diff --git a/tools/observer/autosync.sh b/tools/observer/autosync.sh
index 2847d32c7..cfec76520 100755
--- a/tools/observer/autosync.sh
+++ b/tools/observer/autosync.sh
@@ -3,7 +3,7 @@
 # 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.
-# The observer is restarted whenever the checked-out tools/observer tree differs from the one the running observer
+# The observer is restarted whenever the checked-out observer.mjs or run.sh differs from what the running observer
 # started from, whoever moved HEAD (4 October 2026, 19:35: a pull by hand moved HEAD past an observer fix and the
 # observer kept the old code for ten minutes, because only this loop's own fast-forward used to restart it).
 # Loop: tools/observer/autosync.sh   (log: /tmp/igneum-devnet/autosync.out)
@@ -12,7 +12,9 @@ cd "$(dirname "$0")/../.." || exit 1
 LOG=/tmp/igneum-devnet/autosync.out
 MARK="${OBSERVER_TREE_MARK:-/tmp/igneum-devnet/observer.tree}"   # tree id of tools/observer the running observer was started from
 PATHS="tools/observer site/api"
-observer_tree() { git rev-parse "HEAD:tools/observer" 2>/dev/null; }
+# the code the running observer executes: observer.mjs and its restart loop (not autosync.sh or the README, whose
+# changes used to restart it for nothing, 20:15 on 4 October 2026)
+observer_tree() { git rev-parse "HEAD:tools/observer/observer.mjs" "HEAD:tools/observer/run.sh" 2>/dev/null | tr -d '\n' | shasum | cut -c1-40; }
 marker() { cat "$MARK" 2>/dev/null || echo none; }
 restart_due() { local t; t="$(observer_tree)"; [ -n "$t" ] && [ "$(marker)" != "$t" ]; }
 restart_observer() { # <reason>