## ADDED Requirements

### Requirement: Knowledge retrieval SHALL prefer Spring AI VectorStore when configured
The retrieval service SHALL support Spring AI VectorStore as the preferred vector retrieval abstraction without changing the `lookup_knowledge` tool contract.

#### Scenario: VectorStore mode uses Spring AI
- **WHEN** retrieval vector store mode is configured as `spring-ai`
- **THEN** semantic retrieval SHALL query through Spring AI `VectorStore`
- **AND** the returned candidates SHALL be normalized into the existing vector search result shape

#### Scenario: Auto mode prefers VectorStore
- **WHEN** retrieval vector store mode is configured as `auto`
- **AND** a Spring AI `VectorStore` bean is available
- **THEN** semantic retrieval SHALL attempt Spring AI `VectorStore` before the SDK path

### Requirement: Knowledge retrieval SHALL preserve SDK fallback
The retrieval service SHALL keep the existing Milvus SDK retrieval implementation available.

#### Scenario: SDK mode bypasses VectorStore
- **WHEN** retrieval vector store mode is configured as `sdk`
- **THEN** semantic retrieval SHALL use the existing Milvus SDK path

#### Scenario: Auto fallback uses SDK
- **WHEN** retrieval vector store mode is `auto`
- **AND** Spring AI `VectorStore` is unavailable or fails
- **THEN** semantic retrieval SHALL fall back to the existing Milvus SDK path

### Requirement: Knowledge retrieval SHALL keep score semantics explicit
The retrieval service SHALL preserve score semantics when results come from different retrieval implementations.

#### Scenario: SDK score remains L2 distance
- **WHEN** a candidate is returned by the SDK path
- **THEN** its score semantics SHALL remain compatible with existing L2 distance normalization

#### Scenario: VectorStore score is mapped without changing tool contract
- **WHEN** a candidate is returned by Spring AI `VectorStore`
- **THEN** it SHALL be mapped into the existing result shape
- **AND** trace or comparison code SHALL be able to distinguish it as a VectorStore similarity score when needed

### Requirement: Knowledge retrieval SHALL reuse the existing Milvus collection
Spring AI Milvus integration SHALL be configured to use the existing collection schema unless explicitly changed.

#### Scenario: Existing field mapping
- **WHEN** Spring AI Milvus VectorStore is configured
- **THEN** it SHALL use the existing id, content, vector, and metadata field names
- **AND** it SHALL use the configured embedding dimension and metric type compatible with existing vectors