fix(sdk): fork extension to prevent leaking data

[jezekra1]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @jezekra1, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical issue within the SDK's extension mechanism by ensuring proper data isolation. The core change involves modifying the BaseExtension class to prevent data leakage between requests. This is achieved by introducing a mechanism to create a fresh, isolated instance of an extension for each incoming request, rather than reusing a single instance. A new end-to-end test has also been added to validate this behavior, confirming that data remains distinct and secure across concurrent operations.

Highlights

• Enhanced Constructor: The BaseExtension class's __init__ method now accepts and stores *args and **kwargs, enabling the preservation of initial configuration for new instances.
• Instance Forking Mechanism: A new _fork method has been added to BaseExtension, allowing the creation of a new, identical instance of the extension. This is crucial for ensuring that each request is processed by a fresh, isolated object.
• Request Isolation: The __call__ method of BaseExtension has been updated to utilize the new _fork method. This ensures that every time an extension is invoked for a request, a new instance is created, preventing data from one request from affecting subsequent ones.
• New E2E Test for Isolation: A new end-to-end test, test_extension_is_not_reused, has been added to explicitly verify that extension instances are not inadvertently reused across multiple concurrent requests, confirming the effectiveness of the data isolation fix.

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[gemini-code-assist]

Code Review

This pull request effectively addresses a critical data leakage vulnerability in BaseExtensionServer that could occur during concurrent request processing. The introduction of a _fork method to create request-specific instances is a robust solution. The accompanying end-to-end test successfully validates this fix by simulating concurrent requests. My review includes a couple of minor suggestions for the new test file to improve its robustness and maintainability.

[gemini-code-assist]

The agent function is named chunked_artifact_producer and its docstring says "Agent producing chunked artifacts", but it actually just extracts an API key and yields it. This is misleading and harms maintainability. The name and docstring should be updated to reflect its actual behavior.

Suggested change

	async def chunked_artifact_producer(
	llm_ext: Annotated[LLMServiceExtensionServer, LLMServiceExtensionSpec.single_demand()],
	) -> AsyncGenerator[RunYield, Message]:
	# Agent producing chunked artifacts
	await asyncio.sleep(random() * 0.5)
	api_key = next(iter(llm_ext.data.llm_fulfillments.values())).api_key
	yield api_key
	async with create_server_with_agent(chunked_artifact_producer) as (server, test_client):
	async def api_key_producer(
	llm_ext: Annotated[LLMServiceExtensionServer, LLMServiceExtensionSpec.single_demand()],
	) -> AsyncGenerator[RunYield, Message]:
	# Agent producing an api_key from the extension
	await asyncio.sleep(random() * 0.5)
	api_key = next(iter(llm_ext.data.llm_fulfillments.values())).api_key
	yield api_key
	async with create_server_with_agent(api_key_producer) as (server, test_client):