fix(logs): respect TZ env var for timestamp display, fix Windows timezone (#21859)

src/logging/timestamps.ts

@@ -1,14 +1,36 @@
-export function formatLocalIsoWithOffset(now: Date): string {
-  const year = now.getFullYear();
-  const month = String(now.getMonth() + 1).padStart(2, "0");
-  const day = String(now.getDate()).padStart(2, "0");
-  const h = String(now.getHours()).padStart(2, "0");
-  const m = String(now.getMinutes()).padStart(2, "0");
-  const s = String(now.getSeconds()).padStart(2, "0");
-  const ms = String(now.getMilliseconds()).padStart(3, "0");
-  const tzOffset = now.getTimezoneOffset();
-  const tzSign = tzOffset <= 0 ? "+" : "-";
-  const tzHours = String(Math.floor(Math.abs(tzOffset) / 60)).padStart(2, "0");
-  const tzMinutes = String(Math.abs(tzOffset) % 60).padStart(2, "0");
-  return `${year}-${month}-${day}T${h}:${m}:${s}.${ms}${tzSign}${tzHours}:${tzMinutes}`;
+export function isValidTimeZone(tz: string): boolean {
+  try {
+    new Intl.DateTimeFormat("en", { timeZone: tz });
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+export function formatLocalIsoWithOffset(now: Date, timeZone?: string): string {
+  const explicit = timeZone ?? process.env.TZ;
+  const tz =
+    explicit && isValidTimeZone(explicit)
+      ? explicit
+      : Intl.DateTimeFormat().resolvedOptions().timeZone;
+
+  const fmt = new Intl.DateTimeFormat("en", {
+    timeZone: tz,
+    year: "numeric",
+    month: "2-digit",
+    day: "2-digit",
+    hour: "2-digit",
+    minute: "2-digit",
+    second: "2-digit",
+    hour12: false,
+    fractionalSecondDigits: 3 as 1 | 2 | 3,
+    timeZoneName: "longOffset",
+  });
+
+  const parts = Object.fromEntries(fmt.formatToParts(now).map((p) => [p.type, p.value]));
+
+  const offsetRaw = parts.timeZoneName ?? "GMT";
+  const offset = offsetRaw === "GMT" ? "+00:00" : offsetRaw.slice(3);
+
+  return `${parts.year}-${parts.month}-${parts.day}T${parts.hour}:${parts.minute}:${parts.second}.${parts.fractionalSecond}${offset}`;
 }