Add compaction sidecar kill switch

apps/cli/src/runtime/interactive/session-runtime.test.ts

@@ -327,6 +327,73 @@ describe("createInteractiveSessionRuntime", () => {
 		expect(runtime.getActiveSessionId()).toBe(sessionId);
 	});
 
+	it("manual compact skips sidecar writes when the sidecar flag is off", async () => {
+		const sessionId = "sess-active-sidecar-off";
+		const messages = [
+			{ id: "u1", role: "user" as const, content: "hello" },
+			{ id: "a1", role: "assistant" as const, content: "world" },
+		];
+		const compactionState = createSessionCompactionState({
+			sourceMessages: messages,
+			compactedMessages: [
+				{ id: "summary", role: "user" as const, content: "summary" },
+			],
+			updatedAt: "2026-01-01T00:00:00.000Z",
+		});
+		const manager = {
+			start: vi.fn().mockResolvedValue({
+				sessionId,
+				manifest: createManifest(sessionId),
+				manifestPath: "/tmp/session.json",
+				messagesPath: "/tmp/session.messages.json",
+			}),
+			readMessages: vi.fn().mockResolvedValue(messages),
+			updateSessionCompactionState: vi.fn(),
+			stop: vi.fn().mockResolvedValue(undefined),
+			dispose: vi.fn().mockResolvedValue(undefined),
+			ingestHookEvent: vi.fn().mockResolvedValue(undefined),
+			get: vi.fn(),
+			list: vi.fn(),
+			delete: vi.fn(),
+			send: vi.fn(),
+			getAccumulatedUsage: vi.fn(),
+		};
+		createCliCoreMock.mockResolvedValue(manager);
+		compactInteractiveMessagesMock.mockResolvedValue({
+			compacted: true,
+			canonicalMessages: messages,
+			compactionState,
+		});
+		const { createInteractiveSessionRuntime } = await importRuntime();
+		const runtime = createInteractiveSessionRuntime({
+			config: createConfig(),
+			providerSettingsManager: createProviderSettingsManager(),
+			chatCommandState: createChatCommandState(),
+			requestToolApproval: vi.fn(),
+			resolveToolPolicy: () => ({ autoApprove: true }),
+			askQuestionRef: { current: null },
+			resolveMistakeLimitDecision: undefined,
+			switchToActModeTool: {} as never,
+			onAgentEvent: vi.fn(),
+			onTeamEvent: vi.fn(),
+			onPendingPrompts: vi.fn(),
+			onPendingPromptSubmitted: vi.fn(),
+			isCompactionSidecarEnabled: () => false,
+		});
+
+		await runtime.ensureReady();
+		const result = await runtime.compactCurrentSession();
+
+		expect(result).toEqual({
+			messagesBefore: messages.length,
+			messagesAfter: messages.length,
+			workingContextMessagesAfter: compactionState.messages.length,
+			compacted: true,
+		});
+		expect(manager.updateSessionCompactionState).not.toHaveBeenCalled();
+		expect(runtime.getActiveSessionId()).toBe(sessionId);
+	});
+
 	it("rejects manual compact while the active session is running", async () => {
 		const sessionId = "sess-running";
 		const messages = [{ role: "user" as const, content: "hello" }];

apps/cli/src/runtime/interactive/session-runtime.ts

@@ -3,6 +3,7 @@ import {
 	type AgentHooks,
 	type CheckpointEntry,
 	createSessionCompactionState,
+	createSessionCompactionSidecarEnabledResolver,
 	isSessionNotFoundError,
 	type PendingPromptMutationResult,
 	type ProviderSettingsManager,
@@ -96,8 +97,12 @@ export function createInteractiveSessionRuntime(input: {
 	onTeamEvent: (event: TeamEvent) => void;
 	onPendingPrompts: (event: PendingPromptSnapshot) => void;
 	onPendingPromptSubmitted: (event: PendingPromptSubmittedEvent) => void;
+	isCompactionSidecarEnabled?: () => boolean;
 }) {
 	let sessionManager: CliCore | undefined;
+	const isCompactionSidecarEnabled =
+		input.isCompactionSidecarEnabled ??
+		createSessionCompactionSidecarEnabledResolver();
 	let runtimeHooks: RuntimeHooks | undefined;
 	let unsubscribeAgent = () => {};
 	let unsubscribePendingPrompts = () => {};
@@ -210,7 +215,9 @@ export function createInteractiveSessionRuntime(input: {
 			toolPolicies: input.config.toolPolicies,
 			interactive: true,
 			initialMessages: initial,
-			...(initialCompactionState ? { initialCompactionState } : {}),
+			...(isCompactionSidecarEnabled() && initialCompactionState
+				? { initialCompactionState }
+				: {}),
 			...(sessionMetadata ? { sessionMetadata } : {}),
 			localRuntime: {
 				onTeamRestored: () => {},
@@ -291,6 +298,9 @@ export function createInteractiveSessionRuntime(input: {
 	const readCompactionState = async (
 		sessionId: string,
 	): Promise<SessionCompactionState | undefined> => {
+		if (!isCompactionSidecarEnabled()) {
+			return undefined;
+		}
 		const manager = sessionManager;
 		if (!manager) {
 			return undefined;
@@ -624,6 +634,14 @@ export function createInteractiveSessionRuntime(input: {
 				compacted: false,
 			};
 		}
+		if (!isCompactionSidecarEnabled()) {
+			return {
+				messagesBefore,
+				messagesAfter: result.canonicalMessages.length,
+				workingContextMessagesAfter: result.compactionState.messages.length,
+				compacted: true,
+			};
+		}
 		const updated = await manager.updateSessionCompactionState(
 			sourceSessionId,
 			result.compactionState,

apps/cli/src/runtime/run-interactive.ts

@@ -1,5 +1,6 @@
 import {
 	getCurrentContextSize,
+	createSessionCompactionSidecarEnabledResolver,
 	type ProviderSettings,
 	ProviderSettingsManager,
 	type UserInstructionConfigService,
@@ -25,6 +26,7 @@ import { disableOpenTuiGraphicsProbe } from "../tui/opentui-env";
 import type { QueuedPromptItem } from "../tui/types";
 import { type ChatCommandState, chatCommandHost } from "../utils/chat-commands";
 import { applyCliCompactionMode } from "../utils/compaction-mode";
+import { getCliFeatureFlagsService } from "../utils/feature-flags";
 import {
 	shouldZeroClineFreeModelCost,
 	zeroCliAgentEventCost,
@@ -201,6 +203,8 @@ export async function runInteractive(
 		onPendingPromptSubmitted: (event) => {
 			uiEvents.emit("pending-prompt-submitted", event);
 		},
+		isCompactionSidecarEnabled:
+			createSessionCompactionSidecarEnabledResolver(getCliFeatureFlagsService()),
 	});
 	let modeChangePromise: Promise<void> | undefined;
 	let modeChangeTarget: "plan" | "act" | undefined;