fix(executor): guard against missing content in provider responses

When an LLM provider returns a 200 response without a content field,
the router and evaluator handlers crash with a TypeError trying to
call .trim() on undefined. This happens when a model is unavailable,
rate-limited mid-stream, or returns an unexpected response structure.

Add an explicit check for result.content before accessing it, matching
the existing pattern in shared/response-format.ts (line 91) which
already uses `result.content ?? ''` for this case.

Affected handlers:
- RouterBlockHandler (legacy path, line 127)
- RouterBlockHandler V2 (line 287 fallback after JSON parse failure)
- EvaluatorBlockHandler (line 148)

Added regression tests for all three paths.

Author: lawrence3699

apps/sim/executor/handlers/evaluator/evaluator-handler.test.ts

@@ -287,6 +287,29 @@ describe('EvaluatorBlockHandler', () => {
     expect((result as any).fluency).toBe(0)
   })
 
+  it('should throw a clear error when provider returns no content', async () => {
+    const inputs = {
+      content: 'Test content to evaluate',
+      metrics: [{ name: 'quality', description: 'Quality', range: { min: 0, max: 10 } }],
+      apiKey: 'test-api-key',
+    }
+
+    mockFetch.mockImplementationOnce(() => {
+      return Promise.resolve({
+        ok: true,
+        json: () =>
+          Promise.resolve({
+            model: 'gpt-4o',
+            tokens: { input: 50, output: 0, total: 50 },
+          }),
+      })
+    })
+
+    await expect(handler.execute(mockContext, mockBlock, inputs)).rejects.toThrow(
+      'Provider returned an empty response'
+    )
+  })
+
   it('should extract metric scores ignoring case', async () => {
     const inputs = {
       content: 'Test',

apps/sim/executor/handlers/evaluator/evaluator-handler.ts

@@ -145,6 +145,12 @@ export class EvaluatorBlockHandler implements BlockHandler {
 
       const result = await response.json()
 
+      if (!result.content) {
+        throw new Error(
+          'Provider returned an empty response. The model may be unavailable or the request was malformed.'
+        )
+      }
+
       const parsedContent = this.extractJSONFromResponse(result.content)
 
       const metricScores = this.extractMetricScores(parsedContent, inputs.metrics)

apps/sim/executor/handlers/router/router-handler.test.ts

@@ -244,6 +244,45 @@ describe('RouterBlockHandler', () => {
     await expect(handler.execute(mockContext, mockBlock, inputs)).rejects.toThrow('Server error')
   })
 
+  it('should throw a clear error when provider returns no content', async () => {
+    const inputs = { prompt: 'Choose the best option.', apiKey: 'test-api-key' }
+
+    mockFetch.mockImplementationOnce(() => {
+      return Promise.resolve({
+        ok: true,
+        json: () =>
+          Promise.resolve({
+            model: 'gpt-4o',
+            tokens: { input: 100, output: 0, total: 100 },
+          }),
+      })
+    })
+
+    await expect(handler.execute(mockContext, mockBlock, inputs)).rejects.toThrow(
+      'Provider returned an empty response'
+    )
+  })
+
+  it('should throw a clear error when provider content is empty string', async () => {
+    const inputs = { prompt: 'Choose the best option.', apiKey: 'test-api-key' }
+
+    mockFetch.mockImplementationOnce(() => {
+      return Promise.resolve({
+        ok: true,
+        json: () =>
+          Promise.resolve({
+            content: '',
+            model: 'gpt-4o',
+            tokens: { input: 100, output: 0, total: 100 },
+          }),
+      })
+    })
+
+    await expect(handler.execute(mockContext, mockBlock, inputs)).rejects.toThrow(
+      'Provider returned an empty response'
+    )
+  })
+
   it('should handle Azure OpenAI models with endpoint and API version', async () => {
     const inputs = {
       prompt: 'Choose the best option.',
@@ -587,4 +626,30 @@ describe('RouterBlockHandler V2', () => {
     expect(result.selectedRoute).toBe('route-1')
     expect(result.reasoning).toBe('')
   })
+
+  it('should throw a clear error when provider returns no content (V2)', async () => {
+    const inputs = {
+      context: 'I need help with billing',
+      model: 'gpt-4o',
+      apiKey: 'test-api-key',
+      routes: JSON.stringify([
+        { id: 'route-support', title: 'Support', value: 'Customer support inquiries' },
+      ]),
+    }
+
+    mockFetch.mockImplementationOnce(() => {
+      return Promise.resolve({
+        ok: true,
+        json: () =>
+          Promise.resolve({
+            model: 'gpt-4o',
+            tokens: { input: 150, output: 0, total: 150 },
+          }),
+      })
+    })
+
+    await expect(handler.execute(mockContext, mockRouterV2Block, inputs)).rejects.toThrow(
+      'Provider returned an empty response'
+    )
+  })
 })

apps/sim/executor/handlers/router/router-handler.ts

@@ -124,6 +124,12 @@ export class RouterBlockHandler implements BlockHandler {
 
       const result = await response.json()
 
+      if (!result.content) {
+        throw new Error(
+          'Provider returned an empty response. The model may be unavailable or the request was malformed.'
+        )
+      }
+
       const chosenBlockId = result.content.trim().toLowerCase()
       const chosenBlock = targetBlocks?.find((b) => b.id === chosenBlockId)
 
@@ -273,6 +279,12 @@ export class RouterBlockHandler implements BlockHandler {
 
       const result = await response.json()
 
+      if (!result.content) {
+        throw new Error(
+          'Provider returned an empty response. The model may be unavailable or the request was malformed.'
+        )
+      }
+
       let chosenRouteId: string
       let reasoning = ''