fix(site): use overflow-hidden for prompt text overflow (#23977)

Also had Claude write a couple of stories for the SessionTimeline 🤖 but
they look good

site/src/pages/AIBridgePage/SessionThreadsPage/SessionTimeline/SessionTimeline.stories.tsx

@@ -0,0 +1,128 @@
+import type { Meta, StoryObj } from "@storybook/react-vite";
+import type { AIBridgeThread } from "#/api/typesGenerated";
+import { MockSession } from "#/testHelpers/entities";
+import { SessionTimeline } from "./SessionTimeline";
+
+// A thread with one thinking block and one tool call.
+const mockThread: AIBridgeThread = {
+	id: "thread-1",
+	prompt:
+		"Can you check what files are in the project and summarize the structure?",
+	model: "claude-opus-4-6",
+	provider: "anthropic",
+	started_at: "2026-03-09T09:28:15.000Z",
+	ended_at: "2026-03-09T09:28:47.000Z",
+	token_usage: {
+		input_tokens: 1240,
+		output_tokens: 320,
+		metadata: { cache_read_input_tokens: 900 },
+	},
+	agentic_actions: [
+		{
+			model: "claude-opus-4-6",
+			token_usage: {
+				input_tokens: 620,
+				output_tokens: 160,
+				metadata: {},
+			},
+			thinking: [
+				{
+					text: "The user wants to understand the project structure. I should start by listing the root directory, then drill into interesting sub-directories.",
+				},
+			],
+			tool_calls: [
+				{
+					id: "tool-1",
+					interception_id: "interception-1",
+					provider_response_id: "resp-1",
+					server_url: "http://localhost:3000/mcp",
+					tool: "list_directory",
+					injected: false,
+					input: JSON.stringify({ path: "." }),
+					metadata: {},
+					created_at: "2026-03-09T09:28:20.000Z",
+				},
+			],
+		},
+	],
+};
+
+// A second thread with a long prompt and multiple tool calls.
+const mockThreadLong: AIBridgeThread = {
+	id: "thread-2",
+	prompt:
+		"Please refactor the authentication module so that it uses the new token-based flow we discussed. Make sure to update all the related tests and add inline comments explaining the security rationale for each change.",
+	model: "claude-opus-4-6",
+	provider: "anthropic",
+	started_at: "2026-03-09T10:00:00.000Z",
+	ended_at: "2026-03-09T10:05:30.000Z",
+	token_usage: {
+		input_tokens: 8500,
+		output_tokens: 3200,
+		metadata: {
+			cache_read_input_tokens: 6000,
+			cache_creation_input_tokens: 2000,
+		},
+	},
+	agentic_actions: [
+		{
+			model: "claude-opus-4-6",
+			token_usage: { input_tokens: 2800, output_tokens: 1100, metadata: {} },
+			thinking: [],
+			tool_calls: [
+				{
+					id: "tool-2a",
+					interception_id: "interception-2",
+					provider_response_id: "resp-2",
+					server_url: "http://localhost:3000/mcp",
+					tool: "read_file",
+					injected: false,
+					input: JSON.stringify({ path: "src/auth/index.ts" }),
+					metadata: {},
+					created_at: "2026-03-09T10:00:15.000Z",
+				},
+				{
+					id: "tool-2b",
+					interception_id: "interception-3",
+					provider_response_id: "resp-3",
+					server_url: "http://localhost:3000/mcp",
+					tool: "write_file",
+					injected: false,
+					input: JSON.stringify({
+						path: "src/auth/index.ts",
+						content: "// refactored auth module\n...",
+					}),
+					metadata: {},
+					created_at: "2026-03-09T10:01:00.000Z",
+				},
+			],
+		},
+	],
+};
+
+const noop = () => {};
+
+const meta: Meta<typeof SessionTimeline> = {
+	title: "pages/AIBridgePage/SessionTimeline",
+	component: SessionTimeline,
+	args: {
+		initiator: MockSession.initiator,
+		threads: [mockThread],
+		hasNextPage: false,
+		isFetchingNextPage: false,
+		onFetchNextPage: noop,
+	},
+};
+
+export default meta;
+type Story = StoryObj<typeof SessionTimeline>;
+
+export const OneThread: Story = {};
+
+export const MultipleThreads: Story = {
+	args: { threads: [mockThread, mockThreadLong] },
+};
+
+export const FetchingNextPage: Story = {
+	args: { hasNextPage: true, isFetchingNextPage: true },
+};

site/src/pages/AIBridgePage/SessionThreadsPage/SessionTimeline/SessionTimeline.tsx

@@ -62,7 +62,7 @@ const ExpandableText: FC<ExpandableTextProps> = ({
 							}
 						: undefined
 				}
-				className={cn(className, "overflow-scroll", isExpanded && "pb-9")}
+				className={cn(className, "overflow-hidden", isExpanded && "pb-9")}
 			>
 				{text}
 			</p>