catalog: omit the wall-clock-derived Countdown.targetDate default so the generated catalog (and drift test) no longer flip daily

Add a date-independence test (freezes Date at two different days via a preload).

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

craft/scripts/fake-date-preload.cjs

@@ -0,0 +1,9 @@
+// Test helper: freeze the wall clock for a child process. FAKE_NOW=<ISO date> (node -r this).
+const RealDate = Date;
+const fixed = new RealDate(process.env.FAKE_NOW).getTime();
+if (!Number.isFinite(fixed)) throw new Error('FAKE_NOW must be a valid ISO date');
+class FakeDate extends RealDate {
+  constructor(...a) { if (a.length === 0) super(fixed); else super(...a); }
+  static now() { return fixed; }
+}
+globalThis.Date = FakeDate;

craft/scripts/gen-sitesmith-catalog.mjs

@@ -106,6 +106,14 @@ function extractProps(program, file, name) {
   return out;
 }
 
+/**
+ * Defaults computed from the wall clock when the editor module loads (Countdown.targetDate
+ * = today + 30 days). Emitting them would make the generated catalog (and the drift test)
+ * change every day and would teach the model a stale "default" date, so they are omitted
+ * from the catalog entirely.
+ */
+const VOLATILE_DEFAULTS = new Set(['Countdown.targetDate']);
+
 const COLOR_RE = /^(color|bg|bgValue|gradient)$|(colou?r|bg|background|gradientfrom|gradientto)$/i;
 const isTokenRef = (v) => typeof v === 'string' && /^var\(--wsb-[a-z-]+\)$/.test(v);
 
@@ -148,7 +156,7 @@ export async function buildCatalog() {
       if (COMMON_PROPS.has(p) || p === 'children') continue;
       const e = { ...info };
       delete e.optional;
-      if (p in defaults && !(typeof defaults[p] === 'string' && defaults[p].startsWith('data:'))) e.default = slimDefault(defaults[p]);
+      if (p in defaults && !VOLATILE_DEFAULTS.has(`${name}.${p}`) && !(typeof defaults[p] === 'string' && defaults[p].startsWith('data:'))) e.default = slimDefault(defaults[p]);
       if (info.type !== 'boolean' && info.type !== 'number' && COLOR_RE.test(p)) {
         e.color = true;
         if (isTokenRef(defaults[p])) e.tokenDefault = true;