fix(issues): address date-only review — loud-fail ambiguous dates, finish display sweep (MUL-2925)

Review follow-ups on #3692:
- ParseCalendarDate no longer silently truncates a legacy non-midnight RFC3339
  to the wrong UTC day; it accepts only YYYY-MM-DD or an exact UTC-midnight
  instant and rejects ambiguous ones loudly. Adds util unit tests.
- migration 112 pins the TIMESTAMPTZ->DATE conversion to UTC explicitly via
  AT TIME ZONE 'UTC' (was session-timezone dependent); down migration too.
- Convert remaining date-change display sites to formatDateOnly: inbox detail
  label (web) and mobile activity + inbox labels (were new Date()+local format).
- CLI --start-date/--due-date help now says YYYY-MM-DD, not RFC3339.

Co-authored-by: multica-agent <github@multica.ai>

apps/mobile/components/inbox/detail-label.tsx

@@ -17,6 +17,7 @@ import type {
   IssueStatus,
   IssuePriority,
 } from "@multica/core/types";
+import { formatDateOnly } from "@multica/core/issues/date";
 import { Text } from "@/components/ui/text";
 import { StatusIcon } from "@/components/ui/status-icon";
 import { PriorityIcon } from "@/components/ui/priority-icon";
@@ -64,12 +65,9 @@ const TYPE_LABEL: Record<InboxItemType, string> = {
   quick_create_failed: "Quick-create failed",
 };
 
+// due_date is a calendar day — format timezone-safely (no offset day shift).
 function shortDate(dateStr: string): string {
-  if (!dateStr) return "";
-  return new Date(dateStr).toLocaleDateString("en-US", {
-    month: "short",
-    day: "numeric",
-  });
+  return formatDateOnly(dateStr, { month: "short", day: "numeric" }, "en-US");
 }
 
 function singleLine(value: string | null | undefined): string {

apps/mobile/components/issue/attribute-row.tsx

@@ -23,6 +23,7 @@ import type {
   Issue,
   IssuePriority,
 } from "@multica/core/types";
+import { formatDateOnly } from "@multica/core/issues/date";
 import { Text } from "@/components/ui/text";
 import { StatusIcon } from "@/components/ui/status-icon";
 import { PriorityIcon } from "@/components/ui/priority-icon";
@@ -67,11 +68,11 @@ const ISSUE_PICKER_PATHNAMES = {
   "due-date": "/[workspace]/issue/[id]/picker/due-date",
 } as const satisfies Record<IssuePickerField, string>;
 
+// due_date is a calendar day — format timezone-safely so the day never shifts
+// with the viewer's offset. Mirrors web's formatDate in list-row/board-card.
 function formatDueDate(iso: string | null): string | null {
   if (!iso) return null;
-  const d = new Date(iso);
-  if (Number.isNaN(d.getTime())) return null;
-  return d.toLocaleDateString("en-US", { month: "short", day: "numeric" });
+  return formatDateOnly(iso, { month: "short", day: "numeric" }, "en-US") || null;
 }
 
 export function AttributeRow({ issue }: { issue: Issue }) {

apps/mobile/components/issue/create-form-attribute-row.tsx

@@ -18,6 +18,7 @@ import { ActorAvatar } from "@/components/ui/actor-avatar";
 import { PriorityIcon } from "@/components/ui/priority-icon";
 import { ProjectIcon } from "@/components/ui/project-icon";
 import { StatusIcon } from "@/components/ui/status-icon";
+import { formatDateOnly } from "@multica/core/issues/date";
 import { useActorLookup } from "@/data/use-actor-name";
 import { useNewIssueDraftStore } from "@/data/stores/new-issue-draft-store";
 import { useWorkspaceStore } from "@/data/workspace-store";
@@ -131,8 +132,7 @@ export function CreateFormAttributeRow() {
   );
 }
 
+// due_date is a calendar day — format timezone-safely (no offset day shift).
 function formatDueDate(iso: string): string {
-  const d = new Date(iso);
-  if (Number.isNaN(d.getTime())) return "Due date";
-  return d.toLocaleDateString(undefined, { month: "short", day: "numeric" });
+  return formatDateOnly(iso, { month: "short", day: "numeric" }) || "Due date";
 }

apps/mobile/components/issue/pickers/due-date-picker-body.tsx

@@ -3,40 +3,40 @@
  * (a formSheet route) renders the Done / Clear actions in its own header
  * area — this body only handles the picker spinner + the local draft state.
  *
- * Backend (server/internal/handler/issue.go CreateIssue / UpdateIssue) parses
- * with time.Parse(time.RFC3339, ...) — strict. Mirrors web's
- * packages/views/issues/components/pickers/due-date-picker.tsx which sends
- * d.toISOString().
+ * due_date is a calendar day (date-only "YYYY-MM-DD", no time/timezone — see
+ * @multica/core/issues/date and GH #3618). Mirrors web's
+ * packages/views/issues/components/pickers/due-date-picker.tsx: read the stored
+ * day into a local-midnight Date for the spinner, write back the picked local
+ * day as a date-only string.
  */
 import { useState, useEffect, useImperativeHandle, forwardRef } from "react";
 import { View } from "react-native";
 import DateTimePicker from "@react-native-community/datetimepicker";
+import { toDateOnly, dateOnlyToLocalDate } from "@multica/core/issues/date";
 
 interface Props {
   value: string | null;
 }
 
 export interface DueDatePickerBodyHandle {
-  /** Returns the currently-displayed date as an ISO 8601 string. */
+  /** Returns the currently-displayed day as a date-only "YYYY-MM-DD" string. */
   getIso: () => string;
 }
 
-function isoToDate(iso: string | null): Date {
-  if (!iso) return new Date();
-  const d = new Date(iso);
-  return Number.isNaN(d.getTime()) ? new Date() : d;
+function toLocalDay(value: string | null): Date {
+  return dateOnlyToLocalDate(value) ?? new Date();
 }
 
 export const DueDatePickerBody = forwardRef<DueDatePickerBodyHandle, Props>(
   function DueDatePickerBody({ value }, ref) {
-    const [draft, setDraft] = useState<Date>(() => isoToDate(value));
+    const [draft, setDraft] = useState<Date>(() => toLocalDay(value));
 
     useEffect(() => {
-      setDraft(isoToDate(value));
+      setDraft(toLocalDay(value));
     }, [value]);
 
     useImperativeHandle(ref, () => ({
-      getIso: () => draft.toISOString(),
+      getIso: () => toDateOnly(draft),
     }));
 
     return (

apps/mobile/lib/format-activity.ts

@@ -15,6 +15,7 @@ import type {
   IssueStatus,
   TimelineEntry,
 } from "@multica/core/types";
+import { formatDateOnly } from "@multica/core/issues/date";
 
 const STATUS_LABEL: Record<IssueStatus, string> = {
   backlog: "Backlog",
@@ -44,12 +45,11 @@ function priorityName(p: string | undefined): string {
   return p ?? "?";
 }
 
