test: add router e2e test with mockers to per-merge ci

[PeaBrane]

Overview:

as titled

Summary by CodeRabbit

• Bug Fixes

  • Improved error handling in the scheduler to better manage cases where no endpoints are available, ensuring the scheduler waits for updates instead of exiting unexpectedly.
  • Increased the log severity for failed KV event transmissions from debug to warning, making such issues more visible.

• Tests

  • Added a comprehensive end-to-end test covering concurrent streaming chat completion requests with multiple mocker engine instances and the KV router.
  • Introduced supporting test utilities and process management for reliable test orchestration.

• Chores

  • Added license header to a new test directory file for compliance.

[coderabbitai]

Walkthrough

The changes introduce improved error handling and logging in the KV router's Rust code, specifically for scheduler errors and event dispatch failures. Additionally, new Python end-to-end tests are added to validate the KV router's integration with mock engine instances, including process management and concurrent streaming request verification.

Changes

File(s)	Change Summary
lib/llm/src/kv_router.rs	Raised log level for KV event send failures from debug to warn; no logic changes.
lib/llm/src/kv_router/scheduler.rs	Added explicit handling for NoEndpoints error: logs at trace level, waits for endpoint updates, and retries.
tests/router/init.py	New file with only the Apache 2.0 license header; no functional code.
tests/router/test_router_e2e_with_mockers.py	New end-to-end test: launches mocker and router processes, sends concurrent streaming requests, manages cleanup.

Sequence Diagram(s)

sequenceDiagram
    participant TestRunner
    participant MockerProcess
    participant KVRouterProcess
    participant HFHub
    participant Client

    TestRunner->>HFHub: download_model()
    HFHub-->>TestRunner: (model download success/fail)
    loop For each mocker
        TestRunner->>MockerProcess: start()
    end
    TestRunner->>KVRouterProcess: start()
    loop For each concurrent request
        Client->>KVRouterProcess: POST /v1/chat/completions (streaming)
        KVRouterProcess->>MockerProcess: Forward request
        MockerProcess-->>KVRouterProcess: Streaming response
        KVRouterProcess-->>Client: Streaming response
    end
    TestRunner->>MockerProcess: terminate()
    TestRunner->>KVRouterProcess: terminate()

Loading

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~35 minutes

Poem

In the warren where routers hop and play,
New logs warn when things go astray.
Mockers gather, engines hum,
Streaming chats to everyone.
With tests that run both night and day,
The code grows stronger, come what may!
🐇✨

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