diff --git a/app/desktop/src/platform/useDesktopEdgeEvents.ts b/app/desktop/src/platform/useDesktopEdgeEvents.ts
index a27e8a46f..d5f58fec7 100644
--- a/app/desktop/src/platform/useDesktopEdgeEvents.ts
+++ b/app/desktop/src/platform/useDesktopEdgeEvents.ts
@@ -1,5 +1,6 @@
 import { useEffect, useMemo, useRef, useState } from 'react';
 import { normalizeEdgeEventsToTranscript } from '@shared/transcript';
+import { eventRunId } from '@shared/transcript/edgeEventEvidence';
 import { getAgentActivityStore, type AgentActivityStatus } from '@shared/transcript/agentActivity';
 import type { EventEnvelope } from '@shared/events';
 import type { TranscriptBlock } from '@shared/transcript';
@@ -170,10 +171,6 @@ function eventThreadId(event: EventEnvelope): string | undefined {
   return stringField(event.payload.threadId) ?? stringField(event.scope.threadId);
 }
 
-function eventRunId(event: EventEnvelope): string | undefined {
-  return stringField(event.payload.runId) ?? stringField(event.scope.runId);
-}
-
 function eventTimestampMs(event: EventEnvelope): number {
   const parsed = Date.parse(event.sentAt);
   return Number.isFinite(parsed) ? parsed : Number.POSITIVE_INFINITY;
diff --git a/app/desktop/src/platform/useDesktopWorkbenchModel.ts b/app/desktop/src/platform/useDesktopWorkbenchModel.ts
index d208be93d..19a18682b 100644
--- a/app/desktop/src/platform/useDesktopWorkbenchModel.ts
+++ b/app/desktop/src/platform/useDesktopWorkbenchModel.ts
@@ -9,6 +9,7 @@ import {
   type WorkbenchDataMode,
 } from '@shared/demo';
 import { normalizeThreadItemsToTranscript } from '@shared/transcript';
+import { errorMessage } from '@shared/errors';
 import { appDateLocaleTag } from '@shared/i18n/locale';
 import type { TFunction } from 'i18next';
 import { getI18n } from 'react-i18next';
@@ -613,9 +614,3 @@ function workspaceProjectToProjectInfo(
     feed: [],
   };
 }
-
-function errorMessage(error: unknown, fallback: string): string {
-  if (error instanceof Error && error.message.trim()) return error.message;
-  if (typeof error === 'string' && error.trim()) return error;
-  return fallback;
-}
diff --git a/app/shared/src/errors.test.ts b/app/shared/src/errors.test.ts
index 0bfed5232..f94a49cc3 100644
--- a/app/shared/src/errors.test.ts
+++ b/app/shared/src/errors.test.ts
@@ -1,12 +1,31 @@
 import { describe, expect, it } from 'vitest';
 import {
   AppError,
+  errorMessage,
   isErrorResponse,
   isTurnInProgressError,
   parseError,
   type ErrorBody,
 } from './errors';
 
+describe('errorMessage', () => {
+  it('prefers Error.message', () => {
+    expect(errorMessage(new Error('boom'), 'fallback')).toBe('boom');
+  });
+
+  it('keeps a non-blank thrown string', () => {
+    expect(errorMessage('plain failure', 'fallback')).toBe('plain failure');
+  });
+
+  it('falls back for blank, non-Error and empty values', () => {
+    expect(errorMessage('', 'fallback')).toBe('fallback');
+    expect(errorMessage('   ', 'fallback')).toBe('fallback');
+    expect(errorMessage(new Error('  '), 'fallback')).toBe('fallback');
+    expect(errorMessage({ message: 'nope' }, 'fallback')).toBe('fallback');
+    expect(errorMessage(undefined, 'fallback')).toBe('fallback');
+  });
+});
+
 describe('isTurnInProgressError', () => {
   const turnBody: ErrorBody = {
     error: { code: 'turn_in_progress', message: 'agent instance already has an active task' },
diff --git a/app/shared/src/errors.ts b/app/shared/src/errors.ts
index 6f7258a65..161291958 100644
--- a/app/shared/src/errors.ts
+++ b/app/shared/src/errors.ts
@@ -61,6 +61,20 @@ export function isTurnInProgressError(error: unknown): boolean {
   return error instanceof AppError && error.status === 409 && error.code === 'turn_in_progress';
 }
 
