Feature: Per-tool authorization middleware for agent tool calls

Problem

VoltAgent provides guardrails and tool management, but there's no built-in mechanism for per-tool authorization based on agent identity.

When building multi-agent systems with VoltAgent, different agents in the workflow need different tool access levels. An orchestrator agent might need broad access, while a sub-agent it delegates to should only have read permissions.

Use Case

const agent = new Agent({
  name: 'research-bot',
  tools: [searchDocs, saveNote, deleteNote, deployProd],
});

This agent can call all four tools. In production, you want:

• research-bot can call searchDocs only
• content-bot can call searchDocs + saveNote
• admin-bot can call everything
• Every tool call logged with who called what and whether it was allowed

Proposal

A tool authorization hook in the agent or tool configuration:

const agent = new Agent({
  name: 'research-bot',
  tools: [searchDocs, saveNote, deleteNote],
  toolGuard: async (toolName, context) => {
    // Check against permission rules
    const allowed = context.permissions?.some(
      pattern => matchGlob(pattern, toolName)
    );
    if (!allowed) {
      return { denied: true, reason: `${toolName} not in allowed tools` };
    }
    return { denied: false };
  },
});

This would integrate with VoltAgent's existing guardrails system and enable:

• Per-agent tool restrictions
• Integration with external permission engines (like AgentsID for deny-first agent permissions)
• Audit trail of tool call authorization decisions
• Delegation with automatic scope narrowing

Since VoltAgent already has MCP support, this becomes especially relevant — MCP servers expose many tools, and agents connecting to them need per-tool authorization.

Would this fit within VoltAgent's guardrails architecture, or is there an existing pattern I should use?