## ADDED Requirements

### Requirement: Evaluation harness SHALL compare reports against a baseline
The system SHALL compare a current diagnosis evaluation report against a saved baseline report using deterministic rules.

#### Scenario: Aggregate regression detection
- **WHEN** the current report has a lower pass rate than the baseline report
- **THEN** the diff SHALL record a regression with the old value, new value, and delta

#### Scenario: Cost signal detection
- **WHEN** average tool-call count or average duration changes between reports
- **THEN** the diff SHALL record the baseline value, current value, and delta

#### Scenario: Verdict distribution comparison
- **WHEN** verdict counts differ between reports
- **THEN** the diff SHALL record the verdict distribution changes

### Requirement: Evaluation harness SHALL compare case-level report results
The system SHALL compare case results by case id and report actionable per-case changes.

#### Scenario: Case pass/fail regression
- **WHEN** a case changes from passing in the baseline to failing in the current report
- **THEN** the diff SHALL record a regression for that case

#### Scenario: Evidence coverage regression
- **WHEN** a required evidence tool changes from covered to uncovered for a case
- **THEN** the diff SHALL record a regression naming the case and tool

#### Scenario: Missing case detection
- **WHEN** a baseline case is absent from the current report
- **THEN** the diff SHALL record a regression for the missing case

#### Scenario: New case detection
- **WHEN** a current report contains a case absent from the baseline
- **THEN** the diff SHALL record the case as a non-regression change

### Requirement: Evaluation harness SHALL report baseline diff results
The system SHALL expose baseline diff output in structured JSON and reviewable Markdown formats.

#### Scenario: JSON diff output
- **WHEN** a baseline diff is written as JSON
- **THEN** it SHALL include aggregate summary fields and detailed diff items

#### Scenario: Markdown diff output
- **WHEN** a baseline diff is written as Markdown
- **THEN** it SHALL include a readable summary and a table of diff items