fix(tests): Add hostname parser security regression tests (#1498)

[RanPollak]

Summary

Adds comprehensive regression tests for hostname parser security vulnerabilities to prevent parser differential attacks and allowlist bypasses.

Motivation

Issue #1498 requested test coverage for malformed CONNECT hostnames after the Claude Code SOCKS5 NUL-byte allowlist bypass disclosure. This ensures OpenShell's proxy hostname parser rejects malicious inputs before they reach policy evaluation.

Changes

• Added 9 security-focused regression tests in proxy.rs
• Tests cover: NUL injection, control characters, encoding, spaces, ports, IPv6
• All tests target the parse_target() function

Test Results

• 6 tests currently FAIL, exposing real vulnerabilities:

  • test_nul_byte_in_hostname_rejected - NUL byte injection (CRITICAL)
  • test_control_chars_in_hostname_rejected - CRLF/CR/LF/TAB injection (CRITICAL)
  • test_hostname_with_spaces_rejected - Space handling
  • test_ipv6_bracket_handling - IPv6 bracket validation
  • test_invalid_port_rejected - Port range validation
  • test_missing_port_rejected - Port requirement enforcement

• 3 tests PASS, confirming some protections are in place:

  • test_encoded_hostnames_safe - URL encoding handled safely
  • test_hostname_length_limits - No DoS via length
  • test_hostname_normalization_consistency - Consistent case handling

• 163 existing tests still pass - no regressions

Security Impact

Tests reveal 6 vulnerabilities enabling:

• Parser differential attacks (CRITICAL) - Policy matches "allowed.com" while connection goes to "evil.com" via NUL byte injection
• HTTP request smuggling (HIGH) - CRLF injection can add malicious headers
• Header injection (HIGH) - Control characters can manipulate HTTP protocol

Attack Scenario Example

Attacker CONNECT target: "allowed.com\x00evil.com:443"
Policy evaluation: Matches "allowed.com" → ALLOW  
Actual connection: Goes to "evil.com" → DATA EXFILTRATION

This is the exact vulnerability described in #1498's reference to the Claude Code SOCKS5 bypass.

Implementation Notes

These tests are intentionally failing to expose existing vulnerabilities. They serve as regression coverage and documentation of security issues that need fixing.

Maintainers can:

1. Review and merge these tests to establish regression coverage
2. Implement fixes to make failing tests pass
3. Re-run to confirm vulnerabilities are patched

Next Steps

Follow-up PR will implement fixes to the parse_target() function to make all tests pass by:

• Rejecting hostnames with control characters (NUL, CR, LF, TAB)
• Validating port ranges (1-65535)
• Proper IPv6 bracket handling
• Whitespace normalization

Fixes #1498

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