feat(langchain): add LC-103, agent wires a raw HTTP Requests built-in tool

[jiaxinaspenlin-dotcom]

Summary

Adds LC-103 for LangChain agents that wire langchain_community's Requests* built-in tools directly into an agent.

These tools provide outbound HTTP capability where the method is fixed by the class but the destination can be model-controlled, creating exposure to internal services, cloud metadata endpoints, localhost/admin interfaces, and other resources reachable from the agent host.

What changed

• Added LC-103 to langchain/agent_safety.yaml
• Detects:
  • RequestsGetTool
  • RequestsPostTool
  • RequestsPutTool
  • RequestsPatchTool
  • RequestsDeleteTool
• Uses the existing agent_uses_hosted_tool_class predicate
• No new predicate
• No schema version bump

Rule metadata

• Rule: LC-103
• Severity: medium
• Confidence: 0.75
• Language: python
• Scope: agent

Validation

trustabl rules validate ../trustabl-rules

Result:

OK: 85 rule pack(s), 207 rule(s) valid under rule schema version 14

The engine's existing LangChain hosted-tool discovery was also verified to recognize all five Requests* classes without analyzer changes.

Paired changes

• trustabl/trustabl — engine fixture and fire/silent test coverage
• docs(langchain): add LC-103 rationale for Requests built-in tools trustabl-rulebook#79 — rationale documentation

All coordinated changes use:

feat/langchain-requests-builtin-tool