OpenCode has a `task` tool that supports spawning subagents, but
map-codebase workflow incorrectly listed it under "Runtimes WITHOUT
Task tool". This caused the agent to skip parallel mapping and fall
back to sequential mode, wasting tokens when it self-corrected.
Move OpenCode to the "with Task tool" list and clarify that either
`Task` or `task` (case-insensitive) qualifies. Add regression test.
Fixes#1316
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>