Plugin callbacks not propagated to sub-agent runners in agenttool

[dmora]

Bug

When a Plugin is registered on a Runner via PluginConfig, its callbacks (BeforeToolCallback, AfterToolCallback, etc.) do not fire for tools executed inside a sub-agent invoked via agenttool.

Root Cause

agenttool.Run() creates a new runner.Runner at agent_tool.go:170-177 without forwarding PluginConfig:

r, err := runner.New(runner.Config{
    AppName:         t.agent.Name(),
    Agent:           t.agent,
    SessionService:  sessionService,
    ArtifactService: artifact.InMemoryService(),
    MemoryService:   memory.InMemoryService(),
    // PluginConfig not set — sub-runner has no plugins
})

The parent runner stores its plugin manager in context at runner.go:160:

ctx = plugininternal.ToContext(ctx, r.pluginManager)

The sub-runner's Run() then overwrites the parent's plugin manager with its own empty one at the same line. The parent's plugins are lost.

Impact

• Observability plugins (logging, tracing, metrics) are blind to tool calls inside sub-agents
• BeforeToolCallback / AfterToolCallback only fire for the agenttool wrapper itself, not for function tools inside the sub-agent
• Same issue affects RunLive() (line 337)

Reproduction

1. Create a parent agent with a sub-agent wrapped via agenttool.New()
2. Sub-agent has a function tool (e.g., functiontool.New(...))
3. Register a plugin with BeforeToolCallback on the parent runner
4. Run the parent agent with input that triggers delegation to the sub-agent
5. Observe: plugin callback fires for tool=sub_agent_name but NOT for the inner function tool

Suggested Fix

Add a HasPlugins() method to PluginManager and make runner.Run() / runner.RunLive() conditional:

// runner.go:160 (and :337 for RunLive)
// Only overwrite if this runner has its own plugins — otherwise inherit parent's
if r.pluginManager.HasPlugins() {
    ctx = plugininternal.ToContext(ctx, r.pluginManager)
}

This preserves backwards compatibility: sub-runners with explicit plugins override; sub-runners without plugins (agenttool case) inherit the parent's.

Related

• Same issue reported in adk-python: Plugins don't run in AgentTool adk-python#2809, Custom Invocation Context propogation when using AgentTool adk-python#1746
• The TODO comments in agent_tool.go (lines 174, 200) suggest forwarding services is planned but not yet implemented

[indurireddy-TF]

Hi @dmora You are absolutely right losing observability and plugin context when delegating to a sub-agent creates a significant blind spot. It is definitely intended behavior for the Go SDK to have parity with the Python SDK here, so the sub-runner should be inheriting the parent's plugin context if it doesn't have its own.Thanks for submitting PR.