## ADDED Requirements

### Requirement: Knowledge retrieval SHALL return structured evidence blocks
The `lookup_knowledge` retrieval flow SHALL expose retrieved evidence as structured evidence blocks in addition to the existing compatibility fields.

#### Scenario: Evidence block contains source metadata
- **WHEN** a `lookup_knowledge` call returns evidence
- **THEN** each evidence block SHALL include source, title when available, breadcrumb when available, retrieval layer, content, and hit reasons

#### Scenario: Compatibility fields remain available
- **WHEN** evidence blocks are returned
- **THEN** the existing `primary` and `supplement` result fields SHALL remain available when their source evidence exists

### Requirement: Knowledge retrieval SHALL deduplicate evidence blocks
The retrieval flow SHALL remove duplicate evidence blocks before returning them to the Agent.

#### Scenario: Duplicate source deduplication
- **WHEN** L0 and L1 produce evidence with the same source identity
- **THEN** the retrieval flow SHALL keep a single evidence block for that source
- **AND** the evidence block SHALL preserve hit reasons from both retrieval paths when available

#### Scenario: Postprocess count tracking
- **WHEN** evidence post-processing completes
- **THEN** the tool invocation details SHALL record candidate count and final evidence block count

### Requirement: Knowledge retrieval SHALL persist evidence block summaries
The system SHALL persist compact evidence block summaries in `tool_invocation.retrieval_details`.

#### Scenario: Evidence summaries are persisted
- **WHEN** a `lookup_knowledge` call records a tool invocation
- **THEN** `retrieval_details` SHALL include evidence block summaries containing source, title, retrieval layer, score when available, and hit reasons

#### Scenario: Full content is not duplicated into retrieval details
- **WHEN** evidence block summaries are persisted
- **THEN** full evidence content SHALL be omitted or truncated so the trace record remains compact