fix(copy): make delete confirmations, sleep-debt labels, and the glucose band honest

Three surfaces where the words no longer matched the code, plus the missing
web control for a preference the server already honours.

Delete confirmations. Four dialogs promised permanence on surfaces that
render an Undo: the measurements and mood bulk bodies, the lab-result body,
and the illness-episode body (which said "cannot be undone" sixty lines
below the code that fires the Undo toast). All four now use the same
sentence the single-row measurement and mood dialogs already used. A sweep
of every other confirmation in the tree found the rest accurate — the
biomarker cascade, the mood-tag purge, and the account purge keep their
warning because those deletes really are unrecoverable.

Sleep debt. v1.19.0 replaced the summed shortfall with a running balance
that credits catch-up sleep; the labels still described the old sum, so the
word contradicted the number for anyone who slept in after a short night.
Corrected in all six locales, plus the places the old semantics had
propagated: the Coach system prompt, the OpenAPI field descriptions the
native client reads, and four module docblocks.

Glucose reference band. `hasDiabetes` selects the tighter reference band and
grounds the Coach, but no web surface set it — a web-only account was pinned
to the non-diabetic scale with no way out. The control goes on Targets,
above the per-metric editor, because it answers the same question that page
answers and the two are ordered: it picks the default band, an override
below beats it. The copy says what it is — a reference band, not a
diagnosis, never inferred from a reading, no clinical action taken on it.

The passkey list was reported as always reading "never used". It does not
reproduce: the column is selected by the list route and stamped on every
verified assertion, both since v1.23.0. Pinned with tests on both halves so
the contract cannot quietly regress.

src/app/api/auth/passkeys/__tests__/route.test.ts

@@ -0,0 +1,82 @@
+/**
+ * `GET /api/auth/passkeys` — the passkey management list.
+ *
+ * The management UI renders a "last used" column per credential, and a
+ * passkey that reads "never used" is something a person acts on: they may
+ * delete a working credential believing it is dead. So the field is part of
+ * the route's contract, not an incidental select — dropping it from the
+ * projection would silently turn every row into "never used" without any
+ * type or lint failure.
+ *
+ * The write half (the stamp on a verified assertion) is pinned in
+ * `src/lib/auth/__tests__/passkey.test.ts`.
+ */
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+vi.mock("@/lib/api-handler", () => ({
+  apiHandler: (fn: unknown) => fn,
+  requireAuth: vi.fn(),
+}));
+
+vi.mock("@/lib/db", () => ({
+  prisma: { passkey: { findMany: vi.fn() } },
+}));
+
+vi.mock("@/lib/logging/context", () => ({ annotate: vi.fn() }));
+
+import { GET } from "../route";
+import { requireAuth } from "@/lib/api-handler";
+import { prisma } from "@/lib/db";
+
+const USER = { id: "user-1", username: "u", email: "u@example.com" };
+
+const ROW = {
+  id: "pk-1",
+  name: "Phone",
+  credentialDeviceType: "multiDevice",
+  credentialBackedUp: true,
+  createdAt: new Date("2026-01-01T00:00:00Z"),
+  lastUsedAt: new Date("2026-07-01T10:00:00Z"),
+};
+
+beforeEach(() => {
+  vi.resetAllMocks();
+  vi.mocked(requireAuth).mockResolvedValue({ user: USER } as never);
+  vi.mocked(prisma.passkey.findMany).mockResolvedValue([ROW] as never);
+});
+
+describe("GET /api/auth/passkeys", () => {
+  it("selects lastUsedAt, scoped to the calling user", async () => {
+    await (GET as unknown as () => Promise<Response>)();
+
+    expect(prisma.passkey.findMany).toHaveBeenCalledTimes(1);
+    const args = vi.mocked(prisma.passkey.findMany).mock.calls[0][0];
+
+    expect(args?.where).toEqual({ userId: USER.id });
+    expect(args?.select).toMatchObject({ lastUsedAt: true });
+  });
+
+  it("emits lastUsedAt in the response envelope", async () => {
+    const res = await (GET as unknown as () => Promise<Response>)();
+    const body = await res.json();
+
+    expect(body.error).toBeNull();
+    expect(body.data).toHaveLength(1);
+    expect(body.data[0]).toHaveProperty("lastUsedAt");
+    expect(new Date(body.data[0].lastUsedAt).toISOString()).toBe(
+      "2026-07-01T10:00:00.000Z",
+    );
+  });
+
+  it("passes a never-used credential through as null, not as a missing key", async () => {
+    vi.mocked(prisma.passkey.findMany).mockResolvedValue([
+      { ...ROW, lastUsedAt: null },
+    ] as never);
+
+    const res = await (GET as unknown as () => Promise<Response>)();
+    const body = await res.json();
+
+    expect(Object.keys(body.data[0])).toContain("lastUsedAt");
+    expect(body.data[0].lastUsedAt).toBeNull();
+  });
+});

src/app/api/sleep/rhythm/route.ts

@@ -5,7 +5,8 @@
  * signals the Sleep page + the iOS client render off the SAME canonical night
  * reconstruction the Sleep Score uses:
  *
- *   - `sleepDebt`   — cumulative deficit over the rolling window, with a calm
+ *   - `sleepDebt`   — outstanding balance over the rolling window (surplus
+ *                     sleep pays it down), with a calm
  *                     `partial` state under the night threshold.
  *   - `chronotype`  — MCTQ MSF / MSFsc band + social jetlag, with a `learning`
  *                     state until enough free-day nights exist.