Complex copilot requests timeout with "This message couldn't be processed"

### Description

When using @mssql agent in VS Code, simple requests like "Are you able to help me now" get a positive response - like "Yes, ready when you are". However, larger requests, like "rewrite this SQL script" are timing out. It was working correctly all morning doing the exact type of work, but for the last four hours every sizeable request has timed out.

### Steps to Reproduce

1. Enter a prompt that references an open editor or paste a sizable SQL query directly into the prompt and ask it to make a change. It will say something like "Researching" then return this error: This message couldn't be processed. If this issue persists, please check the logs and open an issue on GitHub.
[https://aka.ms/vscode-mssql-copilot-feedbackAn](vscode-file://vscode-app/c:/Users/JohnS/AppData/Local/Programs/Microsoft%20VS%20Code/df53daabb1/resources/app/out/vs/code/electron-browser/workbench/workbench.html) error occurred: All tool calls failed or timed out.

### Affected Area

- [x] Agent mode
- [ ] Ask mode
- [ ] Slash commands
- [ ] Code generation
- [ ] Connection management
- [ ] Schema exploration and object management
- [ ] Query execution and performance advisor
- [ ] Other (please describe below)

### If you selected "Other", please describe the affected area

_No response_

### Environment Information (Optional)

VS Code version: 1.132.0 (user setup)
Commit: df53daabb18cd157bdb08c7f01c34df936cf12f4
Date: 2026-08-04T15:30:20Z
Electron: 42.7.1
ElectronBuildId: 14760073
Chromium: 148.0.7778.280
Node.js: 24.18.0
V8: 14.8.178.38-electron.0
OS: Windows_NT x64 10.0.26200

### Confirmation

- [x] I have searched existing issues and couldn’t find a match
- [ ] I want to work on this issue

Reproduce the failure in VS Code 1.132.0 using @mssql agent with a sizable SQL prompt or an open editor, then inspect the extension and VS Code logs for the reported tool-call timeout. Done means larger agent requests complete successfully without returning “All tool calls failed or timed out,” with the behavior verified against simple prompts as well.

Written by the indexing model from the issue text.