Problem

When adding MCP servers or as new built-in tools are added, they're automatically
available to all agents. This causes:

• Context window bloat from unused tool prompts
• Need to manually disable tools in every agent configuration
• No way to set a "baseline" of tools that agents inherit

Proposed Solution

Add a global defaultTools array that defines which tools are available to all
agents by default:

{
  "$schema": "https://opencode.ai/config.json",
  "defaultTools": ["read", "grep", "glob", "list"],
  "agent": {
    "myagent": {
      "description": "Custom agent",
      "tools": {
        "webfetch": true
      }
    }
  }
}

Behavior

• If defaultTools not set: Current behavior (all tools enabled by default) -
non-breaking
• If defaultTools is set: Only these tools are available by default, agents can
add more via their tools config
• Users can set "defaultTools": [] (empty array): Zero tools by default, opt-in
per agent

This allows clean agent contexts without repetitive configuration across all
agents.