+// start_date / due_date are calendar days — format timezone-safely (no offset
+// day shift). Mirrors web's formatActivity in issue-detail.tsx.
 function shortDate(date: string | undefined): string {
   if (!date) return "?";
-  return new Date(date).toLocaleDateString("en-US", {
-    month: "short",
-    day: "numeric",
-  });
+  return formatDateOnly(date, { month: "short", day: "numeric" }, "en-US");
 }
 
 export function formatActivity(

packages/core/issues/date.test.ts

@@ -0,0 +1,66 @@
+import { describe, it, expect } from "vitest";
+import {
+  toDateOnly,
+  todayDateOnly,
+  addDaysDateOnly,
+  dateOnlyToUTCDate,
+  dateOnlyToLocalDate,
+  formatDateOnly,
+  isPastDateOnly,
+} from "./date";
+
+describe("issue date-only helpers", () => {
+  it("serializes a picked local day to YYYY-MM-DD with the local calendar", () => {
+    // A calendar picker hands back local midnight of the clicked day.
+    expect(toDateOnly(new Date(2026, 2, 1))).toBe("2026-03-01");
+    expect(toDateOnly(new Date(2026, 0, 5))).toBe("2026-01-05"); // zero-padded
+  });
+
+  it("formats a date-only string timezone-safely (no day shift)", () => {
+    // The bug: a calendar day must render as the same day in every timezone.
+    expect(
+      formatDateOnly("2026-03-01", { month: "short", day: "numeric" }, "en-US"),
+    ).toBe("Mar 1");
+    expect(formatDateOnly("2026-03-01", undefined, "en-US")).toBe("Mar 1");
+    expect(formatDateOnly(null)).toBe("");
+    expect(formatDateOnly("")).toBe("");
+  });
+
+  it("round-trips a picked day back to the same displayed day", () => {
+    const picked = new Date(2026, 2, 1); // user clicks March 1 locally
+    const stored = toDateOnly(picked);
+    expect(stored).toBe("2026-03-01");
+    expect(formatDateOnly(stored, { month: "short", day: "numeric" }, "en-US")).toBe(
+      "Mar 1",
+    );
+  });
+
+  it("anchors a date-only value at UTC midnight", () => {
+    expect(dateOnlyToUTCDate("2026-03-01")?.toISOString()).toBe(
+      "2026-03-01T00:00:00.000Z",
+    );
+    expect(dateOnlyToUTCDate(null)).toBeNull();
+  });
+
+  it("tolerates a legacy RFC3339 instant by reading its UTC day", () => {
+    // Old clients stored local-midnight-as-UTC; read the stored UTC calendar day.
+    expect(dateOnlyToUTCDate("2026-02-28T16:00:00Z")?.toISOString()).toBe(
+      "2026-02-28T00:00:00.000Z",
+    );
+  });
+
+  it("builds a local-midnight Date for the picker's selected day", () => {
+    const d = dateOnlyToLocalDate("2026-03-01");
+    expect(d?.getFullYear()).toBe(2026);
+    expect(d?.getMonth()).toBe(2);
+    expect(d?.getDate()).toBe(1);
+    expect(dateOnlyToLocalDate(null)).toBeUndefined();
+  });
+
+  it("detects past calendar days relative to today", () => {
+    expect(isPastDateOnly(addDaysDateOnly(-1))).toBe(true);
+    expect(isPastDateOnly(todayDateOnly())).toBe(false);
+    expect(isPastDateOnly(addDaysDateOnly(1))).toBe(false);
+    expect(isPastDateOnly(null)).toBe(false);
+  });
+});

packages/core/issues/date.ts

@@ -0,0 +1,97 @@
+// Issue start_date / due_date are calendar days, not instants: the pickers
+// offer no time-of-day input, so "Mar 1" must mean Mar 1 for every viewer
+// regardless of timezone. They are transported as a date-only "YYYY-MM-DD"
+// string. These helpers convert between that string and a Date WITHOUT letting
+// the local timezone shift the day — the bug behind GH #3618 / MUL-2925 was
+// serializing a local-midnight Date via toISOString() (which injects a tz) and
+// reading it back through UTC day boundaries.
+//
+// Pure functions only (no React / DOM) so they can be shared with mobile.
+
+const DATE_ONLY = /^(\d{4})-(\d{2})-(\d{2})/;
+
+function pad(n: number): string {
+  return String(n).padStart(2, "0");
+}
+
+/**
+ * Serialize a Date the user picked in a calendar (local midnight of the chosen
+ * day) to a "YYYY-MM-DD" string, using the LOCAL calendar components so the
+ * stored day matches the day the user clicked.
+ */
+export function toDateOnly(date: Date): string {
+  return `${date.getFullYear()}-${pad(date.getMonth() + 1)}-${pad(date.getDate())}`;
+}
+
+/** Today as a "YYYY-MM-DD" string in the viewer's local calendar. */
+export function todayDateOnly(): string {
+  return toDateOnly(new Date());
+}
+
+/** "YYYY-MM-DD" of `days` from today in the viewer's local calendar. */
+export function addDaysDateOnly(days: number): string {
+  const d = new Date();
+  d.setDate(d.getDate() + days);
+  return toDateOnly(d);
+}
+
+/**
+ * Parse a date-only string into [year, month, day], tolerating a legacy full
+ * ISO timestamp by reading its UTC calendar day. Returns null when unparseable.
+ */
+function parseParts(value: string): [number, number, number] | null {
+  const m = DATE_ONLY.exec(value);
+  if (m) return [Number(m[1]), Number(m[2]), Number(m[3])];
+  const d = new Date(value);
+  if (Number.isNaN(d.getTime())) return null;
+  return [d.getUTCFullYear(), d.getUTCMonth() + 1, d.getUTCDate()];
+}
+
+/**
+ * Date anchored at UTC midnight of the calendar day. Use for timezone-safe
+ * display (format with `timeZone: "UTC"`), gantt day-bucketing, and
+ * chronological comparison.
+ */
+export function dateOnlyToUTCDate(
+  value: string | null | undefined,
+): Date | null {
+  if (!value) return null;
+  const parts = parseParts(value);
+  if (!parts) return null;
+  return new Date(Date.UTC(parts[0], parts[1] - 1, parts[2]));
+}
+
+/**
+ * Date at LOCAL midnight of the calendar day. Use for a calendar picker's
+ * `selected` / `defaultMonth`, which match on the local-time day.
+ */
+export function dateOnlyToLocalDate(
+  value: string | null | undefined,
+): Date | undefined {
+  if (!value) return undefined;
+  const parts = parseParts(value);
+  if (!parts) return undefined;
+  return new Date(parts[0], parts[1] - 1, parts[2]);
+}
+
+/**
+ * Format a calendar day for display, timezone-safely (the day never shifts with
+ * the viewer's timezone). Returns "" for an empty/unparseable value.
+ */
+export function formatDateOnly(
+  value: string | null | undefined,
+  options: Intl.DateTimeFormatOptions = { month: "short", day: "numeric" },
+  locale?: string,
+): string {
+  const d = dateOnlyToUTCDate(value);
+  if (!d) return "";
+  return d.toLocaleDateString(locale, { ...options, timeZone: "UTC" });
+}
+
+/** True when the calendar day is strictly before today (viewer's local day). */
+export function isPastDateOnly(value: string | null | undefined): boolean {
+  const d = dateOnlyToUTCDate(value);
+  if (!d) return false;
+  const today = dateOnlyToUTCDate(todayDateOnly());
+  return today != null && d.getTime() < today.getTime();
+}

packages/core/package.json

@@ -29,6 +29,7 @@
     "./issues/queries": "./issues/queries.ts",
     "./issues/mutations": "./issues/mutations.ts",
     "./issues/timeline-sort": "./issues/timeline-sort.ts",
+    "./issues/date": "./issues/date.ts",
     "./issues/ws-updaters": "./issues/ws-updaters.ts",
     "./issues/config": "./issues/config/index.ts",
     "./issues/config/status": "./issues/config/status.ts",

packages/core/types/issue.ts

@@ -48,6 +48,9 @@ export interface Issue {
   parent_issue_id: string | null;
   project_id: string | null;
   position: number;
+  // Calendar days as date-only "YYYY-MM-DD" (no time, no timezone). Use the
+  // helpers in @multica/core/issues/date to format/compare — never `new Date()`
+  // + local formatting, which shifts the day by the viewer's offset.
   start_date: string | null;
   due_date: string | null;
   metadata: IssueMetadata;

packages/views/inbox/components/inbox-detail-label.tsx

@@ -1,6 +1,7 @@
 "use client";
 
 import { STATUS_CONFIG, PRIORITY_CONFIG } from "@multica/core/issues/config";
+import { formatDateOnly } from "@multica/core/issues/date";
 import { useActorName } from "@multica/core/workspace/hooks";
 import { StatusIcon, PriorityIcon } from "../../issues/components";
 import type { InboxItem, InboxItemType, IssueStatus, IssuePriority } from "@multica/core/types";
@@ -33,12 +34,10 @@ export function useTypeLabels(): Record<InboxItemType, string> {
   };
 }
 
