Do not offer to promote work that already landed

Promotion cherry-picks, which gives the commit a new sha on main. wj-status
compared by sha via main..wj, so after promoting ten commits it still listed all
ten as unpromoted - and would have invited promoting the same work twice.

git cherry compares patch content instead and marks an already-present commit
with a leading '-'. When nothing is genuinely outstanding it now says so, counts
what has already landed, and shows how far the branch is BEHIND main with the
rebase to run. Behind was the state that mattered here and the tool could not
express it at all.

Scope: product

tools/wj-status.sh

@@ -44,10 +44,25 @@ if ! git rev-parse --verify --quiet refs/heads/wj >/dev/null; then
   exit 1
 fi
 
-COMMITS="$(git rev-list --reverse "$RANGE")"
+# git cherry, not rev-list. Promotion CHERRY-PICKS, which gives the commit a new
+# sha on main, so `main..wj` keeps listing work that already landed - and this
+# tool would then invite you to promote it a second time. `git cherry` compares
+# patch content and marks an already-present commit with a leading '-'.
+COMMITS="$(git cherry main wj | awk '$1 == "+" { print $2 }')"
+
+ALREADY="$(git cherry main wj | awk '$1 == "-" { print $2 }' | wc -l)"
 
 if [ -z "$COMMITS" ]; then
   echo "Nothing on wj that main does not have."
+  if [ "$ALREADY" -gt 0 ]; then
+    echo "($ALREADY commit(s) here have already landed on main as cherry-picks.)"
+  fi
+  echo
+  echo "wj is behind main by:"
+  git log --oneline wj..main | sed 's/^/  /' | head -10
+  echo
+  echo "Rebase it before starting new work:"
+  echo "    git checkout wj && git rebase main"
   exit 0
 fi