# Explainer Timeline UI Component (Step-by-Step Verdict Explanation)

## Module
Web

## Status
VERIFIED

## Description
Interactive step-by-step verdict explanation visualization with expand/collapse behavior. ExplainerStepComponent renders individual reasoning steps; ExplainerService provides data from backend; supports progressive disclosure of decision rationale for lineage views.

## Implementation Details
- **Feature directory**: `src/Web/StellaOps.Web/src/app/features/lineage/`
- **Routes**: `lineage.routes.ts`
- **Components**:
  - `attestation-links` (`src/Web/StellaOps.Web/src/app/features/lineage/components/attestation-links/attestation-links.component.ts`)
  - `audit-pack-export` (`src/Web/StellaOps.Web/src/app/features/lineage/components/audit-pack-export/audit-pack-export.component.ts`)
  - `export-options` (`src/Web/StellaOps.Web/src/app/features/lineage/components/audit-pack-export/export-options/export-options.component.ts`)
  - `merkle-display` (`src/Web/StellaOps.Web/src/app/features/lineage/components/audit-pack-export/merkle-display/merkle-display.component.ts`)
  - `signing-options` (`src/Web/StellaOps.Web/src/app/features/lineage/components/audit-pack-export/signing-options/signing-options.component.ts`)
  - `cgs-badge` (`src/Web/StellaOps.Web/src/app/features/lineage/components/cgs-badge/cgs-badge.component.ts`)
  - `compare-panel` (`src/Web/StellaOps.Web/src/app/features/lineage/components/compare-panel/compare-panel.component.ts`)
  - `diff-table` (`src/Web/StellaOps.Web/src/app/features/lineage/components/diff-table/diff-table.component.ts`)
  - `explainer-step` (`src/Web/StellaOps.Web/src/app/features/lineage/components/explainer-timeline/explainer-step/explainer-step.component.ts`)
  - `explainer-timeline` (`src/Web/StellaOps.Web/src/app/features/lineage/components/explainer-timeline/explainer-timeline.component.ts`)
  - `export-dialog` (`src/Web/StellaOps.Web/src/app/features/lineage/components/export-dialog/export-dialog.component.ts`)
  - `keyboard-shortcuts-help` (`src/Web/StellaOps.Web/src/app/features/lineage/components/keyboard-shortcuts-help/keyboard-shortcuts-help.component.ts`)
  - `lineage-compare-panel` (`src/Web/StellaOps.Web/src/app/features/lineage/components/lineage-compare-panel/lineage-compare-panel.component.ts`)
  - `lineage-compare` (`src/Web/StellaOps.Web/src/app/features/lineage/components/lineage-compare/lineage-compare.component.ts`)
  - `lineage-component-diff` (`src/Web/StellaOps.Web/src/app/features/lineage/components/lineage-component-diff/lineage-component-diff.component.ts`)
  - ... and 32 more components
- **Services**:
  - `audit-pack` (`src/Web/StellaOps.Web/src/app/features/lineage/services/audit-pack.service.ts`)
  - `explainer` (`src/Web/StellaOps.Web/src/app/features/lineage/services/explainer.service.ts`)
  - `lineage-export` (`src/Web/StellaOps.Web/src/app/features/lineage/services/lineage-export.service.ts`)
  - `lineage-graph` (`src/Web/StellaOps.Web/src/app/features/lineage/services/lineage-graph.service.ts`)
- **Models**:
  - `src/Web/StellaOps.Web/src/app/features/lineage/components/audit-pack-export/models/audit-pack.models.ts`
  - `src/Web/StellaOps.Web/src/app/features/lineage/components/diff-table/models/diff-table.models.ts`
  - `src/Web/StellaOps.Web/src/app/features/lineage/components/explainer-timeline/models/explainer.models.ts`
  - `src/Web/StellaOps.Web/src/app/features/lineage/components/node-diff-table/models/diff-table.models.ts`
  - `src/Web/StellaOps.Web/src/app/features/lineage/components/pinned-explanation/models/pinned.models.ts`
- **Source**: SPRINT_20251229_001_005_FE_explainer_timeline.md

## E2E Test Plan
- **Setup**:
  - [ ] Log in with a user that has appropriate permissions
  - [ ] Navigate to `/lineage`
  - [ ] Ensure test data exists (scanned artifacts, SBOM data, or seed data as needed)
- **Core verification**:
  - [ ] Verify the component renders correctly with sample data
  - [ ] Verify interactive elements respond to user input
  - [ ] Verify data is fetched and displayed from the correct API endpoints
- **Edge cases**:
  - [ ] Verify graceful handling when backend API is unavailable (error state)
  - [ ] Verify responsive layout at different viewport sizes
  - [ ] Verify accessibility (keyboard navigation, screen reader labels, ARIA attributes)

## Verification
- Run: `docs/qa/feature-checks/runs/web/explainer-timeline-ui-component/run-001/`
- Tier 0 (source): pass (`tier0-source-check.json`)
- Tier 1 (build/tests): pass (`tier1-build-check.json`)
- Tier 2 (behavior): pass (`tier2-e2e-check.json`)
- Verified on (UTC): 2026-02-11