[Subagents] Add mechanism for isolating the tools of subagents from the main agent.

[akh64bit]

What would you like to be added?

Right now there is no tool isolation between the main agent and the subagent.
Add mechanism for tool isolation.

Why is this needed?

This is needed for better manageability of tools.

Additional context

No response

[akh64bit]

I've reviewed the current implementation and wanted to add more details on the current state and proposed solutions for tool isolation:

Current Implementation Analysis

1. Shared Tool Instances: In packages/core/src/agents/local-executor.ts (LocalAgentExecutor.create()), an isolated agentToolRegistry is created, but it's populated by fetching tools directly from the parentToolRegistry.getTool(toolName). The exact same BaseDeclarativeTool instance is registered into the subagent.
2. Per-Invocation Context: While the subagent correctly creates a custom subagentMessageBus (to inject the subagent name into events) and passes it down to the tool's build() method per invocation, the tool object itself remains a singleton across the main agent and subagents.

The Problem with Shared Instances

Because the tool object instances are shared by reference:

• No Agent-Specific Configuration: We cannot easily configure a tool differently for a subagent. For example, we couldn't give a subagent a readFile tool with a restricted directory scope or forced read-only mode, because modifying the tool's properties would also affect the main agent.
• State Leakage: Any internal state, caching, or shared resources (like active browser sessions, internal queues, or cursors) stored on the tool class instance (this.* ) leak across agent boundaries.
• Lifecycle Coupling: Subagents cannot independently initialize, reset, or dispose of tools without disrupting the main agent.

Proposed Solution: Configuration-Based Isolation

To achieve proper tool manageability and isolation without a massive rewrite, we can introduce configuration-based isolation.

1. Extend the Configuration Schema: Add a new configuration option within AgentOverride (in packages/core/src/config/config.ts) to allow specifying tools directly for subagents.

   agents:
     overrides:
       codebase_investigator:
         enabled: true
         tools: ["read_file", "grep_search"] # New field

2. Main Agent Isolation: Currently, the main agent indiscriminately grabs everything from the ToolRegistry. We can introduce an internal flag to tools registered in the ToolRegistry (e.g., hiddenFromMainAgent: true) or introduce a mainAgentTools config option so the main agent only sees what it's supposed to see.
3. Fresh Tool Instantiation for Subagents: When LocalAgentExecutor.create() runs for a subagent, it checks its specific tools array from the config override. Instead of grabbing the shared instance from the global registry, it could be updated to lazily instantiate a fresh copy of those specific tools. This grants both visibility isolation and state/instance isolation.