Materialize recipe input mounts before workflow commands

[chubes4]

Summary

• Materializes generic recipe input mounts through the Playground VFS materialization hook before workflow commands run.
• Keeps staged file materialization in the same setup phase so custom PHPUnit roots from mounted inputs are readable before execution.
• Avoids recursive host mount walks and skips large/cache directories while materializing directory mounts into Playground.
• Extends regression coverage for both generic input mounts and skipped directory materialization.

Testing

• npx tsx tests/mount-materialization.test.ts
• npm run test:recipe-runtime-setup-staged-materialization
• npm run build -- --pretty false

AI assistance

• AI assistance: Yes
• Tool(s): openai/gpt-5.5 via OpenCode
• Used for: Debugging the input mount materialization gap, implementing the fix, and drafting regression tests.