fix(frontend): preserve schedule when switching to custom cron (#6749)

Co-authored-by: haotianqi666 <250384991+haotianqi666@users.noreply.github.com>

README.md

@@ -2796,6 +2796,8 @@ Current MVP limits:
 
 Enable background polling with `config.yaml -> scheduler.enabled`. Manual trigger uses the same scheduled-task resource and execution path.
 
+In the task form, switching an hourly, daily, weekly, or monthly schedule to **Custom cron** starts from its current timing, including selected weekdays or day of the month. Switching back to Custom cron after preset edits uses those edits rather than an older expression.
+
 ### Lifecycle, safety caps and stop conditions
 
 - The tasks page and the REST API (`POST` / `PATCH /api/scheduled-tasks`) accept the same per-run goal (`goal_objective`), safety cap (`max_runs`, `end_at`) and stop condition (`stop_condition`) as a conversation. Sending `null` in a PATCH clears any of these four; an `end_at` without a UTC offset is wall-clock time in the task's timezone.

frontend/AGENTS.md

@@ -140,6 +140,12 @@ matching in `core/scheduled-tasks/search.ts`; clearing search retains other filt
 
 Single-run schedule edits retain the mounted task's original `run_at` while its wall time and timezone match. The parent echoes edits through `initial`; retain a stable snapshot and reset the parent draft during render before remounting with a task key when switching tasks. Use the resolved timezone consistently for the snapshot and displayed wall time. Component and scheduled-task E2E tests cover DST folds and timestamp precision.
 
+The scheduled-task schedule input initializes Custom cron from the current
+preset and its current fields on every transition into the custom editor.
+Do not substitute a daily schedule or restore stale `parts.raw` after preset
+edits. Component tests cover emitted specs; browser tests pin unchanged
+schedules through the task form's PATCH payload on desktop and mobile.
+
 ## Environment
 
 Scheduled-task interval forms preserve the initial `every_seconds` on mount,

frontend/src/components/workspace/scheduled-task-schedule-input.tsx

@@ -223,8 +223,9 @@ export function ScheduledTaskScheduleInput({
       if (next === "monthly" && merged.dayOfMonth == null) {
         merged.dayOfMonth = 1;
       }
-      if (next === "custom" && !merged.raw) {
-        merged.raw = serializeCron("daily", prev);
+      if (next === "custom" && preset !== "custom") {
+        // Open the current schedule, not a daily fallback or an older draft.
+        merged.raw = serializeCron(preset, prev);
       }
       return merged;
     });

frontend/tests/e2e/scheduled-task-cron-preset.spec.ts

@@ -0,0 +1,61 @@
+import { expect, test } from "@playwright/test";
+
+import { mockLangGraphAPI } from "./utils/mock-api";
+
+for (const width of [1280, 375]) {
+  for (const cron of ["30 14 * * 1,3,5", "30 14 21 * *"]) {
+    test(`custom cron preserves ${cron} through saving at width ${width}`, async ({
+      page,
+    }) => {
+      await page.setViewportSize({ width, height: 900 });
+      const patches: Record<string, unknown>[] = [];
+      page.on("request", (request) => {
+        if (
+          request.method() === "PATCH" &&
+          new URL(request.url()).pathname === "/api/scheduled-tasks/cron-task"
+        ) {
+          patches.push(request.postDataJSON() as Record<string, unknown>);
+        }
+      });
+      mockLangGraphAPI(page, {
+        threads: [],
+        scheduledTasks: [
+          {
+            id: "cron-task",
+            thread_id: null,
+            title: "Scheduled report",
+            prompt: "Prepare the report",
+            schedule_type: "cron",
+            schedule_spec: { cron },
+            timezone: "UTC",
+            status: "enabled",
+            next_run_at: "2099-01-21T14:30:00Z",
+            last_run_at: null,
+            last_run_id: null,
+            last_error: null,
+            run_count: 0,
+            created_at: "2026-10-01T00:00:00Z",
+            updated_at: "2026-10-01T00:00:00Z",
+          },
+        ],
+      });
+
+      await page.goto("/workspace/scheduled-tasks");
+      await page
+        .getByTestId("scheduled-task-detail")
+        .getByRole("button", { name: "Edit", exact: true })
+        .click();
+      const form = page.getByTestId("scheduled-task-form");
+      await form.getByTestId("schedule-preset").click();
+      await page.getByRole("option", { name: "Custom cron" }).click();
+      await expect(form.getByLabel("Cron expression")).toHaveValue(cron);
+
+      await form.getByLabel("Title", { exact: true }).fill("Renamed report");
+      await form.getByRole("button", { name: "Save changes" }).click();
+
+      await expect.poll(() => patches.length).toBe(1);
+      expect(patches[0]).toEqual({ title: "Renamed report" });
+      await expect(form).toHaveCount(0);
+    });
+  }
+}

frontend/tests/unit/components/workspace/scheduled-task-schedule-input.dom.test.tsx

@@ -10,6 +10,70 @@ import { I18nProvider } from "@/core/i18n/context";
 afterEach(cleanup);
 
 describe("ScheduledTaskScheduleInput", () => {
+  async function selectPreset(name: string) {
+    fireEvent.keyDown(screen.getByTestId("schedule-preset"), {
+      key: "ArrowDown",
+    });
+    fireEvent.click(await screen.findByRole("option", { name }));
+  }
+
+  function renderCron(cron: string) {
+    const emitted: ScheduleValue[] = [];
+    render(
+      <I18nProvider initialLocale="en-US">
+        <ScheduledTaskScheduleInput
+          initial={{
+            schedule_type: "cron",
+            schedule_spec: { cron },
+            timezone: "UTC",
+          }}
+          onChange={(value) => emitted.push(value)}
+        />
+      </I18nProvider>,
+    );
+    return emitted;
+  }
+
+  test.each(["15 * * * *", "30 14 * * *", "30 14 * * 1,3,5", "30 14 21 * *"])(
+    "keeps %s when opening the custom cron editor",
+    async (cron) => {
+      const emitted = renderCron(cron);
+
+      await selectPreset("Custom cron");
+
+      expect(
+        screen.getByRole("textbox", { name: "Cron expression" }),
+      ).toHaveProperty("value", cron);
+      expect(emitted.at(-1)?.schedule_spec).toEqual({ cron });
+    },
+  );
+
+  test("reopening custom cron uses the current preset instead of a stale expression", async () => {
+    const emitted = renderCron("*/10 * * * *");
+
+    await selectPreset("Weekly");
+    fireEvent.change(screen.getByLabelText("Time"), {
+      target: { value: "16:45" },
+    });
+    expect(emitted.at(-1)?.schedule_spec).toEqual({ cron: "45 16 * * 1" });
+
+    await selectPreset("Custom cron");
+
+    expect(
+      screen.getByRole("textbox", { name: "Cron expression" }),
+    ).toHaveProperty("value", "45 16 * * 1");
+    expect(emitted.at(-1)?.schedule_spec).toEqual({ cron: "45 16 * * 1" });
+
+    fireEvent.change(screen.getByRole("textbox", { name: "Cron expression" }), {
+      target: { value: "*/10 * * * *" },
+    });
+    expect(emitted.at(-1)).toEqual({
+      schedule_type: "cron",
+      schedule_spec: { cron: "*/10 * * * *" },
+      timezone: "UTC",
+    });
+  });
+
   test.each([1, 30, 59])(
     "preserves an existing %s-second interval until explicitly edited",
     (everySeconds) => {