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Execution failed: CAPIError: 400 {"error":{"code":"bad_request","type":"websocket_error","message":"Duplicate item found with id fc_call_ikBrgmi06fcJeO6uIpJJEQbJ. Remove duplicate items from your input and try again."}} #3560
Description
Activity
+1
+1 - after starting a new copilot session, the issue did not re-occur.
I have the same issue with GPT 5.5 and GPT 5.4.
Reacted by Lewis+1 — same underlying failure here.
Observed on Copilot CLI 1.0.54 before auto-update to 1.0.55.
Model in my logs: gpt-5.4 xhigh.
Failure is the same websocket_error / duplicate tool-call item pattern:Duplicate item found with id fc_call_...
Important detail from my logs:
- context usage was only 25.5% (69430 / 272000), so this does not look like a context-window issue
- the same fc_call_* ID was reused across retries
- stack points into getCompletionWithTools / runAgenticLoop
- plain instructions/context size is small; repo instructions file is concise
This looks consistent with a session/tool-call continuation defect rather than user error.
Seems to be working fine in v1.0.52 (you have to use --no-auto-update switch)
+1
- added a commit that references this issue
on Jun 18, 2026
Describe the bug
This started happening suddenly in the evening with the same Copilot CLI version and the same workflow.
Important detail:
"Duplicate item found with id fc_call_..."
This suggests a server-side regression or rollout affecting tool-call session continuation, rather than a local client version issue.
Affected version
GitHub Copilot CLI 1.0.55. Run 'copilot update' to check for updates.
Steps to reproduce the behavior
No response
Expected behavior
No response
Additional context
No response