feat(launcher): skip wallpaper gsettings on Linux, show dev popup instead

Running gsettings on the dev workstation resets monitors on every test cycle.
Linux Electron handler now returns linux_test_mode:true with would_run details
instead of applying. Svelte cfg component shows a debug popup (mirrors Native
Test Mode style). Background sync logs to console and leaves applied-URL unset.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/routes/events/[event_id]/(launcher)/cfg_components/launcher_cfg_wallpaper.svelte

@@ -26,6 +26,9 @@ let apply_status = $state('');
 let restore_status = $state('');
 let last_device_id: string | null = null;
 
+let linux_test_popup_open = $state(false);
+let linux_test_popup_data = $state<Record<string, unknown> | null>(null);
+
 function get_native_device(): NativeDeviceLike | null {
     const store_loc = $ae_loc as { native_device?: NativeDeviceLike };
     return store_loc.native_device ?? null;
@@ -140,7 +143,11 @@ async function handle_apply() {
         account_id: String($ae_api.account_id ?? '')
     });
 
-    if (result?.success) {
+    if (result?.success && (result as any).linux_test_mode) {
+        linux_test_popup_data = result as Record<string, unknown>;
+        linux_test_popup_open = true;
+        set_apply_status('Linux dev mode — see popup');
+    } else if (result?.success) {
         $events_loc.launcher.wallpaper_applied_url = url || null;
         $events_loc.launcher.wallpaper_applied_url_external = url_ext || null;
         set_apply_status('Applied ✓');
@@ -328,3 +335,76 @@ const section_description = $derived(
         {/if}
     </div>
 </Launcher_Cfg_Section>
+
+<!-- Linux Dev Mode Popup — mirrors Native Test Mode style -->
+<!-- Shows what WOULD have been applied; actual gsettings call is skipped to avoid
+     resetting the dev workstation monitors on every test cycle. -->
+{#if linux_test_popup_open && linux_test_popup_data}
+    <!-- svelte-ignore a11y_click_events_have_key_events a11y_no_static_element_interactions -->
+    <div
+        class="fixed inset-0 z-9999 flex items-center justify-center bg-black/70 p-4"
+        role="presentation"
+        onclick={() => (linux_test_popup_open = false)}>
+        <!-- svelte-ignore a11y_click_events_have_key_events a11y_no_static_element_interactions -->
+        <div
+            class="bg-surface-50/95 dark:bg-surface-900/95 border-warning-500/40 relative flex max-h-[90vh] w-full max-w-lg flex-col gap-0 overflow-hidden rounded-xl border shadow-2xl"
+            role="dialog"
+            aria-modal="true"
+            aria-label="Linux Dev Mode — Wallpaper not applied"
+            tabindex="-1"
+            onclick={(e) => e.stopPropagation()}>
+
+            <div class="bg-warning-500/10 border-warning-500/30 flex items-center gap-2 border-b px-4 py-3">
+                <span class="text-warning-600 dark:text-warning-400 font-mono text-xs font-bold uppercase tracking-wider">
+                    🧪 Linux Dev Mode — Wallpaper not applied
+                </span>
+                <button
+                    type="button"
+                    onclick={() => (linux_test_popup_open = false)}
+                    class="btn btn-xs preset-tonal-surface ml-auto">
+                    Close
+                </button>
+            </div>
+
+            <div class="flex flex-col gap-3 overflow-y-auto p-4 font-mono text-xs">
+                <div class="flex flex-col gap-1">
+                    <span class="text-[9px] font-bold uppercase opacity-50">Display Target</span>
+                    <div class="rounded bg-surface-500/10 px-3 py-2">
+                        {linux_test_popup_data.display ?? 'all'}
+                    </div>
+                </div>
+
+                {#if linux_test_popup_data.url}
+                    <div class="flex flex-col gap-1">
+                        <span class="text-[9px] font-bold uppercase opacity-50">Primary URL</span>
+                        <div class="text-primary-500 rounded bg-surface-500/10 px-3 py-2 break-all">
+                            {linux_test_popup_data.url}
+                        </div>
+                    </div>
+                {/if}
+
+                {#if linux_test_popup_data.url_external}
+                    <div class="flex flex-col gap-1">
+                        <span class="text-[9px] font-bold uppercase opacity-50">External / Projector URL</span>
+                        <div class="text-primary-500 rounded bg-surface-500/10 px-3 py-2 break-all">
+                            {linux_test_popup_data.url_external}
+                        </div>
+                    </div>
+                {/if}
+
+                <div class="flex flex-col gap-1">
+                    <span class="text-[9px] font-bold uppercase opacity-50">Would Have Run</span>
+                    <div class="rounded bg-surface-500/10 px-3 py-2 leading-relaxed whitespace-pre-wrap text-success-600 dark:text-success-400">
+                        {#each (linux_test_popup_data.would_run as string[]) as cmd}
+                            <div class="mb-1">{cmd}</div>
+                        {/each}
+                    </div>
+                </div>
+
+                <p class="text-[9px] italic opacity-40">
+                    gsettings is skipped on Linux to avoid resetting dev monitors. On macOS this applies via osascript.
+                </p>
+            </div>
+        </div>
+    </div>
+{/if}

src/routes/events/[event_id]/(launcher)/launcher_background_sync.svelte

@@ -71,7 +71,11 @@ async function apply_wallpaper_if_changed(device_other_json: unknown) {
         account_id: String($ae_api.account_id ?? '')
     });
 
-    if (result?.success) {
+    if (result?.success && (result as any).linux_test_mode) {
+        // Linux dev mode: gsettings was skipped. Log and leave applied URL unset so
+        // the cfg component popup can show the details when triggered manually.
+        console.info('Sync: Wallpaper linux_test_mode — would have applied:', (result as any).would_run);
+    } else if (result?.success) {
         $events_loc.launcher.wallpaper_applied_url = configured_url || null;
         $events_loc.launcher.wallpaper_applied_url_external = configured_url_external || null;
         if (log_lvl) console.log('Sync: Wallpaper applied.');