[Adapter] Support OpenCode CLI

[teseo]

Kind

implement

Goal

Integrate human.md with OpenCode through a plugin that translates session and tool hooks to the neutral contract.

Non-goals

• Supporting undocumented OpenCode internals.
• Forking policy behavior in TypeScript.
• Claiming support for OpenCode Desktop without a separate test.

Invariants

• Plugin loading is idempotent.
• Pre-tool deny decisions are enforced before execution.
• Plugin API version differences produce a clear compatibility diagnostic.
• State is isolated per OpenCode session and cwd.

Behavioral contract / States

Register the supported plugin hooks, emit normalized events, apply allow/deny/advisory decisions, and preserve OpenCode's native error/reporting semantics.

Scope surface

OpenCode plugin entrypoint, configuration/install path, version gate, fixtures, and tests.

Acceptance

• Verify plugin discovery in global and project plugin locations.
• Verify allow, deny, advisory, session start, and session end scenarios.
• Run: node --test tests/test_guard.mjs plus the adapter-specific OpenCode smoke test.
• Test the supported API version and one unsupported version with a deterministic failure message.

Split triggers

• V2 plugin API changes require separate compatibility branches.
• OpenCode's CLI and desktop runtimes expose different hook guarantees.

Dependencies / Parent

Blocked by: #1, #2, #3
Parent Epic: #15