diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index 716b210f..deb0a5e5 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -12,6 +12,7 @@
 
 ### Fixed
 
+- Fixed RPC unknown-command errors to include the request id so clients do not hang waiting for a response ([#5868](https://github.com/earendil-works/pi/issues/5868)).
 - Fixed `/model` autocomplete and model selection searches to match provider/model queries regardless of whether the provider or model token is typed first.
 - Fixed the tree navigator to horizontally pan deep entries so the selected item remains readable ([#5830](https://github.com/earendil-works/pi/issues/5830)).
 
diff --git a/packages/coding-agent/src/modes/rpc/rpc-mode.ts b/packages/coding-agent/src/modes/rpc/rpc-mode.ts
index 9bb1f089..1150b826 100644
--- a/packages/coding-agent/src/modes/rpc/rpc-mode.ts
+++ b/packages/coding-agent/src/modes/rpc/rpc-mode.ts
@@ -667,7 +667,7 @@ export async function runRpcMode(runtimeHost: AgentSessionRuntime): Promise<neve
 
 			default: {
 				const unknownCommand = command as { type: string };
-				return error(undefined, unknownCommand.type, `Unknown command: ${unknownCommand.type}`);
+				return error(id, unknownCommand.type, `Unknown command: ${unknownCommand.type}`);
 			}
 		}
 	};
diff --git a/packages/coding-agent/test/suite/regressions/5868-rpc-unknown-command-id.test.ts b/packages/coding-agent/test/suite/regressions/5868-rpc-unknown-command-id.test.ts
new file mode 100644
index 00000000..7ee70261
--- /dev/null
+++ b/packages/coding-agent/test/suite/regressions/5868-rpc-unknown-command-id.test.ts
@@ -0,0 +1,113 @@
+import { afterEach, describe, expect, test, vi } from "vitest";
+import type { AgentSessionRuntime } from "../../../src/core/agent-session-runtime.ts";
+import { runRpcMode } from "../../../src/modes/rpc/rpc-mode.ts";
+import { createHarness, type Harness } from "../harness.ts";
+
+// Regression for https://github.com/earendil-works/pi/issues/5868
+
+const rpcIo = vi.hoisted(() => ({
+	outputLines: [] as string[],
+	lineHandler: undefined as ((line: string) => void) | undefined,
+}));
+
+vi.mock("../../../src/core/output-guard.js", () => ({
+	flushRawStdout: vi.fn(async () => {}),
+	takeOverStdout: vi.fn(),
+	waitForRawStdoutBackpressure: vi.fn(async () => {}),
+	writeRawStdout: (line: string) => {
+		rpcIo.outputLines.push(line);
+	},
+}));
+
+vi.mock("../../../src/modes/interactive/theme/theme.js", () => ({ theme: {} }));
+
+vi.mock("../../../src/modes/rpc/jsonl.js", () => ({
+	attachJsonlLineReader: vi.fn((_stream: NodeJS.ReadableStream, onLine: (line: string) => void) => {
+		rpcIo.lineHandler = onLine;
+		return () => {
+			rpcIo.lineHandler = undefined;
+		};
+	}),
+	serializeJsonLine: (value: unknown) => `${JSON.stringify(value)}\n`,
+}));
+
+type NodeListener = Parameters<typeof process.on>[1];
+
+type ListenerSnapshot = {
+	stdinEnd: NodeListener[];
+	signals: Map<NodeJS.Signals, NodeListener[]>;
+};
+
+function takeListenerSnapshot(): ListenerSnapshot {
+	const signals: NodeJS.Signals[] = process.platform === "win32" ? ["SIGTERM"] : ["SIGTERM", "SIGHUP"];
+	return {
+		stdinEnd: process.stdin.listeners("end") as NodeListener[],
+		signals: new Map(signals.map((signal) => [signal, process.listeners(signal) as NodeListener[]])),
+	};
+}
+
+function restoreListeners(snapshot: ListenerSnapshot): void {
+	for (const listener of process.stdin.listeners("end") as NodeListener[]) {
+		if (!snapshot.stdinEnd.includes(listener)) {
+			process.stdin.off("end", listener);
+		}
+	}
+
+	for (const [signal, previousListeners] of snapshot.signals) {
+		for (const listener of process.listeners(signal) as NodeListener[]) {
+			if (!previousListeners.includes(listener)) {
+				process.off(signal, listener);
+			}
+		}
+	}
+}
+
+function parseOutputLines(): Array<Record<string, unknown>> {
+	return rpcIo.outputLines
+		.flatMap((line) => line.split("\n"))
+		.filter((line) => line.trim().length > 0)
+		.map((line) => JSON.parse(line) as Record<string, unknown>);
+}
+
+function createRuntimeHost(harness: Harness): AgentSessionRuntime {
+	return {
+		session: harness.session,
+		newSession: vi.fn(async () => ({ cancelled: true })),
+		switchSession: vi.fn(async () => ({ cancelled: true })),
+		fork: vi.fn(async () => ({ cancelled: true, selectedText: "" })),
+		dispose: vi.fn(async () => {}),
+		setRebindSession: vi.fn(),
+	} as unknown as AgentSessionRuntime;
+}
+
+describe("RPC unknown command responses (#5868)", () => {
+	afterEach(() => {
+		rpcIo.outputLines = [];
+		rpcIo.lineHandler = undefined;
+	});
+
+	test("preserves the request id on unknown command errors", async () => {
+		const listenerSnapshot = takeListenerSnapshot();
+		const harness = await createHarness();
+
+		try {
+			void runRpcMode(createRuntimeHost(harness));
+			await vi.waitFor(() => expect(rpcIo.lineHandler).toBeDefined());
+
+			rpcIo.lineHandler?.(JSON.stringify({ id: "test", type: "foobar" }));
+
+			await vi.waitFor(() => {
+				expect(parseOutputLines()).toContainEqual({
+					id: "test",
+					type: "response",
+					command: "foobar",
+					success: false,
+					error: "Unknown command: foobar",
+				});
+			});
+		} finally {
+			harness.cleanup();
+			restoreListeners(listenerSnapshot);
+		}
+	});
+});