[GuideLLM Refactor] backend package updates, rewrites, and tests expansion

[markurtz]

Summary

Refactors the backend package to introduce a new architecture that supports the scheduler refactor. The changes include new object models for requests/responses, adjustments to the registry-based backend system, and integration with the scheduler interface. The refactor replaces the previous response/streaming model with a more flexible request-response pattern that supports timing measurements and distributed execution.

Details

• New object models: Introduced GenerationRequest, GenerationResponse, and GenerationRequestTimings in objects.py to standardize data flow between scheduler and backends
• Backend architecture refactor: Redesigned Backend base class to extend RegistryMixin and BackendInterface, enabling automatic registration and scheduler integration
• Process lifecycle management: Added process_startup() and process_shutdown() methods to support distributed worker processes with proper resource management
• OpenAI backend modernization: Rewrote OpenAIHTTPBackend with improved error handling, streaming support, beginning support for multimodal content processing, and configuration management
• Registry system: Implemented automatic backend registration using decorators, replacing manual registry management
• Scheduler integration: Backends now implement BackendInterface with resolve() method for processing generation requests with timing metadata
• Removed deprecated modules: Eliminated response.py with its streaming response types in favor of the new object model
• Enhanced test coverage: Added comprehensive unit tests for all new components with smoke, sanity, and regression test categories

Test Plan

• Execute new backend module test suites covering smoke, sanity, and regression scenarios
• Verify OpenAI backend functionality with mocked HTTP responses for both streaming and non-streaming modes
• Test backend registry and factory pattern functionality
• Validate integration with scheduler interfaces and timing measurement
• Ensure proper resource management during process startup/shutdown cycles

Related Issues

• Part of the larger scheduler refactor initiative

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Use of AI

• Includes AI-assisted code completion
• Includes code generated by an AI application
• [] Includes AI-generated tests (NOTE: AI written tests should have a docstring that includes ## WRITTEN BY AI ##)

[Copilot]

Pull Request Overview

Refactors the backend architecture to introduce new request/response models, a registry-based Backend interface with process lifecycle, and a modernized OpenAI HTTP backend with streaming and multimodal support. Also replaces deprecated response types and significantly expands unit tests.

• Introduces GenerationRequest, GenerationResponse, and GenerationRequestTimings models
• Rewrites OpenAIHTTPBackend with streaming, timing, and registry integration
• Adds process_startup/process_shutdown lifecycle and removes legacy response module

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/guidellm/backend/backend.py	Defines new Backend base class integrating RegistryMixin and BackendInterface; updates factory and lifecycle contract.
src/guidellm/backend/openai.py	Complete rewrite of OpenAIHTTPBackend, adds paths/keys constants, streaming, multimodal handling, and validation logic.
src/guidellm/backend/objects.py	Adds standardized request/response/timings Pydantic models.
src/guidellm/backend/response.py	Removes deprecated streaming response and request args models.
src/guidellm/backend/init.py	Updates exports to new models and backend.
tests/unit/backend/test_openai_backend.py	Expands tests for new backend behavior, streaming, timings, and registry integration.
tests/unit/backend/test_objects.py	New tests for the new object models and their properties.
tests/unit/backend/test_backend.py	Tests Backend base class behaviors and registry.
tests/unit/backend/test_response.py	Removes tests for deprecated response module.
tests/unit/backend/test_openai_backend_custom_configs.py	Removes tests tied to old settings-driven header behavior.

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