fix: prevent path traversal in remote file synchronization

[g0w6y]

This PR fixes a critical path traversal vulnerability in the fetchRemote method of the Files class. Previously, remote filenames containing traversal sequences (e.g., ../../) were resolved without validation, allowing files to be written outside the intended project directory.

Changes

Established a Security Boundary: Resolved the absolute path of the contentDir to serve as a "jail" for file operations.

Path Normalization: Used path.resolve to normalize remote filenames and extensions into absolute local paths.

Boundary Validation: Implemented a check to ensure that the resolvedPath starts with the absoluteContentDir followed by the platform-specific path separator.

Security Error Handling: Added logic to throw a Security Error if a file resolution attempt falls outside the project directory, halting potentially malicious write operations.

Impact This fix prevents an attacker with control over a remote Apps Script project from performing arbitrary file writes on a user's local machine during a clasp pull or clasp clone. This effectively neutralizes a potential Remote Code Execution (RCE) vector.

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