fix: land cron tz one-shot handling and prerelease config warnings (#53224) (thanks @RolfHegr)

src/cli/cron-cli.test.ts

@@ -658,6 +658,27 @@ describe("cron cli", () => {
     expect(params.schedule.at).toBe("2026-03-23T21:00:00.000Z");
   });
 
+  it("applies --tz to --at correctly across DST boundaries on cron add", async () => {
+    await runCronCommand([
+      "cron",
+      "add",
+      "--name",
+      "tz-at-dst-test",
+      "--at",
+      "2026-03-29T01:30:00",
+      "--tz",
+      "Europe/Oslo",
+      "--session",
+      "isolated",
+      "--message",
+      "test",
+    ]);
+
+    const params = getGatewayCallParams<{ schedule: { kind: string; at: string } }>("cron.add");
+    expect(params.schedule.kind).toBe("at");
+    expect(params.schedule.at).toBe("2026-03-29T00:30:00.000Z");
+  });
+
   it("sets explicit stagger for cron edit", async () => {
     await runCronCommand(["cron", "edit", "job-1", "--cron", "0 * * * *", "--stagger", "30s"]);
 
@@ -685,6 +706,24 @@ describe("cron cli", () => {
     await expectCronEditWithScheduleLookupExit({ kind: "every", everyMs: 60_000 }, ["--exact"]);
   });
 
+  it("applies --tz to --at for offset-less datetimes on cron edit", async () => {
+    const patch = await runCronEditAndGetPatch([
+      "--at",
+      "2026-03-23T23:00:00",
+      "--tz",
+      "Europe/Oslo",
+    ]);
+
+    expect(patch?.patch?.schedule).toEqual({
+      kind: "at",
+      at: "2026-03-23T22:00:00.000Z",
+    });
+  });
+
+  it("rejects --tz with --every on cron edit", async () => {
+    await expectCronCommandExit(["cron", "edit", "job-1", "--every", "10m", "--tz", "UTC"]);
+  });
+
   it("patches failure alert settings on cron edit", async () => {
     callGatewayFromCli.mockClear();
 

src/cli/cron-cli/register.cron-edit.ts

@@ -158,6 +158,9 @@ export function registerCronEditCommand(cron: Command) {
           if (scheduleChosen > 1) {
             throw new Error("Choose at most one schedule change");
           }
+          if (typeof opts.tz === "string" && opts.every) {
+            throw new Error("--tz is only valid with --cron or offset-less --at");
+          }
           if (requestedStaggerMs !== undefined && (opts.at || opts.every)) {
             throw new Error("--stagger/--exact are only valid for cron schedules");
           }

src/cli/cron-cli/shared.ts

@@ -89,6 +89,8 @@ export function parseCronStaggerMs(params: {
   return parsed;
 }
 
+const OFFSETLESS_ISO_DATETIME_RE = /^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}(:\d{2})?(\.\d+)?$/;
+
 /**
  * Parse a one-shot `--at` value into an ISO string (UTC).
  *
@@ -104,20 +106,10 @@ export function parseAt(input: string, tz?: string): string | null {
 
   // If a timezone is provided and the input looks like an offset-less ISO datetime,
   // resolve it in the given IANA timezone so users get the time they expect.
-  if (tz) {
-    const isoNoOffset = /^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}(:\d{2})?(\.\d+)?$/.test(raw);
-    if (isoNoOffset) {
-      try {
-        // Use Intl to find the UTC offset for the given tz at the specified local time.
-        // We first parse naively as UTC to get a rough Date, then compute the real offset.
-        const naiveMs = new Date(`${raw}Z`).getTime();
-        if (!Number.isNaN(naiveMs)) {
-          const offset = getTimezoneOffsetMs(naiveMs, tz);
-          return new Date(naiveMs - offset).toISOString();
-        }
-      } catch {
-        // Fall through to default parsing if tz is invalid
-      }
+  if (tz && OFFSETLESS_ISO_DATETIME_RE.test(raw)) {
+    const resolved = parseOffsetlessAtInTimezone(raw, tz);
+    if (resolved) {
+      return resolved;
     }
   }
 
@@ -132,6 +124,26 @@ export function parseAt(input: string, tz?: string): string | null {
   return null;
 }
 
+function parseOffsetlessAtInTimezone(raw: string, tz: string): string | null {
+  try {
+    new Intl.DateTimeFormat("en-US", { timeZone: tz }).format(new Date());
+
+    const naiveMs = new Date(`${raw}Z`).getTime();
+    if (Number.isNaN(naiveMs)) {
+      return null;
+    }
+
+    // Re-check the offset at the first candidate instant so DST boundaries
+    // land on the intended wall-clock time instead of drifting by one hour.
+    const firstOffsetMs = getTimezoneOffsetMs(naiveMs, tz);
+    const candidateMs = naiveMs - firstOffsetMs;
+    const finalOffsetMs = getTimezoneOffsetMs(candidateMs, tz);
+    return new Date(naiveMs - finalOffsetMs).toISOString();
+  } catch {
+    return null;
+  }
+}
+
 /**
  * Get the UTC offset in milliseconds for a given IANA timezone at a given UTC instant.
  * Positive means ahead of UTC (e.g. +3600000 for CET).
@@ -160,7 +172,7 @@ function getTimezoneOffsetMs(utcMs: number, tz: string): number {
     get("year"),
     get("month") - 1,
     get("day"),
-    get("hour") === 24 ? 0 : get("hour"),
+    get("hour"),
     get("minute"),
     get("second"),
   );