diff --git a/tools/observer/autosync.sh b/tools/observer/autosync.sh
new file mode 100755
index 000000000..48cb9b05f
--- /dev/null
+++ b/tools/observer/autosync.sh
@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+# Keeps the shared checkout's observer and public API in step with origin/master, so a change an agent pushed to
+# tools/observer or site/api is running here within five minutes (4 October 2026: the live API said "observer has
+# not reported the proving layer" for an hour because the shared checkout was three commits behind origin).
+# Fast-forwards only; if the shared checkout is ahead or dirty in those paths it logs and waits for a human.
+# Loop: tools/observer/autosync.sh   (log: /tmp/igneum-devnet/autosync.out)
+cd "$(dirname "$0")/../.." || exit 1
+LOG=/tmp/igneum-devnet/autosync.out; mkdir -p "$(dirname "$LOG")"; exec >>"$LOG" 2>&1
+PATHS="tools/observer site/api"
+while :; do
+  git fetch -q origin master 2>/dev/null
+  local_sha=$(git rev-parse HEAD); remote_sha=$(git rev-parse origin/master)
+  if [ "$local_sha" != "$remote_sha" ]; then
+    if [ -z "$(git status --porcelain -- $PATHS)" ] && git merge-base --is-ancestor HEAD origin/master; then
+      changed=$(git diff --name-only HEAD origin/master -- $PATHS)
+      if git merge -q --ff-only origin/master; then
+        echo "$(date -u +%FT%TZ) fast-forwarded to $(git rev-parse --short HEAD)"
+        if [ -n "$changed" ]; then
+          pid=$(pgrep -f "node tools/observer/observer.mjs" | head -1)
+          if [ -n "$pid" ]; then kill "$pid" && echo "$(date -u +%FT%TZ) observer $pid restarted for: $(echo "$changed" | tr '\n' ' ')"; fi
+        fi
+      else
+        echo "$(date -u +%FT%TZ) fast-forward failed (local $local_sha, origin $remote_sha)"
+      fi
+    else
+      echo "$(date -u +%FT%TZ) not fast-forwardable or dirty in $PATHS (local $local_sha, origin $remote_sha); waiting"
+    fi
+  fi
+  sleep 300
+done