diff --git a/src/telegram/bot.create-telegram-bot.accepts-group-messages-mentionpatterns-match-without-botusername.test.ts b/src/telegram/bot.create-telegram-bot.accepts-group-messages-mentionpatterns-match-without-botusername.test.ts
index 1379b6e6f..a648b9511 100644
--- a/src/telegram/bot.create-telegram-bot.accepts-group-messages-mentionpatterns-match-without-botusername.test.ts
+++ b/src/telegram/bot.create-telegram-bot.accepts-group-messages-mentionpatterns-match-without-botusername.test.ts
@@ -1,8 +1,5 @@
 import { beforeEach, describe, expect, it, vi } from "vitest";
-import {
-  escapeRegExp,
-  formatLocalEnvelopeTimestamp,
-} from "../../test/helpers/envelope-timestamp.js";
+import { escapeRegExp, formatEnvelopeTimestamp } from "../../test/helpers/envelope-timestamp.js";
 import { resetInboundDedupe } from "../auto-reply/reply/inbound-dedupe.js";
 import { createTelegramBot } from "./bot.js";
 
@@ -180,7 +177,7 @@ describe("createTelegramBot", () => {
     expect(payload.WasMentioned).toBe(true);
     expect(payload.SenderName).toBe("Ada");
     expect(payload.SenderId).toBe("9");
-    const expectedTimestamp = formatLocalEnvelopeTimestamp(new Date("2025-01-09T00:00:00Z"));
+    const expectedTimestamp = formatEnvelopeTimestamp(new Date("2025-01-09T00:00:00Z"));
     const timestampPattern = escapeRegExp(expectedTimestamp);
     expect(payload.Body).toMatch(
       new RegExp(`^\\[Telegram Test Group id:7 (\\+\\d+[smhd] )?${timestampPattern}\\]`),
@@ -225,7 +222,7 @@ describe("createTelegramBot", () => {
     expect(payload.SenderName).toBe("Ada Lovelace");
     expect(payload.SenderId).toBe("99");
     expect(payload.SenderUsername).toBe("ada");
-    const expectedTimestamp = formatLocalEnvelopeTimestamp(new Date("2025-01-09T00:00:00Z"));
+    const expectedTimestamp = formatEnvelopeTimestamp(new Date("2025-01-09T00:00:00Z"));
     const timestampPattern = escapeRegExp(expectedTimestamp);
     expect(payload.Body).toMatch(
       new RegExp(`^\\[Telegram Ops id:42 (\\+\\d+[smhd] )?${timestampPattern}\\]`),
diff --git a/src/telegram/bot.create-telegram-bot.installs-grammy-throttler.test.ts b/src/telegram/bot.create-telegram-bot.installs-grammy-throttler.test.ts
index 141532796..e27e119f0 100644
--- a/src/telegram/bot.create-telegram-bot.installs-grammy-throttler.test.ts
+++ b/src/telegram/bot.create-telegram-bot.installs-grammy-throttler.test.ts
@@ -1,8 +1,5 @@
 import { beforeEach, describe, expect, it, vi } from "vitest";
-import {
-  escapeRegExp,
-  formatLocalEnvelopeTimestamp,
-} from "../../test/helpers/envelope-timestamp.js";
+import { escapeRegExp, formatEnvelopeTimestamp } from "../../test/helpers/envelope-timestamp.js";
 import { resetInboundDedupe } from "../auto-reply/reply/inbound-dedupe.js";
 import { createTelegramBot, getTelegramSequentialKey } from "./bot.js";
 import { resolveTelegramFetch } from "./fetch.js";
@@ -332,7 +329,7 @@ describe("createTelegramBot", () => {
 
       expect(replySpy).toHaveBeenCalledTimes(1);
       const payload = replySpy.mock.calls[0][0];
-      const expectedTimestamp = formatLocalEnvelopeTimestamp(new Date("2025-01-09T00:00:00Z"));
+      const expectedTimestamp = formatEnvelopeTimestamp(new Date("2025-01-09T00:00:00Z"));
       const timestampPattern = escapeRegExp(expectedTimestamp);
       expect(payload.Body).toMatch(
         new RegExp(
diff --git a/src/telegram/bot.test.ts b/src/telegram/bot.test.ts
index 2d04d6aa4..21f52c50d 100644
--- a/src/telegram/bot.test.ts
+++ b/src/telegram/bot.test.ts
@@ -10,10 +10,7 @@ import { listSkillCommandsForAgents } from "../auto-reply/skill-commands.js";
 import { resetInboundDedupe } from "../auto-reply/reply/inbound-dedupe.js";
 import * as replyModule from "../auto-reply/reply.js";
 import { expectInboundContextContract } from "../../test/helpers/inbound-contract.js";
-import {
-  escapeRegExp,
-  formatLocalEnvelopeTimestamp,
-} from "../../test/helpers/envelope-timestamp.js";
+import { escapeRegExp, formatEnvelopeTimestamp } from "../../test/helpers/envelope-timestamp.js";
 import { createTelegramBot, getTelegramSequentialKey } from "./bot.js";
 import { resolveTelegramFetch } from "./fetch.js";
 
