feat(dates): read ordinal ranges with a stated UTC offset

Adds parseOrdinalDateTimeRange for "November 9th, 05:00 - December 4th,
2023, 04:59 (UTC-5)". Ordinal days anchor the pattern at both ends so it
cannot claim text the looser readers should get, and the year rolls back
across New Year as parseMonthDayRange does.

The offset is required rather than defaulted. parseSlashDateTimeRange has
to read its wall-clock times as UTC because its source states no zone;
here the zone is part of the format, so a cell without one returns null
instead of being silently read five hours early. Calendar validation runs
on the stated local fields, before the shift, or "February 30th, 23:00
(UTC-5)" would convert into a real instant in March.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

test/dates.test.ts

@@ -6,6 +6,7 @@ import {
   parseMonthDayRange,
   parseMonthDayYear,
   parseOpenRange,
+  parseOrdinalDateTimeRange,
   parseSlashDateTimeRange,
   parseYearFirstSlashRange,
 } from "../src/ingest/dates.ts";
@@ -234,3 +235,98 @@ describe("parseYearFirstSlashRange", () => {
     expect(parseYearFirstSlashRange("2026/07/30 – 08/20")).toBeNull();
   });
 });
+
+describe("parseOrdinalDateTimeRange", () => {
+  test("reads ordinal days, times and a stated offset", () => {
+    const range = parseOrdinalDateTimeRange(
+      "August 13th, 05:00 - September 21st, 2026, 04:59 (UTC-5)",
+    );
+    // 05:00 at UTC-5 is 10:00Z. Reading the wall clock as UTC — which is all
+    // parseSlashDateTimeRange can do, because its source states no offset —
+    // would put both boundaries five hours early.
+    expect(range?.start.iso).toBe("2026-08-13T10:00:00.000Z");
+    expect(range?.end.iso).toBe("2026-09-21T09:59:00.000Z");
+    expect(range?.start.precision).toBe("exact");
+    expect(range?.end.precision).toBe("exact");
+  });
+
+  test("takes the year from the end when the start omits it", () => {
+    const range = parseOrdinalDateTimeRange(
+      "November 9th, 05:00 - December 4th, 2023, 04:59 (UTC-5)",
+    );
+    expect(range?.start.iso).toBe("2023-11-09T10:00:00.000Z");
+    expect(range?.end.iso).toBe("2023-12-04T09:59:00.000Z");
+  });
+
+  test("rolls the start year back across New Year", () => {
+    const range = parseOrdinalDateTimeRange(
+      "December 28th, 05:00 - January 18th, 2024, 04:59 (UTC-5)",
+    );
+    expect(range?.start.iso).toBe("2023-12-28T10:00:00.000Z");
+    expect(range?.end.iso).toBe("2024-01-18T09:59:00.000Z");
+  });
+
+  test("honours a year stated on both halves", () => {
+    const range = parseOrdinalDateTimeRange(
+      "December 28th, 2023, 05:00 - January 18th, 2024, 04:59 (UTC-5)",
+    );
+    expect(range?.start.iso).toBe("2023-12-28T10:00:00.000Z");
+    expect(range?.end.iso).toBe("2024-01-18T09:59:00.000Z");
+  });
+
+  test("returns null when no year is stated at all", () => {
+    // The one row on the Reverse: 1999 page in this shape. There is no year to
+    // infer from and inventing one is the failure this module exists to avoid.
+    expect(
+      parseOrdinalDateTimeRange("February 20th, 05:00 - March 27th, 04:59 (UTC-5)"),
+    ).toBeNull();
+  });
+
+  test("returns null when the offset is not stated", () => {
+    // A missing timezone is a missing fact. Defaulting it to UTC would be a
+    // guess dressed as data.
+    expect(
+      parseOrdinalDateTimeRange("August 13th, 05:00 - September 21st, 2026, 04:59"),
+    ).toBeNull();
+  });
+
+  test("requires the ordinal suffix that anchors the format", () => {
+    expect(
+      parseOrdinalDateTimeRange("August 13, 05:00 - September 21, 2026, 04:59 (UTC-5)"),
+    ).toBeNull();
+  });
+
+  test("does not match a range buried in prose", () => {
+    expect(
+      parseOrdinalDateTimeRange(
+        "Runs August 13th, 05:00 - September 21st, 2026, 04:59 (UTC-5) for everyone",
+      ),
+    ).toBeNull();
+  });
+
+  test("rejects an impossible date in the timezone it was written in", () => {
+    // Validating after the offset shift would turn this into a real instant in
+    // March instead of rejecting it.
+    expect(
+      parseOrdinalDateTimeRange(
+        "February 30th, 05:00 - March 27th, 2026, 04:59 (UTC-5)",
+      ),
+    ).toBeNull();
+  });
+
+  test("signs the minutes of a half-hour offset with the hours", () => {
+    // -3:30 is three and a half hours behind UTC, not three behind and thirty
+    // ahead: 05:00 at UTC-3:30 is 08:30Z.
+    const range = parseOrdinalDateTimeRange(
+      "August 13th, 05:00 - September 21st, 2026, 04:59 (UTC-3:30)",
+    );
+    expect(range?.start.iso).toBe("2026-08-13T08:30:00.000Z");
+  });
+
+  test("accepts a tilde separator", () => {
+    const range = parseOrdinalDateTimeRange(
+      "August 13th, 05:00 ~ September 21st, 2026, 04:59 (UTC-5)",
+    );
+    expect(range?.start.iso).toBe("2026-08-13T10:00:00.000Z");
+  });
+});