Terminal and agent command output is inaccessible after output and scrollback limits are reached

## Problem

When an agent runs a build or test command that produces substantial output, the terminal view and conversation surface impose output and scrollback limits. Once those limits are reached, the beginning of the command output is no longer visible or retrievable through the terminal surface.

This is not merely inconvenient for long-running builds. The first lines commonly contain the command, working directory, configuration, compiler invocation, and the first diagnostic. Losing them makes it impossible to review the complete execution record and can make the agent effectively unusable for debugging.

## Expected behavior

The complete command output should remain available through at least one reliable, user-visible mechanism. Suitable solutions could include:

- an expandable output artifact with unrestricted access;
- a command-specific transcript that can be opened and searched;
- controls to retrieve the beginning, middle, or end of output by byte or line range;
- a way to export the complete output without relying on terminal scrollback.

The terminal display may remain bounded for performance, but the underlying command transcript should not be discarded or made inaccessible.

## Actual behavior

After output or scrollback limits are reached, the first part of the output cannot be viewed in the terminal. The assistant may be able to summarize or store output separately, but the user cannot reliably inspect the complete result in the interface.

## Impact

This prevents trustworthy review of builds, tests, flashing prerequisites, and diagnostic commands. It is especially serious when the first diagnostic appears before the retained portion of the output.

## Environment

- Visual Studio Code on Linux
- GitHub Copilot agent workflow
- Integrated terminal commands producing long output

Please route this issue to the component responsible for retaining and exposing agent command output if it is not owned by the integrated terminal itself.