test(coach): pin the window/absence discriminant to the reported case

The fixture is the report: a fortnight of glucose readings from April 2024 on an
account that displays them everywhere else. The clock is pinned so it cannot age
out of the window it was written to sit outside of.

Covers the four states an empty window read can resolve to, that a never-recorded
metric and a historical one differ in the SAME run, that a mean is withheld
across mixed units rather than fabricated, that the manifest advertises the range
instead of "absent", that both instructions branch on the reason code, and that a
miss carrying figures reaches the prose verifier's authoritative set. Adds the
medication-compliance page to the failed-read sweep and pins the narration
blocks' failure annotation.

src/components/__tests__/failed-read-never-empty.test.tsx

@@ -155,6 +155,10 @@ describe("read-failure branch is wired on every swept surface", () => {
     "src/components/custom-metrics/custom-metric-values-list.tsx",
     "src/app/achievements/page.tsx",
     "src/components/insights/nutrients/micronutrients-card.tsx",
+    // A failed comprehensive read used to fall through to "you haven't added
+    // any medications yet" — with a CTA inviting someone on a full daily
+    // regimen to re-enter what the app already holds.
+    "src/app/insights/medications/page.tsx",
     // The three sleep-rhythm cards share one read, so the PAGE owns the single
     // error notice rather than each card painting its own copy of it.
     "src/app/insights/sleep/page.tsx",