--fast-forward-merge with >1 local commits silently drops the other side's work

Lore version

lore 0.9.0+783

Installation method

Prebuilt release binary

Operating system / architecture

Windows -- x86_64

Steps to reproduce

1. A pushes a new file A.txt
2. B, before calling lore sync, creates 2 local commits, changing B.txt and C.txt
3. B calls lore branch push --fast-forward-merge to let the server auto-merge the 2 local commits

Result: The first commit is merged successfully, the second commit is just fast forwarded on top of the server merge, basically overwriting the entire tree with its state, silently without any errors. Any user that now syncs is missing the file A.txt entirely.

history (A's commit is still in it): 4 C.txt (fast forward) 3 B.txt (merged) 2 new A.txt 1 seed

Expected vs actual behavior

Pushing n local commits via --fast-forward-merge should result in one merge commit on the server incorporating all n commits as if I would have used a branch to merge.

Component

Server

Server context

No response

Regression?

No response

Relevant logs or output