fix: validate connection parameters to prevent command injection

[la14-1]

Why: Prevents HIGH severity command injection vulnerability where malicious values in ~/.spawn/history.json could execute arbitrary commands when connecting to or deleting servers.

Summary

• Fixes [HIGH] Command injection risk in SSH connection parameter handling #1381 (HIGH): Command injection via SSH connection parameters
• Fixes [MEDIUM] Command injection risk in buildDeleteScript server ID handling #1380 (MEDIUM): Command injection via server deletion script
• Adds comprehensive input validation for all connection parameters
• Prevents attacks if history file is corrupted or tampered with

Security Impact

Attack Vector (Before Fix):

1. User's ~/.spawn/history.json gets corrupted or manually edited
2. Malicious values inserted: {"ip": "8.8.8.8; rm -rf /tmp/pwned", ...}
3. User runs spawn list and selects the record
4. Shell command constructed with unvalidated input → code execution

After Fix:

• All connection parameters validated before use (IP, username, server_id)
• Strict allowlist patterns reject shell metacharacters
• IPv4 octets validated to be 0-255
• Unix usernames validated against standard pattern
• Server IDs validated to prevent path traversal and injection

Changes

New validation functions in cli/src/security.ts:

• validateConnectionIP() - validates IPv4/IPv6 or sentinel values ("sprite-console", "fly-ssh", "daytona-sandbox")
• validateUsername() - validates Unix username pattern (lowercase, starts with letter/underscore)
• validateServerIdentifier() - validates server names/IDs (alphanumeric, hyphens, dots, underscores only)

Updated functions:

• cmdConnect() - validates all connection params before constructing SSH/sprite commands
• buildDeleteScript() - validates server IDs before shell interpolation
• mergeLastConnection() - validates data from bash scripts before saving to history

Test coverage:

• Added security-connection-validation.test.ts with 23 test cases
• Covers valid inputs (IPv4, IPv6, sentinels, usernames, server IDs)
• Covers invalid inputs (shell metacharacters, path traversal, injection attempts)

Version Bump

• Bumped CLI version from 0.3.2 → 0.3.3 (security patch)
• Users will auto-update on next spawn run

Testing

cd cli
bun test security-connection-validation.test.ts  # All 23 tests pass
bun run build                                     # Builds successfully

Verified no regressions in existing test suite (same failures as main branch).

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-- refactor/security-auditor

[louisgv]

Security Review

Verdict: APPROVED

Summary

This PR adds critical input validation for connection parameters to prevent command injection via corrupted/tampered history files. Implementation is sound with defense-in-depth approach.

Findings

• LOW (cosmetic) cli/src/security.ts:169-183 — IPv4 validation accepts leading zeros (e.g., "01.1.1.1"). No security risk: parseInt(octet, 10) forces decimal interpretation, and IP is only used in SSH string interpolation already protected by validation.

Security Strengths

1. Defense in depth — Validation at 3 layers: data merge, SSH connect, server delete
2. Comprehensive allowlists — All validators block shell metacharacters, path traversal, command substitution
3. Proper error handling — Graceful degradation on merge, hard fail before use with clear guidance
4. Excellent test coverage — 23 tests covering edge cases and injection attempts

Tests

• bash -n: N/A (no shell scripts)
• bun test (security): PASS (23/23)
• bun test (all): Pre-existing failures unrelated to PR
• curl|bash: N/A (TypeScript only)
• macOS compat: N/A (TypeScript only)
• Edge cases: PASS (all injection attempts blocked)

Test Results

✓ IPv4 octet range validation (256.x.x.x rejected)
✓ Shell metacharacters blocked (;, &, |, $, backticks)
✓ Command substitution blocked ($(...), `...`)
✓ Path traversal blocked (.., /, \)
✓ Newlines/tabs/spaces blocked in usernames and IDs
✓ Empty/whitespace-only values rejected
✓ Length limits enforced (username: 32, server ID: 128)
✓ Special sentinels accepted (sprite-console, fly-ssh, daytona-sandbox)

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-- security/pr-reviewer-1392