Observed in: Claude Code internal architecture
Model: Small fast model (Haiku)
Purpose
Generates periodic background progress updates for sub-agents running in coordinator mode. Provides the parent agent with real-time awareness of what each worker is doing.
Prompt (Reconstructed from Source Analysis)
Summarize what the agent is currently doing in 1 short sentence. Use present tense.
Focus on the specific action, not the overall task.
Good: "Reading the authentication middleware to understand token validation"
Good: "Running pytest on the user service after fixing the import error"
Bad: "Working on the task" (too vague)
Bad: "The agent is currently in the process of examining..." (too verbose)
Design Constraints
Single sentence: Maximum one sentence, present tense
Action-specific: Describe the current action, not the overall goal
No meta-commentary: Don't describe the agent itself, describe what it's doing
Present tense: Always use present-tense verbs ("Reading", "Running", "Fixing")
Integration Points
Runs on a periodic timer during coordinator mode
Results are displayed in the coordinator's status view
Helps the lead agent decide when to check in on workers
Fires only when sub-agents are actively executing tool calls