Minimal DI for workflow nodes via node_factory constructor injection

[laipz8200]

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1. Is this request related to a challenge you're experiencing? Tell me about your story.

I’m building workflow-based apps where nodes depend on services like HTTP clients, memory systems, and RAG/retrieval. Right now those dependencies are effectively fixed or global, so swapping implementations per workflow/app is difficult and testing nodes requires patching globals. I want a simple injection mechanism so nodes can receive dependencies explicitly and I can choose implementations per workflow without forking nodes or adding ad‑hoc conditionals.

2. Additional context or comments

Proposal (minimal DI approach):

• Use constructor injection for node dependencies (e.g., HttpClient, MemoryStore, RagRetriever).
• Update node_factory to resolve and pass these dependencies when instantiating nodes.
• Keep default behavior unchanged by providing default implementations in node_factory if no overrides are configured.
• Allow configuration (initially internal) to choose alternative implementations per workflow/app/run.
• Focus on a small set of core dependencies first (HTTP client + memory + RAG), expand later.

Acceptance criteria (minimal scope):

• Existing workflows continue to run without config changes.
• Nodes can declare dependencies in their constructor.
• node_factory injects defaults or configured implementations.
• Unit tests for node instantiation + dependency resolution paths.

Notes:

• This keeps DI centralized and avoids a heavy framework; it’s a targeted change to node_factory plus constructor signatures.

3. Can you help us with this feature?

• I am interested in contributing to this feature.