The correct option is Vertex AI Agent Builder.

This service is designed to build production agents that can call tools and APIs, orchestrate multi step workflows, and ground responses in enterprise data. It can connect to multiple internal systems through extensions and connectors, apply company policies with controlled system instructions, and maintain a consistent brand voice through prompt design and safety controls. It also supports retrieval and grounding so the agent can fetch order and delivery details before taking actions.

Vertex AI Search focuses on enterprise retrieval and grounding, which helps answer questions from internal data, but it does not by itself provide end to end workflow orchestration or robust tool execution needed to call multiple systems and apply complex policies.

Gemini Advanced is a consumer offering for individual use rather than a managed platform for building enterprise agents. It does not provide the enterprise grade orchestration, connectors, and deployment capabilities required here.

Fine tune a foundation model with Model Garden would adjust model behavior or style but it does not add the ability to connect to internal systems, execute tools, or manage workflows. It would also risk stale knowledge for order and delivery data that changes frequently.

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