fix(ui): render thinking/reasoning block content as markdown (#24611)

* fix(ui): render thinking/reasoning block content as markdown

* feat(ui): add toggle setting for thinking block markdown rendering

tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessageAgenticContent.svelte

@@ -56,6 +56,7 @@
 
 	const showToolCallInProgress = $derived(config().showToolCallInProgress as boolean);
 	const showThoughtInProgress = $derived(config().showThoughtInProgress as boolean);
+	const renderThinkingAsMarkdown = $derived(config().renderThinkingAsMarkdown as boolean);
 
 	const hasReasoningError = $derived(
 		isLastAssistantMessage ? !!agenticLastError(message.convId) : false
@@ -316,9 +317,13 @@
 			onToggle={() => toggleExpanded(index, section)}
 		>
 			<div class="pt-3">
+				{#if renderThinkingAsMarkdown}
+					<MarkdownContent content={section.content} attachments={message?.extra} />
+				{:else}
 					<div class="text-xs leading-relaxed break-words whitespace-pre-wrap">
 						{section.content}
 					</div>
+				{/if}
 			</div>
 		</CollapsibleContentBlock>
 	{:else if section.type === AgenticSectionType.REASONING_PENDING}
@@ -336,9 +341,13 @@
 			onToggle={() => toggleExpanded(index, section)}
 		>
 			<div class="pt-3">
+				{#if renderThinkingAsMarkdown}
+					<MarkdownContent content={section.content} attachments={message?.extra} />
+				{:else}
 					<div class="text-xs leading-relaxed break-words whitespace-pre-wrap">
 						{section.content}
 					</div>
+				{/if}
 			</div>
 		</CollapsibleContentBlock>
 	{/if}

tools/ui/src/lib/constants/settings-keys.ts

@@ -33,6 +33,7 @@ export const SETTINGS_KEYS = {
 	SHOW_MODEL_TAGS: 'showModelTags',
 	SHOW_BUILD_VERSION: 'showBuildVersion',
 	SHOW_SYSTEM_MESSAGE: 'showSystemMessage',
+	RENDER_THINKING_AS_MARKDOWN: 'renderThinkingAsMarkdown',
 	// Sampling
 	TEMPERATURE: 'temperature',
 	DYNATEMP_RANGE: 'dynatemp_range',

tools/ui/src/lib/constants/settings-registry.ts

@@ -282,6 +282,18 @@ const SETTINGS_REGISTRY: Record<string, SettingsSectionEntry> = {
 					paramType: SyncableParameterType.BOOLEAN
 				}
 			},
+			{
+				key: SETTINGS_KEYS.RENDER_THINKING_AS_MARKDOWN,
+				label: 'Render thinking as Markdown',
+				help: 'Render the reasoning/thinking block content as formatted Markdown instead of plain text.',
+				defaultValue: true,
+				type: SettingsFieldType.CHECKBOX,
+				section: SETTINGS_SECTION_SLUGS.DISPLAY,
+				sync: {
+					serverKey: SETTINGS_KEYS.RENDER_THINKING_AS_MARKDOWN,
+					paramType: SyncableParameterType.BOOLEAN
+				}
+			},
 			{
 				key: SETTINGS_KEYS.FULL_HEIGHT_CODE_BLOCKS,
 				label: 'Use full height code blocks',