[Ciniesta]

Stop defaulting KB source LLM calls to Luna. When no model is explicitly configured, let prediction resolve the KB’s default model and enforce account restrictions

[Copilot]

🔵 Needs a closer look

The new model=None routing and KB-scope account restrictions depend on unavailable external implementations, while local tests mock these boundaries, leaving deployed dependency contracts unverified.

No open issues 🎉

What changed in this PR

This PR lets NucliaDB agent calls inherit the Knowledge Box’s configured model instead of defaulting to Luna, while preserving explicit model overrides and validating KB scope.

Changes:

• Makes the KB source model optional and leaves default resolution to prediction.
• Passes model and KB context through routing and helper calls, requiring an explicit routing model across different KBs.
• Adds tests for model inheritance, overrides, serialization, and scope validation.

File	Description
tests/​db/​test_transform.py	Verifies transformed KB agents leave the model unset.
agents/​nucliadb/​tests/​test_config.py	Tests the unset default and JSON round-trip behavior.
agents/​nucliadb/​tests/​test_agent.py	Tests routing, model precedence, helper calls, and scope checks.
agents/​nucliadb/​src/​hyperforge_nucliadb_agentic/​config.py	Makes the generative model optional for KB inheritance.
agents/​nucliadb/​src/​hyperforge_nucliadb_agentic/​agent.py	Propagates model and KB scope and preserves inherited defaults.

_{Review effort: Balanced}