diff --git a/test/tests/010-watch-websocket.sh b/test/tests/010-watch-websocket.sh
new file mode 100755
index 0000000..fa68c6d
--- /dev/null
+++ b/test/tests/010-watch-websocket.sh
@@ -0,0 +1,62 @@
+#!/usr/bin/env bash
+# Test: `fmsg watch` streams a cross-instance new_msg over the WebSocket.
+#
+# Alice (hairpin) runs `fmsg --json watch --events new_msg --once` in the
+# background; Bob (example) sends her a message. Asserts: the first line
+# printed is {"type":"ready"} (emitted after the upgrade so callers know when
+# to do a `list` catch-up), the next is a new_msg envelope whose data carries
+# Bob's message in the list-item shape (id, from, topic), and --once exits 0.
+# Then asserts a watch on a quiet inbox with --timeout exits 2 (no event).
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+# shellcheck source=../test-lib.sh
+source "$SCRIPT_DIR/../test-lib.sh"
+
+TEST_TOKEN="$(date +%s)-$$"
+TOPIC="watch-$TEST_TOKEN"
+BODY="watch websocket test $TEST_TOKEN"
+WATCH_OUT="$(mktemp)"
+trap 'rm -f "$WATCH_OUT"' EXIT
+
+echo "    Starting watch as $ALICE_ADDR (background, --once, 60s timeout)"
+fmsg_as "$HAIRPIN_API_URL" "$ALICE_API_KEY" --json watch --events new_msg --once --timeout 60s > "$WATCH_OUT" 2>&1 &
+WATCH_PID=$!
+
+# Wait for the socket to be open before sending, so the event can't be missed.
+for _ in $(seq 1 100); do
+  grep -q '"type":"ready"' "$WATCH_OUT" 2>/dev/null && break
+  sleep 0.2
+done
+grep -q '"type":"ready"' "$WATCH_OUT" || { cat "$WATCH_OUT"; fail_test "watch never printed the ready line"; }
+
+echo "    Sending: $BOB_ADDR -> $ALICE_ADDR"
+SEND_OUTPUT=$(fmsg_as "$EXAMPLE_API_URL" "$BOB_API_KEY" send --topic "$TOPIC" "$ALICE_ADDR" "$BODY")
+echo "$SEND_OUTPUT"
+
+set +e
+wait "$WATCH_PID"
+WATCH_EXIT=$?
+set -e
+echo "    watch output:"
+cat "$WATCH_OUT"
+
+[ "$WATCH_EXIT" -eq 0 ] || fail_test "watch --once exited $WATCH_EXIT, expected 0"
+[ "$(head -n1 "$WATCH_OUT")" = '{"type":"ready"}' ] || fail_test "first line was not the ready marker"
+
+EVENT_LINE=$(sed -n 2p "$WATCH_OUT")
+echo "$EVENT_LINE" | grep -q '"type":"new_msg"' || fail_test "second line is not a new_msg event"
+echo "$EVENT_LINE" | grep -q "\"from\":\"$BOB_ADDR\"" || fail_test "event was not from $BOB_ADDR"
+echo "$EVENT_LINE" | grep -q "\"topic\":\"$TOPIC\"" || fail_test "event did not carry topic $TOPIC"
+echo "$EVENT_LINE" | grep -Eq '"id":[0-9]+' || fail_test "event data has no id"
+[ "$(wc -l < "$WATCH_OUT")" -eq 2 ] || fail_test "expected exactly 2 lines (ready + event) with --once"
+
+echo "    Quiet inbox: watch --timeout 3s should exit 2"
+set +e
+fmsg_as "$EXAMPLE_API_URL" "$CAROL_API_KEY" --json watch --events new_msg --timeout 3s > "$WATCH_OUT" 2>&1
+QUIET_EXIT=$?
+set -e
+[ "$QUIET_EXIT" -eq 2 ] || { cat "$WATCH_OUT"; fail_test "quiet watch exited $QUIET_EXIT, expected 2"; }
+[ "$(head -n1 "$WATCH_OUT")" = '{"type":"ready"}' ] || fail_test "quiet watch did not print ready"
+
+echo "    OK: watch streamed a cross-instance new_msg and timed out cleanly on a quiet inbox"