Agent Teams: teammate messages render with '⏺ Human:' prefix, indistinguishable from user input

Problem

When using Agent Teams, teammate messages delivered via SendMessage are rendered in the terminal with the same ⏺ Human: prefix as actual user input. There is no visual distinction between:

• A message the user typed
• A message a teammate agent sent via SendMessage(type="message", recipient="team-lead", ...)

This causes confusion — the user sees teammate reports appearing as if they were their own input.

Expected Behavior

Teammate messages should be visually distinct from user input. For example:

• ⏺ Teammate (backend-coder): instead of ⏺ Human:
• Or use the color field from SendMessage for visual differentiation
• Or a different icon/prefix entirely

The SendMessage tool already provides summary and sender identity (from field in inbox JSON) — this metadata could be used for rendering.

Reproduction

1. Create a team: TeamCreate(team_name="test")
2. Spawn a teammate: Task(name="worker", team_name="test", subagent_type="general-purpose", prompt="Send a message to team-lead saying hello")
3. Observe: the teammate's message appears as ⏺ Human: in the lead's terminal

Environment

• Claude Code CLI (terminal mode)
• macOS Darwin 25.4.0
• Agent Teams enabled via CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS

Impact

• Users cannot distinguish their own input from teammate messages
• Creates confusion about conversation flow
• No setting, CLI flag, or hook exists to customize this label