Add event-driven wallpaper rotation

tests/quickshell/wallpaper-service-contract.sh

@@ -154,6 +154,48 @@ jq -e '.path == "/images/a.jpg" and .mode == "per-monitor"
 [[ "$(tail -1 "$command_log")" == 'hyprctl hyprpaper wallpaper HDMI-A-1,/images/b.jpg' ]] \
     || fail 'transaction continued after the failed output'
 
+printf '\n' >"$control"
+printf '%s\n' '{}' >"$active_state"
+: >"$command_log"
+qs_for_harness ipc call wallpaper-service-test seedSlideshow \
+    ' ["/images/a.jpg","/images/b.jpg","/images/c.jpg"]' false >/dev/null
+seeded="$(qs_for_harness ipc call wallpaper-service-test status)"
+jq -e '.slideshowTimerRunning == true and .slideshowPath == "/images/a.jpg"' \
+    <<<"$seeded" >/dev/null || fail "multi-image slideshow did not arm: $seeded"
+qs_for_harness ipc call wallpaper-service-test advanceSlideshow >/dev/null
+advanced="$(wait_idle)"
+jq -e '.mode == "slideshow" and .path == "/images/a.jpg"
+    and .slideshowPath == "/images/b.jpg"
+    and .activeByOutput == {"DP-2":"/images/b.jpg","HDMI-A-1":"/images/b.jpg"}' \
+    <<<"$advanced" >/dev/null || fail "automatic advance persisted policy or lost runtime state: $advanced"
+
+printf 'wrong\n' >"$control"
+qs_for_harness ipc call wallpaper-service-test advanceSlideshow >/dev/null
+automatic_failure="$(wait_idle)"
+jq -e '.path == "/images/a.jpg" and .slideshowPath == "/images/b.jpg"
+    and .slideshowTimerRunning == true
+    and .lastError == "Hyprpaper did not confirm that background."' \
+    <<<"$automatic_failure" >/dev/null \
+    || fail "failed automatic advance changed runtime policy or stopped normal scheduling: $automatic_failure"
+printf '\n' >"$control"
+
+qs_for_harness ipc call wallpaper-service-test seedSlideshow ' ["/images/a.jpg"]' false >/dev/null
+single_item="$(qs_for_harness ipc call wallpaper-service-test status)"
+jq -e '.slideshowTimerRunning == false' <<<"$single_item" >/dev/null \
+    || fail "one-item slideshow armed a repeating timer: $single_item"
+
+qs_for_harness ipc call wallpaper-service-test applySingle /images/a.jpg >/dev/null
+wait_idle >/dev/null
+printf '%s\n' '{}' >"$active_state"
+: >"$command_log"
+qs_for_harness ipc call wallpaper-service-test rapidOutputs >/dev/null
+sleep 0.6
+hotplug="$(wait_idle)"
+[[ "$(rg -c '^hyprctl hyprpaper listactive$' "$command_log")" -eq 1 ]] \
+    || fail "rapid output changes did not coalesce: $(<"$command_log")"
+jq -e '.lastError == "" and .activeByOutput == {"DP-2":"/images/a.jpg","HDMI-A-1":"/images/a.jpg"}' \
+    <<<"$hotplug" >/dev/null || fail "hotplug reapply was not verified: $hotplug"
+
 if rg -n 'ReferenceError|TypeError|Binding loop|Unable to assign|Cannot assign' "$shell_log"; then
     fail 'service harness emitted a QML runtime warning'
 fi