diff --git a/tools/observer/autosync.sh b/tools/observer/autosync.sh
index 78df973e7..2847d32c7 100755
--- a/tools/observer/autosync.sh
+++ b/tools/observer/autosync.sh
@@ -32,10 +32,13 @@ while :; do
   local_sha=$(git rev-parse HEAD); remote_sha=$(git rev-parse origin/master)
   if [ "$local_sha" != "$remote_sha" ]; then
     if [ -z "$(git status --porcelain -- $PATHS)" ] && git merge-base --is-ancestor HEAD origin/master; then
-      if git merge -q --ff-only origin/master; then
+      if git merge -q --ff-only origin/master 2>/tmp/igneum-devnet/autosync-ff.err; then
         echo "$(date -u +%FT%TZ) fast-forwarded to $(git rev-parse --short HEAD)"
       else
-        echo "$(date -u +%FT%TZ) fast-forward failed (local $local_sha, origin $remote_sha)"
+        # name what blocks it: files dirty here that the incoming commits also change (4 October 2026, 20:05: results
+        # files edited in the shared checkout against a commit of the same files; the observer sat behind master)
+        blocking=$(comm -12 <(git status --porcelain | awk '{print $2}' | sort) <(git diff --name-only HEAD origin/master | sort) | head -5 | tr '\n' ' ')
+        echo "$(date -u +%FT%TZ) fast-forward failed (local ${local_sha:0:7}, origin ${remote_sha:0:7}): $(head -c 200 /tmp/igneum-devnet/autosync-ff.err | tr '\n' ' ') blocking: ${blocking:-none found}"
       fi
     else
       echo "$(date -u +%FT%TZ) not fast-forwardable or dirty in $PATHS (local $local_sha, origin $remote_sha); waiting"