diff --git a/apps/web/src/app/api/agents/actions/route.ts b/apps/web/src/app/api/agents/actions/route.ts
index ddcdbf1d0..4d12daeca 100644
--- a/apps/web/src/app/api/agents/actions/route.ts
+++ b/apps/web/src/app/api/agents/actions/route.ts
@@ -1,4 +1,5 @@
 import { NextResponse } from 'next/server';
+import { formatApiError } from '@/lib/error-handling';
 import { runActionAgent } from '@/lib/action-agent';
 import { AVAILABLE_TOOL_NAMES } from '@/lib/action-agent';
 import { hasGeminiKey } from '@/lib/gemini-client';
@@ -56,7 +57,7 @@ export async function POST(request: Request): Promise<NextResponse> {
     });
   } catch (error) {
     console.error('Action agent error:', error);
-    const message = error instanceof Error ? error.message : String(error);
+    const message = formatApiError(error).message;
 
     // Only the agent's own validation/config guards are client errors (400).
     // Match exact phrases so an upstream provider error that merely mentions
diff --git a/apps/web/src/app/api/extract-events/route.ts b/apps/web/src/app/api/extract-events/route.ts
index 8eb8f8b56..7bba4386d 100644
--- a/apps/web/src/app/api/extract-events/route.ts
+++ b/apps/web/src/app/api/extract-events/route.ts
@@ -1,4 +1,5 @@
 import OpenAI from 'openai';
+import { formatApiError } from '@/lib/error-handling';
 import { Type } from '@google/genai';
 import { NextResponse } from 'next/server';
 import { getGeminiClient, hasGeminiKey } from '@/lib/gemini-client';
@@ -255,7 +256,7 @@ Respond with ONLY valid JSON matching the required structure.`;
     return NextResponse.json({ success: true, provider, data: parsed });
   } catch (error) {
     console.error('Event extraction error:', error);
-    const message = error instanceof Error ? error.message : String(error);
+    const message = formatApiError(error).message;
 
     return NextResponse.json({
       success: false,
diff --git a/apps/web/src/app/api/jobs/[jobId]/route.ts b/apps/web/src/app/api/jobs/[jobId]/route.ts
index c9da65176..adfd0eb28 100644
--- a/apps/web/src/app/api/jobs/[jobId]/route.ts
+++ b/apps/web/src/app/api/jobs/[jobId]/route.ts
@@ -1,4 +1,5 @@
 import { NextResponse } from 'next/server';
+import { formatApiError } from '@/lib/error-handling';
 import { backendHeaders } from '@/lib/pipeline-backend';
 
 const rawBackendUrl = process.env.BACKEND_URL || '';
@@ -39,8 +40,8 @@ export async function GET(
     });
   } catch (error) {
     return NextResponse.json(
-      { error: error instanceof Error ? error.message : String(error) },
+      { error: formatApiError(error).message },
       { status: 502 },
     );
   }
-}
\ No newline at end of file
+}
diff --git a/apps/web/src/app/api/search/route.ts b/apps/web/src/app/api/search/route.ts
index 96d40b62d..0ce7646e7 100644
--- a/apps/web/src/app/api/search/route.ts
+++ b/apps/web/src/app/api/search/route.ts
@@ -1,4 +1,5 @@
 import { NextRequest, NextResponse } from 'next/server';
+import { formatApiError } from '@/lib/error-handling';
 import { getSearchIndex, resolveSearchIndexName } from '@/lib/upstash-search';
 import type { SearchDocument } from '@/lib/upstash-search';
 
@@ -44,7 +45,7 @@ export async function POST(req: NextRequest) {
   } catch (error) {
     console.error('Upstash search error:', error);
     return NextResponse.json(
-      { error: 'search_failed', detail: error instanceof Error ? error.message : String(error) },
+      { error: 'search_failed', detail: formatApiError(error).message },
       { status: 502 },
     );
   }
@@ -108,7 +109,7 @@ export async function PUT(req: NextRequest) {
   } catch (error) {
     console.error('Upstash upsert error:', error);
     return NextResponse.json(
-      { error: 'upsert_failed', detail: error instanceof Error ? error.message : String(error) },
+      { error: 'upsert_failed', detail: formatApiError(error).message },
       { status: 502 },
     );
   }
diff --git a/apps/web/src/lib/gemini-client.ts b/apps/web/src/lib/gemini-client.ts
index 61c977abc..8fc5f31df 100644
--- a/apps/web/src/lib/gemini-client.ts
+++ b/apps/web/src/lib/gemini-client.ts
@@ -1,4 +1,5 @@
 import 'server-only';
+import { formatApiError } from '@/lib/error-handling';
 