+/**
+ * Best-effort user-facing message for a caught value.
+ *
+ * Every platform had its own copy of this and one of them silently dropped the
+ * `string` case, so a thrown string surfaced as the generic fallback. This is
+ * the single definition: `Error.message`, then a non-blank thrown string, then
+ * the caller's fallback.
+ */
+export function errorMessage(error: unknown, fallback: string): string {
+  if (error instanceof Error && error.message.trim()) return error.message;
+  if (typeof error === 'string' && error.trim()) return error;
+  return fallback;
+}
+
 export async function parseError(response: Response): Promise<AppError> {
   try {
     const body = await response.json();
diff --git a/app/web/src/App.tsx b/app/web/src/App.tsx
index 4851e9858..309d98c48 100644
--- a/app/web/src/App.tsx
+++ b/app/web/src/App.tsx
@@ -3,6 +3,7 @@ import { useCallback, useMemo, useState, useSyncExternalStore } from 'react';
 import { useTranslation } from 'react-i18next';
 import { AgentHubWorkbench } from '@agenthub/workbench';
 import { fetchAllPages } from '@shared/hub/paginate';
+import { errorMessage } from '@shared/errors';
 import { webQueryKeys } from '@shared/stores/queryKeys';
 import { CHATVIEW_I18N_NAMESPACE } from '@shared/chatview/i18n/resources';
 import type { AgentConfig, ContactMember, ProjectDraft, ProjectInfo, SkillMarketItem, MCPMarketItem } from '@agenthub/workbench';
@@ -421,11 +422,6 @@ function WebWorkbenchRoot() {
   );
 }
 
-function errorMessage(error: unknown, fallback: string): string {
-  if (error instanceof Error && error.message.trim()) return error.message;
-  return fallback;
-}
-
 function normalizeHubSkillToMarketItem(raw: Record<string, unknown>): SkillMarketItem {
   const item: SkillMarketItem = {
     id: String(raw.id ?? ''),
diff --git a/app/web/src/platform/useWebWorkbenchModel.test.ts b/app/web/src/platform/useWebWorkbenchModel.test.ts
index 5fb6b9109..f3cda392b 100644
--- a/app/web/src/platform/useWebWorkbenchModel.test.ts
+++ b/app/web/src/platform/useWebWorkbenchModel.test.ts
@@ -27,16 +27,6 @@ import {
   useWebSessionAutoMarkRead,
 } from './useWebWorkbenchModel';
 import { webTranscript } from './webPlatform';
-import { errorMessage } from './webWorkbenchError';
-
-describe('webWorkbenchError', () => {
-  it('prefers Error.message, then string, then fallback', () => {
-    expect(errorMessage(new Error('boom'), 'fallback')).toBe('boom');
-    expect(errorMessage('  string-error  ', 'fallback')).toBe('  string-error  ');
-    expect(errorMessage(null, 'fallback')).toBe('fallback');
-    expect(errorMessage(new Error('   '), 'fallback')).toBe('fallback');
-  });
-});
 
 describe('useWebWorkbenchModel helpers', () => {
   it('maps Hub contacts into shared workbench contacts', () => {
diff --git a/app/web/src/platform/useWebWorkbenchModel.ts b/app/web/src/platform/useWebWorkbenchModel.ts
index 672333249..2c910e419 100644
--- a/app/web/src/platform/useWebWorkbenchModel.ts
+++ b/app/web/src/platform/useWebWorkbenchModel.ts
@@ -88,7 +88,7 @@ import {
   resolveWebTranscriptMessages,
   resolveWebWorkbenchTranscript,
 } from './webWorkbenchTranscript';
-import { errorMessage } from './webWorkbenchError';
+import { errorMessage } from '@shared/errors';
 
 const hubClient = createHubClient({ getToken: getAccessToken });
 
