fix: preserve draft content when tab is suspended or editor remounts

Gate auto-save on initialization to prevent empty content from overwriting
cached drafts on remount. Flush drafts synchronously on visibilitychange/
pagehide so Chromium tab suspension cannot drop pending debounced saves.
Restore cached draft over saved memo content when they differ (inline editing).

web/src/components/MemoEditor/hooks/useAutoSave.ts

-import { useEffect } from "react";
+import { useEffect, useRef } from "react";
 import { cacheService } from "../services";
 
-export const useAutoSave = (content: string, username: string, cacheKey: string | undefined) => {
+export const useAutoSave = (content: string, username: string, cacheKey: string | undefined, enabled = true) => {
+  const latestContentRef = useRef(content);
+
+  useEffect(() => {
+    latestContentRef.current = content;
+  }, [content]);
+
   useEffect(() => {
+    if (!enabled) return;
+
     const key = cacheService.key(username, cacheKey);
     cacheService.save(key, content);
-  }, [content, username, cacheKey]);
+  }, [content, username, cacheKey, enabled]);
+
+  useEffect(() => {
+    if (!enabled) return;
+
+    const key = cacheService.key(username, cacheKey);
+    const flushDraft = () => {
+      cacheService.saveNow(key, latestContentRef.current);
+    };
+    const handleVisibilityChange = () => {
+      if (document.visibilityState === "hidden") {
+        flushDraft();
+      }
+    };
+
+    window.addEventListener("pagehide", flushDraft);
+    document.addEventListener("visibilitychange", handleVisibilityChange);
+
+    return () => {
+      // Flush on unmount (e.g. editor closes) to ensure the draft is persisted
+      // before the component is torn down — distinct from the visibility flush above.
+      flushDraft();
+      window.removeEventListener("pagehide", flushDraft);
+      document.removeEventListener("visibilitychange", handleVisibilityChange);
+    };
+  }, [username, cacheKey, enabled]);
 };

web/src/components/MemoEditor/hooks/useMemoInit.ts

-import { useEffect, useRef } from "react";
+import { useEffect, useRef, useState } from "react";
 import type { Memo, Visibility } from "@/types/proto/api/v1/memo_service_pb";
 import type { EditorRefActions } from "../Editor";
 import { cacheService, memoService } from "../services";
@@ -16,15 +16,25 @@ interface UseMemoInitOptions {
 export const useMemoInit = ({ editorRef, memo, cacheKey, username, autoFocus, defaultVisibility }: UseMemoInitOptions) => {
   const { actions, dispatch } = useEditorContext();
   const initializedRef = useRef(false);
+  const [isInitialized, setIsInitialized] = useState(false);
 
   useEffect(() => {
     if (initializedRef.current) return;
     initializedRef.current = true;
+    const key = cacheService.key(username, cacheKey);
+    const cachedContent = cacheService.load(key);
 
     if (memo) {
-      dispatch(actions.initMemo(memoService.fromMemo(memo)));
+      const initialState = memoService.fromMemo(memo);
+      // Prefer cached draft over the saved memo content when the user had unsaved
+      // changes (e.g. tab was suspended mid-edit). Uses strict string comparison
+      // against memo.content — both values come from the same proto serialization
+      // path, so format is consistent and whitespace differences are intentional.
+      if (cachedContent.trim() && cachedContent !== memo.content) {
+        initialState.content = cachedContent;
+      }
+      dispatch(actions.initMemo(initialState));
     } else {
-      const cachedContent = cacheService.load(cacheService.key(username, cacheKey));
       if (cachedContent) {
         dispatch(actions.updateContent(cachedContent));
       }
@@ -36,5 +46,9 @@ export const useMemoInit = ({ editorRef, memo, cacheKey, username, autoFocus, de
     if (autoFocus) {
       setTimeout(() => editorRef.current?.focus(), 100);
     }
+
+    setIsInitialized(true);
   }, [memo, cacheKey, username, autoFocus, defaultVisibility, actions, dispatch, editorRef]);
+
+  return { isInitialized };
 };

web/src/components/MemoEditor/index.tsx

@@ -54,10 +54,10 @@ const MemoEditorImpl: React.FC<MemoEditorProps> = ({
   // Get default visibility from user settings
   const defaultVisibility = userGeneralSetting?.memoVisibility ? convertVisibilityFromString(userGeneralSetting.memoVisibility) : undefined;
 
-  useMemoInit({ editorRef, memo, cacheKey, username: currentUser?.name ?? "", autoFocus, defaultVisibility });
+  const { isInitialized } = useMemoInit({ editorRef, memo, cacheKey, username: currentUser?.name ?? "", autoFocus, defaultVisibility });
 
   // Auto-save content to localStorage
-  useAutoSave(state.content, currentUser?.name ?? "", cacheKey);
+  useAutoSave(state.content, currentUser?.name ?? "", cacheKey, isInitialized);
 
   // Focus mode management with body scroll lock
   useFocusMode(state.ui.isFocusMode);

web/src/components/MemoEditor/services/cacheService.ts

@@ -26,6 +26,20 @@ export const cacheService = {
     pendingSaves.set(key, timeoutId);
   },
 
+  saveNow: (key: string, content: string) => {
+    const pendingSave = pendingSaves.get(key);
+    if (pendingSave) {
+      window.clearTimeout(pendingSave);
+      pendingSaves.delete(key);
+    }
+
+    if (content.trim()) {
+      localStorage.setItem(key, content);
+    } else {
+      localStorage.removeItem(key);
+    }
+  },
+
   load(key: string): string {
     return localStorage.getItem(key) || "";
   },