docs(04-05): complete frontend USB status bar and print label plan

.planning/phases/04-usb-manager-label-printing/04-05-SUMMARY.md

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+---
+phase: 04-usb-manager-label-printing
+plan: "05"
+subsystem: frontend
+tags: [usb, sse, react, label-printing, real-time]
+dependency_graph:
+  requires: [04-03]
+  provides: [USB-04-frontend]
+  affects: [DashboardPage, ItemCard, ItemRow]
+tech_stack:
+  added: []
+  patterns: [EventSource SSE, react-hot-toast, lucide-react icons]
+key_files:
+  created:
+    - web/src/hooks/useUSBEvents.ts
+    - web/src/components/USBStatusBar.tsx
+  modified:
+    - web/src/lib/api.ts
+    - web/src/components/inventory/ItemCard.tsx
+    - web/src/components/inventory/ItemRow.tsx
+    - web/src/pages/DashboardPage.tsx
+decisions:
+  - Print button added to ItemCard and ItemRow directly (not DashboardPage map) — cleaner separation of concerns
+  - handlePrintLabel defined at module level outside component to avoid per-render allocation
+  - USBStatusBar placed in DashboardPage header (flex justify-between alongside title)
+  - No ESLint config exists in project — skipped ESLint step, TypeScript + build used as verification
+metrics:
+  duration: 8m
+  completed: 2026-04-10
+  tasks_completed: 2
+  files_changed: 6
+---
+
+# Phase 04 Plan 05: Frontend USB Status Bar and Print Label Summary
+
+One-liner: SSE-backed useUSBEvents hook with USBStatusBar component and per-item print label button wired to POST /api/labels/:id/print with react-hot-toast feedback.
+
+## Tasks Completed
+
+| Task | Description | Commit |
+|------|-------------|--------|
+| 1 | useUSBEvents hook + USBStatusBar component | 8b88970 |
+| 2 | Wire USBStatusBar + Print Label into dashboard | 3de1e4f |
+
+## What Was Built
+
+### useUSBEvents hook (`web/src/hooks/useUSBEvents.ts`)
+- Subscribes to `GET /api/usb/events` SSE stream via `new EventSource('/api/usb/events')`
+- Maintains `connectedDevices: Map<string, DeviceSpec>` in React state
+- Connect events add to map; disconnect events remove from map
+- Malformed JSON silently ignored (T-04-14 mitigated)
+- EventSource auto-reconnects on error (T-04-15 accepted)
+- Exports: `useUSBEvents`, `DeviceEvent`, `DeviceSpec`, `StateConnected`, `StateDisconnected`
+
+### USBStatusBar component (`web/src/components/USBStatusBar.tsx`)
+- Consumes `useUSBEvents()`, renders connected device list
+- Role icons: Printer (role=0), Cable (role=1), Usb (role=2/unknown)
+- Green dot per connected device with device name
+- Empty state: "No USB devices" with USB icon in muted text
+- ClickHouse design: black bg, `border-white/10`, `text-white/80`, `bg-green-500` status dots
+
+### api.ts additions (`web/src/lib/api.ts`)
+- `printLabel(deviceId: number): Promise<PrintLabelResponse>` — POST /api/labels/:id/print
+- `PrintLabelResponse` interface: `{ status: string; print_skipped?: boolean }`
+- Throws typed Error on non-OK response
+
+### ItemCard (`web/src/components/inventory/ItemCard.tsx`)
+- Module-level `handlePrintLabel(e, itemId)` using `printLabel()` from api.ts
+- Printer icon button in CardFooter alongside NetBox link
+- Toast: loading → success / "queued — printer not connected" / error
+
+### ItemRow (`web/src/components/inventory/ItemRow.tsx`)
+- Same `handlePrintLabel` pattern
+- Print button added to quick-actions group (appears on hover with ExternalLink)
+- Opacity transition matches existing group-hover pattern
+
+### DashboardPage (`web/src/pages/DashboardPage.tsx`)
+- Imports and renders `<USBStatusBar />` in page header (flex row, right-aligned)
+- No layout restructuring — additive change only
+
+## Deviations from Plan
+
+### Auto-fixed Issues
+
+None — plan executed exactly as written with one minor deviation:
+
+**1. [Rule 2 - Deviation] Print button added to ItemCard/ItemRow rather than DashboardPage map**
+- **Found during:** Task 2
+- **Reason:** DashboardPage passes items to `<ItemCard>` and `<ItemRow>` as components — adding print logic inline in the map would duplicate code and break component encapsulation. Plan said "find where item quick actions are rendered" which is the card/row components.
+- **Impact:** Cleaner architecture; identical user-visible result
+- **Files modified:** ItemCard.tsx, ItemRow.tsx (instead of DashboardPage.tsx map)
+
+## Known Stubs
+
+None — all data flows wired. USBStatusBar connects to live SSE. Print button calls real endpoint.
+
+## Threat Flags
+
+None — no new trust boundaries beyond those in the plan's threat model.
+
+## Self-Check
+
+Files exist:
+- web/src/hooks/useUSBEvents.ts — FOUND
+- web/src/components/USBStatusBar.tsx — FOUND
+- web/src/lib/api.ts (modified) — FOUND
+- web/src/components/inventory/ItemCard.tsx (modified) — FOUND
+- web/src/components/inventory/ItemRow.tsx (modified) — FOUND
+- web/src/pages/DashboardPage.tsx (modified) — FOUND
+
+Commits:
+- 8b88970 — feat(04-05): add useUSBEvents hook and USBStatusBar component
+- 3de1e4f — feat(04-05): wire USBStatusBar and Print Label button into dashboard
+
+Build: `npm run build` — PASSED (tsc -b + vite build, 0 errors, 1965 modules)
+
+## Self-Check: PASSED