Replaces the runTurn/callModel/Anthropic-API-key path in POST /turn with
runClaudeTurn (claude CLI) backed by a per-turn MCP config that spawns
companion-stdio.js. Extracts pending_change_id from tool_result events
defensively (structuredContent → text-JSON fallback). Rewrites companion
test to inject fake-claude-draft.js via app.locals.claudeExe.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
