Long-running MCP tool calls produce repeated progress indicator lines instead of updating in-place

[m-nash]

Describe the bug

When an MCP tool call blocks for an extended period (e.g., a tool that waits for an external event before returning), the CLI's progress indicator produces repeated lines in the terminal instead of updating the existing line in-place.

○ my_long_running_tool
  ◉ Waiting for result (Esc to cancel · 55 B)

○ my_long_running_tool
  ∙ Waiting for result (Esc to cancel · 55 B)

○ my_long_running_tool
  ◎ Waiting for result (Esc to cancel · 55 B)

○ my_long_running_tool
  ◉ Waiting for result (Esc to cancel · 55 B)

○ my_long_running_tool
  ∙ Waiting for result (Esc to cancel · 55 B)

This repeats every few seconds and continues for the duration of the tool call, filling the screen with duplicate lines. The same behavior also occurs with read_agent(wait: true) calls on background agents, producing repeated "Waiting for result…" lines.

Steps to reproduce

1. Create an MCP server with a tool that blocks for a long time (e.g., waits on a semaphore, external signal, or long timeout before returning)
2. Configure the server in mcp.json with a long timeout:

   {
     "mcpServers": {
       "my-server": {
         "command": "my-server",
         "args": [],
         "timeout": 3600000
       }
     }
   }

3. Have the agent call the blocking tool
4. Observe the terminal — the progress indicator line is appended repeatedly instead of being updated in-place

Expected behavior

The progress indicator for a pending tool call should update the same line in the terminal (using ANSI cursor control), not append a new line on each spinner tick. A single long-running tool call should produce at most one visible progress line that animates its spinner character in-place.

Affected version

• Copilot CLI version: 0.0.414
• OS: Windows 11 (Windows Terminal)
• MCP server timeout: configured at 3,600,000ms (1 hour)

Additional context

• The timeout config in mcp.json is working correctly — the tool is NOT timing out or retrying
• The spinner characters (◉, ∙, ◎) cycle, suggesting it's the same animation intended to update one line
• This makes patterns like "launch a background agent, block on MCP tool until it signals completion" impractical, since the main terminal fills with noise while waiting

[javierfurus]

Experiencing the same issue - in GNOME terminal it seems to work as intended for most of the time, however, in Kitty or in Nvim copilot just keep spamming the terminal with new lines.