[Migration] Phase 5: Remove OpenCode Dependency

[aWN4Y25pa2EK]

Overview

Replace @opencode-ai/sdk dependency with native OpenRouter extended thinking via AI SDK.

Parent Epic: #19
Depends on: #21

Acceptance Criteria

• opencode-client.ts removed or replaced with AI SDK wrapper
• opencode_reason tool uses AI SDK with :thinking model variant
• SSE streaming preserved for real-time reasoning output
• @opencode-ai/sdk removed from package.json
• OpenCode config section removed from config.ts

Files to Modify

• src/tools/opencode-client.ts → DELETE or refactor
• src/holons/adk/tools.ts - Update openCodeReasonTool
• src/config.ts - Remove opencode section
• package.json - Remove @opencode-ai/sdk

Technical Notes

Extended thinking via OpenRouter:

import { streamText } from 'ai';
import { openrouter } from '@openrouter/ai-sdk-provider';

const result = await streamText({
  model: openrouter('anthropic/claude-opus-4.5:thinking'),
  prompt: problem,
  providerOptions: {
    openrouter: {
      reasoning: { effort: 'high' }
    }
  }
});

// Access reasoning tokens
const reasoning = result.reasoning;
const usage = result.usage; // includes reasoningTokens

Migration Path

1. Create new src/tools/extended-reasoning.ts using AI SDK
2. Update openCodeReasonTool to use new implementation
3. Verify reasoning output matches previous quality
4. Remove old OpenCode client and dependency

Testing

• Test extended reasoning on complex decomposition tasks
• Verify reasoning tokens tracked in usage
• Check SSE streaming works for real-time output
• Compare output with OpenCode baseline

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Part of Hybrid ADK + AI SDK Migration