Point the landing recipe at the rebase hazard it can create

Landing by rebase leaves the old branch tip orphaned, and reconciling it with a
-s ours merge is how this branch got one. The rule against rebasing over such a
merge is further down the file; the recipe that creates the condition now says
so where the work happens.

AGENT-BRIEF.md

@@ -28,6 +28,14 @@ export FORGEJO_PASS_ENTRY=vivarium/forgejo-certified-sandbox GIT_TERMINAL_PROMPT
 unset SSH_ASKPASS DISPLAY
 
 git fetch origin && git rebase origin/main        # you resolve every conflict, not main
+                                                  # ...UNLESS this branch has ever recorded a
+                                                  # `-s ours` merge — then MERGE, never rebase.
+                                                  # See "Never rebase a branch that has ever
+                                                  # recorded a `-s ours` merge" below; landing by
+                                                  # rebase and reconciling the old tip with
+                                                  # `-s ours` is what puts one there, so the very
+                                                  # next landing on the same branch is the one
+                                                  # this catches. `git log --merges` tells you.
 
 if main-capture capture --wait; then              # --wait retries with backoff while held;
                                                   # release ONLY a lock you actually took