docs: add v1.4 Collection Tools design spec

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/superpowers/specs/2026-04-03-v1.4-collection-tools-design.md

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+# v1.4 Collection Tools Design
+
+**Date:** 2026-04-03
+**Milestone:** v1.4 Collection Tools
+**Scope:** Setup impact preview, item quantity, CSV import/export, item duplication
+
+## Feature 1: Setup Impact Preview
+
+Already fully designed in `.planning/phases/13-setup-impact-preview/`. Two plans exist:
+- **13-01**: Pure `computeImpactDeltas` function + `useImpactDeltas` hook + uiStore state (TDD)
+- **13-02**: `SetupImpactSelector` + `ImpactDeltaBadge` components wired into thread detail
+
+Execute the existing plans as-is. No design changes needed.
+
+## Feature 2: Item Quantity
+
+### Schema
+
+Add `quantity INTEGER NOT NULL DEFAULT 1` to `items` table via Drizzle migration.
+
+```ts
+quantity: integer("quantity").notNull().default(1),
+```
+
+### Validation
+
+Add to `createItemSchema` in `src/shared/schemas.ts`:
+```ts
+quantity: z.number().int().positive().optional(),
+```
+
+Flows to `updateItemSchema` via `.partial()` automatically.
+
+### Service Layer
+
+No special business logic — quantity is a stored field.
+
+**Totals computation changes:**
+- `totals.service.ts`: `getCategoryTotals()` and `getGlobalTotals()` must multiply `weightGrams * quantity` and `priceCents * quantity` in their SQL SUM aggregations.
+- `setup.service.ts`: `getSetupWithItems()` and `getAllSetups()` — when computing setup totals, multiply item weight/price by the item's quantity.
+
+### UI
+
+- **ItemForm**: Number input for quantity (min=1), placed below price field. Defaults to 1.
+- **ItemCard**: Show "x2" badge next to item name when quantity > 1. No badge when quantity is 1.
+- **Totals**: Already computed server-side with the quantity multiplication. No client-side changes for totals.
+- **Setup weight/cost**: The item's quantity determines its weight/cost contribution when included in a setup (one `setup_items` row, but totals reflect quantity).
+
+### Thread Resolution
+
+When a thread is resolved and a candidate is copied to an item, the new item gets `quantity: 1` (default). No special handling needed.
+
+## Feature 3: CSV Import/Export
+
+### Export
+
+**Endpoint:** `GET /api/items/export`
+- Returns CSV with headers: `name,quantity,weightGrams,priceCents,category,notes,productUrl`
+- `Content-Type: text/csv`
+- `Content-Disposition: attachment; filename="gearbox-export.csv"`
+- Weight in grams, price in cents (raw values, no formatting)
+- Category column contains category name (not ID)
+
+**Service:** `exportItemsCsv(db)` returns a CSV string. Joins items with categories for name lookup.
+
+### Import
+
+**Endpoint:** `POST /api/items/import`
+- Accepts multipart form upload (CSV file)
+- Parses rows, validates required fields (name is required, others optional)
+- Category matching: looks up by name (case-insensitive). Creates new category if not found.
+- Quantity defaults to 1 if not present in CSV
+- Returns `{ imported: number, created_categories: string[], errors: string[] }`
+- Skips rows with errors, continues processing remaining rows
+
+**Service:** `importItemsCsv(db, csvContent: string)` parses and inserts items.
+
+### UI
+
+Settings page gets an "Import/Export" section:
+- "Export CSV" button — triggers download via `GET /api/items/export`
+- "Import CSV" file input — accepts .csv files, shows count of parsed rows, confirm button to upload
+- Success/error feedback after import completes
+
+## Feature 4: Item Duplication
+
+### API
+
+**Endpoint:** `POST /api/items/:id/duplicate`
+- Copies all fields from source item: name, weightGrams, priceCents, categoryId, notes, productUrl, imageFilename, imageSourceUrl, quantity
+- Appends " (copy)" to the name
+- New `createdAt`/`updatedAt` timestamps
+- Returns the new item
+
+**Service:** `duplicateItem(db, id)` — fetches source item, inserts copy, returns new item.
+
+### UI
+
+- Add "Duplicate" action to ItemCard (alongside existing edit/delete actions)
+- Duplicating opens the edit panel pre-filled with the new item so the user can rename or adjust
+
+## Phase Ordering
+
+1. **Item Quantity** — schema change first since CSV import/export and totals depend on it
+2. **Setup Impact Preview** — execute existing Phase 13 plans
+3. **Item Duplication** — small, self-contained
+4. **CSV Import/Export** — depends on quantity field existing in schema
+
+## Out of Scope
+
+- Quantity per setup (setup_items.quantity) — items table quantity is sufficient for v1.4
+- CSV export with formatted weights/prices — raw values are more portable
+- Image export/import via CSV — images are local files, not CSV-compatible
+- Bulk edit from CSV preview — import creates, doesn't update existing items