[FEATURE] sandbox.filesystem needs metadata-only (traverse-only) path grants

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

sandbox.filesystem needs metadata-only (traverse-only) path grants -- entries that allow getcwd() traversal without granting recursive read access to subtree contents.

• Problem: sandbox.filesystem.allowRead entries are recursive -- a literal path like "/Users/mikeowens" grants full read on entire subtree

AND overrides denyRead entries

• Desired behavior: metadata-only (traverse-only) grant -- allows getcwd() path traversal without exposing subtree contents
• Use case: running sandboxed git in ~/git/ repos when CWD is under ~ (blocked by denyOnly: ["~"])
• Workaround: none currently -- any allowRead entry broad enough to fix getcwd() exposes sensitive files

Proposed Solution

add separate sandbox.filesystem.allowReadMetadata

Alternative Solutions

_No response_

Priority

High - voids sandboxing

Feature Category

CLI commands and flags

Use Case Example

Working in /sandbox sessions but need to run git commands.

Additional Context

_No response_