semi implemented and features implemented save checkpoint

docs/features/unchecked/web/explainer-timeline-ui-component.md

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+# Explainer Timeline UI Component (Step-by-Step Verdict Explanation)
+
+## Module
+Web
+
+## Status
+IMPLEMENTED
+
+## 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)