ui : keep reasoning submenu visible regardless of model state

tools/ui/src/lib/components/app/chat/ChatForm/ChatFormActions/ChatFormActionAdd/ChatFormActionAddReasoningSubmenu.svelte

@@ -8,10 +8,9 @@
 	const reasoning = useReasoningMenu();
 </script>
 
-{#if reasoning.modelSupportsThinking}
-	<DropdownMenu.Sub>
+<DropdownMenu.Sub>
 		<DropdownMenu.SubTrigger class="flex cursor-pointer items-center gap-2">
-			{#if reasoning.thinkingEnabled}
+			{#if reasoning.isReasoningActive}
 				<Lightbulb class="{ICON_CLASS_DEFAULT} shrink-0 text-amber-400" />
 			{:else if reasoning.isOff}
 				<LightbulbOff class="{ICON_CLASS_DEFAULT} shrink-0 text-muted-foreground" />
@@ -20,7 +19,7 @@
 			{/if}
 
 			<span
-				class="text-sm inline-flex gap-2 {!reasoning.thinkingEnabled
+				class="text-sm inline-flex gap-2 {!reasoning.isReasoningActive
 					? 'text-muted-foreground'
 					: ''}"
 			>
@@ -74,4 +73,3 @@
 			{/each}
 		</DropdownMenu.SubContent>
 	</DropdownMenu.Sub>
-{/if}

tools/ui/src/lib/hooks/use-reasoning-menu.svelte.ts

@@ -8,6 +8,7 @@ import { getConversationModel } from '$lib/utils';
 export interface UseReasoningMenuReturn {
 	readonly modelSupportsThinking: boolean;
 	readonly thinkingEnabled: boolean;
+	readonly isReasoningActive: boolean;
 	readonly isOff: boolean;
 	readonly currentEffort: ReasoningEffort;
 	readonly levels: ReasoningEffortLevel[];
@@ -59,6 +60,12 @@ export function useReasoningMenu(): UseReasoningMenuReturn {
 	const thinkingEnabled = $derived(
 		currentEffort !== ReasoningEffort.OFF && currentEffort !== ReasoningEffort.DEFAULT
 	);
+	// Thinking is effectively on (lightbulb lit) either when an explicit effort
+	// is selected, or when the effort is left at "Default" and the model
+	// supports thinking.
+	const isReasoningActive = $derived(
+		thinkingEnabled || (currentEffort === ReasoningEffort.DEFAULT && modelSupportsThinking)
+	);
 
 	return {
 		get currentEffort() {
@@ -82,6 +89,9 @@ export function useReasoningMenu(): UseReasoningMenuReturn {
 		get thinkingEnabled() {
 			return thinkingEnabled;
 		},
+		get isReasoningActive() {
+			return isReasoningActive;
+		},
 		tokenLabel(level: ReasoningEffortLevel): string | null {
 			if (level.value === ReasoningEffort.DEFAULT) return 'Model default';