fix(plugin-timeline): judge gantt dates by TYPE — string, finite number, or Date

.changeset/6781-gantt-date-type-rule.md

@@ -0,0 +1,43 @@
+---
+'@object-ui/plugin-timeline': patch
+---
+
+Gantt dates are now judged by TYPE: a `string`, a finite `number`, or a `Date`
+— anything else is refused (objectui#6781, maintainer ruling 2026-08-30).
+
+**This is a reject-direction change. Metadata that renders a chart today can
+stop rendering one.** `new Date(x)` runs ToPrimitive on anything, so values that
+are not dates at all used to become instants silently. These now produce the
+same loud diagnostic #6759 and #6770 already use — an alert naming the authored
+path and the offending value — instead of a chart:
+
+| authored gantt date — a row item's `startDate` / `endDate`, or a **truthy** `minDate` / `maxDate` pin | before | after |
+| --- | --- | --- |
+| `false` | a 649-column axis starting Jan 1970, bar `width: -100%`, no warning | refused, named |
+| `true` | the same 1970 axis | refused, named |
+| `['2024-01-01']` | drew a normal-looking chart | refused, named |
+| `[0]` | drew a chart dated to the **year 2000** | refused, named |
+| `{ toString() { return '2024-01-01' } }` | drew a normal-looking chart | refused, named |
+| a `bigint` or a `symbol` | threw an uncaught `TypeError` mid-render | refused, named |
+
+**Falsy pins are not affected, and never were.** A `minDate` / `maxDate` of
+`false`, `0` or `''` is discarded by the renderer's existing truthy-only `||`
+before anything judges it: such a pin never produced a 1970 axis and it is not
+refused now — the chart simply uses the range computed from the rows, exactly as
+it did before. The before/after readings above are row-date readings.
+
+**If your gantt stops drawing after this upgrade, the diagnostic names the exact
+authored path** (e.g. `items[0].items[0].endDate`). Fix it at the producer: emit
+a date string (`'2024-01-01'`), a millisecond timestamp (`1704067200000`), or a
+`Date`. A boolean or an object arriving in a date field means an upstream
+mapping picked the wrong column — the chart was drawing 1970 from it before, and
+that render was never right.
+
+**`0` keeps working, deliberately.** It is a legitimate epoch timestamp — under
+a millisecond encoding an author who writes `0` means 1970-01-01 — so it is
+accepted and renders exactly as it did before. `NaN` and `Infinity` are refused,
+as they already were.
+
+Unchanged for everyone else: valid string / numeric / `Date` dates draw the same
+axis and the same bar geometry, an empty gantt keeps its one-bucket sentinel,
+and `null` / absent dates keep the identical diagnostic they got before.