## What happened

The clock widget's calendar popup (`omarchy.clock` plugin) shows the wrong weekday for dates after Chile's DST "spring forward" transition. On 2026-09-15 (a Tuesday), the popup calendar for September 2026 shows `15` under the `WED` column instead of `TUE`. The whole week row (12–18) is shifted one weekday to the right.

The bar's own clock label is correct at the same time (`Tuesday 10:36`), and the first week of the month (1–5, before the DST transition) renders correctly with `1` under `TUE`. The misalignment starts exactly at the week that crosses the DST transition (Sat 2026-09-05 23:59:59 -04 → Sun 2026-09-06 01:00 -03).

## What was expected

The whole month grid should stay consistent with the actual calendar/ISO weekday, independent of a DST transition occurring mid-month.

## Steps to reproduce

1. Set system timezone to `America/Santiago` (has a DST "spring forward" transition on the first Sunday of September).
2. Let system date reach a day in September after that transition (e.g. 2026-09-15).
3. Click the bar clock to open the calendar popup.
4. Compare the weekday shown for `15` against an authoritative calendar — it is off by one, and the whole trailing part of the month is shifted.

## Diagnosis

I dug into `/usr/share/omarchy/shell/plugins/panels/clock/Model.js` (`monthGrid`). Its day-by-day grid builder advances a `Date` with `cursor.setDate(cursor.getDate() + 1)`, starting from local midnight.

- System `tzdata` is current (`2026c`) and correctly encodes the Chile transition (`zdump -v America/Santiago` confirms `Sat 2026-09-05 23:59:59 -04 → Sun 2026-09-06 01:00 -03`, i.e. local `00:00–00:59` on 2026-09-06 does not exist).
- Re-implementing the exact same `monthGrid` algorithm in Node (V8), using the same system tzdata/`TZ=America/Santiago`, produces the **correct** grid for September 2026 (`15` under `TUE`).
- The Quickshell process itself was started fresh, after the DST transition (`ps` shows it started 2026-09-15 09:52, well after 2026-09-06), so this isn't a stale-process/cached-offset issue — and the bar's "now" label is correct at the same moment.

That combination points at Qt/QML's date engine (Quickshell runs on Qt6/QJSEngine, using ICU for locale/i18n — `qt6-base 6.11.2-3`, `icu 78.3-1` on this system) handling the DST "spring forward" day differently from a standard ECMA-262 engine when a `Date` is incremented by day across it, rather than a bug in the omarchy-authored JS logic itself (which matches spec behavior in Node).

## System details

- Omarchy version: 4.0.3-1
- qt6-base: 6.11.2-3
- icu: 78.3-1
- tzdata: 2026c-1
- Timezone: America/Santiago (-03, DST active)
- Locale: en_US.UTF-8

## Attachments

Two screenshots attached showing: (1) the calendar popup with `15` boxed under `WED`, month footer reading "SEPTEMBER 2026"; (2) the bar itself at the same time correctly reading "Tuesday 10:36".