fix(core): execute renamed tool definitions

[opencode-agent]

Summary

• preserve each hooked tool definition's registered implementation when a session context hook renames its key
• advertise the renamed definition to the model while routing calls back to the captured registry name
• keep hook-removed and unregistered tools unavailable

Tests

• bun test test/session-runner.test.ts --timeout 30000
• bun typecheck

Requested by: @rekram1-node (Aiden Cline via Slack)