fix(web): resolve tag sidebar filtering and reactivity issues

This fixes multiple issues with the tag sidebar and activity calendar:

1. Tag disappearing bug: When filtering by a tag, the sidebar now shows all tags instead of only the selected tag
2. Activity calendar filtering: Calendar now shows full activity history instead of filtered results
3. Auto-update on memo changes: Sidebar tags and calendar now update automatically when creating/editing memos without requiring manual page refresh

Technical changes:
- Modified useFilteredMemoStats to fetch unfiltered UserStats from backend API for Home/Profile pages
- Fixed key mismatch bug in userStore where stats were stored with inconsistent keys
- Added statsStateId update in fetchUserStats to trigger reactivity
- Updated MainLayout to pass appropriate userName based on page context
- Archived/Explore pages continue to compute from cached memos (correct behavior)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

web/src/hooks/useFilteredMemoStats.ts

@@ -1,7 +1,7 @@
 import dayjs from "dayjs";
 import { countBy } from "lodash-es";
 import { useEffect, useState } from "react";
-import { memoStore } from "@/store";
+import { memoStore, userStore } from "@/store";
 import type { StatisticsData } from "@/types/statistics";
 
 export interface FilteredMemoStats {
@@ -11,20 +11,51 @@ export interface FilteredMemoStats {
 }
 
 /**
- * Hook to compute statistics and tags from memos in the store cache.
- *
- * This provides a unified approach for all pages (Home, Explore, Archived, Profile):
- * - Uses memos already loaded in the store by PagedMemoList
- * - Computes statistics and tags from those cached memos
- * - Updates automatically when memos are created, updated, or deleted
- * - No separate API call needed, reducing network overhead
- *
- * @returns Object with statistics data, tag counts, and loading state
- *
- * Note: This hook now computes stats from the memo store cache rather than
- * making a separate API call. It relies on PagedMemoList to populate the store.
+ * Convert user name to user stats key.
+ * Backend returns UserStats with name "users/{id}/stats" but we pass "users/{id}"
+ * @param userName - User name in format "users/{id}"
+ * @returns Stats key in format "users/{id}/stats"
  */
-export const useFilteredMemoStats = (): FilteredMemoStats => {
+const getUserStatsKey = (userName: string): string => {
+  return `${userName}/stats`;
+};
+
+export interface UseFilteredMemoStatsOptions {
+  /**
+   * User name to fetch stats for (e.g., "users/123")
+   *
+   * When provided:
+   * - Fetches backend user stats via GetUserStats API
+   * - Returns unfiltered tags and activity (all NORMAL memos for that user)
+   * - Tags remain stable even when memo filters are applied
+   *
+   * When undefined:
+   * - Computes stats from cached memos in the store
+   * - Reflects current filters (useful for Explore/Archived pages)
+   *
+   * IMPORTANT: Backend user stats only include NORMAL (non-archived) memos.
+   * Do NOT use for Archived page context.
+   */
+  userName?: string;
+}
+
+/**
+ * Hook to compute statistics and tags for the sidebar.
+ *
+ * Data sources by context:
+ * - **Home/Profile**: Uses backend UserStats API (unfiltered, normal memos only)
+ * - **Archived/Explore**: Computes from cached memos (filtered by page context)
+ *
+ * Benefits of using backend stats:
+ * - Tag list remains stable when memo filters are applied
+ * - Activity calendar shows full history, not just filtered results
+ * - Prevents "disappearing tags" issue when filtering by tag
+ *
+ * @param options - Configuration options
+ * @returns Object with statistics data, tag counts, and loading state
+ */
+export const useFilteredMemoStats = (options: UseFilteredMemoStatsOptions = {}): FilteredMemoStats => {
+  const { userName } = options;
   const [data, setData] = useState<FilteredMemoStats>({
     statistics: {
       activityStats: {},
@@ -34,33 +65,65 @@ export const useFilteredMemoStats = (): FilteredMemoStats => {
   });
   // React to memo store changes (create, update, delete)
   const memoStoreStateId = memoStore.state.stateId;
+  // React to user stats changes (for tag counts)
+  const userStatsStateId = userStore.state.statsStateId;
 
   useEffect(() => {
-    // Compute statistics and tags from memos already in the store
-    // This avoids making a separate API call and relies on PagedMemoList to populate the store
-    const computeStatsFromCache = () => {
-      const displayTimeList: Date[] = [];
-      const tagCount: Record<string, number> = {};
+    const computeStats = async () => {
+      let activityStats: Record<string, number> = {};
+      let tagCount: Record<string, number> = {};
+      let useBackendStats = false;
 
-      // Use memos already loaded in the store
-      const memos = memoStore.state.memos;
+      // Try to use backend user stats if userName is provided
+      if (userName) {
+        // Check if stats are already cached, otherwise fetch them
+        const statsKey = getUserStatsKey(userName);
+        let userStats = userStore.state.userStatsByName[statsKey];
 
-      for (const memo of memos) {
-        // Add display time for calendar
-        if (memo.displayTime) {
-          displayTimeList.push(memo.displayTime);
+        if (!userStats) {
+          try {
+            await userStore.fetchUserStats(userName);
+            userStats = userStore.state.userStatsByName[statsKey];
+          } catch (error) {
+            console.error("Failed to fetch user stats:", error);
+            // Will fall back to computing from cache below
+          }
         }
 
