feat(opencode): add LINE Messaging API integration

[monthop-gmail]

Closes #13801

Summary

• Add packages/line/ - LINE Messaging API integration for OpenCode, following the same pattern as the existing Slack integration (packages/slack/)
• Each LINE user gets their own OpenCode session via createOpencode() from @opencode-ai/sdk
• Messages are forwarded to the AI coding agent, and responses are sent back through LINE
• Real-time tool update notifications via event subscription
• Handles LINE's 5000 char message limit with smart chunking (respects code blocks)

How it works

User (LINE app)
  ↕  LINE Messaging API webhook
packages/line/ (Bun HTTP server)
  ↕  @opencode-ai/sdk
OpenCode Server (auto-started)
  ↕
Project Filesystem

Commands

• Send any text message → forwarded to OpenCode as a coding prompt
• /new - Start a new coding session
• /abort - Cancel the current prompt
• /sessions - Show active session info

Files

File	Description
packages/line/package.json	Dependencies: @opencode-ai/sdk, @line/bot-sdk
packages/line/src/index.ts	Main entry - LINE webhook + OpenCode bridge (~290 lines)
packages/line/.env.example	Required env vars
packages/line/tsconfig.json	TypeScript config (same as Slack)
packages/line/README.md	Setup instructions

Test plan

• Create LINE Messaging API channel at https://developers.line.biz
• Set .env with LINE credentials
• Run cd packages/line && bun dev
• Expose webhook via ngrok or cloudflare tunnel
• Send text message in LINE → verify OpenCode processes and responds
• Send /new → verify new session created
• Send /abort → verify prompt cancelled
• Send long prompt → verify chunked response

Tested locally with Docker setup and real LINE channel - working end-to-end.

🤖 Generated with Claude Code

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