fix(feed): a custom date bound applies once its year is a plausible upload year, not per typed digit (E28)

A native date field reports a complete date on every keystroke of its year (0002, 0020, 0202, 2026),
so one typed year refetched the feed four times. The field holds a draft while focused; leaving it
empty clears the bound, leaving it half-typed restores it.

frontend/src/components/DateFilterSelect.dom.test.tsx

@@ -0,0 +1,58 @@
+// @vitest-environment jsdom
+//
+// E28 (owner): a native date field reports a complete, valid date on every keystroke of its year, so
+// typing 2026 applied 0002, 0020, 0202 and 2026 — four feed refetches for one year.
+import { describe, it, expect, vi, afterEach } from "vitest";
+import { render, cleanup, screen, fireEvent } from "@testing-library/react";
+
+vi.mock("react-i18next", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("react-i18next")>();
+  return {
+    ...actual,
+    useTranslation: () => ({ t: (key: string) => key, i18n: { language: "en" } }),
+  };
+});
+
+import DateFilterSelect from "./DateFilterSelect";
+import { type FeedFilters } from "../lib/api";
+
+afterEach(cleanup);
+
+function mount(filters: Partial<FeedFilters>) {
+  const setFilters = vi.fn();
+  render(
+    <DateFilterSelect
+      filters={filters as FeedFilters}
+      setFilters={setFilters}
+      presets={[{ days: 7, key: "1week" }]}
+    />,
+  );
+  fireEvent.click(screen.getByRole("button", { name: /sidebar\.datePresetLabel/ }));
+  const [from] = document.querySelectorAll<HTMLInputElement>('input[type="date"]');
+  return { setFilters, from: from! };
+}
+
+describe("a custom range bound", () => {
+  it("is applied once, when the typed year becomes a plausible upload year", () => {
+    const { setFilters, from } = mount({ dateTo: "2026-09-01" });
+    for (const day of ["0002-01-15", "0020-01-15", "0202-01-15", "2026-01-15"]) {
+      fireEvent.change(from, { target: { value: day } });
+    }
+    expect(setFilters).toHaveBeenCalledTimes(1);
+    expect(setFilters.mock.calls[0]![0]).toMatchObject({ dateFrom: "2026-01-15" });
+  });
+
+  it("is cleared when the field is left empty, and kept when it is left half-typed", () => {
+    const { setFilters, from } = mount({ dateFrom: "2026-01-15" });
+    fireEvent.change(from, { target: { value: "0202-01-15" } });
+    fireEvent.blur(from);
+    expect(setFilters).not.toHaveBeenCalled();
+    expect(from.value).toBe("2026-01-15");
+
+    fireEvent.change(from, { target: { value: "" } });
+    expect(setFilters).not.toHaveBeenCalled();
+    fireEvent.blur(from);
+    expect(setFilters).toHaveBeenCalledTimes(1);
+    expect(setFilters.mock.calls[0]![0]).toMatchObject({ dateFrom: undefined });
+  });
+});

frontend/src/components/DateFilterSelect.tsx

@@ -4,7 +4,12 @@ import { CalendarDays, Check } from "lucide-react";
 import { PopoverItem, PopoverSurface } from "./ui/AnchoredPopover";
 import { useAnchoredPopover } from "./ui/anchoredPopoverHooks";
 import { type FeedFilters } from "../lib/api";
-import { deriveDateKey, selectDateChip, type DatePreset } from "../lib/dateFilter";
+import {
+  deriveDateKey,
+  isCommittableDay,
+  selectDateChip,
+  type DatePreset,
+} from "../lib/dateFilter";
 import { Button } from "./ui/Button";
 import { SelectTrigger } from "./ui/SelectTrigger";
 import { Input } from "./ui/Input";
@@ -134,45 +139,24 @@ export default function DateFilterSelect({
           })}
         </div>
 
