fix(coding-agent): retry RPC stdout backpressure

closes #4897

packages/coding-agent/src/modes/rpc/rpc-mode.ts

@@ -19,7 +19,12 @@ import type {
 	ExtensionWidgetOptions,
 	WorkingIndicatorOptions,
 } from "../../core/extensions/index.ts";
-import { takeOverStdout, writeRawStdout } from "../../core/output-guard.ts";
+import {
+	flushRawStdout,
+	takeOverStdout,
+	waitForRawStdoutBackpressure,
+	writeRawStdout,
+} from "../../core/output-guard.ts";
 import { killTrackedDetachedChildren } from "../../utils/shell.ts";
 import { type Theme, theme } from "../interactive/theme/theme.ts";
 import { attachJsonlLineReader, serializeJsonLine } from "./jsonl.ts";
@@ -49,6 +54,7 @@ export async function runRpcMode(runtimeHost: AgentSessionRuntime): Promise<neve
 	takeOverStdout();
 	let session = runtimeHost.session;
 	let unsubscribe: (() => void) | undefined;
+	let unsubscribeBackpressure: (() => void) | undefined;
 
 	const output = (obj: RpcResponse | RpcExtensionUIRequest | object) => {
 		writeRawStdout(serializeJsonLine(obj));
@@ -343,9 +349,13 @@ export async function runRpcMode(runtimeHost: AgentSessionRuntime): Promise<neve
 		});
 
 		unsubscribe?.();
+		unsubscribeBackpressure?.();
 		unsubscribe = session.subscribe((event) => {
 			output(event);
 		});
+		unsubscribeBackpressure = session.agent.subscribe(async () => {
+			await waitForRawStdoutBackpressure();
+		});
 	};
 
 	const registerSignalHandlers = (): void => {
@@ -357,7 +367,7 @@ export async function runRpcMode(runtimeHost: AgentSessionRuntime): Promise<neve
 		for (const signal of signals) {
 			const handler = () => {
 				killTrackedDetachedChildren();
-				void shutdown(signal === "SIGHUP" ? 129 : 143);
+				void shutdown(signal === "SIGHUP" ? 129 : 143, signal);
 			};
 			process.on(signal, handler);
 			signalCleanupHandlers.push(() => process.off(signal, handler));
@@ -665,7 +675,7 @@ export async function runRpcMode(runtimeHost: AgentSessionRuntime): Promise<neve
 	 */
 	let detachInput = () => {};
 
-	async function shutdown(exitCode = 0): Promise<never> {
+	async function shutdown(exitCode = 0, signal?: NodeJS.Signals): Promise<never> {
 		if (shuttingDown) {
 			process.exit(exitCode);
 		}
@@ -674,9 +684,13 @@ export async function runRpcMode(runtimeHost: AgentSessionRuntime): Promise<neve
 			cleanup();
 		}
 		unsubscribe?.();
+		unsubscribeBackpressure?.();
 		await runtimeHost.dispose();
 		detachInput();
 		process.stdin.pause();
+		if (signal !== "SIGTERM") {
+			await flushRawStdout();
+		}
 		process.exit(exitCode);
 	}
 
@@ -697,6 +711,7 @@ export async function runRpcMode(runtimeHost: AgentSessionRuntime): Promise<neve
 					`Failed to parse command: ${parseError instanceof Error ? parseError.message : String(parseError)}`,
 				),
 			);
+			await waitForRawStdoutBackpressure();
 			return;
 		}
 
@@ -721,6 +736,7 @@ export async function runRpcMode(runtimeHost: AgentSessionRuntime): Promise<neve
 			const response = await handleCommand(command);
 			if (response) {
 				output(response);
+				await waitForRawStdoutBackpressure();
 			}
 			await checkShutdownRequested();
 		} catch (commandError: unknown) {
@@ -731,6 +747,7 @@ export async function runRpcMode(runtimeHost: AgentSessionRuntime): Promise<neve
 					commandError instanceof Error ? commandError.message : String(commandError),
 				),
 			);
+			await waitForRawStdoutBackpressure();
 		}
 	};