diff --git a/packages/coding-agent/src/core/session-manager.ts b/packages/coding-agent/src/core/session-manager.ts
index a7edb634..49b0f422 100644
--- a/packages/coding-agent/src/core/session-manager.ts
+++ b/packages/coding-agent/src/core/session-manager.ts
@@ -36,6 +36,7 @@ export interface SessionHeader {
 }
 
 export interface NewSessionOptions {
+	id?: string;
 	parentSession?: string;
 }
 
@@ -721,7 +722,7 @@ export class SessionManager {
 	}
 
 	newSession(options?: NewSessionOptions): string | undefined {
-		this.sessionId = randomUUID();
+		this.sessionId = options?.id ?? randomUUID();
 		const timestamp = new Date().toISOString();
 		const header: SessionHeader = {
 			type: "session",
diff --git a/packages/coding-agent/test/session-manager/custom-session-id.test.ts b/packages/coding-agent/test/session-manager/custom-session-id.test.ts
new file mode 100644
index 00000000..8cded2d2
--- /dev/null
+++ b/packages/coding-agent/test/session-manager/custom-session-id.test.ts
@@ -0,0 +1,35 @@
+import { describe, expect, it } from "vitest";
+import { SessionManager } from "../../src/core/session-manager.js";
+
+describe("SessionManager.newSession with custom id", () => {
+	it("uses the provided id instead of generating one", () => {
+		const session = SessionManager.inMemory();
+		session.newSession({ id: "my-custom-id" });
+		expect(session.getSessionId()).toBe("my-custom-id");
+	});
+
+	it("generates a random id when no id is provided", () => {
+		const session = SessionManager.inMemory();
+		session.newSession();
+		const id = session.getSessionId();
+		expect(id).toBeDefined();
+		expect(id).not.toBe("");
+	});
+
+	it("generates a random id when options is provided without id", () => {
+		const session = SessionManager.inMemory();
+		session.newSession({ parentSession: "parent.jsonl" });
+		const id = session.getSessionId();
+		expect(id).toBeDefined();
+		expect(id).not.toBe("");
+	});
+
+	it("includes the custom id in the session header", () => {
+		const session = SessionManager.inMemory();
+		session.newSession({ id: "header-test-id" });
+
+		const header = session.getHeader();
+		expect(header).not.toBeNull();
+		expect(header!.id).toBe("header-test-id");
+	});
+});