feat: add switch_agent tool for model-initiated agent switching

[marius-kilocode]

Summary

• Adds a switch_agent tool that allows the AI model to request switching between primary agents (code, plan, debug, orchestrator) during a conversation
• Uses the existing permission system (ctx.ask) so users can configure it as ask (default, prompts user), allow (auto-approve), or deny (block) in their opencode.json
• Fixes TUI agent indicator not updating when a mid-turn agent switch occurs via synthetic user message

How it works

1. The tool dynamically lists available agents in its description (same pattern as the task tool listing subagents)
2. When invoked, it validates the target agent, asks for permission via ctx.ask(), then creates a synthetic user message with the new agent name
3. The existing session loop picks up the new agent from lastUser.agent - no loop changes needed
4. The TUI now reactively tracks lastUserMessage().id to update the agent indicator on mid-turn switches

Files changed

File	Change
packages/opencode/src/tool/switch-agent.ts	New tool implementation
packages/opencode/src/tool/switch-agent.txt	Tool description template with {agents} placeholder
packages/opencode/src/tool/registry.ts	Register SwitchAgentTool
packages/opencode/src/agent/agent.ts	Add switch_agent permission: deny default, ask for code/plan/debug/orchestrator
packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx	Reactive agent sync on mid-turn switch
packages/opencode/test/agent/switch-agent.test.ts	9 permission tests

User configuration

{
  "agent": {
    "code": {
      "permission": {
        "switch_agent": "allow"
      }
    }
  }
}

[kiloconnect]

WARNING: always: ["*"] makes "Always allow" approval apply to all future agent switches

For switch_agent, approving "always" effectively allows switching to any agent without prompting, which can act like a permission escalation path. Scoping the persisted approval to the requested agent name keeps the UX ("always allow this") while reducing blast radius.

Suggested change

	always: ["*"],
	always: [params.agent],

[kiloconnect]

Code Review Summary

Status: 1 Issues Found | Recommendation: Address before merge

Overview

Severity	Count
CRITICAL	0
WARNING	1
SUGGESTION	0

Issue Details (click to expand)

WARNING

File	Line	Issue
packages/opencode/src/tool/switch-agent.ts	76	always: ["*"] scopes "always allow" too broadly for agent switching

Other Observations (not in diff)

Issues found in unchanged code that cannot receive inline comments:

File	Line	Issue

Files Reviewed (5 files)

• packages/opencode/src/agent/agent.ts - 0 issues
• packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx - 0 issues
• packages/opencode/src/tool/registry.ts - 0 issues
• packages/opencode/src/tool/switch-agent.ts - 1 issue
• packages/opencode/test/agent/switch-agent.test.ts - 0 issues

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