fix: handle missing KV cache without crashing engine

[lvhan028]

No description provided.

[Copilot]

Pull request overview

This PR improves robustness around engine sleep/wakeup by rejecting inference requests while sleeping and preventing PyTorch-engine inference from crashing when KV/state cache engines are missing (e.g., after sleep or partial wakeup).

Changes:

• Make sleep/wakeup flows async end-to-end (OpenAI server → AsyncEngine → backend engines/executors), with thread offloading where appropriate.
• Add an epoch-stamping mechanism to drop work that bound a session before a stop-all/abort-all event, avoiding races during sleep.
• Convert missing cache situations into structured internal-engine errors instead of uncaught exceptions, and propagate them through the engine loop.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
lmdeploy/turbomind/turbomind.py	Makes TurboMind sleep/wakeup async via asyncio.to_thread wrappers.
lmdeploy/serve/openai/api_server.py	Rejects inference requests while sleeping; stamps session epoch; makes /sleep and /wakeup await engine operations.
lmdeploy/serve/managers/session_manager.py	Adds Session.epoch tracking and logs epoch on abort.
lmdeploy/serve/core/async_engine.py	Adds stale-session dropping via epoch; makes sleep/wakeup await backend; adjusts metrics increments for new abort/error paths.
lmdeploy/pytorch/engine/mp_engine/base.py	Converts MP engine sleep/wakeup RPC calls to async.
lmdeploy/pytorch/engine/mp_engine/base_worker.py	Converts MP worker sleep/wakeup to async and awaits engine methods.
lmdeploy/pytorch/engine/model_agent/agent.py	Introduces CacheNotReadyError, guards cache usage, and converts cache-missing failures into batched outputs with an engine error message.
lmdeploy/pytorch/engine/model_agent/init.py	Exposes CacheNotReadyError from the model_agent package.
lmdeploy/pytorch/engine/executor/uni_executor.py	Adds async sleep/wakeup plumbing for the single-device executor.
lmdeploy/pytorch/engine/executor/ray_executor.py	Makes sleep/wakeup async and offloads blocking RPC calls to threads.
lmdeploy/pytorch/engine/executor/mp_executor.py	Adds async sleep/wakeup implemented via collective_rpc_async.
lmdeploy/pytorch/engine/executor/base.py	Updates executor interface: wakeup is now async.
lmdeploy/pytorch/engine/executor/base_worker.py	Updates worker wrapper interface: wakeup is now async.
lmdeploy/pytorch/engine/engine.py	Makes engine sleep/wakeup async and awaits executor implementations.
lmdeploy/pytorch/engine/engine_loop.py	Treats engine_error_msg in BatchedOutputs as an internal engine error and finishes running requests accordingly.

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[Copilot]

Docstring refers to http_bind_epoch, but the stamped attribute is session.epoch (set in api_server.VariableInterface.get_session). Consider updating the wording to avoid suggesting a non-existent field/name.

Suggested change

	"""If session is stamped ``http_bind_epoch`` by api_server and
	"""If api_server stamped the session's ``epoch`` and