+// start_date / due_date are calendar days — format timezone-safely so the day
+// never shifts with the viewer's offset (see @multica/core/issues/date).
 function shortDate(dateStr: string): string {
-  if (!dateStr) return "";
-  return new Date(dateStr).toLocaleDateString("en-US", {
-    month: "short",
-    day: "numeric",
-  });
+  return formatDateOnly(dateStr, { month: "short", day: "numeric" }, "en-US");
 }
 
 export function InboxDetailLabel({ item }: { item: InboxItem }) {

packages/views/issues/actions/issue-actions-menu-items.tsx

@@ -18,6 +18,7 @@ import {
   UserMinus,
 } from "lucide-react";
 import type { AgentTask, Issue } from "@multica/core/types";
+import { todayDateOnly, addDaysDateOnly } from "@multica/core/issues/date";
 import { api } from "@multica/core/api";
 import {
   ALL_STATUSES,
@@ -106,13 +107,6 @@ export function IssueActionsMenuItems({
     openDeleteConfirm,
   } = actions;
 
-  const now = () => new Date();
-  const inDays = (days: number) => {
-    const d = new Date();
-    d.setDate(d.getDate() + days);
-    return d.toISOString();
-  };
-
   // Subscribe to the issue's task list so the cache is warm by the time the
   // user clicks "Copy local workdir path". The query only fires while the
   // menu is open (Base UI portals the menu content lazily) — list views
@@ -205,13 +199,13 @@ export function IssueActionsMenuItems({
           {t(($) => $.actions.start_date)}
         </P.SubTrigger>
         <P.SubContent>
-          <P.Item onClick={() => updateField({ start_date: now().toISOString() })}>
+          <P.Item onClick={() => updateField({ start_date: todayDateOnly() })}>
             {t(($) => $.actions.start_today)}
           </P.Item>
-          <P.Item onClick={() => updateField({ start_date: inDays(1) })}>
+          <P.Item onClick={() => updateField({ start_date: addDaysDateOnly(1) })}>
             {t(($) => $.actions.start_tomorrow)}
           </P.Item>
-          <P.Item onClick={() => updateField({ start_date: inDays(7) })}>
+          <P.Item onClick={() => updateField({ start_date: addDaysDateOnly(7) })}>
             {t(($) => $.actions.start_next_week)}
           </P.Item>
           {issue.start_date && (
@@ -232,13 +226,13 @@ export function IssueActionsMenuItems({
           {t(($) => $.actions.due_date)}
         </P.SubTrigger>
         <P.SubContent>
-          <P.Item onClick={() => updateField({ due_date: now().toISOString() })}>
+          <P.Item onClick={() => updateField({ due_date: todayDateOnly() })}>
             {t(($) => $.actions.due_today)}
           </P.Item>
-          <P.Item onClick={() => updateField({ due_date: inDays(1) })}>
+          <P.Item onClick={() => updateField({ due_date: addDaysDateOnly(1) })}>
             {t(($) => $.actions.due_tomorrow)}
           </P.Item>
-          <P.Item onClick={() => updateField({ due_date: inDays(7) })}>
+          <P.Item onClick={() => updateField({ due_date: addDaysDateOnly(7) })}>
             {t(($) => $.actions.due_next_week)}
           </P.Item>
           {issue.due_date && (

packages/views/issues/components/board-card.tsx

@@ -7,6 +7,7 @@ import type { AnimateLayoutChanges } from "@dnd-kit/sortable";
 import { CSS } from "@dnd-kit/utilities";
 import { toast } from "sonner";
 import type { Issue, UpdateIssueRequest } from "@multica/core/types";
+import { formatDateOnly, isPastDateOnly } from "@multica/core/issues/date";
 import { CalendarClock, CalendarDays } from "lucide-react";
 import { useQuery } from "@tanstack/react-query";
 import { ActorAvatar } from "../../common/actor-avatar";
@@ -28,10 +29,7 @@ import { IssueAgentActivityIndicator } from "./issue-agent-activity-indicator";
 import { useT } from "../../i18n";
 
 function formatDate(date: string): string {
-  return new Date(date).toLocaleDateString("en-US", {
-    month: "short",
-    day: "numeric",
-  });
+  return formatDateOnly(date, { month: "short", day: "numeric" }, "en-US");
 }
 
 function descriptionPreview(markdown: string): string {
@@ -261,7 +259,7 @@ export const BoardCardContent = memo(function BoardCardContent({
                       trigger={
                         <span
                           className={`flex items-center gap-1 text-xs ${
-                            new Date(issue.due_date!) < new Date()
+                            isPastDateOnly(issue.due_date)
                               ? "text-destructive"
                               : "text-muted-foreground"
                           }`}
@@ -275,7 +273,7 @@ export const BoardCardContent = memo(function BoardCardContent({
                 ) : (
                   <span
                     className={`flex shrink-0 items-center gap-1 text-xs ${
-                      new Date(issue.due_date!) < new Date()
+                      isPastDateOnly(issue.due_date)
                         ? "text-destructive"
                         : "text-muted-foreground"
                     }`}

packages/views/issues/components/gantt-view.tsx

@@ -8,6 +8,7 @@ import { useViewStore, useViewStoreApi } from "@multica/core/issues/stores/view-
 import type { GanttZoom } from "@multica/core/issues/stores/view-store";
 import { projectListOptions } from "@multica/core/projects/queries";
 import type { Issue, IssueStatus } from "@multica/core/types";
+import { dateOnlyToUTCDate } from "@multica/core/issues/date";
 import { cn } from "@multica/ui/lib/utils";
 import {
   Tooltip,
@@ -43,11 +44,11 @@ function daysBetween(a: Date, b: Date): number {
   return Math.round((b.getTime() - a.getTime()) / MS_PER_DAY);
 }
 
+// Issue dates arrive as date-only "YYYY-MM-DD" strings (calendar days). Anchor
+// each to UTC midnight so the bar lands on exactly that day, independent of the
+// viewer's timezone. See @multica/core/issues/date.
 function parseDay(iso: string | null): Date | null {
-  if (!iso) return null;
-  const d = new Date(iso);
-  if (Number.isNaN(d.getTime())) return null;
-  return startOfDayUTC(d);
+  return dateOnlyToUTCDate(iso);
 }
 
 function isWeekendUTC(d: Date): boolean {

packages/views/issues/components/issue-detail.tsx

@@ -44,6 +44,7 @@ import { ActorAvatar } from "../../common/actor-avatar";
 import { PropRow } from "../../common/prop-row";
 import type { Attachment, Issue, IssueStatus, IssuePriority, TimelineEntry, UpdateIssueRequest } from "@multica/core/types";
 import { STATUS_CONFIG, PRIORITY_CONFIG } from "@multica/core/issues/config";
+import { formatDateOnly } from "@multica/core/issues/date";
 import { useUpdateIssue } from "@multica/core/issues/mutations";
 import { toast } from "sonner";
 import { StatusIcon, PriorityIcon, StatusPicker, PriorityPicker, StartDatePicker, DueDatePicker, AssigneePicker, LabelPicker } from ".";
@@ -168,10 +169,7 @@ function SubscriberPopoverContent({
 
 function shortDate(date: string | null): string {
   if (!date) return "—";
-  return new Date(date).toLocaleDateString("en-US", {
-    month: "short",
-    day: "numeric",
-  });
+  return formatDateOnly(date, { month: "short", day: "numeric" }, "en-US");
 }
 
 type ActivityT = ReturnType<typeof useT<"issues">>["t"];
@@ -221,12 +219,12 @@ function formatActivity(
     }
     case "start_date_changed": {
       if (!details.to) return t(($) => $.activity.start_date_removed);
-      const formatted = new Date(details.to).toLocaleDateString("en-US", { month: "short", day: "numeric" });
+      const formatted = formatDateOnly(details.to, { month: "short", day: "numeric" }, "en-US");
       return t(($) => $.activity.start_date_set, { date: formatted });
     }
     case "due_date_changed": {
       if (!details.to) return t(($) => $.activity.due_date_removed);
-      const formatted = new Date(details.to).toLocaleDateString("en-US", { month: "short", day: "numeric" });
+      const formatted = formatDateOnly(details.to, { month: "short", day: "numeric" }, "en-US");
       return t(($) => $.activity.due_date_set, { date: formatted });
     }
     case "title_changed":

packages/views/issues/components/list-row.tsx

@@ -7,6 +7,7 @@ import type { AnimateLayoutChanges } from "@dnd-kit/sortable";
 import { CSS } from "@dnd-kit/utilities";
 import { AppLink } from "../../navigation";
 import type { Issue } from "@multica/core/types";
+import { formatDateOnly } from "@multica/core/issues/date";
 import { ActorAvatar } from "../../common/actor-avatar";
 import { useIssueSelectionStore } from "@multica/core/issues/stores/selection-store";
 import { useWorkspacePaths } from "@multica/core/paths";
@@ -26,10 +27,7 @@ export interface ChildProgress {
 }
 
 function formatDate(date: string): string {
-  return new Date(date).toLocaleDateString("en-US", {
-    month: "short",
-    day: "numeric",
-  });
+  return formatDateOnly(date, { month: "short", day: "numeric" }, "en-US");
 }
 
 function ListRowContent({

packages/views/issues/components/pickers/due-date-picker.tsx

@@ -3,6 +3,12 @@
 import { useState } from "react";
 import { CalendarDays } from "lucide-react";
 import type { UpdateIssueRequest } from "@multica/core/types";
+import {
+  toDateOnly,
+  dateOnlyToLocalDate,
+  formatDateOnly,
+  isPastDateOnly,
+} from "@multica/core/issues/date";
 import { Calendar } from "@multica/ui/components/ui/calendar";
 import {
   Popover,
@@ -31,8 +37,8 @@ export function DueDatePicker({
 }) {
   const { t } = useT("issues");
   const [open, setOpen] = useState(defaultOpen);
-  const date = dueDate ? new Date(dueDate) : undefined;
-  const isOverdue = date ? date < new Date() : false;
+  const date = dateOnlyToLocalDate(dueDate);
+  const isOverdue = isPastDateOnly(dueDate);
 
   return (
     <Popover open={open} onOpenChange={setOpen}>
@@ -45,7 +51,7 @@ export function DueDatePicker({
             <CalendarDays className="h-3.5 w-3.5 text-muted-foreground" />
             {date ? (
               <span className={isOverdue ? "text-destructive" : ""}>
-                {date.toLocaleDateString("en-US", { month: "short", day: "numeric" })}
+                {formatDateOnly(dueDate, { month: "short", day: "numeric" }, "en-US")}
               </span>
             ) : (
               <span className="text-muted-foreground">{t(($) => $.pickers.due_date.trigger_label)}</span>
@@ -58,7 +64,7 @@ export function DueDatePicker({
           mode="single"
           selected={date}
           onSelect={(d: Date | undefined) => {
-            onUpdate({ due_date: d ? d.toISOString() : null });
+            onUpdate({ due_date: d ? toDateOnly(d) : null });
             setOpen(false);
           }}
         />

packages/views/issues/components/pickers/start-date-picker.tsx

@@ -3,6 +3,11 @@
 import { useState } from "react";
 import { CalendarClock } from "lucide-react";
 import type { UpdateIssueRequest } from "@multica/core/types";
+import {
+  toDateOnly,
+  dateOnlyToLocalDate,
+  formatDateOnly,
+} from "@multica/core/issues/date";
 import { Calendar } from "@multica/ui/components/ui/calendar";
 import {
   Popover,
@@ -37,7 +42,7 @@ export function StartDatePicker({
   const [internalOpen, setInternalOpen] = useState(defaultOpen);
   const open = controlledOpen ?? internalOpen;
   const setOpen = controlledOnOpenChange ?? setInternalOpen;
-  const date = startDate ? new Date(startDate) : undefined;
+  const date = dateOnlyToLocalDate(startDate);
 
   return (
     <Popover open={open} onOpenChange={setOpen}>
@@ -50,7 +55,7 @@ export function StartDatePicker({
             <CalendarClock className="h-3.5 w-3.5 text-muted-foreground" />
             {date ? (
               <span>
-                {date.toLocaleDateString("en-US", { month: "short", day: "numeric" })}
+                {formatDateOnly(startDate, { month: "short", day: "numeric" }, "en-US")}
               </span>
             ) : (
               <span className="text-muted-foreground">{t(($) => $.pickers.start_date.trigger_label)}</span>
@@ -63,7 +68,7 @@ export function StartDatePicker({
           mode="single"
           selected={date}
           onSelect={(d: Date | undefined) => {
-            onUpdate({ start_date: d ? d.toISOString() : null });
+            onUpdate({ start_date: d ? toDateOnly(d) : null });
             setOpen(false);
           }}
         />

server/cmd/multica/cmd_issue.go

@@ -291,8 +291,8 @@ func init() {
 	issueCreateCmd.Flags().String("assignee-id", "", "Assignee UUID — member, agent, or squad (mutually exclusive with --assignee)")
 	issueCreateCmd.Flags().String("parent", "", "Parent issue ID")
 	issueCreateCmd.Flags().String("project", "", "Project ID")
-	issueCreateCmd.Flags().String("start-date", "", "Start date (RFC3339 format)")
-	issueCreateCmd.Flags().String("due-date", "", "Due date (RFC3339 format)")
+	issueCreateCmd.Flags().String("start-date", "", "Start date (calendar day, YYYY-MM-DD)")
+	issueCreateCmd.Flags().String("due-date", "", "Due date (calendar day, YYYY-MM-DD)")
 	issueCreateCmd.Flags().Bool("allow-duplicate", false, "Allow creating an issue even when an active duplicate exists")
 	issueCreateCmd.Flags().String("output", "json", "Output format: table or json")
 	issueCreateCmd.Flags().StringSlice("attachment", nil, "File path(s) to attach (can be specified multiple times)")
@@ -307,8 +307,8 @@ func init() {
 	issueUpdateCmd.Flags().String("assignee", "", "New assignee name (member, agent, or squad; fuzzy match)")
 	issueUpdateCmd.Flags().String("assignee-id", "", "New assignee UUID — member, agent, or squad (mutually exclusive with --assignee)")
 	issueUpdateCmd.Flags().String("project", "", "Project ID")
-	issueUpdateCmd.Flags().String("start-date", "", "New start date (RFC3339 format; pass empty string to clear)")
-	issueUpdateCmd.Flags().String("due-date", "", "New due date (RFC3339 format)")
+	issueUpdateCmd.Flags().String("start-date", "", "New start date (calendar day, YYYY-MM-DD; pass empty string to clear)")
+	issueUpdateCmd.Flags().String("due-date", "", "New due date (calendar day, YYYY-MM-DD)")
 	issueUpdateCmd.Flags().String("parent", "", "Parent issue ID (use --parent \"\" to clear)")
 	issueUpdateCmd.Flags().String("output", "json", "Output format: table or json")
 

server/cmd/server/notification_listeners_test.go

@@ -753,7 +753,7 @@ func TestNotification_DueDateChanged(t *testing.T) {
 	addTestSubscriber(t, issueID, "member", testUserID, "creator")
 	addTestSubscriber(t, issueID, "member", sub1ID, "assignee")
 
-	dueDate := "2026-04-15T00:00:00Z"
+	dueDate := "2026-04-15"
 	bus.Publish(events.Event{
 		Type:        protocol.EventIssueUpdated,
 		WorkspaceID: testWorkspaceID,
@@ -814,7 +814,7 @@ func TestNotification_StartDateChanged(t *testing.T) {
 	addTestSubscriber(t, issueID, "member", testUserID, "creator")
 	addTestSubscriber(t, issueID, "member", sub1ID, "assignee")
 
-	startDate := "2026-04-01T00:00:00Z"
+	startDate := "2026-04-01"
 	bus.Publish(events.Event{
 		Type:        protocol.EventIssueUpdated,
 		WorkspaceID: testWorkspaceID,

server/internal/handler/handler.go

@@ -190,6 +190,7 @@ func ptrToText(s *string) pgtype.Text               { return util.PtrToText(s) }
 func strToText(s string) pgtype.Text                { return util.StrToText(s) }
 func timestampToString(t pgtype.Timestamptz) string { return util.TimestampToString(t) }
 func timestampToPtr(t pgtype.Timestamptz) *string   { return util.TimestampToPtr(t) }
+func dateToPtr(d pgtype.Date) *string               { return util.DateToPtr(d) }
 func uuidToPtr(u pgtype.UUID) *string               { return util.UUIDToPtr(u) }
 func int8ToPtr(v pgtype.Int8) *int64                { return util.Int8ToPtr(v) }
 

server/internal/handler/issue.go

@@ -11,7 +11,6 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
-	"time"
 	"unicode"
 
 	"github.com/go-chi/chi/v5"
@@ -28,25 +27,25 @@ import (
 
 // IssueResponse is the JSON response for an issue.
 type IssueResponse struct {
-	ID            string                  `json:"id"`
-	WorkspaceID   string                  `json:"workspace_id"`
-	Number        int32                   `json:"number"`
-	Identifier    string                  `json:"identifier"`
-	Title         string                  `json:"title"`
-	Description   *string                 `json:"description"`
-	Status        string                  `json:"status"`
-	Priority      string                  `json:"priority"`
-	AssigneeType  *string                 `json:"assignee_type"`
-	AssigneeID    *string                 `json:"assignee_id"`
-	CreatorType   string                  `json:"creator_type"`
-	CreatorID     string                  `json:"creator_id"`
-	ParentIssueID *string                 `json:"parent_issue_id"`
-	ProjectID     *string                 `json:"project_id"`
-	Position      float64                 `json:"position"`
-	StartDate     *string                 `json:"start_date"`
-	DueDate       *string                 `json:"due_date"`
-	CreatedAt     string                  `json:"created_at"`
-	UpdatedAt     string                  `json:"updated_at"`
+	ID            string  `json:"id"`
+	WorkspaceID   string  `json:"workspace_id"`
+	Number        int32   `json:"number"`
+	Identifier    string  `json:"identifier"`
+	Title         string  `json:"title"`
+	Description   *string `json:"description"`
+	Status        string  `json:"status"`
+	Priority      string  `json:"priority"`
+	AssigneeType  *string `json:"assignee_type"`
+	AssigneeID    *string `json:"assignee_id"`
+	CreatorType   string  `json:"creator_type"`
+	CreatorID     string  `json:"creator_id"`
+	ParentIssueID *string `json:"parent_issue_id"`
+	ProjectID     *string `json:"project_id"`
+	Position      float64 `json:"position"`
+	StartDate     *string `json:"start_date"`
+	DueDate       *string `json:"due_date"`
+	CreatedAt     string  `json:"created_at"`
+	UpdatedAt     string  `json:"updated_at"`
 	// Metadata is the per-issue KV map (see issue_metadata.go). Always emitted
 	// (empty object when unset) so frontend code can `issue.metadata[key]`
 	// without nil-guarding the parent field.
@@ -80,8 +79,8 @@ func issueToResponse(i db.Issue, issuePrefix string) IssueResponse {
 		ParentIssueID: uuidToPtr(i.ParentIssueID),
 		ProjectID:     uuidToPtr(i.ProjectID),
 		Position:      i.Position,
-		StartDate:     timestampToPtr(i.StartDate),
-		DueDate:       timestampToPtr(i.DueDate),
+		StartDate:     dateToPtr(i.StartDate),
+		DueDate:       dateToPtr(i.DueDate),
 		CreatedAt:     timestampToString(i.CreatedAt),
 		UpdatedAt:     timestampToString(i.UpdatedAt),
 		Metadata:      parseIssueMetadata(i.Metadata),
@@ -107,8 +106,8 @@ func issueListRowToResponse(i db.ListIssuesRow, issuePrefix string) IssueRespons
 		ParentIssueID: uuidToPtr(i.ParentIssueID),
 		ProjectID:     uuidToPtr(i.ProjectID),
 		Position:      i.Position,
-		StartDate:     timestampToPtr(i.StartDate),
-		DueDate:       timestampToPtr(i.DueDate),
+		StartDate:     dateToPtr(i.StartDate),
+		DueDate:       dateToPtr(i.DueDate),
 		CreatedAt:     timestampToString(i.CreatedAt),
 		UpdatedAt:     timestampToString(i.UpdatedAt),
 		Metadata:      parseIssueMetadata(i.Metadata),
@@ -164,8 +163,8 @@ func openIssueRowToResponse(i db.ListOpenIssuesRow, issuePrefix string) IssueRes
 		ParentIssueID: uuidToPtr(i.ParentIssueID),
 		ProjectID:     uuidToPtr(i.ProjectID),
 		Position:      i.Position,
-		StartDate:     timestampToPtr(i.StartDate),
-		DueDate:       timestampToPtr(i.DueDate),
+		StartDate:     dateToPtr(i.StartDate),
+		DueDate:       dateToPtr(i.DueDate),
 		CreatedAt:     timestampToString(i.CreatedAt),
 		UpdatedAt:     timestampToString(i.UpdatedAt),
 		Metadata:      parseIssueMetadata(i.Metadata),
@@ -199,10 +198,10 @@ func assigneeGroupID(assigneeType pgtype.Text, assigneeID pgtype.UUID) string {
 // SearchIssueResponse extends IssueResponse with search metadata.
 type SearchIssueResponse struct {
 	IssueResponse
-	MatchSource                string  `json:"match_source"`
-	MatchedSnippet             *string `json:"matched_snippet,omitempty"`
-	MatchedDescriptionSnippet  *string `json:"matched_description_snippet,omitempty"`
-	MatchedCommentSnippet      *string `json:"matched_comment_snippet,omitempty"`
+	MatchSource               string  `json:"match_source"`
+	MatchedSnippet            *string `json:"matched_snippet,omitempty"`
+	MatchedDescriptionSnippet *string `json:"matched_description_snippet,omitempty"`
+	MatchedCommentSnippet     *string `json:"matched_comment_snippet,omitempty"`
 }
 
 // extractSnippet extracts a snippet of text around the first occurrence of query.
@@ -2051,24 +2050,24 @@ func (h *Handler) CreateIssue(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	var startDate pgtype.Timestamptz
+	var startDate pgtype.Date
 	if req.StartDate != nil && *req.StartDate != "" {
-		t, err := time.Parse(time.RFC3339, *req.StartDate)
+		d, err := util.ParseCalendarDate(*req.StartDate)
 		if err != nil {
-			writeError(w, http.StatusBadRequest, "invalid start_date format, expected RFC3339")
+			writeError(w, http.StatusBadRequest, "invalid start_date format, expected YYYY-MM-DD")
 			return
 		}
-		startDate = pgtype.Timestamptz{Time: t, Valid: true}
+		startDate = d
 	}
 
-	var dueDate pgtype.Timestamptz
+	var dueDate pgtype.Date
 	if req.DueDate != nil && *req.DueDate != "" {
-		t, err := time.Parse(time.RFC3339, *req.DueDate)
+		d, err := util.ParseCalendarDate(*req.DueDate)
 		if err != nil {
-			writeError(w, http.StatusBadRequest, "invalid due_date format, expected RFC3339")
+			writeError(w, http.StatusBadRequest, "invalid due_date format, expected YYYY-MM-DD")
 			return
 		}
-		dueDate = pgtype.Timestamptz{Time: t, Valid: true}
+		dueDate = d
 	}
 
 	// Use a transaction to atomically guard against active duplicates,
@@ -2363,26 +2362,26 @@ func (h *Handler) UpdateIssue(w http.ResponseWriter, r *http.Request) {
 	}
 	if _, ok := rawFields["start_date"]; ok {
 		if req.StartDate != nil && *req.StartDate != "" {
-			t, err := time.Parse(time.RFC3339, *req.StartDate)
+			d, err := util.ParseCalendarDate(*req.StartDate)
 			if err != nil {
-				writeError(w, http.StatusBadRequest, "invalid start_date format, expected RFC3339")
+				writeError(w, http.StatusBadRequest, "invalid start_date format, expected YYYY-MM-DD")
 				return
 			}
-			params.StartDate = pgtype.Timestamptz{Time: t, Valid: true}
+			params.StartDate = d
 		} else {
-			params.StartDate = pgtype.Timestamptz{Valid: false} // explicit null = clear date
+			params.StartDate = pgtype.Date{Valid: false} // explicit null = clear date
 		}
 	}
 	if _, ok := rawFields["due_date"]; ok {
 		if req.DueDate != nil && *req.DueDate != "" {
-			t, err := time.Parse(time.RFC3339, *req.DueDate)
+			d, err := util.ParseCalendarDate(*req.DueDate)
 			if err != nil {
-				writeError(w, http.StatusBadRequest, "invalid due_date format, expected RFC3339")
+				writeError(w, http.StatusBadRequest, "invalid due_date format, expected YYYY-MM-DD")
 				return
 			}
-			params.DueDate = pgtype.Timestamptz{Time: t, Valid: true}
+			params.DueDate = d
 		} else {
-			params.DueDate = pgtype.Timestamptz{Valid: false} // explicit null = clear date
+			params.DueDate = pgtype.Date{Valid: false} // explicit null = clear date
 		}
 	}
 	if _, ok := rawFields["parent_issue_id"]; ok {
@@ -2474,10 +2473,10 @@ func (h *Handler) UpdateIssue(w http.ResponseWriter, r *http.Request) {
 	priorityChanged := req.Priority != nil && prevIssue.Priority != issue.Priority
 	descriptionChanged := req.Description != nil && textToPtr(prevIssue.Description) != resp.Description
 	titleChanged := req.Title != nil && prevIssue.Title != issue.Title
-	prevStartDate := timestampToPtr(prevIssue.StartDate)
+	prevStartDate := dateToPtr(prevIssue.StartDate)
 	startDateChanged := prevStartDate != resp.StartDate && (prevStartDate == nil) != (resp.StartDate == nil) ||
 		(prevStartDate != nil && resp.StartDate != nil && *prevStartDate != *resp.StartDate)
-	prevDueDate := timestampToPtr(prevIssue.DueDate)
+	prevDueDate := dateToPtr(prevIssue.DueDate)
 	dueDateChanged := prevDueDate != resp.DueDate && (prevDueDate == nil) != (resp.DueDate == nil) ||
 		(prevDueDate != nil && resp.DueDate != nil && *prevDueDate != *resp.DueDate)
 
@@ -2896,24 +2895,24 @@ func (h *Handler) BatchUpdateIssues(w http.ResponseWriter, r *http.Request) {
 		}
 		if _, ok := rawUpdates["start_date"]; ok {
 			if req.Updates.StartDate != nil && *req.Updates.StartDate != "" {
-				t, err := time.Parse(time.RFC3339, *req.Updates.StartDate)
+				d, err := util.ParseCalendarDate(*req.Updates.StartDate)
 				if err != nil {
 					continue
 				}
-				params.StartDate = pgtype.Timestamptz{Time: t, Valid: true}
+				params.StartDate = d
 			} else {
-				params.StartDate = pgtype.Timestamptz{Valid: false}
+				params.StartDate = pgtype.Date{Valid: false}
 			}
 		}
 		if _, ok := rawUpdates["due_date"]; ok {
 			if req.Updates.DueDate != nil && *req.Updates.DueDate != "" {
-				t, err := time.Parse(time.RFC3339, *req.Updates.DueDate)
+				d, err := util.ParseCalendarDate(*req.Updates.DueDate)
 				if err != nil {
 					continue
 				}
-				params.DueDate = pgtype.Timestamptz{Time: t, Valid: true}
+				params.DueDate = d
 			} else {
-				params.DueDate = pgtype.Timestamptz{Valid: false}
+				params.DueDate = pgtype.Date{Valid: false}
 			}
 		}
 

server/internal/service/autopilot.go

@@ -185,8 +185,8 @@ func (s *AutopilotService) dispatchCreateIssue(ctx context.Context, ap db.Autopi
 		CreatorID:     leader.ID,
 		ParentIssueID: pgtype.UUID{},
 		Position:      newPosition,
-		StartDate:     pgtype.Timestamptz{},
-		DueDate:       pgtype.Timestamptz{},
+		StartDate:     pgtype.Date{},
+		DueDate:       pgtype.Date{},
 		Number:        issueNumber,
 		ProjectID:     ap.ProjectID,
 		OriginType:    pgtype.Text{String: "autopilot", Valid: true},

server/internal/service/task.go

@@ -2036,8 +2036,8 @@ func issueToMap(issue db.Issue, issuePrefix string) map[string]any {
 		"creator_id":      util.UUIDToString(issue.CreatorID),
 		"parent_issue_id": util.UUIDToPtr(issue.ParentIssueID),
 		"position":        issue.Position,
-		"start_date":      util.TimestampToPtr(issue.StartDate),
-		"due_date":        util.TimestampToPtr(issue.DueDate),
+		"start_date":      util.DateToPtr(issue.StartDate),
+		"due_date":        util.DateToPtr(issue.DueDate),
 		"created_at":      util.TimestampToString(issue.CreatedAt),
 		"updated_at":      util.TimestampToString(issue.UpdatedAt),
 	}

server/internal/util/pgx.go

@@ -92,6 +92,44 @@ func TimestampToPtr(t pgtype.Timestamptz) *string {
 	return &s
 }
 
+// DateToPtr formats a pgtype.Date as a date-only "YYYY-MM-DD" string, or nil
+// when unset. Issue start_date/due_date are calendar days with no time-of-day
+// or timezone, so they must never be rendered through an instant.
+func DateToPtr(d pgtype.Date) *string {
+	if !d.Valid {
+		return nil
+	}
+	s := d.Time.Format(time.DateOnly)
+	return &s
+}
+
+// ParseCalendarDate parses a calendar day from a "YYYY-MM-DD" string into a
+// pgtype.Date carrying no time-of-day or timezone.
+//
+// For backward compatibility it ALSO accepts an RFC3339 timestamp, but ONLY
+// when it lands exactly on a UTC day boundary (e.g. "2026-03-01T00:00:00Z"),
+// which unambiguously denotes that calendar day. A non-midnight instant is a
+// legacy local-midnight-as-UTC value (e.g. UTC+8 sends "2026-02-28T16:00:00Z"
+// for the picked day 2026-03-01) whose intended calendar day is unrecoverable —
+// it is rejected loudly rather than silently stored as the wrong day. New
+// clients always send "YYYY-MM-DD".
+func ParseCalendarDate(s string) (pgtype.Date, error) {
+	if t, err := time.Parse(time.DateOnly, s); err == nil {
+		return pgtype.Date{Time: t, Valid: true}, nil
+	}
+	if t, err := time.Parse(time.RFC3339, s); err == nil {
+		u := t.UTC()
+		if u.Hour() == 0 && u.Minute() == 0 && u.Second() == 0 && u.Nanosecond() == 0 {
+			return pgtype.Date{
+				Time:  time.Date(u.Year(), u.Month(), u.Day(), 0, 0, 0, 0, time.UTC),
+				Valid: true,
+			}, nil
+		}
+		return pgtype.Date{}, fmt.Errorf("invalid date %q: timestamps must be a UTC midnight boundary (e.g. 2026-03-01T00:00:00Z); use YYYY-MM-DD", s)
+	}
+	return pgtype.Date{}, fmt.Errorf("invalid date %q: expected YYYY-MM-DD", s)
+}
+
 func UUIDToPtr(u pgtype.UUID) *string {
 	if !u.Valid {
 		return nil

server/internal/util/pgx_test.go

@@ -1,6 +1,11 @@
 package util
 
-import "testing"
+import (
+	"testing"
+	"time"
+
+	"github.com/jackc/pgx/v5/pgtype"
+)
 
 func TestParseUUID_Valid(t *testing.T) {
 	u, err := ParseUUID("550e8400-e29b-41d4-a716-446655440000")
@@ -45,3 +50,67 @@ func TestMustParseUUID_RoundTrip(t *testing.T) {
 		t.Fatalf("round-trip mismatch: got %q want %q", got, s)
 	}
 }
+
+func TestParseCalendarDate_DateOnly(t *testing.T) {
+	d, err := ParseCalendarDate("2026-03-01")
+	if err != nil {
+		t.Fatalf("expected nil error, got %v", err)
+	}
+	if got := DateToPtr(d); got == nil || *got != "2026-03-01" {
+		t.Fatalf("round-trip mismatch: got %v want 2026-03-01", got)
+	}
+}
+
+func TestParseCalendarDate_AcceptsUTCMidnight(t *testing.T) {
+	// A UTC-midnight instant unambiguously denotes that calendar day.
+	d, err := ParseCalendarDate("2026-03-01T00:00:00Z")
+	if err != nil {
+		t.Fatalf("expected nil error, got %v", err)
+	}
+	if got := DateToPtr(d); got == nil || *got != "2026-03-01" {
+		t.Fatalf("got %v want 2026-03-01", got)
+	}
+}
+
+func TestParseCalendarDate_RejectsNonMidnightInstant(t *testing.T) {
+	// The legacy bug: UTC+8 picking 2026-03-01 sent 2026-02-28T16:00:00Z. Its
+	// intended calendar day is unrecoverable, so reject instead of silently
+	// storing the wrong day (2026-02-28).
+	cases := []string{
+		"2026-02-28T16:00:00Z", // UTC+8 local midnight
+		"2026-03-01T05:00:00Z", // UTC-5 local midnight
+		"2026-03-01T00:00:00+08:00",
+	}
+	for _, s := range cases {
+		t.Run(s, func(t *testing.T) {
+			if _, err := ParseCalendarDate(s); err == nil {
+				t.Fatalf("expected error for non-midnight instant %q, got nil", s)
+			}
+		})
+	}
+}
+
+func TestParseCalendarDate_RejectsGarbage(t *testing.T) {
+	for _, s := range []string{"", "not-a-date", "03/01/2026", "2026-13-40"} {
+		t.Run(s, func(t *testing.T) {
+			if _, err := ParseCalendarDate(s); err == nil {
+				t.Fatalf("expected error for %q, got nil", s)
+			}
+		})
+	}
+}
+
+func TestDateToPtr_NullIsNil(t *testing.T) {
+	if got := DateToPtr(pgtype.Date{Valid: false}); got != nil {
+		t.Fatalf("expected nil for invalid date, got %v", *got)
+	}
+}
+
+// Guard against a localtime regression: DateToPtr must emit the stored calendar
+// day regardless of the host process timezone.
+func TestDateToPtr_StableAcrossTimezone(t *testing.T) {
+	d := pgtype.Date{Time: time.Date(2026, 3, 1, 0, 0, 0, 0, time.UTC), Valid: true}
+	if got := DateToPtr(d); got == nil || *got != "2026-03-01" {
+		t.Fatalf("got %v want 2026-03-01", got)
+	}
+}

server/migrations/112_issue_dates_to_date.down.sql

@@ -0,0 +1,6 @@
+-- Revert to TIMESTAMPTZ, interpreting each calendar day as UTC midnight
+-- explicitly (independent of the session TimeZone): `date::timestamp` yields
+-- midnight with no zone, and `AT TIME ZONE 'UTC'` stamps it as the UTC instant.
+ALTER TABLE issue
+    ALTER COLUMN start_date TYPE TIMESTAMPTZ USING start_date::timestamp AT TIME ZONE 'UTC',
+    ALTER COLUMN due_date TYPE TIMESTAMPTZ USING due_date::timestamp AT TIME ZONE 'UTC';

server/migrations/112_issue_dates_to_date.up.sql

@@ -0,0 +1,16 @@
+-- Issue start_date / due_date are calendar days: a user picks a day (the
+-- pickers have no time-of-day input), so "Mar 1" must mean Mar 1 for everyone
+-- regardless of timezone. Storing them as TIMESTAMPTZ folded the writer's
+-- local midnight into a UTC instant, shifting the displayed day by the local
+-- offset in non-UTC timezones (GH #3618 / MUL-2925). DATE carries no time or
+-- timezone, so the picked day is preserved as-is.
+--
+-- Existing rows are truncated at the UTC day boundary, matching what the Gantt
+-- already showed for them. `AT TIME ZONE 'UTC'` pins the conversion to UTC
+-- explicitly so it does not depend on the migration session's TimeZone setting
+-- (a bare `::date` cast would be session-timezone dependent). The original
+-- local-day intent of legacy rows is unrecoverable from a bare instant, so this
+-- is the best-effort conversion.
+ALTER TABLE issue
+    ALTER COLUMN start_date TYPE DATE USING (start_date AT TIME ZONE 'UTC')::date,
+    ALTER COLUMN due_date TYPE DATE USING (due_date AT TIME ZONE 'UTC')::date;

