fix(ai): prevent duplicated system prompts in PydanticAI completions#8356
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Light2Dark merged 2 commits intomarimo-team:mainfrom Feb 18, 2026
Merged
fix(ai): prevent duplicated system prompts in PydanticAI completions#8356Light2Dark merged 2 commits intomarimo-team:mainfrom
Light2Dark merged 2 commits intomarimo-team:mainfrom
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## Summary Add a test that verifies the `completion` method does not pass redundant instructions to the PydanticAI agent, which causes system prompt duplication in API requests. ## Description of Changes This test currently fails because `system_prompt` is passed to both the `Agent()` constructor (via `create_agent`) and `agent.run()`, causing PydanticAI's `_get_instructions` to concatenate them.
## Summary The `system_prompt` was being passed to both the `Agent` constructor and `agent.run()`, causing PydanticAI's `_get_instructions` to duplicate it. Remove the redundant `instructions` argument from `agent.run()`. ## Description of Changes In `PydanticProvider.completion()`, `system_prompt` was already passed to `create_agent()`, which initializes the agent with those instructions. Passing it again to `agent.run()` caused duplication because `Agent._get_instructions()` concatenates constructor-level instructions with run-level `additional_instructions`. Removing `instructions=system_prompt` from `agent.run()` resolves this.
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recheck |
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I have read the CLA Document and I hereby sign the CLA |
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Thanks @fpreiss , I think you are right. Do you also want to address the other parts? I believe they aren't hit because only on certain codepaths but would be good to get them |
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Feb 18, 2026
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Yes, I'm willing to take care of this within the next week. |
LiquidGunay
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Feb 21, 2026
…arimo-team#8356) I intercepted the outgoing API request and observed the following duplicated content in the system message during tab completion: ```json { "messages": [ { "content": "You are a python code completion assistant... \nYou are a python code completion assistant...", "role": "system" }, ... ] } ``` ## Cause This is caused by the internal concatenation logic of `pydantic_ai.agent.__init__.Agent._get_instructions` and how `completion` in `marimo/_server/ai/providers.py` is providing the `system_prompt` to both - the `Agent`'s constructor and the `agent.run` method. ## Fix The fix removes `instructions=system_prompt` from `agent.run()`, leaving only the constructor-level instructions. ## Notes A similar duplication issue likely exists in `stream_text()` (also in `providers.py`), where `system_prompt` may be passed to both `create_agent()` and `agent.run_stream()`. I have not verified this e2e though. ## 📋 Checklist - [x] I have read the [contributor guidelines](https://github.com/marimo-team/marimo/blob/main/CONTRIBUTING.md). - [x] Tests have been added for the changes made. - [x] Pull request title is a good summary of the changes - it will be used in the [release notes](https://github.com/marimo-team/marimo/releases).
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I intercepted the outgoing API request and observed the following duplicated content in the system message during tab completion:
{ "messages": [ { "content": "You are a python code completion assistant... \nYou are a python code completion assistant...", "role": "system" }, ... ] }Cause
This is caused by the internal concatenation logic of
pydantic_ai.agent.__init__.Agent._get_instructionsand howcompletioninmarimo/_server/ai/providers.pyis providing thesystem_promptto both - theAgent's constructor and theagent.runmethod.Fix
The fix removes
instructions=system_promptfromagent.run(), leaving only the constructor-level instructions.Notes
A similar duplication issue likely exists in
stream_text()(also inproviders.py), wheresystem_promptmay be passed to bothcreate_agent()andagent.run_stream(). I have not verified this e2e though.📋 Checklist