fix(subagent): ensure spawned subagents receive tools (#1713)

[darrenzeng2025]

Summary

Fix #1713: Subagents spawned via spawn tool have no tools

Problem

The spawn tool creates subagents that were not receiving any tools, causing API requests to lack the tools field. This happened because SubagentManager was initialized with an empty ToolRegistry instead of the agent's actual tools.

Root Cause

In pkg/agent/loop.go, the registerSharedTools() function created a SubagentManager but never called SetTools() to pass the agent's tool registry:

subagentManager := tools.NewSubagentManager(provider, agent.Model, agent.Workspace)
subagentManager.SetLLMOptions(agent.MaxTokens, agent.Temperature)
// Missing: subagentManager.SetTools(agent.Tools)

Solution

Added the missing SetTools() call to pass the agent's tool registry to the subagent manager:

subagentManager.SetTools(agent.Tools)

Changes

1. pkg/agent/loop.go: Added subagentManager.SetTools(agent.Tools) in registerSharedTools()
2. pkg/tools/subagent_tool_test.go: Added tests to verify SetTools behavior:
   • TestSubagentManager_SetTools: Verifies tools are properly passed
   • TestSubagentManager_SetTools_NilRegistry: Tests nil handling
   • TestSubagentManager_DefaultToolsNotNil: Verifies default initialization

Testing

The fix ensures that spawned subagents now have access to the same tools as the parent agent, allowing proper tool execution in the subagent's RunToolLoop.