When running agent.execute() with gemini computer use, gets error: Cannot read properties of undefined (reading 'parts')

[gigasami]

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Environment Information

Please provide the following information to help us reproduce and resolve your issue:

Stagehand:

• Language/SDK: python
• Stagehand version: 0.5.4

AI Provider:

• Provider: google gemini
• Model: gemini-2.5-computer-use-preview-10-2025

Issue Description

It seems like the agent fails to execute when it gets an empty or undefined response from gemini api, plz fix 

Steps to Reproduce

1. run the agent for more than 1-2 minutes, I get this from time to time

Minimal Reproduction Code

config = StagehandConfig(
  env="BROWSERBASE",
  api_key=os.getenv("BROWSERBASE_API_KEY"),
  project_id=os.getenv("BROWSERBASE_PROJECT_ID"),
  headless=True,
  dom_settle_timeout_ms=3000,
  browserbase_session_create_params={
      "browser_settings": {
          "context": {
              "id": os.getenv("BROWSERBASE_CONTEXT_ID"),
              "persist": True
          },
          "viewport": {
              "width": 1288,
              "height": 711
          }
      },
      "user_metadata": {
          "test_name": test.name,
          "suite_id": self.suite_id
      }
  },
  model_name="google/gemini-2.5-flash-preview-05-20",
  model_client_options={"apiKey": os.getenv("GEMINI_API_KEY")}
)

# Initialize Stagehand
stagehand = Stagehand(config)
await stagehand.init()

# Create agent
agent = stagehand.agent(
model="gemini-2.5-computer-use-preview-10-2025",
instructions=(
    "You are a helpful web navigation assistant that helps test user interfaces. "
),
options={"apiKey": os.getenv("GEMINI_API_KEY")}
)

result = await agent.execute(instruction=instruction, max_steps=40)

Error Messages / Log trace

2025-10-20 03:11:33 ERROR - Error executing step: Cannot read properties of 
undefined (reading 'parts')
2025-10-20 03:11:33 ERROR - Error executing agent task: Cannot read properties 
of undefined (reading 'parts')

{'sessionId': 'f44c4ba2-6d61-4200-a8b2-09a2436361a4'}

Screenshots / Videos

[Attach screenshots or videos here]

[derekmeegan]

Hey! Thanks for opening this issue, could you let me know what the instructions that you provide to agent.execute?

[gigasami]

@derekmeegan I just give it some ui test scenarios to test

an example:

# Test: Filtering Functionality

**Scope:** Verify that clicking on the filter icon opens the filter panel, that all filters expand correctly, and that selectable filters display their options. Specifically, agent name must always show options.

---

## Step 1 — Initial State
**Action:** Load the Tickets page.  
**Pass Criteria:**  
- All columns with the sort icon are visible. 
**Fail Criteria:**
- Any column is missing, truncated.

---

## Step 2 — Open Filter Panel
**Action:** Click the filter icon (right above the table, on the right of time range dropdown).  
**Pass Criteria:**  
- The filter panel opens on the right side.  
- All expected filter categories are visible.  
**Fail Criteria:**  
- Panel does not open.  
- UI becomes unresponsive.

---

## Step 3 — Expand Filter
**Action:**  
- click on **Agent name filter** in the panel (scroll if needed). You should click again to collapse the options when you need to.
- Check whether a dropdown or options list is displayed after clicking.  

**Pass Criteria:**  
- Each filter expands without UI errors. 
- **Agent name** filter **must display non-empty options**.  
**Fail Criteria:**  
- Any filter fails to expand.
- UI breaks or becomes unresponsive.  
- Agent name filter show no options.

---

## Step 4 — Apply a Filter on Agent Name
**Action:**  
- Expand the **Agent name** filter.  
- Select a single agent option take the most recent agent name from the first row of tickets table.  

**Pass Criteria:**  
- The table updates to show only rows matching the selected agent.
**Fail Criteria:**  
- Table does not update.  
- Wrong rows remain visible.

---

## Step 5 — Clear the Filter
**Action:** Clear all filters.  
**Pass Criteria:**  
- Table returns to the unfiltered state. 
**Fail Criteria:**  
- Filter remains applied. 
- Table does not refresh.

---

### Expected Outcome
The filter panel opens when the icon is clicked. Filters with selectable options expand properly, applying and clearing filters updates the table accurately without UI errors.

Your last message should be a summary of the steps you took to complete the test.
You should explain thoroughy what you did to complete the test and what went wrong if it failed.
At the very end of your final message, write exactly one of these tokens on its own line:
test_passed or test_failed. Do not include anything after that token.

[derekmeegan]

Is this error getting thrown consistently or intermittenly?

[gigasami]

it is getting thrown intermittently

[gigasami]

I saw it once again in this session: 88a4b455-8bf9-4156-b0d7-4b502f7dadd7