[WIP][KVConnector] Retrive KV events from LMCache

[hickeyma]

Purpose

Updates to the LMCache connector to enable KV events generated by LMCache to be retrieved and published by the scheduler.

This is part of the solution for:

• [RFC] Add KV events LMCache/LMCache#1846 to enable KV events to be generated in LMCache
• RFC [RFC]: KV-Cache Interoperability API Standardization which proposes "formalizing KV Events as the public contract for any component emitting or consuming KV-Cache lifecycle events, including external indexers, routers, and engines".

Note to reviewers: Do NOT merge until the following merge first:

1. Updated code to use event property instead of the stats property. Property added in [Core] Send kv events from worker side to scheduler side #28309.
2. [RFC] Add KV events LMCache/LMCache#1846 is merged first.

Test Plan

Test Result

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[gemini-code-assist]

Code Review

This pull request introduces functionality to retrieve KV events from LMCache by adding a new LMCacheKVEvents class and integrating it into the LMCacheConnectorV1. This is a good step towards better KV-cache interoperability. However, the implementation of LMCacheKVEvents contains several critical bugs in the aggregate, is_empty, and reduce methods that would prevent it from working as intended. My review includes specific code suggestions to fix these issues and ensure the new functionality is robust and correct.

[chatgpt-codex-connector]

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[markmc]

My initial reaction is that if a connector needs to send events from the worker-side to the scheduler-side, we should add events to KVConnectorOutput and not abuse the generic nature of KVConnectorStats

[hickeyma]

My initial reaction is that if a connector needs to send events from the worker-side to the scheduler-side, we should add events to KVConnectorOutput and not abuse the generic nature of KVConnectorStats

I agree @markmc, thanks. This is my first effort by piggybacking on the stats. I will push a separate PR which adds events to KVConnectorOutput first and then rebase this accordingly..

[hickeyma]

Thanks @markmc for the review and feedback. Pushed PR #28309 for adding events property to KVConnectorOutput and also updated this PR accordingly.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @hickeyma.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork