[repo:objectui] Pure date fields shift one day for viewers west of UTC — '2026-08-01' renders 7月31日 in PDT; the display formatter parses the date-only string via new Date('YYYY-MM-DD') (UTC midnight) then reads local getters #14887

Summary

A pure date field stored as 2026-08-01 is displayed as 7月31日 in a browser whose local timezone is west of UTC (observed: macOS in PDT, UTC-7). The date-only ISO string is parsed with new Date('2026-08-01') (UTC midnight) and then read back with local getters, so every date-only value shifts one calendar day for any user west of UTC — and the relative branch in the same formatter (#14885) is off by one for the same reason (2026-08-31 reads 4天前 on 2026-09-03).

The stored value is correct; only the display is wrong. Same formatter as #14885, different defect (value correctness vs. presentation choice).

Minimal reproduction

Platform 17.2.0 console. Machine timezone America/Los_Angeles (PDT, UTC-7); date → Thu Sep 3 03:35 PDT 2026.

Object kpi_plan with period_start: Field.date({ label: '周期开始' }), seeded period_start: '2026-08-01', period_end: '2026-08-31'.

GET /api/v1/data/kpi_plan → "period_start":"2026-08-01","period_end":"2026-08-31"

List cell 周期开始 → 7月31日     ← expected 8月1日
List cell 周期结束 → 4天前       ← expected 3天前 (or, per #14885, 8月31日)

Same page opened from a UTC+8 browser earlier the same day shows 8月1日 / 3天前 — the display depends on the viewer's timezone although the value has no time component.

Where

ui-components chunk, date display formatter:

function Ltt(e, t) {
  ...
  let n = e instanceof Date ? e : new Date(e);     // '2026-08-01' → 2026-08-01T00:00:00Z
  let r = new Date(),
      i = new Date(r.getFullYear(), r.getMonth(), r.getDate()),
      a = new Date(n.getFullYear(), n.getMonth(), n.getDate()).getTime() - i.getTime();  // local getters → Jul 31 in UTC-7
  let o = Math.round(a / 864e5);
  if (o < -7 || o > 7) return k9(n, void 0, t);   // k9 → toLocaleDateString(...) on the shifted Date
  ...

Per ECMAScript, a date-only ISO form is parsed as UTC while date-time forms without offset are parsed as local — so new Date('YYYY-MM-DD') is exactly the wrong constructor for a calendar date.

Expected

• A date value (no time component) renders the same calendar date for every viewer, in every timezone. Parse YYYY-MM-DD into local components (new Date(y, m - 1, d)) or format the string directly; never through a UTC-midnight Date.
• Same care in the date input/editor and in export, if they share the helper (not checked).
• datetime fields keep timezone conversion — that is the case where it is wanted.

Environment

@objectstack/console 17.2.0 · objectstack dev · Chrome on macOS, tz PDT. App: objectstack-ai/kpi, object kpi_plan. Related: #14885 (relative rendering of the same field).