refactor: use Zod validation for executionError getter

- Export zExecutionErrorWsMessage schema from apiSchema
- Use safeParse instead of type casts in TaskItemImpl.executionError
- Add logging on validation failure for debugging
- Keep errorMessage extraction in useJobErrorReporting via the getter

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/stores/queueStore.test.ts

@@ -233,56 +233,8 @@ describe('TaskItemImpl', () => {
     })
   })
 
-  describe('error extraction getters', () => {
-    it('errorMessage returns undefined when no execution_error message', () => {
-      const taskItem = new TaskItemImpl(
-        'History',
-        [0, 'prompt-id', {}, { client_id: 'client-id' }, []],
-        { status_str: 'success', messages: [], completed: true }
-      )
-      expect(taskItem.errorMessage).toBeUndefined()
-    })
-
-    it('errorMessage returns undefined when status has no messages', () => {
-      const taskItem = new TaskItemImpl(
-        'History',
-        [0, 'prompt-id', {}, { client_id: 'client-id' }, []],
-        { status_str: 'error', completed: false } as any
-      )
-      expect(taskItem.errorMessage).toBeUndefined()
-    })
-
-    it('errorMessage returns the exception_message from execution_error', () => {
-      const taskItem = new TaskItemImpl(
-        'History',
-        [0, 'prompt-id', {}, { client_id: 'client-id' }, []],
-        {
-          status_str: 'error',
-          completed: false,
-          messages: [
-            ['execution_start', { prompt_id: 'prompt-id', timestamp: 1 }],
-            [
-              'execution_error',
-              {
-                prompt_id: 'prompt-id',
-                timestamp: 2,
-                node_id: 'node-1',
-                node_type: 'KSampler',
-                executed: [],
-                exception_message: 'GPU out of memory',
-                exception_type: 'RuntimeError',
-                traceback: ['line 1', 'line 2'],
-                current_inputs: {},
-                current_outputs: {}
-              }
-            ]
-          ]
-        }
-      )
-      expect(taskItem.errorMessage).toBe('GPU out of memory')
-    })
-
-    it('executionError returns undefined when no execution_error message', () => {
+  describe('executionError getter', () => {
+    it('returns undefined when no execution_error message', () => {
       const taskItem = new TaskItemImpl(
         'History',
         [0, 'prompt-id', {}, { client_id: 'client-id' }, []],
@@ -291,7 +243,7 @@ describe('TaskItemImpl', () => {
       expect(taskItem.executionError).toBeUndefined()
     })
 
-    it('executionError returns the full error object from execution_error', () => {
+    it('returns the full error object from execution_error', () => {
       const errorDetail = {
         prompt_id: 'prompt-id',
         timestamp: 2,

src/stores/queueStore.ts

@@ -322,14 +322,6 @@ export class TaskItemImpl {
     return this.status?.messages || []
   }
 
-  /**
-   * Extracts the execution error message from status messages.
-   * Used by error reporting UI components.
-   */
-  get errorMessage(): string | undefined {
-    return this.executionError?.exception_message
-  }
-
   /**
    * Extracts the full execution error from status messages.
    * Returns the ExecutionErrorWsMessage for detailed error dialogs.