playground display issue for long responses

[rumarlon]

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Describe the Bug:
When the playground generates a long output the scrolling doesn't work and snaps to the latest message. While scrolling using the scroll bar the screen flickers making it difficult to read.

Steps to Reproduce:
Please provide a numbered list of steps to reproduce the behavior:

1. Create agent with agent-cli
2. Invoke adk playground
3. Request an answer that will create a long LLM response
4. Try to scroll up
5. If you don't see the issue immediately make an additional request that outputs a long response.
6. Try to scroll up and notice the snap to bottom and flicker

Expected Behavior:
The scroll bar should always work even if the LLM response is long.

Observed Behavior:
No error messages just UI issues when scrolling long LLM answers

Environment Details:

• ADK Library Version (pip show google-adk): adk, version 2.5.0
• Desktop OS:** [e.g., macOS, Linux, Windows]: Mac OS, Chrome browser
• Python Version (python -V): Python 3.14.5

Model Information:

• Are you using LiteLLM: No
• Which model is being used: gemini-3.6-flash

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Regression:
Did this work in a previous version of ADK? If so, which one? unknown

Logs:
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text file.

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Additional Context:
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Minimal Reproduction Code:
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How often has this issue occurred?:

• Always (100%)