diff --git a/app/web/src/platform/webWorkbenchError.ts b/app/web/src/platform/webWorkbenchError.ts
deleted file mode 100644
index 330bad225..000000000
--- a/app/web/src/platform/webWorkbenchError.ts
+++ /dev/null
@@ -1,5 +0,0 @@
-export function errorMessage(error: unknown, fallback: string): string {
-  if (error instanceof Error && error.message.trim()) return error.message;
-  if (typeof error === 'string' && error.trim()) return error;
-  return fallback;
-}
diff --git a/app/web/src/platform/webWorkbenchExecutionTargets.ts b/app/web/src/platform/webWorkbenchExecutionTargets.ts
index 98b55f38a..2c52259df 100644
--- a/app/web/src/platform/webWorkbenchExecutionTargets.ts
+++ b/app/web/src/platform/webWorkbenchExecutionTargets.ts
@@ -2,7 +2,7 @@ import type { WorkbenchDataMode } from '@shared/demo';
 import { isWorkbenchRealDataMode } from '@shared/demo';
 import type { TranscriptBlock } from '@shared/transcript';
 import type { ExecutionTargetInventoryItem } from '@/api/executionTargetQueries';
-import { errorMessage } from './webWorkbenchError';
+import { errorMessage } from '@shared/errors';
 
 export type WebExecutionTargetStatusState =
   | 'hidden'
diff --git a/app/web/src/platform/webWorkbenchHelpers.test.ts b/app/web/src/platform/webWorkbenchHelpers.test.ts
index 305ec908a..405f52fab 100644
--- a/app/web/src/platform/webWorkbenchHelpers.test.ts
+++ b/app/web/src/platform/webWorkbenchHelpers.test.ts
@@ -1,14 +1,8 @@
 import { describe, expect, it } from 'vitest';
-import { errorMessage } from './webWorkbenchError';
 import { projectDraftToHubRequest } from './webWorkbenchProjects';
 import { executionTargetLabel, resolveWebExecutionTargetStatus } from './webWorkbenchExecutionTargets';
 
 describe('webWorkbench helper seam', () => {
-  it('errorMessage covers non-Error objects', () => {
-    expect(errorMessage({ message: 'nope' }, 'fallback')).toBe('fallback');
-    expect(errorMessage('', 'fallback')).toBe('fallback');
-  });
-
   it('projectDraftToHubRequest falls back to default name', () => {
     expect(projectDraftToHubRequest({ name: '   ', description: 'x' })).toEqual({
       name: '未命名项目',
diff --git a/app/web/src/platform/webWorkbenchProjects.ts b/app/web/src/platform/webWorkbenchProjects.ts
index dcbe33af9..a59e69c0d 100644
--- a/app/web/src/platform/webWorkbenchProjects.ts
+++ b/app/web/src/platform/webWorkbenchProjects.ts
@@ -10,7 +10,7 @@ import type {
   WorkspaceProjectThread,
   WorkspaceProjectThreadMessage,
 } from '@/api/hubClient';
-import { errorMessage } from './webWorkbenchError';
+import { errorMessage } from '@shared/errors';
 
 export function resolveWebWorkbenchProjects(
   projects: WorkspaceProject[] | undefined,
diff --git a/app/web/src/platform/webWorkbenchTranscript.ts b/app/web/src/platform/webWorkbenchTranscript.ts
index bbcc7adbb..4ec1fcd1a 100644
--- a/app/web/src/platform/webWorkbenchTranscript.ts
+++ b/app/web/src/platform/webWorkbenchTranscript.ts
@@ -17,7 +17,7 @@ import {
 } from '@shared/transcript';
 import type { FileDiff } from '@shared/types/chat';
 import { webHubEmptyTranscript } from './webPlatform';
-import { errorMessage } from './webWorkbenchError';
+import { errorMessage } from '@shared/errors';
 
 export function resolveWebRuntimeEvidence(transcript: TranscriptBlock[]): RuntimeEvidenceSnapshot {
   const runId = resolveCurrentTranscriptRunId(transcript);