 /**
  * Shared Gemini/Google AI client factory.
@@ -97,7 +98,7 @@ export function getGeminiRoutingLabel(): string {
  * Map provider errors to stable codes for API responses and logs.
  */
 export function classifyGeminiError(error: unknown): ClassifiedGeminiError {
-  const message = error instanceof Error ? error.message : String(error);
+  const message = formatApiError(error).message;
 
   if (message.includes('BILLING_DISABLED')) {
     return {
@@ -170,4 +171,4 @@ export function getGeminiClient(): GoogleGenAI {
     _lastMode = mode;
   }
   return _gemini;
-}
\ No newline at end of file
+}
diff --git a/apps/web/src/lib/gemini-video-analyzer.ts b/apps/web/src/lib/gemini-video-analyzer.ts
index cfdb2746f..4744b322d 100644
--- a/apps/web/src/lib/gemini-video-analyzer.ts
+++ b/apps/web/src/lib/gemini-video-analyzer.ts
@@ -1,4 +1,5 @@
 import 'server-only';
+import { formatApiError } from '@/lib/error-handling';
 
 /**
  * Agentic Video Intelligence Engine — Gemini + Google Search grounding.
@@ -297,7 +298,7 @@ export async function analyzeVideoWithGemini(
       const resultText = response.text || '{}';
       return parseAnalysisResult(resultText);
     } catch (error: unknown) {
-      const errorMessage = error instanceof Error ? error.message : String(error);
+      const errorMessage = formatApiError(error).message;
       const retryable =
         error instanceof AnalysisParseError ||
         errorMessage.includes('503') ||
diff --git a/apps/web/src/lib/pipeline-backend-health.ts b/apps/web/src/lib/pipeline-backend-health.ts
index cfd4aa42d..113e4e43a 100644
--- a/apps/web/src/lib/pipeline-backend-health.ts
+++ b/apps/web/src/lib/pipeline-backend-health.ts
@@ -1,4 +1,5 @@
 import 'server-only';
+import { formatApiError } from '@/lib/error-handling';
 
 import { backendHeaders } from '@/lib/pipeline-backend';
 
@@ -63,7 +64,7 @@ export async function checkBackendHealth(
       configured: true,
       available: false,
       host: backendHost(url),
-      reason: error instanceof Error ? error.message : String(error),
+      reason: formatApiError(error).message,
     };
   }
 }
@@ -80,4 +81,4 @@ export async function parseBackendJson<T>(response: Response): Promise<T | null>
   } catch {
     return null;
   }
-}
\ No newline at end of file
+}
diff --git a/apps/web/src/lib/transcription-service-improved.ts b/apps/web/src/lib/transcription-service-improved.ts
index 0b933df37..7b29f0fee 100644
--- a/apps/web/src/lib/transcription-service-improved.ts
+++ b/apps/web/src/lib/transcription-service-improved.ts
@@ -1,4 +1,5 @@
 import 'server-only';
+import { formatApiError } from '@/lib/error-handling';
 
 import OpenAI from 'openai';
 import { fetchYouTubeMetadata, formatMetadataAsContext } from '@/lib/youtube-metadata';
@@ -125,7 +126,7 @@ export async function fetchTranscript({
     } catch (error) {
       console.warn(
         'Backend transcript unavailable:',
-        error instanceof Error ? error.message : String(error)
+        formatApiError(error).message
       );
       // Continue to fallback strategies
     }
@@ -143,7 +144,7 @@ export async function fetchTranscript({
     } catch (error) {
       console.warn(
         'YouTube metadata fetch failed:',
-        error instanceof Error ? error.message : String(error)
+        formatApiError(error).message
       );
       // Continue without metadata
     }
@@ -207,7 +208,7 @@ INSTRUCTIONS:
         };
       }
     } catch (error) {
-      const errorMsg = error instanceof Error ? error.message : String(error);
+      const errorMsg = formatApiError(error).message;
       console.warn('Gemini transcription failed:', errorMsg);
 
       // Handle specific errors
@@ -262,7 +263,7 @@ Be thorough — capture all key points, quotes, technical details, and chapter b
         };
       }
     } catch (error) {
-      const errorMsg = error instanceof Error ? error.message : String(error);
+      const errorMsg = formatApiError(error).message;
       console.warn('OpenAI transcription failed:', errorMsg);
 
       if (errorMsg.includes('429')) {