fix(coach): do not count the freshness stamp as a figure in a series block

A block trimmed to its unit and freshness stamp passed the figure check,
because asOf.daysAgo is a number. The check now skips the asOf and scope
fields, so that shape answers retrieval_failed like any other block
without a reading.

src/lib/ai/coach/__tests__/series-long-window.test.ts

@@ -244,6 +244,12 @@ describe("get_metric_series inside a chat turn", () => {
     for (const empty of [
       { unit: "kg" },
       { omitted: "trimmed for prompt budget" },
+      // The shape the budget pass really leaves: the unit and the freshness
+      // stamp, whose `daysAgo` is a number but not a reading.
+      {
+        unit: "kg",
+        asOf: { daysAgo: 3, isToday: false, currentForTodayClaims: false },
+      },
     ]) {
       buildCoachSnapshot.mockReset();
       buildCoachSnapshot.mockResolvedValue(snapshot({ fatMass: empty }));

src/lib/ai/coach/tools/executor.ts

@@ -619,11 +619,22 @@ function isRecord(value: unknown): value is Record<string, unknown> {
   return typeof value === "object" && value !== null && !Array.isArray(value);
 }
 
-/** Whether a payload holds at least one finite number anywhere. */
+/**
+ * Fields that describe a block rather than measure anything: the freshness
+ * stamp (`asOf.daysAgo` is a number, but no reading), and the scope echo. A
+ * block trimmed to `{ unit, asOf }` holds no figure.
+ */
+const METADATA_FIELDS: ReadonlySet<string> = new Set(["asOf", "scope"]);
+
+/** Whether a payload holds at least one finite measured number anywhere. */
 function carriesFigures(value: unknown): boolean {
   if (typeof value === "number") return Number.isFinite(value);
   if (Array.isArray(value)) return value.some(carriesFigures);
-  if (isRecord(value)) return Object.values(value).some(carriesFigures);
+  if (isRecord(value)) {
+    return Object.entries(value).some(
+      ([key, child]) => !METADATA_FIELDS.has(key) && carriesFigures(child),
+    );
+  }
   return false;
 }