fix(illness): log a day of a recovered illness inside the episode

"Log day" always opened on today and let the picker run to today, so
for an illness marked recovered on Monday a note added on Thursday was
filed three days after the recovery, and the day view showed a sick day
with no illness beside it. Both places that open the sheet now hand it
the episode's last day: today while it runs, the recovery day (read in
the profile zone, as the server reads it) once it ended. The picker
opens there and offers nothing later.

src/components/illness/__tests__/illness-view-nesting.test.tsx

@@ -47,7 +47,10 @@ vi.mock("@/components/symptoms/symptoms-section", () => ({
   SymptomsSection: () => null,
 }));
 vi.mock("../new-episode-sheet", () => ({ NewEpisodeSheet: () => null }));
-vi.mock("../log-day-sheet", () => ({ LogDaySheet: () => null }));
+vi.mock("../log-day-sheet", () => ({
+  LogDaySheet: () => null,
+  useLastLoggableDay: (today: string) => today,
+}));
 vi.mock("@/components/day/day-link", () => ({
   DAY_LINK_SLOT: "{date}",
   DayLinkStated: ({ children }: { children: React.ReactNode }) => children,

src/components/illness/__tests__/log-day-sheet-last-day.test.ts

@@ -0,0 +1,48 @@
+import { describe, expect, it } from "vitest";
+
+import { lastLoggableDay } from "../log-day-sheet";
+
+/**
+ * "Log day" on an illness opens on the day it suggests and bounds the picker
+ * there. For a recovered episode that used to be today, so one tap on Save
+ * filed a sick day days after the recovery, and the day view then showed it
+ * with no illness running beside it.
+ */
+describe("lastLoggableDay", () => {
+  it("is today while the episode runs", () => {
+    expect(lastLoggableDay("2026-11-12", null, "Europe/Berlin")).toBe(
+      "2026-11-12",
+    );
+  });
+
+  it("is the recovery day once the episode ended before today", () => {
+    expect(
+      lastLoggableDay(
+        "2026-11-12",
+        "2026-11-09T08:00:00.000Z",
+        "Europe/Berlin",
+      ),
+    ).toBe("2026-11-09");
+  });
+
+  it("stays today when the episode ended today", () => {
+    expect(
+      lastLoggableDay(
+        "2026-11-12",
+        "2026-11-12T08:00:00.000Z",
+        "Europe/Berlin",
+      ),
+    ).toBe("2026-11-12");
+  });
+
+  it("reads the recovery day in the profile zone", () => {
+    // 23:30 UTC is already the next day in Berlin.
+    expect(
+      lastLoggableDay(
+        "2026-11-12",
+        "2026-11-09T23:30:00.000Z",
+        "Europe/Berlin",
+      ),
+    ).toBe("2026-11-10");
+  });
+});

src/components/illness/illness-episode-detail.tsx

@@ -30,7 +30,7 @@ import { canReadBodySites } from "@/hooks/use-body-sites";
 
 import { IllnessCorrelationCard } from "./illness-correlation-card";
 import { IllnessDayTimeline } from "./illness-day-timeline";
-import { LogDaySheet } from "./log-day-sheet";
+import { LogDaySheet, useLastLoggableDay } from "./log-day-sheet";
 import { NewEpisodeSheet } from "./new-episode-sheet";
 import { EpisodeMenu } from "./episode-menu";
 import { useIllnessEpisode, useResolveEpisode } from "./use-illness";
@@ -66,6 +66,7 @@ export function IllnessEpisodeDetail({ episodeId }: { episodeId: string }) {
   const [logOpen, setLogOpen] = useState(false);
   const [editOpen, setEditOpen] = useState(false);
   const today = todayLocal();
+  const logLastDay = useLastLoggableDay(today, episode?.resolvedAt);
 
   if (isError) {
     return (
@@ -226,7 +227,7 @@ export function IllnessEpisodeDetail({ episodeId }: { episodeId: string }) {
             open={logOpen}
             onOpenChange={setLogOpen}
             episodeId={episode.id}
-            date={today}
+            date={logLastDay}
             onsetDate={episode.onsetAt.slice(0, 10)}
           />
           <NewEpisodeSheet

src/components/illness/illness-view.tsx

@@ -42,7 +42,7 @@ import { cn } from "@/lib/utils";
 import { useTranslations, useFormatters } from "@/lib/i18n/context";
 import { applyOrder, useModuleListPrefs } from "@/lib/module-list-prefs";
 
