diff --git a/src/auto-reply/reply/commands-export-session.test.ts b/src/auto-reply/reply/commands-export-session.test.ts
index 09f132b114f..6e7a162e7b5 100644
--- a/src/auto-reply/reply/commands-export-session.test.ts
+++ b/src/auto-reply/reply/commands-export-session.test.ts
@@ -1,4 +1,5 @@
-import { beforeEach, describe, expect, it, vi } from "vitest";
+import path from "node:path";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import type { HandleCommandsParams } from "./commands-types.js";
 
 const hoisted = await vi.hoisted(async () => {
@@ -119,6 +120,10 @@ function makeParams(): HandleCommandsParams {
 }
 
 describe("buildExportSessionReply", () => {
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
   beforeEach(() => {
     vi.clearAllMocks();
     hoisted.resolveDefaultSessionStorePathMock.mockReturnValue("/tmp/target-store/sessions.json");
@@ -231,6 +236,32 @@ describe("buildExportSessionReply", () => {
     expect(html).toContain('const base64 = document.getElementById("session-data").textContent;');
   });
 
+  it("suffixes colliding default export filenames instead of overwriting", async () => {
+    const { buildExportSessionReply } = await import("./commands-export-session.js");
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date("2026-05-05T10:11:12.345Z"));
+    const collision = Object.assign(new Error("exists"), { code: "EEXIST" });
+    hoisted.writeFileMock.mockRejectedValueOnce(collision).mockResolvedValueOnce(undefined);
+
+    const reply = await buildExportSessionReply(makeParams());
+
+    const expectedBase = path.join(
+      "/tmp/workspace",
+      "openclaw-session-session--2026-05-05T10-11-12.html",
+    );
+    const expectedSuffix = path.join(
+      "/tmp/workspace",
+      "openclaw-session-session--2026-05-05T10-11-12-2.html",
+    );
+    expect(hoisted.writeFileMock.mock.calls[0]?.[0]).toBe(expectedBase);
+    expect(hoisted.writeFileMock.mock.calls[0]?.[2]).toMatchObject({
+      encoding: "utf-8",
+      flag: "wx",
+    });
+    expect(hoisted.writeFileMock.mock.calls[1]?.[0]).toBe(expectedSuffix);
+    expect(reply.text).toContain("📄 File: openclaw-session-session--2026-05-05T10-11-12-2.html");
+  });
+
   it("preserves replacement text with dollar sequences", async () => {
     const { buildExportSessionReply } = await import("./commands-export-session.js");
     hoisted.exportHtmlTemplateContents.set(
diff --git a/src/auto-reply/reply/commands-export-session.ts b/src/auto-reply/reply/commands-export-session.ts
index 6f0e830e2e6..d372aff20b0 100644
--- a/src/auto-reply/reply/commands-export-session.ts
+++ b/src/auto-reply/reply/commands-export-session.ts
@@ -131,6 +131,28 @@ async function fileExists(pathName: string): Promise<boolean> {
   }
 }
 
+function addCollisionSuffix(filePath: string, suffix: number): string {
+  const ext = path.extname(filePath);
+  const baseName = path.basename(filePath, ext);
+  return path.join(path.dirname(filePath), `${baseName}-${suffix}${ext}`);
+}
+
+async function writeNewDefaultExportFile(filePath: string, html: string): Promise<string> {
+  for (let suffix = 1; suffix <= 100; suffix++) {
+    const candidate = suffix === 1 ? filePath : addCollisionSuffix(filePath, suffix);
+    try {
+      await fsp.writeFile(candidate, html, { encoding: "utf-8", flag: "wx" });
+      return candidate;
+    } catch (error) {
+      if (typeof error === "object" && error && "code" in error && error.code === "EEXIST") {
+        continue;
+      }
+      throw error;
+    }
+  }
+  throw new Error(`Could not find an unused export filename near ${filePath}`);
+}
+
 async function readSessionDataFromTranscript(sessionFile: string): Promise<{
   header: SessionHeader | null;
   entries: PiSessionEntry[];
@@ -193,7 +215,7 @@ export async function buildExportSessionReply(params: HandleCommandsParams): Pro
   // 6. Determine output path
   const timestamp = new Date().toISOString().replace(/[:.]/g, "-").slice(0, 19);
   const defaultFileName = `openclaw-session-${entry.sessionId.slice(0, 8)}-${timestamp}.html`;
-  const outputPath = args.outputPath
+  let outputPath = args.outputPath
     ? path.resolve(
         args.outputPath.startsWith("~")
           ? args.outputPath.replace("~", process.env.HOME ?? "")
@@ -206,7 +228,11 @@ export async function buildExportSessionReply(params: HandleCommandsParams): Pro
   await fsp.mkdir(outputDir, { recursive: true });
 
   // 7. Write file
-  await fsp.writeFile(outputPath, html, "utf-8");
+  if (args.outputPath) {
+    await fsp.writeFile(outputPath, html, "utf-8");
+  } else {
+    outputPath = await writeNewDefaultExportFile(outputPath, html);
+  }
 
   const relativePath = path.relative(params.workspaceDir, outputPath);
   const displayPath = relativePath.startsWith("..") ? outputPath : relativePath;