feat(parser): add ISO8601 duration parser

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/server/parsers/iso8601-duration.ts

@@ -0,0 +1,14 @@
+const PATTERN = /^P(?:(\d+)D)?(?:T(?:(\d+)H)?(?:(\d+)M)?(?:(\d+)S)?)?$/;
+
+export function parseIso8601Duration(input: string | null | undefined): number | null {
+  if (typeof input !== 'string' || input.length === 0) return null;
+  if (input === 'P' || input === 'PT') return null;
+  const m = PATTERN.exec(input);
+  if (!m) return null;
+  const [, d, h, min, s] = m;
+  if (!d && !h && !min && !s) return null;
+  const days = d ? parseInt(d, 10) : 0;
+  const hours = h ? parseInt(h, 10) : 0;
+  const mins = min ? parseInt(min, 10) : 0;
+  return days * 24 * 60 + hours * 60 + mins;
+}

tests/unit/iso8601-duration.test.ts

@@ -0,0 +1,23 @@
+import { describe, it, expect } from 'vitest';
+import { parseIso8601Duration } from '../../src/lib/server/parsers/iso8601-duration';
+
+describe('parseIso8601Duration', () => {
+  it.each([
+    ['PT30M', 30],
+    ['PT1H', 60],
+    ['PT1H30M', 90],
+    ['PT2H15M', 135],
+    ['PT0M', 0],
+    ['P1DT2H', 26 * 60],
+    ['PT90M', 90]
+  ] as const)('parses %s to %i minutes', (input, expected) => {
+    expect(parseIso8601Duration(input)).toBe(expected);
+  });
+
+  it.each([[''], [null], [undefined], ['garbage'], ['30 min'], ['PT']])(
+    'returns null for invalid input %j',
+    (input) => {
+      expect(parseIso8601Duration(input as string)).toBeNull();
+    }
+  );
+});