fix(rig): the test paged a human about a unit that did not exist (#115)

Minutes after test-sc-watchdog exited, PLN got a STICKY desktop notification:

    "3 restarts in 10 min. Giving up — this needs your eyes.
     journalctl --user -u scwd-test-1269280.service -n 50"

scwd-test-1269280.service was the test's own FAKE transient unit. By the time the
notification was read, it had been torn down — so the suggested command returns
nothing, about a failure that never happened, while the real rig was playing fine.

Two defects in one message. The test could reach a real notification daemon at all;
and the give-up path is deliberately urgency=critical/sticky, which is correct for a
real outage and actively harmful for a fake one — it cannot be dismissed by waiting.

Fix: SCWD_NO_NOTIFY=1, honoured by notify() and set by the harness. A test must never
be able to page a human about something that is not real.

Re-run green: 7 passed, 0 failed, and silent. The log still shows the rate limiter
walking (0 prior) -> (1 prior) -> (2 prior) -> GIVING UP, so suppressing the toast
did not suppress the evidence — the assertion reads the log, not the notification.

Same family as the flap it was written to catch: a supervisory tool whose side
effects escape the scope it was reasoning about.

tools/sc-watchdog.sh

@@ -82,6 +82,12 @@ log() { printf '%s %s\n' "$(date +%H:%M:%S)" "$*" >&2; }
 # rig was busy recovering itself. If everything is sticky, nothing is urgent.
 notify() {
   local urgency="$1" timeout="$2" title="$3" body="$4"
+  # SCWD_NO_NOTIFY: for the test harness. The first test run fired REAL sticky desktop
+  # notifications about a FAKE unit ("3 restarts in 10 min. Giving up — this needs your
+  # eyes. journalctl --user -u scwd-test-1269280.service"), which reached PLN minutes
+  # after the test had finished and named a unit that no longer existed. A test must
+  # never be able to page a human about something that is not real.
+  [ "${SCWD_NO_NOTIFY:-0}" = "1" ] && return 0
   command -v notify-send >/dev/null 2>&1 || return 0
   notify-send -a "ParVagues" -u "$urgency" -t "$timeout" "$title" "$body" 2>/dev/null || true
 }

tools/tests/test-sc-watchdog.sh

@@ -65,7 +65,10 @@ else
 fi
 
 # --- 2. the watchdog notices and restarts ---------------------------------------
-SCWD_UNIT="$UNIT" SCWD_PROC="$PROC" SCWD_STATE="$STATE" \
+# SCWD_NO_NOTIFY=1: a test must never page a human about a fake unit. The first run
+# fired real STICKY notifications naming scwd-test-<pid>.service, which reached PLN
+# after the test had exited and after that unit had ceased to exist.
+SCWD_UNIT="$UNIT" SCWD_PROC="$PROC" SCWD_STATE="$STATE" SCWD_NO_NOTIFY=1 \
   ./tools/sc-watchdog.sh >"$TMP/wd.log" 2>&1 &
 WD_PID=$!