feat: add autoExpandDiffs setting to auto-expand diffs in chat messages

Adds a new boolean setting "autoExpandDiffs" (default: false) under
Settings > UI. When enabled, file edit diffs in chat messages are
automatically expanded instead of requiring a click on the collapsed
filename bar.

The CodeAccordion component already enforces a 300px max height with
scrollbar, so auto-expanded diffs will not overwhelm the chat view.

Changes:
- packages/types: add autoExpandDiffs to GlobalSettings schema and ExtensionState
- webview-ui context: add default and hydration for autoExpandDiffs
- ChatView: add useEffect that auto-expands diff tool messages when setting is on
- UISettings: add checkbox toggle for the new setting
- SettingsView: wire the new setting through cached state
- i18n: add English translation strings
- Tests: update test fixtures for change-detection, unsaved-changes, UISettings

Closes #10955

packages/types/src/global-settings.ts

@@ -201,6 +201,11 @@ export const globalSettingsSchema = z.object({
 	includeTaskHistoryInEnhance: z.boolean().optional(),
 	historyPreviewCollapsed: z.boolean().optional(),
 	reasoningBlockCollapsed: z.boolean().optional(),
+	/**
+	 * Whether to auto-expand diffs in "Roo wants to edit this file" chat messages.
+	 * @default false
+	 */
+	autoExpandDiffs: z.boolean().optional(),
 	/**
 	 * Controls the keyboard behavior for sending messages in the chat input.
 	 * - "send": Enter sends message, Shift+Enter creates newline (default)

packages/types/src/vscode-extension-host.ts

@@ -299,6 +299,7 @@ export type ExtensionState = Pick<
 	| "openRouterImageGenerationSelectedModel"
 	| "includeTaskHistoryInEnhance"
 	| "reasoningBlockCollapsed"
+	| "autoExpandDiffs"
 	| "enterBehavior"
 	| "includeCurrentTime"
 	| "includeCurrentCost"

webview-ui/src/components/chat/ChatView.tsx

@@ -93,6 +93,7 @@ const ChatViewComponent: React.ForwardRefRenderFunction<ChatViewRef, ChatViewPro
 		cloudIsAuthenticated,
 		messageQueue = [],
 		showWorktreesInHomeScreen,
+		autoExpandDiffs,
 	} = useExtensionState()
 
 	// Show a WarningRow when the user sends a message with a retired provider.
@@ -1261,6 +1262,49 @@ const ChatViewComponent: React.ForwardRefRenderFunction<ChatViewRef, ChatViewPro
 		return result
 	}, [isCondensing, visibleMessages])
 
+	// Auto-expand diff tool messages when the autoExpandDiffs setting is enabled.
+	// This watches for new messages that contain file-edit diffs and marks them as expanded
+	// so users don't need to click on each collapsed diff block to review changes.
+	const DIFF_TOOL_NAMES = useMemo(
+		() =>
+			new Set([
+				"editedExistingFile",
+				"appliedDiff",
+				"newFileCreated",
+				"insertContent",
+				"searchAndReplace",
+				"search_and_replace",
+			]),
+		[],
+	)
+
+	useEffect(() => {
+		if (!autoExpandDiffs) return
+
+		const newExpansions: Record<number, boolean> = {}
+
+		for (const msg of groupedMessages) {
+			// Skip messages already tracked in expandedRows
+			if (expandedRows[msg.ts] !== undefined) continue
+
+			if (msg.type === "ask" && msg.ask === "tool") {
+				try {
+					const tool = JSON.parse(msg.text || "{}")
+					// Handle both single diff tools and batch diff messages
+					if (DIFF_TOOL_NAMES.has(tool.tool) || tool.tool === "batchDiffApproval") {
+						newExpansions[msg.ts] = true
+					}
+				} catch {
+					// ignore parse errors
+				}
+			}
+		}
+
+		if (Object.keys(newExpansions).length > 0) {
+			setExpandedRows((prev) => ({ ...prev, ...newExpansions }))
+		}
+	}, [autoExpandDiffs, groupedMessages, expandedRows, DIFF_TOOL_NAMES])
+
 	// Scroll lifecycle is managed by a dedicated hook to keep ChatView focused
 	// on message handling and UI orchestration.
 	const {

webview-ui/src/components/settings/SettingsView.tsx

@@ -199,6 +199,7 @@ const SettingsView = forwardRef<SettingsViewRef, SettingsViewProps>(({ onDone, t
 		openRouterImageApiKey,
 		openRouterImageGenerationSelectedModel,
 		reasoningBlockCollapsed,
+		autoExpandDiffs,
 		enterBehavior,
 		includeCurrentTime,
 		includeCurrentCost,
@@ -412,6 +413,7 @@ const SettingsView = forwardRef<SettingsViewRef, SettingsViewProps>(({ onDone, t
 					followupAutoApproveTimeoutMs,
 					includeTaskHistoryInEnhance: includeTaskHistoryInEnhance ?? true,
 					reasoningBlockCollapsed: reasoningBlockCollapsed ?? true,
+					autoExpandDiffs: autoExpandDiffs ?? false,
 					enterBehavior: enterBehavior ?? "send",
 					includeCurrentTime: includeCurrentTime ?? true,
 					includeCurrentCost: includeCurrentCost ?? true,
@@ -891,6 +893,7 @@ const SettingsView = forwardRef<SettingsViewRef, SettingsViewProps>(({ onDone, t
 						{renderTab === "ui" && (
 							<UISettings
 								reasoningBlockCollapsed={reasoningBlockCollapsed ?? true}
+								autoExpandDiffs={autoExpandDiffs ?? false}
 								enterBehavior={enterBehavior ?? "send"}
 								setCachedStateField={setCachedStateField}
 							/>

