fallback to a model when none is available on the chat widget

[meganrogge]

fix https://github.com/microsoft/vscode-copilot-evaluation/issues/2709

[Copilot]

Pull request overview

This PR updates the terminal OutputMonitor’s option auto-reply flow to handle cases where the Chat widget doesn’t currently expose an active model, addressing microsoft/vscode-copilot-evaluation#2709.

Changes:

• Add fallback model resolution for option prompts when the Chat widget has no currentLanguageModel.
• Make model-based option suggestion resilient to model lookup/request failures, and fall back to the first option when auto-reply is enabled.
• Extend the OutputMonitor test setup with configuration/chat widget service stubs and add a new auto-reply fallback test.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/vs/workbench/contrib/terminalContrib/chatAgentTools/test/browser/outputMonitor.test.ts	Adds service stubs required by OutputMonitor and introduces a new test for auto-reply fallback behavior.
src/vs/workbench/contrib/terminalContrib/chatAgentTools/browser/tools/monitoring/outputMonitor.ts	Implements fallback language model selection and guarded model querying when choosing a default terminal prompt option.