fix(opencode): keep resumed session bind out of turn tracking

[Yt4aZaveta]

Summary

Resumed OpenCode sessions bind from session.updated events. The bind signal was sending the native session ID as both threadId and turnId, so RuntimeGateway remembered it as a turn before the first prompt. The following session.status:busy event was then discarded as a stale turn start.

This change keeps the native session ID as threadId only. Resumed sessions retain their identity and the first busy event transitions them to working; child-session filtering and stale-turn protection remain unchanged.

Validation

• node --test --test-concurrency=1 tests/agent-runtime-gateway.test.mjs tests/opencode-result.test.mjs — 21 passed
• The regression test OpenCode resumed sessions bind from native updates before status events, while child updates remain isolated passes.
• git diff --check main...HEAD passes.

Known unrelated test failure

The full npm test run currently fails at tests/opencode-auto.test.mjs:64, where the test expects edit: allow and bash: allow while the current base-protection behavior returns restricted rules. This PR changes only src/agent-runtime/opencode-plugin.mjs.