Fix sandbox workspace artifact materialization

[chubes4]

Summary

• Use the canonical Data Machine Code datamachine-code/workspace-adopt ability in sandbox setup, with the old ability name as a fallback.
• Add a real recipe-run regression smoke proving Playground workspace writes materialize into changed-files.json and patch.diff.
• Covers the artifact path involved in agent-task-run should materialize sandbox workspace writes into patch artifacts #845 while the upstream mounted workspace_write normalization fix lands separately in fix: normalize mounted workspace writes Extra-Chill/data-machine-code#614.

Fixes #845.

Testing

• npm run build
• npx tsx scripts/agent-sandbox-code-smoke.ts
• npx tsx scripts/recipe-workspace-vfs-materialization-smoke.ts

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Diagnosed the sandbox artifact materialization path, drafted the sandbox adoption update and regression smoke, and ran targeted verification. Chris remains responsible for review and merge.