feat(mood): resolve sleep, activity, vitals and symptoms at read time

- one resolver reads the day's figures from the modules that own them; nothing
  is copied onto the mood row, so correcting a sleep session corrects it here
  in the same moment
- absence answers { present: false } rather than zero, because a night nobody
  recorded and a night of no sleep are different facts
- a module switched off blanks its whole block instead of filtering down to an
  empty one
- keyed by the local day so the capture sheet can ask before an entry exists

src/app/api/mood/linked-context/route.ts

@@ -0,0 +1,74 @@
+/**
+ * `GET /api/mood/linked-context?date=YYYY-MM-DD` — what the modules that own
+ * sleep, activity, vitals and body symptoms already know about one day.
+ *
+ * Keyed by the local day rather than by an entry id, deliberately: the capture
+ * sheet needs these figures BEFORE an entry exists, and a route that could
+ * only answer for a saved row would leave the one surface that most wants
+ * them unable to ask. The detail view passes the entry's own `date` and `tz`
+ * and gets the same answer.
+ *
+ * Nothing here is stored on the mood row. Every figure is read from its owning
+ * module on each request, which is what makes a corrected sleep session show
+ * up on the mood entry with nothing to re-sync.
+ */
+import { NextRequest } from "next/server";
+import { z } from "zod/v4";
+
+import { apiHandler, requireRecordAuth } from "@/lib/api-handler";
+import { apiSuccess, returnAllZodIssues } from "@/lib/api-response";
+import { annotate } from "@/lib/logging/context";
+import { requireModuleEnabled } from "@/lib/modules/gate";
+import { resolveLinkedDayContext } from "@/lib/mood/linked-context";
+import { DEFAULT_TIMEZONE } from "@/lib/mood/date-key";
+
+export const dynamic = "force-dynamic";
+
+const querySchema = z.object({
+  date: z.string().regex(/^\d{4}-\d{2}-\d{2}$/),
+  // The zone the day is anchored to. Absent falls back to the account's own
+  // display timezone, which is what a fresh capture sheet means; the detail
+  // view passes the entry's stored `tz` so a row logged elsewhere keeps its
+  // own day boundaries.
+  tz: z.string().min(1).max(64).optional(),
+});
+
+export const GET = apiHandler(async (request: NextRequest) => {
+  const { user } = await requireRecordAuth("read", "mind");
+
+  const gate = await requireModuleEnabled(user.id, "mood");
+  if (!gate.enabled) return gate.response;
+
+  const parsed = querySchema.safeParse(
+    Object.fromEntries(request.nextUrl.searchParams),
+  );
+  if (!parsed.success) {
+    annotate({
+      action: { name: "mood.linked-context.validation-failed" },
+      meta: { issue_count: parsed.error.issues.length },
+    });
+    return returnAllZodIssues(parsed.error, 422, {
+      errorCode: "mood.linkedContext.invalid",
+    });
+  }
+
+  const linked = await resolveLinkedDayContext(user.id, {
+    date: parsed.data.date,
+    tz: parsed.data.tz ?? user.timezone ?? DEFAULT_TIMEZONE,
+  });
+
+  annotate({
+    action: { name: "mood.linked-context.read" },
+    // Which blocks the person can see at all, so a support question about a
+    // missing figure can be answered without asking them to describe their
+    // module settings.
+    meta: {
+      day: linked.day,
+      sleep_available: linked.sleep.available,
+      activity_available: linked.activity.available,
+      body_available: linked.body.available,
+    },
+  });
+
+  return apiSuccess(linked);
+});