Phase 10: Add security hardening and threat-model tests

[ashishsinghbora]

Goal

Treat Magicloder as a local service that handles arbitrary remote URLs and filesystem paths.

Scope

• Write a threat model for SSRF, local-file access, path traversal, malicious redirects, resource exhaustion and untrusted response headers.
• Validate schemes and reject unsupported protocols.
• Add safe redirect policy.
• Prevent writes outside allowed directories where sandboxing is enabled.
• Add maximum file size, timeout, retry and queue limits.
• Sanitize filenames derived from URLs/content-disposition.
• Avoid logging secrets or sensitive local paths unnecessarily.
• Harden WebSocket/API authentication and origin handling.
• Add security-focused tests and a dependency scanning workflow.

Acceptance criteria

• Threat model is committed.
• Security tests cover SSRF/path traversal/resource exhaustion cases.
• Fuzz/property tests cover URL and filename handling where practical.
• CI runs security/dependency checks.