# Three-Pane Layout (Categories/Items/Proof)

## Module
Web

## Status
VERIFIED

## Description
The compare feature implements a three-pane layout with categories, items, and proof panes for side-by-side comparison workflows.

## Implementation Details
- **Feature directory**: `src/Web/StellaOps.Web/src/app/features/compare/components/`
- **Components**:
  - `three-pane-layout` (`src/Web/StellaOps.Web/src/app/features/compare/components/three-pane-layout.component.ts`)
  - `categories-pane` (`src/Web/StellaOps.Web/src/app/features/compare/components/categories-pane.component.ts`)
  - `items-pane` (`src/Web/StellaOps.Web/src/app/features/compare/components/items-pane.component.ts`)
  - `proof-pane` (`src/Web/StellaOps.Web/src/app/features/compare/components/proof-pane.component.ts`)
  - `compare-view` integration (`src/Web/StellaOps.Web/src/app/features/compare/components/compare-view.component.ts`)
- **Services**:
  - `delta-compute` (`src/Web/StellaOps.Web/src/app/features/compare/services/delta-compute.service.ts`)
- **Behavior coverage**:
  - `src/Web/StellaOps.Web/src/tests/compare/three-pane-layout.behavior.spec.ts`
- **Source**: Feature matrix scan (corrected during QA verification)

## E2E Test Plan
- **Setup**:
  - [ ] Log in with a user that has appropriate permissions
  - [ ] Navigate to compare workflow route
  - [ ] Ensure compare session test data exists (baseline/current scan pair)
- **Core verification**:
  - [ ] Verify the three panes render with deterministic panel ordering
  - [ ] Verify category selection updates item filter and resets item selection
  - [ ] Verify selected item/category propagate into proof/categories panes
- **Edge cases**:
  - [ ] Verify graceful handling when no category is selected (filter clear)
  - [ ] Verify responsive layout behavior at reduced viewport widths
  - [ ] Verify keyboard/accessibility semantics for pane interactions

## Verification
- Run ID: `docs/qa/feature-checks/runs/web/three-pane-layout/run-001/`
- Date (UTC): 2026-02-11
- Tier 0: PASS (source/symbol verification for compare three-pane components and behavior spec).
- Tier 1: PASS (`npm run test` focused suite: 18 files / 92 tests; `npm run build` passed with known baseline warnings).
- Tier 2: PASS (behavioral verification of pane rendering, explain-mode/role propagation, deterministic filtering transitions, and cross-pane state propagation).