-        // Count tags
-        if (memo.tags && memo.tags.length > 0) {
-          for (const tag of memo.tags) {
-            tagCount[tag] = (tagCount[tag] || 0) + 1;
+        if (userStats) {
+          // Use activity timestamps from user stats
+          if (userStats.memoDisplayTimestamps && userStats.memoDisplayTimestamps.length > 0) {
+            activityStats = countBy(userStats.memoDisplayTimestamps.map((date) => dayjs(date).format("YYYY-MM-DD")));
           }
+          // Use tag counts from user stats
+          if (userStats.tagCount) {
+            tagCount = userStats.tagCount;
+          }
+          useBackendStats = true;
         }
       }
 
-      // Compute activity calendar data
-      const activityStats = countBy(displayTimeList.map((date) => dayjs(date).format("YYYY-MM-DD")));
+      // Fallback: compute from cached memos if backend stats not available
+      // Also used for Explore and Archived contexts
+      if (!useBackendStats) {
+        const displayTimeList: Date[] = [];
+        const memos = memoStore.state.memos;
+
+        for (const memo of memos) {
+          // Collect display timestamps for activity calendar
+          if (memo.displayTime) {
+            displayTimeList.push(memo.displayTime);
+          }
+          // Count tags
+          if (memo.tags && memo.tags.length > 0) {
+            for (const tag of memo.tags) {
+              tagCount[tag] = (tagCount[tag] || 0) + 1;
+            }
+          }
+        }
+
+        activityStats = countBy(displayTimeList.map((date) => dayjs(date).format("YYYY-MM-DD")));
+      }
 
       setData({
         statistics: { activityStats },
@@ -69,8 +132,8 @@ export const useFilteredMemoStats = (): FilteredMemoStats => {
       });
     };
 
-    computeStatsFromCache();
-  }, [memoStoreStateId]);
+    computeStats();
+  }, [memoStoreStateId, userStatsStateId, userName]);
 
   return data;
 };

web/src/layouts/MainLayout.tsx

@@ -1,17 +1,21 @@
 import { observer } from "mobx-react-lite";
-import { useMemo } from "react";
+import { useEffect, useMemo, useState } from "react";
 import { matchPath, Outlet, useLocation } from "react-router-dom";
 import type { MemoExplorerContext } from "@/components/MemoExplorer";
 import { MemoExplorer, MemoExplorerDrawer } from "@/components/MemoExplorer";
 import MobileHeader from "@/components/MobileHeader";
+import useCurrentUser from "@/hooks/useCurrentUser";
 import { useFilteredMemoStats } from "@/hooks/useFilteredMemoStats";
 import useResponsiveWidth from "@/hooks/useResponsiveWidth";
 import { cn } from "@/lib/utils";
 import { Routes } from "@/router";
+import { userStore } from "@/store";
 
 const MainLayout = observer(() => {
   const { md, lg } = useResponsiveWidth();
   const location = useLocation();
+  const currentUser = useCurrentUser();
+  const [profileUserName, setProfileUserName] = useState<string | undefined>();
 
   // Determine context based on current route
   const context: MemoExplorerContext = useMemo(() => {
@@ -22,8 +26,46 @@ const MainLayout = observer(() => {
     return "home"; // fallback
   }, [location.pathname]);
 
+  // Extract username from URL for profile context
+  useEffect(() => {
+    const match = matchPath("/u/:username", location.pathname);
+    if (match && context === "profile") {
+      const username = match.params.username;
+      if (username) {
+        // Fetch or get user to obtain user name (e.g., "users/123")
+        // Note: User stats will be fetched by useFilteredMemoStats
+        userStore
+          .getOrFetchUserByUsername(username)
+          .then((user) => {
+            setProfileUserName(user.name);
+          })
+          .catch((error) => {
+            console.error("Failed to fetch profile user:", error);
+            setProfileUserName(undefined);
+          });
+      }
+    } else {
+      setProfileUserName(undefined);
+    }
+  }, [location.pathname, context]);
+
+  // Determine which user name to use for stats
+  // - home: current user (uses backend user stats for normal memos)
+  // - profile: viewed user (uses backend user stats for normal memos)
+  // - archived: undefined (compute from cached archived memos, since user stats only includes normal memos)
+  // - explore: undefined (compute from cached memos)
+  const statsUserName = useMemo(() => {
+    if (context === "home") {
+      return currentUser?.name;
+    } else if (context === "profile") {
+      return profileUserName;
+    }
+    return undefined; // archived and explore contexts compute from cache
+  }, [context, currentUser, profileUserName]);
+
   // Fetch stats from memo store cache (populated by PagedMemoList)
-  const { statistics, tags } = useFilteredMemoStats();
+  // For user-scoped contexts, use backend user stats for tags (unaffected by filters)
+  const { statistics, tags } = useFilteredMemoStats({ userName: statsUserName });
 
   return (
     <section className="@container w-full min-h-full flex flex-col justify-start items-center">

web/src/store/user.ts

@@ -52,7 +52,8 @@ class LocalState {
     if (!this.currentUser) {
       return undefined;
     }
-    return this.userStatsByName[this.currentUser];
+    // Backend returns stats with key "users/{id}/stats"
+    return this.userStatsByName[`${this.currentUser}/stats`];
   }
 
   constructor() {
@@ -267,13 +268,14 @@ const userStore = (() => {
           }
         } else {
           const userStats = await userServiceClient.getUserStats({ name: user });
-          userStatsByName[user] = userStats;
+          userStatsByName[userStats.name] = userStats; // Use userStats.name as key for consistency
         }
         state.setPartial({
           userStatsByName: {
             ...state.userStatsByName,
             ...userStatsByName,
           },
+          statsStateId: uniqueId(), // Update state ID to trigger reactivity
         });
       } catch (error) {
         throw StoreError.wrap("FETCH_USER_STATS_FAILED", error);