diff --git a/src/modules/knowledge-items/knowledge-items.repository.ts b/src/modules/knowledge-items/knowledge-items.repository.ts
index f799783..fb78bb8 100644
--- a/src/modules/knowledge-items/knowledge-items.repository.ts
+++ b/src/modules/knowledge-items/knowledge-items.repository.ts
@@ -24,7 +24,7 @@ function detectSourceType(content?: string | null, title?: string): string | nul
   if (content.trimStart().startsWith('<')) return 'html';
 
   // Markdown patterns
-  if (/^#{1,6}\s/.test(content) || /^[-*]\s/.test(content) || /\[.+\]\(.+\)/.test(content)) {
+  if (/^#{1,6}\s/.test(content) || /^[-*]\s/.test(content) || /\[.+?\]\(.+?\)/.test(content)) {
     return 'markdown';
   }
 
@@ -84,7 +84,8 @@ export class KnowledgeItemsRepository {
   }
 
   async findByKnowledgeBaseId(knowledgeBaseId: string, opts?: { sortBy?: string; order?: string }) {
-    const sortBy = opts?.sortBy ?? 'default';
+    const validSortBy = ['createdAt', 'updatedAt', 'fileSize', 'default'];
+    const sortBy = (opts?.sortBy && validSortBy.includes(opts.sortBy)) ? opts.sortBy : 'default';
     const order = opts?.order === 'asc' ? 'asc' : 'desc';
 
     let orderBy: any;
diff --git a/src/modules/knowledge-items/knowledge-items.service.ts b/src/modules/knowledge-items/knowledge-items.service.ts
index 21cf44d..691e428 100644
--- a/src/modules/knowledge-items/knowledge-items.service.ts
+++ b/src/modules/knowledge-items/knowledge-items.service.ts
@@ -1,10 +1,12 @@
-import { Injectable, NotFoundException, ForbiddenException, BadRequestException } from '@nestjs/common';
+import { Injectable, NotFoundException, ForbiddenException, BadRequestException, Logger } from '@nestjs/common';
 import { KnowledgeItemsRepository } from './knowledge-items.repository';
 import { StorageService } from '../../infrastructure/storage/storage.service';
 import { CosStorageProvider } from '../../infrastructure/storage/cos-storage.provider';
 
 @Injectable()
 export class KnowledgeItemsService {
+  private readonly logger = new Logger(KnowledgeItemsService.name);
+
   constructor(
     private readonly repository: KnowledgeItemsRepository,
     private readonly storage: StorageService,
@@ -49,8 +51,8 @@ export class KnowledgeItemsService {
         enriched.fileSize = Number(headInfo.size);
       }
       return enriched;
-    } catch {
-      // If URL parsing fails, return original item unchanged
+    } catch (err) {
+      this.logger.warn(`enrichItem failed for item, returning original: ${(err as Error)?.message}`);
     }
     return item;
   }
diff --git a/src/modules/learning-activity/learning-activity.service.ts b/src/modules/learning-activity/learning-activity.service.ts
index f927180..b3c3729 100644
--- a/src/modules/learning-activity/learning-activity.service.ts
+++ b/src/modules/learning-activity/learning-activity.service.ts
@@ -89,7 +89,18 @@ export class LearningActivityService {
       } : undefined,
     };
 
-    const aiResult = await this.trendWorkflow.execute(trendInput);
+    // AI analysis with 15s timeout fallback
+    let aiResult: any = {};
+    try {
+      aiResult = await Promise.race([
+        this.trendWorkflow.execute(trendInput),
+        new Promise<any>((_, reject) =>
+          setTimeout(() => reject(new Error('AI trend analysis timeout')), 15000)
+        ),
+      ]);
+    } catch (err) {
+      aiResult = { periodSummary: 'AI 分析暂不可用', overallScore: 0, overallDirection: 'stable', trends: [], strengths: [], weaknesses: [], recommendations: [], nextFocusAreas: [] };
+    }
     return { ...aiResult, dailySeries };
   }
 
@@ -99,10 +110,12 @@ export class LearningActivityService {
     for (let i = days - 1; i >= 0; i--) {
       const d = new Date(now);
       d.setDate(d.getDate() - i);
-      const dateStr = d.toISOString().split('T')[0];
+      // Use local date string to avoid UTC timezone shift issues
+      const dateStr = `${d.getFullYear()}-${String(d.getMonth() + 1).padStart(2, '0')}-${String(d.getDate()).padStart(2, '0')}`;
       const dayActs = activities.filter((a) => {
         const ad = a.activityDate instanceof Date ? a.activityDate : new Date(a.activityDate);
-        return ad.toISOString().split('T')[0] === dateStr;
+        const adStr = `${ad.getFullYear()}-${String(ad.getMonth() + 1).padStart(2, '0')}-${String(ad.getDate()).padStart(2, '0')}`;
+        return adStr === dateStr;
       });
       const minutes = Math.round(dayActs.reduce((s: number, a: any) => s + a.durationSeconds, 0) / 60);
       series.push({