diff --git a/core/util/historyUtils.ts b/core/util/historyUtils.ts
index fc0939c7bcf..c52493281d7 100644
--- a/core/util/historyUtils.ts
+++ b/core/util/historyUtils.ts
@@ -10,13 +10,10 @@ import { getContinueGlobalPath } from "../util/paths.js";
 
 // If useful elsewhere, helper funcs should move to core/util/index.ts or similar
 function getOffsetDatetime(date: Date): Date {
-  const offset = date.getTimezoneOffset();
-  const offsetHours = Math.floor(offset / 60);
-  const offsetMinutes = offset % 60;
-  date.setHours(date.getHours() - offsetHours);
-  date.setMinutes(date.getMinutes() - offsetMinutes);
-
-  return date;
+  // Shift by the whole offset at once: splitting it into hours and minutes
+  // rounds the wrong way for zones east of UTC that aren't a whole number of
+  // hours ahead, e.g. UTC+05:30 would be treated as UTC+06:30.
+  return new Date(date.getTime() - date.getTimezoneOffset() * 60 * 1000);
 }
 
 function asBasicISOString(date: Date): string {
diff --git a/core/util/historyUtils.vitest.ts b/core/util/historyUtils.vitest.ts
new file mode 100644
index 00000000000..caec41d849f
--- /dev/null
+++ b/core/util/historyUtils.vitest.ts
@@ -0,0 +1,50 @@
+import fs from "fs";
+import os from "os";
+import path from "path";
+
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+import { shareSession } from "./historyUtils";
+
+describe("shareSession", () => {
+  const originalTz = process.env.TZ;
+  let outputDir: string;
+
+  const shareAt = async (timeZone: string, isoTime: string) => {
+    process.env.TZ = timeZone;
+    vi.useFakeTimers({ toFake: ["Date"] });
+    vi.setSystemTime(new Date(isoTime));
+
+    const ide = { writeFile: vi.fn(), openFile: vi.fn() };
+    const fileUrl = await shareSession(ide as any, [], outputDir);
+    return path.basename(fileUrl);
+  };
+
+  beforeEach(() => {
+    outputDir = fs.mkdtempSync(path.join(os.tmpdir(), "continue-share-"));
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+    process.env.TZ = originalTz;
+    fs.rmSync(outputDir, { recursive: true, force: true });
+  });
+
+  it("names the file after local time in whole-hour timezones", async () => {
+    // UTC-04:00 in August
+    const name = await shareAt("America/New_York", "2026-08-17T10:00:00.000Z");
+    expect(name).toBe("20260817T060000_session.md");
+  });
+
+  it("names the file after local time in half-hour timezones", async () => {
+    // UTC+05:30
+    const name = await shareAt("Asia/Kolkata", "2026-08-17T10:00:00.000Z");
+    expect(name).toBe("20260817T153000_session.md");
+  });
+
+  it("names the file after local time in quarter-hour timezones", async () => {
+    // UTC+05:45
+    const name = await shareAt("Asia/Kathmandu", "2026-08-17T10:00:00.000Z");
+    expect(name).toBe("20260817T154500_session.md");
+  });
+});