feat(adk): allow emit internal event by agent tools

[shentongmartin]

ADK: Emit Internal Events from Agent Tools

Summary

• Adds an opt-in mechanism for agent tools to emit internal AgentEvents to their parent agent.
• Provides a concrete tool option for binding an event generator and a config flag to auto-inject it in nested runs.
• Improves tracing, debugging, and orchestration of multi-agent workflows without breaking existing APIs.

Problem

• When an agent is wrapped as a tool and used inside another agent, its internal events are not visible to the parent.
• This limits live telemetry and provenance tracking across tool boundaries.

Solution

• Introduce a tool option to pass an event generator into agent tools and forward events upstream.
• Add a ToolsConfig flag on ChatModelAgent to automatically inject this option when running nested tools.

Implementation

• adk/agent_tool.go:80 adds WithAgentToolEventGenerator(gen *AsyncGenerator[*AgentEvent]).
• adk/agent_tool.go:99 forwards events in invokableAgentTool.InvokableRun.
• adk/chatmodel.go:87–89 adds ToolsConfig.EmitInternalEvents.
• adk/chatmodel.go:744–746 auto-injects the tool option during ChatModelAgent runs when enabled.

Configuration

• Enable event emission for nested tools in ChatModelAgent:

agent, _ := adk.NewChatModelAgent(ctx, &adk.ChatModelAgentConfig{
  Model: mdl,
  ToolsConfig: adk.ToolsConfig{
    ToolsNodeConfig: compose.ToolsNodeConfig{
      Tools: []tool.BaseTool{adk.NewAgentTool(ctx, subAgent)},
    },
    EmitInternalEvents: true,
  },
})

Compatibility

• Default is unchanged; event emission is off unless explicitly enabled.
• APIs are additive; existing code continues to work.

[codecov]

Codecov Report

❌ Patch coverage is 84.37500% with 10 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@d293091). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
adk/agent_tool.go	82.75%	3 Missing and 2 partials ⚠️
adk/chatmodel.go	75.00%	2 Missing and 1 partial ⚠️
adk/flow.go	88.23%	1 Missing and 1 partial ⚠️

Additional details and impacted files

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  Coverage        ?   79.15%           
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  Files           ?      123           
  Lines           ?    11562           
  Branches        ?        0           
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  Hits            ?     9152           
  Misses          ?     1691           
  Partials        ?      719           

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