 SED-1514-cbc-config bebb5c55
│ │  CRUD endpoints in public-api
│ ○  qlussoqn?? [email protected] 2025-07-09 16:09:26 203f9a24
│ │  Increment cache key
│ ○  tuqyvosm?? [email protected] 2025-07-09 16:09:26 90d18289
│ │  Fetch CBC in integrate-with-gopacs instead of matching on meter EAN code
│ ○  nypllzxw?? [email protected] 2025-07-09 16:09:26 914f1be1
│ │  Use EAN code type in UFTP messages
│ ○  nrwumwtx?? [email protected] 2025-07-09 16:08:54 e1252456
├─╯  Add grid connection contract types and add CRUD endpoints in resource API
◆  rpklytko [email protected] 2025-07-09 09:53:00 main v0.9.303 git_head() a5a36627
│  Format imports (#508)
 ~  (elided revisions)

When I try to create a new change on top of any of the rebased changes I get

# jj new nm
Error: Revset `nm` resolved to more than one revision
Hint: The revset `nm` resolved to these revisions:
  nmvkwzml?? bebb5c55 SED-1514-cbc-config | CRUD endpoints in public-api
  nmvkwzml?? 1e75d79c CRUD endpoints in public-api
Hint: Some of these commits have the same change id. Abandon the unneeded commits with `jj abandon <commit_id>`.

I tried to undo the rebase with jj undo but I had already ran some other operations after the rebase so that didn't work. I then tried to restore to a previous good state with jj op restore but that didn't solve the duplicate change id's.

Yesterday I ran into the same error and solved it by manually removing the duplicate changes based on their commit id's. This was very annoying so I'd like to find a different solution this time. How do I get my repo in a working condition again? And how do I avoid this problem in the future?

Yesterday I may have done a rebase using git instead of jj because of muscle memory. Did that cause this problem?

[avsaase]

After some troubleshooting on discord we've found that this is caused by the automated tagging of commits in our CI. jj git fetch unconditionally fetches all tags from the remote and

the tag exists, which makes the commit it points to visible, which means there are multiple visible commits with the same change id, which is divergence

In my case I don't care about the tags on my local machine so a workaround is to add this alias to my jj config to delete all tags after fetching:

fetch = ["util", "exec", "--", "bash", "-c", """
set -euo pipefail
jj git fetch > /dev/null 2>&1
git tag | xargs git tag -d > /dev/null 2>&1
"""]

It's not pretty but it works.