security: add log injection attack prevention with input sanitization (#667)

* security: add log injection attack prevention with input sanitization

- Created src/utils/log_sanitizer.py to sanitize user-controlled input before logging
- Prevents log injection attacks using newlines, tabs, carriage returns, etc.
- Escapes dangerous characters: \n, \r, \t, \0, \x1b
- Provides specialized functions for different input types:
  - sanitize_log_input: general purpose sanitization
  - sanitize_thread_id: for user-provided thread IDs
  - sanitize_user_content: for user messages (more aggressive truncation)
  - sanitize_agent_name: for agent identifiers
  - sanitize_tool_name: for tool names
  - sanitize_feedback: for user interrupt feedback
  - create_safe_log_message: template-based safe message creation

- Updated src/server/app.py to sanitize all user input in logging:
  - Thread IDs from request parameter
  - Message content from user
  - Agent names and node information
  - Tool names and feedback

- Updated src/agents/tool_interceptor.py to sanitize:
  - Tool names during execution
  - User feedback during interrupt handling
  - Tool input data

- Added 29 comprehensive unit tests covering:
  - Classic newline injection attacks
  - Carriage return injection
  - Tab and null character injection
  - HTML/ANSI escape sequence injection
  - Combined multi-character attacks
  - Truncation and length limits

Fixes potential log forgery vulnerability where malicious users could inject
fake log entries via unsanitized input containing control characters.

tests/unit/graph/test_plan_validation.py

@@ -1,8 +1,9 @@
 # Copyright (c) 2025 Bytedance Ltd. and/or its affiliates
 # SPDX-License-Identifier: MIT
 
+from unittest.mock import MagicMock, patch
+
 import pytest
-from unittest.mock import patch, MagicMock
 
 from src.graph.nodes import validate_and_fix_plan