TPI) Agent Host Copilot terminal output streaming

[anthonykim1]

Refs: #324825, #327067

• macOS
• linux
• windows

Complexity: 4

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Verify that Agent Host Copilot streams output from the Copilot SDK built-in shell tool live in the chat terminal UI.

Prerequisites:

• Use the latest VS Code Insiders
• Sign in to GitHub Copilot
• Enable chat.agentHost.enabled
• Set chat.agentHost.customTerminalTool.enabled to false so Agent Host uses the Copilot SDK built-in shell tool

Part 1: Command output

• Start an Agent Host Copilot session
• Ask the agent: "Run something that prints a random number every second for the next 20 seconds"
• The agent can use a command such as:

  for i in $(seq 1 20); do echo "[$i] $RANDOM"; sleep 1; done

• Confirm each numbered result appears progressively while the command is running instead of all output appearing after completion
• Confirm the terminal UI automatically expands while new output is arriving
• Confirm the command changes from running to completed when it finishes

Part 2: Successful and failing commands

• Run a command that succeeds and confirm its completed state reflects a successful exit
• Run a command that exits with a non-zero status and confirm its completed state reflects the failure
• Confirm the final output remains visible and readable after both commands complete

Part 3: Output integrity

• Run commands that produce:
  • multiple output lines
  • enough output to exercise retained or truncated output
• Confirm output is not duplicated, reordered, stale, or missing
• Confirm output from one shell call does not appear in another shell call
• Confirm the final completed output is consistent with what was shown while the command was running

Part 4: Completed output and session history

• Run several terminal commands in the same Agent Host Copilot session
• Collapse and expand completed shell calls and confirm their output is preserved
• Reload the window or resume the session and confirm completed shell output is restored correctly
• Confirm completed output does not create an additional terminal in the Terminal panel

Part 5: Exploratory

• Use the built-in shell naturally during an Agent Host Copilot coding session
• Try commands that produce ongoing output, such as builds, tests, and npm install
• Note any cases where:
  • output does not appear until the command completes
  • output is duplicated, stale, reordered, or missing
  • a completed command continues to appear as running
  • completed output disappears after reload or resume
  • a built-in shell call unexpectedly creates a terminal in the Terminal panel