-import { LogDaySheet } from "./log-day-sheet";
+import { LogDaySheet, useLastLoggableDay } from "./log-day-sheet";
 import { NewEpisodeSheet } from "./new-episode-sheet";
 import { EpisodeMenu } from "./episode-menu";
 import { IllnessInsightsCard } from "./illness-insights-card";
@@ -384,6 +384,7 @@ export function IllnessView() {
   const [logEpisodeId, setLogEpisodeId] = useState<string | null>(null);
 
   const logEpisode = episodes?.find((e) => e.id === logEpisodeId) ?? null;
+  const logLastDay = useLastLoggableDay(today, logEpisode?.resolvedAt);
 
   /**
    * Group the flat list into active / resolved, nesting flares and recurring
@@ -532,7 +533,7 @@ export function IllnessView() {
             if (!open) setLogEpisodeId(null);
           }}
           episodeId={logEpisodeId}
-          date={today}
+          date={logLastDay}
           onsetDate={logEpisode?.onsetAt.slice(0, 10)}
         />
       ) : null}

src/components/illness/log-day-sheet.tsx

@@ -24,7 +24,12 @@ import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
 import { Textarea } from "@/components/ui/textarea";
 import { cn } from "@/lib/utils";
-import { useFormatters, useTranslations } from "@/lib/i18n/context";
+import {
+  useDisplayTimezone,
+  useFormatters,
+  useTranslations,
+} from "@/lib/i18n/context";
+import { userDayKey } from "@/lib/tz/format";
 import { useUnitDisplay } from "@/hooks/use-unit-display";
 
 import { ILLNESS_SYMPTOM_CATALOG } from "./symptom-catalog";
@@ -35,7 +40,11 @@ interface LogDaySheetProps {
   open: boolean;
   onOpenChange: (open: boolean) => void;
   episodeId: string;
-  /** The day to seed the picker with (usually today). */
+  /**
+   * The last day of the episode (`YYYY-MM-DD`): the day the picker opens on
+   * and the latest it offers. Today while the episode runs, its recovery day
+   * once it ended (`useLastLoggableDay`).
+   */
   date: string;
   /**
    * Episode onset day (`YYYY-MM-DD`) — the earliest day the picker allows, so
@@ -45,6 +54,29 @@ interface LogDaySheetProps {
   onsetDate?: string;
 }
 
+/**
+ * The last day a log can belong to: today, or the recovery day when the
+ * episode ended before today. The recovery day is read in the profile zone,
+ * the zone the server reads it in.
+ */
+export function lastLoggableDay(
+  today: string,
+  resolvedAt: string | null | undefined,
+  timeZone: string,
+): string {
+  if (!resolvedAt) return today;
+  const resolvedDay = userDayKey(new Date(resolvedAt), timeZone);
+  return resolvedDay < today ? resolvedDay : today;
+}
+
+/** `lastLoggableDay` in the viewer's profile zone. */
+export function useLastLoggableDay(
+  today: string,
+  resolvedAt: string | null | undefined,
+): string {
+  return lastLoggableDay(today, resolvedAt, useDisplayTimezone());
+}
+
 /** Mini toggle chip — the shared selection vocabulary. */
 function Chip({
   active,
@@ -147,8 +179,8 @@ export function LogDaySheet({
   const { toDisplay, fromDisplay, unitFor } = useUnitDisplay();
   const feverUnit = unitFor("BODY_TEMPERATURE");
 
-  // The day being logged — seeded from `date` (today), but the picker lets the
-  // user backdate within [onset, today] for the retrospective journal.
+  // The day being logged — seeded from `date` (the episode's last day), and
+  // the picker lets the user backdate within [onset, date] for the journal.
   const [selectedDate, setSelectedDate] = useState(date);
   // Re-seed the picker each time the sheet opens (the open transition).
   const [pickerWasOpen, setPickerWasOpen] = useState(false);