server/pkg/db/generated/issue.sql.go

@@ -181,21 +181,21 @@ INSERT INTO issue (
 `
 
 type CreateIssueParams struct {
-	WorkspaceID   pgtype.UUID        `json:"workspace_id"`
-	Title         string             `json:"title"`
-	Description   pgtype.Text        `json:"description"`
-	Status        string             `json:"status"`
-	Priority      string             `json:"priority"`
-	AssigneeType  pgtype.Text        `json:"assignee_type"`
-	AssigneeID    pgtype.UUID        `json:"assignee_id"`
-	CreatorType   string             `json:"creator_type"`
-	CreatorID     pgtype.UUID        `json:"creator_id"`
-	ParentIssueID pgtype.UUID        `json:"parent_issue_id"`
-	Position      float64            `json:"position"`
-	StartDate     pgtype.Timestamptz `json:"start_date"`
-	DueDate       pgtype.Timestamptz `json:"due_date"`
-	Number        int32              `json:"number"`
-	ProjectID     pgtype.UUID        `json:"project_id"`
+	WorkspaceID   pgtype.UUID `json:"workspace_id"`
+	Title         string      `json:"title"`
+	Description   pgtype.Text `json:"description"`
+	Status        string      `json:"status"`
+	Priority      string      `json:"priority"`
+	AssigneeType  pgtype.Text `json:"assignee_type"`
+	AssigneeID    pgtype.UUID `json:"assignee_id"`
+	CreatorType   string      `json:"creator_type"`
+	CreatorID     pgtype.UUID `json:"creator_id"`
+	ParentIssueID pgtype.UUID `json:"parent_issue_id"`
+	Position      float64     `json:"position"`
+	StartDate     pgtype.Date `json:"start_date"`
+	DueDate       pgtype.Date `json:"due_date"`
+	Number        int32       `json:"number"`
+	ProjectID     pgtype.UUID `json:"project_id"`
 }
 
 func (q *Queries) CreateIssue(ctx context.Context, arg CreateIssueParams) (Issue, error) {
@@ -259,23 +259,23 @@ INSERT INTO issue (
 `
 
 type CreateIssueWithOriginParams struct {
-	WorkspaceID   pgtype.UUID        `json:"workspace_id"`
-	Title         string             `json:"title"`
-	Description   pgtype.Text        `json:"description"`
-	Status        string             `json:"status"`
-	Priority      string             `json:"priority"`
-	AssigneeType  pgtype.Text        `json:"assignee_type"`
-	AssigneeID    pgtype.UUID        `json:"assignee_id"`
-	CreatorType   string             `json:"creator_type"`
-	CreatorID     pgtype.UUID        `json:"creator_id"`
-	ParentIssueID pgtype.UUID        `json:"parent_issue_id"`
-	Position      float64            `json:"position"`
-	StartDate     pgtype.Timestamptz `json:"start_date"`
-	DueDate       pgtype.Timestamptz `json:"due_date"`
-	Number        int32              `json:"number"`
-	ProjectID     pgtype.UUID        `json:"project_id"`
-	OriginType    pgtype.Text        `json:"origin_type"`
-	OriginID      pgtype.UUID        `json:"origin_id"`
+	WorkspaceID   pgtype.UUID `json:"workspace_id"`
+	Title         string      `json:"title"`
+	Description   pgtype.Text `json:"description"`
+	Status        string      `json:"status"`
+	Priority      string      `json:"priority"`
+	AssigneeType  pgtype.Text `json:"assignee_type"`
+	AssigneeID    pgtype.UUID `json:"assignee_id"`
+	CreatorType   string      `json:"creator_type"`
+	CreatorID     pgtype.UUID `json:"creator_id"`
+	ParentIssueID pgtype.UUID `json:"parent_issue_id"`
+	Position      float64     `json:"position"`
+	StartDate     pgtype.Date `json:"start_date"`
+	DueDate       pgtype.Date `json:"due_date"`
+	Number        int32       `json:"number"`
+	ProjectID     pgtype.UUID `json:"project_id"`
+	OriginType    pgtype.Text `json:"origin_type"`
+	OriginID      pgtype.UUID `json:"origin_id"`
 }
 
 func (q *Queries) CreateIssueWithOrigin(ctx context.Context, arg CreateIssueWithOriginParams) (Issue, error) {
@@ -821,8 +821,8 @@ type ListIssuesRow struct {
 	CreatorID     pgtype.UUID        `json:"creator_id"`
 	ParentIssueID pgtype.UUID        `json:"parent_issue_id"`
 	Position      float64            `json:"position"`
-	StartDate     pgtype.Timestamptz `json:"start_date"`
-	DueDate       pgtype.Timestamptz `json:"due_date"`
+	StartDate     pgtype.Date        `json:"start_date"`
+	DueDate       pgtype.Date        `json:"due_date"`
 	CreatedAt     pgtype.Timestamptz `json:"created_at"`
 	UpdatedAt     pgtype.Timestamptz `json:"updated_at"`
 	Number        int32              `json:"number"`
@@ -961,8 +961,8 @@ type ListOpenIssuesRow struct {
 	CreatorID     pgtype.UUID        `json:"creator_id"`
 	ParentIssueID pgtype.UUID        `json:"parent_issue_id"`
 	Position      float64            `json:"position"`
-	StartDate     pgtype.Timestamptz `json:"start_date"`
-	DueDate       pgtype.Timestamptz `json:"due_date"`
+	StartDate     pgtype.Date        `json:"start_date"`
+	DueDate       pgtype.Date        `json:"due_date"`
 	CreatedAt     pgtype.Timestamptz `json:"created_at"`
 	UpdatedAt     pgtype.Timestamptz `json:"updated_at"`
 	Number        int32              `json:"number"`
@@ -1138,18 +1138,18 @@ RETURNING id, workspace_id, title, description, status, priority, assignee_type,
 `
 
 type UpdateIssueParams struct {
-	ID            pgtype.UUID        `json:"id"`
-	Title         pgtype.Text        `json:"title"`
-	Description   pgtype.Text        `json:"description"`
-	Status        pgtype.Text        `json:"status"`
-	Priority      pgtype.Text        `json:"priority"`
-	AssigneeType  pgtype.Text        `json:"assignee_type"`
-	AssigneeID    pgtype.UUID        `json:"assignee_id"`
-	Position      pgtype.Float8      `json:"position"`
-	StartDate     pgtype.Timestamptz `json:"start_date"`
-	DueDate       pgtype.Timestamptz `json:"due_date"`
-	ParentIssueID pgtype.UUID        `json:"parent_issue_id"`
-	ProjectID     pgtype.UUID        `json:"project_id"`
+	ID            pgtype.UUID   `json:"id"`
+	Title         pgtype.Text   `json:"title"`
+	Description   pgtype.Text   `json:"description"`
+	Status        pgtype.Text   `json:"status"`
+	Priority      pgtype.Text   `json:"priority"`
+	AssigneeType  pgtype.Text   `json:"assignee_type"`
+	AssigneeID    pgtype.UUID   `json:"assignee_id"`
+	Position      pgtype.Float8 `json:"position"`
+	StartDate     pgtype.Date   `json:"start_date"`
+	DueDate       pgtype.Date   `json:"due_date"`
+	ParentIssueID pgtype.UUID   `json:"parent_issue_id"`
+	ProjectID     pgtype.UUID   `json:"project_id"`
 }
 
 func (q *Queries) UpdateIssue(ctx context.Context, arg UpdateIssueParams) (Issue, error) {

server/pkg/db/generated/models.go

@@ -347,7 +347,7 @@ type Issue struct {
 	AcceptanceCriteria []byte             `json:"acceptance_criteria"`
 	ContextRefs        []byte             `json:"context_refs"`
 	Position           float64            `json:"position"`
-	DueDate            pgtype.Timestamptz `json:"due_date"`
+	DueDate            pgtype.Date        `json:"due_date"`
 	CreatedAt          pgtype.Timestamptz `json:"created_at"`
 	UpdatedAt          pgtype.Timestamptz `json:"updated_at"`
 	Number             int32              `json:"number"`
@@ -355,7 +355,7 @@ type Issue struct {
 	OriginType         pgtype.Text        `json:"origin_type"`
 	OriginID           pgtype.UUID        `json:"origin_id"`
 	FirstExecutedAt    pgtype.Timestamptz `json:"first_executed_at"`
-	StartDate          pgtype.Timestamptz `json:"start_date"`
+	StartDate          pgtype.Date        `json:"start_date"`
 	Metadata           []byte             `json:"metadata"`
 }