fix(mcp-filesystem): allow recursive directory creation - #1981

Summary

Fixes #1978

create_directory documents recursive creation, but it calls the shared path validator before fs.mkdir(..., { recursive: true }). When more than one path component is missing, validation rejects the immediate parent and the recursive mkdir is never reached.

This change adds an opt-in allowMissingParents path for create_directory only. It walks upward to the nearest existing ancestor only for ENOENT, verifies that ancestor's real path remains inside an allowed directory, and preserves the existing validation behavior for every other filesystem tool. Existing symlink targets outside the allowed root are still rejected.

Verification

• Added MCP in-memory regression coverage for two missing directory levels.
• Added a symlink-boundary regression proving creation does not escape the allowed root.
• pnpm --filter @agent-infra/mcp-server-filesystem test — 5 passed.
• pnpm exec prettier --check and pnpm exec eslint on changed files — passed.
• pnpm exec tsc -p packages/agent-infra/mcp-servers/filesystem/tsconfig.json --noEmit — passed.
• Built @agent-infra/logger, mcp-http-server, and @agent-infra/mcp-server-filesystem in dependency order; ESM, CJS, and declaration output succeeded.
• git diff --check — passed.

The full workspace install also attempted an Electron postinstall download, which timed out externally; Electron is not used by this package and the focused dependency/build checks above completed successfully.

Checklist

• Added or updated necessary tests.
• Updated documentation to align with changes (not applicable; existing tool documentation already promises recursive creation).
• Verified no breaking changes.
• My change does not involve the above items.

AI assistance

Codex assisted with issue investigation and test design. The submitted implementation and every changed line were reviewed against the issue, repository conventions, and the validation results above.