@@ -454,7 +451,7 @@ describe("createTelegramBot", () => {
 
       expect(replySpy).toHaveBeenCalledTimes(1);
       const payload = replySpy.mock.calls[0][0];
-      const expectedTimestamp = formatLocalEnvelopeTimestamp(new Date("2025-01-09T00:00:00Z"));
+      const expectedTimestamp = formatEnvelopeTimestamp(new Date("2025-01-09T00:00:00Z"));
       const timestampPattern = escapeRegExp(expectedTimestamp);
       expect(payload.Body).toMatch(
         new RegExp(
@@ -593,7 +590,7 @@ describe("createTelegramBot", () => {
     const payload = replySpy.mock.calls[0][0];
     expectInboundContextContract(payload);
     expect(payload.WasMentioned).toBe(true);
-    const expectedTimestamp = formatLocalEnvelopeTimestamp(new Date("2025-01-09T00:00:00Z"));
+    const expectedTimestamp = formatEnvelopeTimestamp(new Date("2025-01-09T00:00:00Z"));
     const timestampPattern = escapeRegExp(expectedTimestamp);
     expect(payload.Body).toMatch(
       new RegExp(`^\\[Telegram Test Group id:7 (\\+\\d+[smhd] )?${timestampPattern}\\]`),
@@ -639,7 +636,7 @@ describe("createTelegramBot", () => {
     expect(replySpy).toHaveBeenCalledTimes(1);
     const payload = replySpy.mock.calls[0][0];
     expectInboundContextContract(payload);
-    const expectedTimestamp = formatLocalEnvelopeTimestamp(new Date("2025-01-09T00:00:00Z"));
+    const expectedTimestamp = formatEnvelopeTimestamp(new Date("2025-01-09T00:00:00Z"));
     const timestampPattern = escapeRegExp(expectedTimestamp);
     expect(payload.Body).toMatch(
       new RegExp(`^\\[Telegram Ops id:42 (\\+\\d+[smhd] )?${timestampPattern}\\]`),
diff --git a/src/web/auto-reply.web-auto-reply.reconnects-after-connection-close.test.ts b/src/web/auto-reply.web-auto-reply.reconnects-after-connection-close.test.ts
index 870a018d5..f40e4e3ab 100644
--- a/src/web/auto-reply.web-auto-reply.reconnects-after-connection-close.test.ts
+++ b/src/web/auto-reply.web-auto-reply.reconnects-after-connection-close.test.ts
@@ -3,10 +3,7 @@ import fs from "node:fs/promises";
 import os from "node:os";
 import path from "node:path";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
-import {
-  escapeRegExp,
-  formatLocalEnvelopeTimestamp,
-} from "../../test/helpers/envelope-timestamp.js";
+import { escapeRegExp, formatEnvelopeTimestamp } from "../../test/helpers/envelope-timestamp.js";
 
 vi.mock("../agents/pi-embedded.js", () => ({
   abortEmbeddedPiRun: vi.fn().mockReturnValue(false),
@@ -332,8 +329,8 @@ describe("web auto-reply", () => {
       expect(resolver).toHaveBeenCalledTimes(2);
       const firstArgs = resolver.mock.calls[0][0];
       const secondArgs = resolver.mock.calls[1][0];
-      const firstTimestamp = formatLocalEnvelopeTimestamp(new Date("2025-01-01T00:00:00Z"));
-      const secondTimestamp = formatLocalEnvelopeTimestamp(new Date("2025-01-01T01:00:00Z"));
+      const firstTimestamp = formatEnvelopeTimestamp(new Date("2025-01-01T00:00:00Z"));
+      const secondTimestamp = formatEnvelopeTimestamp(new Date("2025-01-01T01:00:00Z"));
       const firstPattern = escapeRegExp(firstTimestamp);
       const secondPattern = escapeRegExp(secondTimestamp);
       expect(firstArgs.Body).toMatch(
diff --git a/test/helpers/envelope-timestamp.ts b/test/helpers/envelope-timestamp.ts
index 135063e41..934608204 100644
--- a/test/helpers/envelope-timestamp.ts
+++ b/test/helpers/envelope-timestamp.ts
@@ -1,5 +1,17 @@
-export function formatLocalEnvelopeTimestamp(date: Date): string {
+type EnvelopeTimestampZone = string;
+
+function formatUtcTimestamp(date: Date): string {
+  const yyyy = String(date.getUTCFullYear()).padStart(4, "0");
+  const mm = String(date.getUTCMonth() + 1).padStart(2, "0");
+  const dd = String(date.getUTCDate()).padStart(2, "0");
+  const hh = String(date.getUTCHours()).padStart(2, "0");
+  const min = String(date.getUTCMinutes()).padStart(2, "0");
+  return `${yyyy}-${mm}-${dd}T${hh}:${min}Z`;
+}
+
+function formatZonedTimestamp(date: Date, timeZone?: string): string {
   const parts = new Intl.DateTimeFormat("en-US", {
+    timeZone,
     year: "numeric",
     month: "2-digit",
     day: "2-digit",
@@ -27,6 +39,17 @@ export function formatLocalEnvelopeTimestamp(date: Date): string {
   return `${yyyy}-${mm}-${dd} ${hh}:${min}${tz ? ` ${tz}` : ""}`;
 }
 
+export function formatEnvelopeTimestamp(date: Date, zone: EnvelopeTimestampZone = "utc"): string {
+  const normalized = zone.trim().toLowerCase();
+  if (normalized === "utc" || normalized === "gmt") return formatUtcTimestamp(date);
+  if (normalized === "local" || normalized === "host") return formatZonedTimestamp(date);
+  return formatZonedTimestamp(date, zone);
+}
+
+export function formatLocalEnvelopeTimestamp(date: Date): string {
+  return formatEnvelopeTimestamp(date, "local");
+}
+
 export function escapeRegExp(value: string): string {
   return value.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
 }