## 1. Evidence Model

- [x] 1.1 Add an `EvidenceBlock` DTO.
- [x] 1.2 Add evidence block list and postprocess count fields to `LookupResult`.

## 2. Evidence Postprocess

- [x] 2.1 Build evidence blocks from L0 matches and L1 candidates in `LookupKnowledgeTool`.
- [x] 2.2 Deduplicate evidence by stable source key.
- [x] 2.3 Preserve existing primary/supplement compatibility behavior.

## 3. Trace Recording

- [x] 3.1 Extend `ToolInvocationRecorder.LookupKnowledgeRecord` with evidence block summaries and postprocess counts.
- [x] 3.2 Persist evidence block summaries in `retrieval_details`.

## 4. Tests

- [x] 4.1 Add or update tests for evidence block creation and deduplication.
- [x] 4.2 Add or update tests for persisted evidence block summaries.
- [x] 4.3 Run targeted tests and the RAG retrieval baseline evaluator.

## 5. Validation

- [x] 5.1 Run OpenSpec validation for the change.
- [x] 5.2 Review git diff to confirm only expected code/spec/test files changed.