1. Objectives & Impact ("What does it do?")

• Context & Background: As part of Issue #5361, a temporary patch was applied to MCPTool and McpToolset to set GOOGLE_API_PREVENT_AGENT_TOKEN_SHARING_FOR_GCP_SERVICES = "false" internally. This was because the underlying mcp_session_manager relied on a custom implementation of asyncio which lacked mTLS bound token support, leading to 401 Unauthorized errors in Agent Engine runtimes.
• Implementation Mechanism: The PR cleanly removes the dynamic assignment of this environment variable during constructor execution of MCPTool and McpToolset. It reverts this setting control entirely back to the application environment, preventing unintended process-wide configuration rewrites.
• Affected Surface: No public-facing API signatures, attributes, or visibility modifiers are altered. The change is robust and entirely backward-compatible.

2. Justification & Value ("Is it a valid and useful change?")

• Workspace Verification:
  • Investigated current workspace files: mcp_tool.py and mcp_toolset.py (using view_file and grep_search).
  • Found that: In the baseline code, both classes systematically overwrite os.environ["GOOGLE_API_PREVENT_AGENT_TOKEN_SHARING_FOR_GCP_SERVICES"] = "false" on construction.
• Value Assessment: Exceptionally high. Environment variables are process-global. Having a library or SDK component dynamically mutate them under-the-hood represents an implicit configuration bypass. If a user intentionally locks down their agent engine using "true" to enforce bound tokens elsewhere, initializing an MCP tool would silently disable this system security policy process-wide.
• Scope & Depth: Systematic & Architectural Fix. This addresses the underlying root-cause side effect cleanly rather than applying superficial point patches.

3. Principle & Style Alignment Checklist ("Does it follow rules?")

• Public API & Visibility Boundaries:
  • Status: Pass
  • Analysis: No signature adjustments. No public symbols added or removed. Unused imports are cleaned up.
• Code Quality, Typing & Conventions:
  • Status: Pass
  • Analysis: import os was safely removed from both main modules as it is no longer required. Formatting conforms perfectly to standard style requirements.
• Robustness & Edge Cases:
  • Status: Pass
  • Analysis: Restoring explicit environment controls ensures that deployment/infrastructure administrators can tune policies through secure orchestrators (e.g., Kubernetes env / GKE Metadata Server) without the application codebase reverting state dynamically during class initialization.
• Test Integrity & Quality:
  • Status: Pass
  • Analysis: High-quality unit tests added to both test_mcp_tool.py and test_mcp_toolset.py. It uses monkeypatch to simulate an environment-configured bound token policy, verifies constructability, and asserts that the policy is conserved post-construction.