Gemini 3.8 agent repeatedly executes identical file searches and enters a search loop

## Copilot Chat Version

@github/copilot 1.0.84-canary.70.gdb75d0d.unsigned

## VS Code Version

Version: 1.137.0-insider (user setup)

Commit: 9aaf490382bd0ecdd72db3d2f308cdf1fdc6a79d

Electron: 42.10.0

Chromium: 148.0.7778.280

Node.js: 24.18.1

OS: Windows_NT x64 10.0.26100

## Feature Area

Agent Mode

## Model

Gemini 3.8

## Description

The agent repeatedly executes identical file search operations and appears unable to use previous search results. It enters a loop where the same set of files is searched repeatedly, returning the same results each time.

I have only observed this behavior with Gemini 3.8. I have not noticed similar looping with other models.

## Steps to Reproduce

Ask the agent to perform a refactoring or code investigation involving MAUI infrastructure classes.

During execution, the agent repeatedly issues the same search requests instead of progressing to the next step.

Example sequence:

```text
MauiTestContext.cs -> 1 match
IMauiScope.cs -> 1 match
IMauiPage.cs -> 1 match
IMauiContainerObject.cs -> 1 match
ContainerObjectBase.cs -> 1 match
TestContextScope.cs -> no matches

Possibly related to:

#257107
#258039
#259842
#12754
However, in this case the looping behavior consists of repeated file-search tool calls returning identical results on every iteration.