Support OpenCode v2 plugin API

[dbpolito]

Ticket

SKIPPED

Description

Add OpenCode v2 plugin support to the existing adapter package while preserving OpenCode 1 behavior. The implementation shares core Zod tool definitions across both APIs, keeps Navigator and Rift on the v1 surface where the required host APIs exist, and documents the version-specific capability boundary.

Checklist

Dual Plugin Support

• Load OpenCode 1 through the legacy server plugin entry
• Load OpenCode 2 through the new setup definition
• Preserve v2 subtask and inline command behavior

Shared Tools

• Reuse the six core tool definitions and schemas across both APIs
• Keep Navigator and Rift fully available on OpenCode 1
• Exclude unsupported Navigator tools from OpenCode 2

Documentation

• Document installation for both plugin APIs
• Clarify the OpenCode 1 Navigator boundary

Validation

• Verify that bun run compile succeeds
• Confirm that bun run typecheck succeeds
• Confirm that all 151 tests pass
• Check that the OpenCode package build succeeds

[kompassdev]

★★★★☆

Overall this is a careful dual-API refactor: I verified the { id, server, setup } default export against the OpenCode 1.18.7 loader contract (readV1Plugin detect + PluginModule.server), confirmed legacy-plugin.ts matches the published v1 plugin API (the real tool helper is identity and already zod 4-based), and checked the v2 usage against the beta SDK types (SessionPromptInput, AgentDraft, Tool.Result). One behavioral divergence in the reimplemented command template expansion is worth fixing before this ships.