fix(utils): add path traversal validation for ShardedWal groupId

[Copilot]

The groupId parameter in ShardedWal can come from user input or environment variables and is used directly in path.join() operations without validation. This allows path traversal attacks via values like ../../../etc/passwd or ..\\windows\\system32.

Changes

• Added validateGroupId() function to reject:

  • Path separators (/, \)
  • Relative path components (., ..)
  • Null bytes
  • Empty/whitespace values
  • Paths that normalize unsafely

• Updated constructor to use != null checks instead of truthy checks, ensuring empty strings are validated rather than falling through to auto-generation

• Applied validation to all groupId sources: explicit constructor parameter, environment variables (measureNameEnvVar), and auto-generated values

// Before: vulnerable to path traversal
new ShardedWal({ 
  groupId: '../../../etc',  // ❌ writes to /path/to/base/../../../etc/
  // ...
});

// After: validation blocks attack
new ShardedWal({ 
  groupId: '../../../etc',  // ✓ throws "groupId cannot contain path separators"
  // ...
});

Testing

Added 10 test cases covering path traversal attempts, null bytes, relative paths, and valid groupIds. CodeQL scan confirms no remaining vulnerabilities.

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