-        {/* Reveal-on-select: the from/to fields appear once Custom is the chosen option. The inputs
-            stop non-Escape keys so the date-segment arrows act on the field, not the menu's list nav. */}
+        {/* Reveal-on-select: the from/to fields appear once Custom is the chosen option. */}
         {key === "custom" && (
           <div className="mt-1 flex flex-col gap-1.5 border-t border-border px-1 pt-2">
             <label className="flex items-center justify-between gap-2 text-xs">
               <span className="text-muted">{t("sidebar.from")}</span>
-              <Input
-                size="sm"
-                type="date"
-                value={filters.dateFrom ?? ""}
-                onKeyDown={(e) => {
-                  if (e.key !== "Escape") e.stopPropagation();
-                }}
-                onChange={(e) =>
-                  setFilters({
-                    ...filters,
-                    dateFrom: e.target.value || undefined,
-                    maxAgeDays: undefined,
-                    year: undefined,
-                  })
+              <DayField
+                value={filters.dateFrom}
+                onCommit={(v) =>
+                  setFilters({ ...filters, dateFrom: v, maxAgeDays: undefined, year: undefined })
                 }
               />
             </label>
             <label className="flex items-center justify-between gap-2 text-xs">
               <span className="text-muted">{t("sidebar.to")}</span>
-              <Input
-                size="sm"
-                type="date"
-                value={filters.dateTo ?? ""}
-                onKeyDown={(e) => {
-                  if (e.key !== "Escape") e.stopPropagation();
-                }}
-                onChange={(e) =>
-                  setFilters({
-                    ...filters,
-                    dateTo: e.target.value || undefined,
-                    maxAgeDays: undefined,
-                    year: undefined,
-                  })
+              <DayField
+                value={filters.dateTo}
+                onCommit={(v) =>
+                  setFilters({ ...filters, dateTo: v, maxAgeDays: undefined, year: undefined })
                 }
               />
             </label>
@@ -191,3 +175,37 @@ export default function DateFilterSelect({
     </>
   );
 }
+
+// One bound of the custom range. What the field shows is a draft while it has focus (`draft ?? value`):
+// the bound is applied only once the draft is a plausible day (`isCommittableDay` says why), so typing a
+// year no longer refetches the feed per digit; a date picked from the calendar applies at once. Leaving
+// the field settles it: emptied, the bound is cleared; half-typed or implausible, it shows the bound again.
+// It stops non-Escape keys so the date-segment arrows act on the field, not the menu's list navigation.
+function DayField({
+  value,
+  onCommit,
+}: {
+  value: string | undefined;
+  onCommit: (day: string | undefined) => void;
+}) {
+  const [draft, setDraft] = useState<string>();
+  return (
+    <Input
+      size="sm"
+      type="date"
+      value={draft ?? value ?? ""}
+      onKeyDown={(e) => {
+        if (e.key !== "Escape") e.stopPropagation();
+      }}
+      onChange={(e) => {
+        const day = e.target.value;
+        setDraft(day);
+        if (isCommittableDay(day) && day !== value) onCommit(day);
+      }}
+      onBlur={() => {
+        if (draft === "" && value) onCommit(undefined);
+        setDraft(undefined);
+      }}
+    />
+  );
+}

frontend/src/lib/dateFilter.ts

@@ -61,3 +61,15 @@ export function selectDateChip(
     customOpen: false,
   };
 }
+
+// The first year an upload can have: YouTube opened in 2005.
+const FIRST_UPLOAD_YEAR = 2005;
+
+/** Whether a native date field's value is a bound worth filtering by. The field reports a COMPLETE
+ *  date on every keystroke of its year — typing 2026 passes 0002, 0020 and 0202, each a valid date to
+ *  the browser — so applying every value refetched the feed four times for one year (E28). A bound is
+ *  applied once it is a plausible upload day; a half-typed field reports "" and is not one either. */
+export function isCommittableDay(s: string): boolean {
+  const m = /^(\d{4})-\d{2}-\d{2}$/.exec(s);
+  return !!m && Number(m[1]) >= FIRST_UPLOAD_YEAR;
+}