diff --git a/packages/coding-agent/src/core/agent-session-runtime.ts b/packages/coding-agent/src/core/agent-session-runtime.ts
index a89fef835..b4756d4cf 100644
--- a/packages/coding-agent/src/core/agent-session-runtime.ts
+++ b/packages/coding-agent/src/core/agent-session-runtime.ts
@@ -292,12 +292,11 @@ export class AgentSessionRuntime {
 				return { cancelled: false, selectedText };
 			}
 
-			const sourceManager = SessionManager.open(currentSessionFile, sessionDir);
-			const forkedSessionPath = sourceManager.createBranchedSession(targetLeafId);
+			const sessionManager = SessionManager.open(currentSessionFile, sessionDir);
+			const forkedSessionPath = sessionManager.createBranchedSession(targetLeafId);
 			if (!forkedSessionPath) {
 				throw new Error("Failed to create forked session");
 			}
-			const sessionManager = SessionManager.open(forkedSessionPath, sessionDir);
 			await this.teardownCurrent("fork", sessionManager.getSessionFile());
 			this.apply(
 				await this.createRuntime({
diff --git a/packages/coding-agent/test/suite/agent-session-runtime.test.ts b/packages/coding-agent/test/suite/agent-session-runtime.test.ts
index 4d839ecfb..69c817ac3 100644
--- a/packages/coding-agent/test/suite/agent-session-runtime.test.ts
+++ b/packages/coding-agent/test/suite/agent-session-runtime.test.ts
@@ -1,6 +1,6 @@
 import { existsSync, mkdirSync, realpathSync, rmSync } from "node:fs";
 import { tmpdir } from "node:os";
-import { join } from "node:path";
+import { join, parse } from "node:path";
 import { fauxAssistantMessage, registerFauxProvider } from "@earendil-works/pi-ai";
 import { afterEach, describe, expect, it } from "vitest";
 import {
@@ -274,6 +274,8 @@ describe("AgentSessionRuntime characterization", () => {
 			{ type: "session_shutdown", reason: "fork", targetSessionFile: runtime.session.sessionFile },
 			{ type: "session_start", reason: "fork", previousSessionFile },
 		]);
+		const sessionFileName = parse(runtime.session.sessionFile!).name;
+		expect(sessionFileName.endsWith(`_${runtime.session.sessionId}`)).toBe(true);
 
 		events.length = 0;
 		cancelNextFork = true;