Concurrent headless cursor-agent invocations fail without delay

Bug Reports
1

Where does the bug appear (feature/product)?

Cursor CLI

Describe the Bug

Summary

When two cursor-agent processes are launched nearly simultaneously in a non-TTY environment, one exits immediately with status 1 and no output. Sequential or delayed starts succeed, but true parallel execution is unreliable. Blocking multi-agent orchestrators from running concurrent sessions.

Impact

Any automation (e.g., MCP orchestrators) that needs to run multiple cursor-agent sessions concurrently must serialize them, drastically reducing throughput.
Workaround
Run the agents one at a time with a small delay (≈100 ms) before starting the next command. This avoids the crash but sacrifices parallelism.

Steps to Reproduce

sh -c '
  cursor-agent --approve-mcps --model=composer-1 --print agent "List three popular pizza toppings." &
  pid1=$!
  cursor-agent --approve-mcps --model=composer-1 --print agent "Share a quirky pizza trivia." &
  pid2=$!
  wait $pid1; status1=$?
  wait $pid2; status2=$?
  echo "status1=$status1 status2=$status2"
'

Expected Behavior

Both processes complete with status 0, each printing its pizza response.

Actual behavior

One process prints a normal response with status 0. The second exits almost instantly with status 1 and no output (status1=1 status2=0 or vice versa). This persists even if you add a short delay (100–250 ms) between starts when they’re still launched “in parallel” from the same script. Fully sequential runs with a deliberate gap work reliably, but they are no longer truly parallel.

Operating System

MacOS

Current Cursor Version (Menu → About Cursor → Copy)

Version: 2025.11.06-8fe8a63

Additional Information

tested the same with claude and codex and they both worked even if launched in parallel

Does this stop you from using Cursor

Sometimes - I can sometimes use Cursor

2

Hey, thanks for the report. This appears to be a race condition in cursor-agent when multiple instances start simultaneously, likely related to session initialization or file locking.

I’ll pass this to the team because:

  • You provided clear reproduction steps
  • The workaround (serialization) defeats the purpose of parallel execution for MCP orchestrators
  • Other CLIs (claude, codex) handle concurrent launches correctly

For now, the 100 ms delay you found is still the best option. The team will investigate why cursor-agent can’t handle concurrent starts like other tools.

1 Like
4

@deanrie Thank you for the fast reply!

I’ll keep the current solution as the default.
I have the real parallelism code ready to be turned on with a feature flag so I can test out quickly any fixes as well.

Let me know if you need any further info or actions from me :folded_hands:

And thank you for your service and product!

Love it!

1 Like
5

I can confirm that on version 2025.11.25-d5b3271, the command returns:

Pizza trivia: The Hawaiian pizza (ham and pineapple) was invented in Canada, not Hawaii. Sam Panopoulos, a Greek immigrant who ran a restaurant in Chatham, Ontario, added pineapple to pizza in 1962. He named it “Hawaiian” after the brand of canned pineapple he used. It remains divisive—some love it, others consider pineapple on pizza controversial.

Three popular pizza toppings:

Pepperoni — spicy cured sausage

Mushrooms — sautéed or fresh

Extra cheese — mozzarella or a blend

Other common options: sausage, peppers, onions, olives, and bacon.
status1=0 status2=0

as expected!

thank you :folded_hands:

1 Like