fix: handle null/undefined token values in ContextCondenseRow to prevent UI crash

- Added null-safe operators for prevContextTokens, newContextTokens, and cost
- Fallback to "0" for null/undefined token values
- Added comprehensive test coverage for edge cases
- Fixes #6914

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

@@ -33,9 +33,12 @@ export const ContextCondenseRow = ({ cost, prevContextTokens, newContextTokens,
 					<span className="codicon codicon-compress text-blue-400" />
 					<span className="font-bold text-vscode-foreground">{t("chat:contextCondense.title")}</span>
 					<span className="text-vscode-descriptionForeground text-sm">
-						{prevContextTokens.toLocaleString()} → {newContextTokens.toLocaleString()} {t("tokens")}
+						{prevContextTokens?.toLocaleString() ?? "0"} → {newContextTokens?.toLocaleString() ?? "0"}{" "}
+						{t("tokens")}
 					</span>
-					<VSCodeBadge className={cost > 0 ? "opacity-100" : "opacity-0"}>${cost.toFixed(2)}</VSCodeBadge>
+					<VSCodeBadge className={cost > 0 ? "opacity-100" : "opacity-0"}>
+						${(cost ?? 0).toFixed(2)}
+					</VSCodeBadge>
 				</div>
 				<span className={`codicon codicon-chevron-${isExpanded ? "up" : "down"}`}></span>
 			</div>

webview-ui/src/components/chat/__tests__/ContextCondenseRow.spec.tsx

@@ -0,0 +1,175 @@
+// npx vitest run src/components/chat/__tests__/ContextCondenseRow.spec.tsx
+
+import React from "react"
+import { render, fireEvent } from "@/utils/test-utils"
+import { ContextCondenseRow, CondensingContextRow, CondenseContextErrorRow } from "../ContextCondenseRow"
+
+// Mock i18n
+vi.mock("react-i18next", () => ({
+	useTranslation: () => ({
+		t: (key: string) => key,
+	}),
+}))
+
+// Mock VSCode components
+vi.mock("@vscode/webview-ui-toolkit/react", () => ({
+	VSCodeBadge: function MockVSCodeBadge({ children, className }: { children: React.ReactNode; className?: string }) {
+		return <span className={className}>{children}</span>
+	},
+}))
+
+// Mock Markdown component
+vi.mock("../Markdown", () => ({
+	Markdown: function MockMarkdown({ markdown }: { markdown: string }) {
+		return <div data-testid="markdown">{markdown}</div>
+	},
+}))
+
+// Mock ProgressIndicator component
+vi.mock("../ProgressIndicator", () => ({
+	ProgressIndicator: function MockProgressIndicator() {
+		return <div data-testid="progress-indicator">Loading...</div>
+	},
+}))
+
+describe("ContextCondenseRow", () => {
+	it("renders with valid token values", () => {
+		const { getByText } = render(
+			<ContextCondenseRow
+				cost={1.5}
+				prevContextTokens={1000}
+				newContextTokens={500}
+				summary="Context condensed successfully"
+			/>,
+		)
+
+		expect(getByText("chat:contextCondense.title")).toBeInTheDocument()
+		expect(getByText(/1,000 → 500 tokens/)).toBeInTheDocument()
+		expect(getByText("$1.50")).toBeInTheDocument()
+	})
+
+	it("handles null token values gracefully", () => {
+		const { getByText } = render(
+			<ContextCondenseRow
+				cost={0}
+				prevContextTokens={null as any}
+				newContextTokens={null as any}
+				summary="Context condensed"
+			/>,
+		)
+
+		expect(getByText("chat:contextCondense.title")).toBeInTheDocument()
+		// Should display "0" for null values
+		expect(getByText(/0 → 0 tokens/)).toBeInTheDocument()
+	})
+
+	it("handles undefined token values gracefully", () => {
+		const { getByText } = render(
+			<ContextCondenseRow
+				cost={undefined as any}
+				prevContextTokens={undefined as any}
+				newContextTokens={undefined as any}
+				summary="Context condensed"
+			/>,
+		)
+
+		expect(getByText("chat:contextCondense.title")).toBeInTheDocument()
+		// Should display "0" for undefined values
+		expect(getByText(/0 → 0 tokens/)).toBeInTheDocument()
+		expect(getByText("$0.00")).toBeInTheDocument()
+	})
+
+	it("handles mixed null and valid token values", () => {
+		const { getByText } = render(
+			<ContextCondenseRow
+				cost={2.5}
+				prevContextTokens={2000}
+				newContextTokens={null as any}
+				summary="Context condensed"
+			/>,
+		)
+
+		expect(getByText("chat:contextCondense.title")).toBeInTheDocument()
+		// Should display "2,000 → 0 tokens" for mixed values
+		expect(getByText(/2,000 → 0 tokens/)).toBeInTheDocument()
+		expect(getByText("$2.50")).toBeInTheDocument()
+	})
+
+	it("expands and collapses when clicked", () => {
+		const { getByText, queryByTestId } = render(
+			<ContextCondenseRow
+				cost={1.5}
+				prevContextTokens={1000}
+				newContextTokens={500}
+				summary="Context condensed successfully"
+			/>,
+		)
+
+		// Initially collapsed
+		expect(queryByTestId("markdown")).not.toBeInTheDocument()
+
+		// Click to expand
+		const header = getByText("chat:contextCondense.title").parentElement?.parentElement
+		fireEvent.click(header!)
+
+		// Should show summary
+		expect(queryByTestId("markdown")).toBeInTheDocument()
+		expect(getByText("Context condensed successfully")).toBeInTheDocument()
+
+		// Click to collapse
+		fireEvent.click(header!)
+
+		// Should hide summary
+		expect(queryByTestId("markdown")).not.toBeInTheDocument()
+	})
+
+	it("hides badge when cost is 0", () => {
+		const { container } = render(
+			<ContextCondenseRow cost={0} prevContextTokens={1000} newContextTokens={500} summary="Context condensed" />,
+		)
+
+		const badge = container.querySelector(".opacity-0")
+		expect(badge).toBeInTheDocument()
+	})
+
+	it("shows badge when cost is greater than 0", () => {
+		const { container } = render(
+			<ContextCondenseRow
+				cost={1.5}
+				prevContextTokens={1000}
+				newContextTokens={500}
+				summary="Context condensed"
+			/>,
+		)
+
+		const badge = container.querySelector(".opacity-100")
+		expect(badge).toBeInTheDocument()
+	})
+})
+
+describe("CondensingContextRow", () => {
+	it("renders with progress indicator", () => {
+		const { getByText, getByTestId } = render(<CondensingContextRow />)
+
+		expect(getByTestId("progress-indicator")).toBeInTheDocument()
+		expect(getByText("chat:contextCondense.condensing")).toBeInTheDocument()
+	})
+})
+
+describe("CondenseContextErrorRow", () => {
+	it("renders with error text", () => {
+		const errorText = "Failed to condense context: API error"
+		const { getByText } = render(<CondenseContextErrorRow errorText={errorText} />)
+
+		expect(getByText("chat:contextCondense.errorHeader")).toBeInTheDocument()
+		expect(getByText(errorText)).toBeInTheDocument()
+	})
+
+	it("renders without error text", () => {
+		const { getByText, queryByText } = render(<CondenseContextErrorRow />)
+
+		expect(getByText("chat:contextCondense.errorHeader")).toBeInTheDocument()
+		// Should not show any error text when not provided
+		expect(queryByText(/Failed/)).not.toBeInTheDocument()
+	})
+})