webview-ui/src/components/settings/UISettings.tsx

@@ -11,12 +11,14 @@ import { ExtensionStateContextType } from "@/context/ExtensionStateContext"
 
 interface UISettingsProps extends HTMLAttributes<HTMLDivElement> {
 	reasoningBlockCollapsed: boolean
+	autoExpandDiffs: boolean
 	enterBehavior: "send" | "newline"
 	setCachedStateField: SetCachedStateField<keyof ExtensionStateContextType>
 }
 
 export const UISettings = ({
 	reasoningBlockCollapsed,
+	autoExpandDiffs,
 	enterBehavior,
 	setCachedStateField,
 	...props
@@ -38,6 +40,10 @@ export const UISettings = ({
 		})
 	}
 
+	const handleAutoExpandDiffsChange = (value: boolean) => {
+		setCachedStateField("autoExpandDiffs", value)
+	}
+
 	const handleEnterBehaviorChange = (requireCtrlEnter: boolean) => {
 		const newBehavior = requireCtrlEnter ? "newline" : "send"
 		setCachedStateField("enterBehavior", newBehavior)
@@ -72,6 +78,24 @@ export const UISettings = ({
 						</div>
 					</SearchableSetting>
 
+					{/* Auto-Expand Diffs Setting */}
+					<SearchableSetting
+						settingId="ui-auto-expand-diffs"
+						section="ui"
+						label={t("settings:ui.autoExpandDiffs.label")}>
+						<div className="flex flex-col gap-1">
+							<VSCodeCheckbox
+								checked={autoExpandDiffs}
+								onChange={(e: any) => handleAutoExpandDiffsChange(e.target.checked)}
+								data-testid="auto-expand-diffs-checkbox">
+								<span className="font-medium">{t("settings:ui.autoExpandDiffs.label")}</span>
+							</VSCodeCheckbox>
+							<div className="text-vscode-descriptionForeground text-sm ml-5 mt-1">
+								{t("settings:ui.autoExpandDiffs.description")}
+							</div>
+						</div>
+					</SearchableSetting>
+
 					{/* Enter Key Behavior Setting */}
 					<SearchableSetting
 						settingId="ui-enter-behavior"

webview-ui/src/components/settings/__tests__/SettingsView.change-detection.spec.tsx

@@ -302,6 +302,7 @@ describe("SettingsView - Change Detection Fix", () => {
 		openRouterImageApiKey: undefined,
 		openRouterImageGenerationSelectedModel: undefined,
 		reasoningBlockCollapsed: true,
+		autoExpandDiffs: false,
 		...overrides,
 	})
 

webview-ui/src/components/settings/__tests__/SettingsView.unsaved-changes.spec.tsx

@@ -307,6 +307,7 @@ describe("SettingsView - Unsaved Changes Detection", () => {
 		openRouterImageApiKey: undefined,
 		openRouterImageGenerationSelectedModel: undefined,
 		reasoningBlockCollapsed: true,
+		autoExpandDiffs: false,
 	}
 
 	beforeEach(() => {

webview-ui/src/components/settings/__tests__/UISettings.spec.tsx

@@ -5,6 +5,7 @@ import { UISettings } from "../UISettings"
 describe("UISettings", () => {
 	const defaultProps = {
 		reasoningBlockCollapsed: false,
+		autoExpandDiffs: false,
 		enterBehavior: "send" as const,
 		setCachedStateField: vi.fn(),
 	}

webview-ui/src/context/ExtensionStateContext.tsx

@@ -235,6 +235,7 @@ export const ExtensionStateContextProvider: React.FC<{ children: React.ReactNode
 		terminalZdotdir: false, // Default ZDOTDIR handling setting
 		historyPreviewCollapsed: false, // Initialize the new state (default to expanded)
 		reasoningBlockCollapsed: true, // Default to collapsed
+		autoExpandDiffs: false, // Default to collapsed diffs
 		enterBehavior: "send", // Default: Enter sends, Shift+Enter creates newline
 		cloudUserInfo: null,
 		cloudIsAuthenticated: false,
@@ -488,6 +489,7 @@ export const ExtensionStateContextProvider: React.FC<{ children: React.ReactNode
 	const contextValue: ExtensionStateContextType = {
 		...state,
 		reasoningBlockCollapsed: state.reasoningBlockCollapsed ?? true,
+		autoExpandDiffs: state.autoExpandDiffs ?? false,
 		didHydrateState,
 		showWelcome,
 		theme,

webview-ui/src/i18n/locales/en/settings.json

@@ -160,6 +160,10 @@
 			"label": "Collapse Thinking messages by default",
 			"description": "When enabled, thinking blocks will be collapsed by default until you interact with them"
 		},
+		"autoExpandDiffs": {
+			"label": "Auto-expand diffs in chat messages",
+			"description": "When enabled, file edit diffs will be automatically expanded instead of collapsed behind the filename"
+		},
 		"requireCtrlEnterToSend": {
 			"label": "Require {{primaryMod}}+Enter to send messages",
 			"description": "When enabled, you must press {{primaryMod}}+Enter to send messages instead of just Enter"