Test: terminal chat agent `cwd` awareness

[meganrogge]

Refs #17486

• [ ] Windows
• [ ] macOS
• [ ] Linux

Complexity: 4

Authors: @meganrogge, @roblourens

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Terminal Chat Agent: cwd Awareness

We've introduced current working directory (cwd) awareness to the terminal chat agent this iteration to address issues like #17486. Note that this only applies to non-background terminals.

Key Changes

• Terminal and chat session tracking has been refactored.
• This refactor and other changes enable the agent to accurately understand the terminal's cwd when shell integration is active and a Copilot terminal is present.

Test Instructions

1. Open a new terminal with shell integration enabled.
   • You can confirm shell integration is working by hovering over the terminal tab and checking that it says Shell Integration: Rich (see screenshot below).
2. Run terminal commands via the chat agent in agent mode.
3. Verify that:
   • The command executes in the correct working directory.
   • Chat accurately reflects the current directory in its responses or logic.
   • Closing sessions closes the terminals.
   • Reloading the window persists Copilot terminals.

💡 This feature depends on shell integration, so please ensure it’s active during testing.