TEST-80-NOTIFYACCESS: Add notify-reload signal handler validation test

Add a new integration test to verify the signal handler validation for
Type=notify-reload services, as introduced in the previous commit.

The test adds a shell harness and four service files to cover all scenarios:

1. `notify-reload-no-handler.service`: Verifies that the service fails to
   start with Result=protocol when the handler is missing at the first
   READY=1.

2. `notify-reload-sigstop.service`: Verifies that SIGSTOP is exempt from
   handler validation because it cannot be caught or blocked.

3. `notify-reload-toggle-handler.service`: Verifies that removing the
   handler at runtime results in a warning on reload, but the signal is still
   sent, causing the service to terminate from unhandled SIGHUP.

4. `notify-reload-well-behaved.service`: Verifies the happy path where a
   service with a handler starts and reloads successfully.

Use bounded FIFO operations and journal cursors so failures are prompt and log
assertions cannot race a relative time window.

test/units/TEST-80-NOTIFYACCESS.sh

@@ -172,4 +172,85 @@ assert_eq "$(systemctl show fdstore-nopin.service -P NFileDescriptorStore)" 0
 assert_eq "$(systemctl show fdstore-pin.service -P SubState)" dead
 assert_eq "$(systemctl show fdstore-nopin.service -P SubState)" dead
 
+# Test notify-reload signal handler validation
+
+cleanup_notify_reload() {
+    systemctl stop notify-reload-no-handler.service \
+        notify-reload-sigstop.service \
+        notify-reload-toggle-handler.service \
+        notify-reload-well-behaved.service || :
+    systemctl reset-failed notify-reload-no-handler.service \
+        notify-reload-sigstop.service \
+        notify-reload-toggle-handler.service \
+        notify-reload-well-behaved.service || :
+    rm -f /tmp/reload-nohandler-in /tmp/reload-nohandler-out \
+        /tmp/reload-nohandler-cursor \
+        /tmp/reload-sigstop-in /tmp/reload-sigstop-out \
+        /tmp/reload-toggle-in /tmp/reload-toggle-out \
+        /tmp/reload-toggle-cursor \
+        /tmp/reload-wellbehaved-in /tmp/reload-wellbehaved-out
+}
+
+trap cleanup_notify_reload EXIT
+cleanup_notify_reload
+
+# Test 1: Service without signal handler should fail to start
+mkfifo /tmp/reload-nohandler-in /tmp/reload-nohandler-out
+journalctl -q -n 0 --cursor-file=/tmp/reload-nohandler-cursor
+(! systemctl start notify-reload-no-handler.service)
+assert_eq "$(systemctl show notify-reload-no-handler.service -P SubState)" "failed"
+assert_eq "$(systemctl show notify-reload-no-handler.service -P Result)" "protocol"
+# Verify error was logged about missing signal handler
+journalctl --sync
+journalctl -u notify-reload-no-handler.service --cursor-file=/tmp/reload-nohandler-cursor \
+    --grep "lacks handler for reload signal" >/dev/null
+systemctl reset-failed notify-reload-no-handler.service
+rm -f /tmp/reload-nohandler-in /tmp/reload-nohandler-out
+
+# Test 2: SIGSTOP cannot be caught or blocked, so it is exempt from handler validation
+mkfifo /tmp/reload-sigstop-in /tmp/reload-sigstop-out
+systemctl start notify-reload-sigstop.service
+assert_eq "$(systemctl show notify-reload-sigstop.service -P SubState)" "running"
+systemctl stop notify-reload-sigstop.service
+rm -f /tmp/reload-sigstop-in /tmp/reload-sigstop-out
+
+# Test 3: Service that removes handler should warn on reload but still reload
+mkfifo /tmp/reload-toggle-in /tmp/reload-toggle-out
+systemctl start notify-reload-toggle-handler.service
+assert_eq "$(systemctl show notify-reload-toggle-handler.service -P SubState)" "running"
+
+# Command service to remove its signal handler
+timeout 10 bash -c 'echo "remove-handler" >/tmp/reload-toggle-in'
+response="$(timeout 10 cat /tmp/reload-toggle-out)"
+assert_eq "$response" "handler-removed"
+
+# Reload should succeed (with warning) even though handler is gone - service will be killed by SIGHUP
+# but that's intentional after the first start succeeds
+journalctl -q -n 0 --cursor-file=/tmp/reload-toggle-cursor
+systemctl reload --no-block notify-reload-toggle-handler.service
+# The service will die from SIGHUP since the handler is removed
+timeout 10 bash -c 'while systemctl is-active --quiet notify-reload-toggle-handler.service; do sleep .5; done'
+# Verify warning was logged
+journalctl --sync
+journalctl -u notify-reload-toggle-handler.service --cursor-file=/tmp/reload-toggle-cursor \
+    --grep "lacks handler for reload signal" >/dev/null
+rm -f /tmp/reload-toggle-in /tmp/reload-toggle-out
+
+# Test 4: Well-behaved service with handler should work correctly
+mkfifo /tmp/reload-wellbehaved-in /tmp/reload-wellbehaved-out
+systemctl start notify-reload-well-behaved.service
+assert_eq "$(systemctl show notify-reload-well-behaved.service -P SubState)" "running"
+
+# Reload should succeed
+systemctl reload --no-block notify-reload-well-behaved.service
+timeout 10 bash -c 'until [[ $(systemctl show notify-reload-well-behaved.service -P SubState) == "reload-signal" ]]; do sleep .5; done'
+response="$(timeout 10 cat /tmp/reload-wellbehaved-out)"
+assert_eq "$response" "reload"
+timeout 10 bash -c 'until [[ $(systemctl show notify-reload-well-behaved.service -P SubState) == "running" ]]; do sleep .5; done'
+assert_eq "$(systemctl show notify-reload-well-behaved.service -P ReloadResult)" "success"
+
+timeout 10 bash -c 'echo "exit" >/tmp/reload-wellbehaved-in'
+systemctl stop notify-reload-well-behaved.service
+rm -f /tmp/reload-wellbehaved-in /tmp/reload-wellbehaved-out
+
 touch /testok