hvac: add gateway delete (retire the old Modbus gateway config)

There was no way to remove an mhi_gateways row either, alongside the
already-fixed device-delete gap — exposed by the same Modbus->MQTT
switchover. Adds DELETE /api/mhi-gateways/:id (manage_devices cap) and a
'Delete gateway' button. Devices referencing the gateway are NOT deleted
(mhi_gateway_id just goes NULL per the existing ON DELETE SET NULL FK) —
the confirm dialog says so and points at the separate device-delete flow
for retiring the stale mhi_modbus rows too.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/routes/mhi-gateways.js

@@ -54,6 +54,19 @@ export async function mhiGatewayRoutes(app) {
     return rows[0]
   })
 
+  // DELETE /api/mhi-gateways/:id — remove a gateway config entirely. Main use:
+  // retiring a gateway after it's switched to native MQTT (see lib/mqtt.js) and
+  // its Modbus register-map config is no longer needed. Devices that reference
+  // this gateway (device_type='mhi_modbus') are NOT deleted — mhi_gateway_id
+  // just goes NULL (ON DELETE SET NULL) — delete those rows separately via
+  // DELETE /api/devices/:id if they're being retired too.
+  app.delete('/api/mhi-gateways/:id', { preHandler: requireCap('manage_devices') }, async (req, reply) => {
+    const { rows } = await pool.query('SELECT id FROM mhi_gateways WHERE id = $1', [req.params.id])
+    if (!rows.length) return reply.status(404).send({ error: 'Gateway not found' })
+    await pool.query('DELETE FROM mhi_gateways WHERE id = $1', [req.params.id])
+    return { ok: true }
+  })
+
   // POST /api/mhi-gateways/:id/test-connection — live Modbus read of the
   // gateway comm status register (same check as scripts/test-modbus-connection.py)
   app.post('/api/mhi-gateways/:id/test-connection', { preHandler: requireCap('manage_devices') }, async (req, reply) => {

frontend/src/api.ts

@@ -113,6 +113,9 @@ export function updateMhiGateway(id: number, body: Partial<{ name: string; host:
 export function testMhiGatewayConnection(id: number): Promise<{ ok: boolean; note?: string; error?: string }> {
   return request(`/mhi-gateways/${id}/test-connection`, { method: 'POST', body: JSON.stringify({}) })
 }
+export function deleteMhiGateway(id: number): Promise<{ ok: boolean }> {
+  return request(`/mhi-gateways/${id}`, { method: 'DELETE' })
+}
 export async function importMhiRegisterMap(id: number, file: File): Promise<MhiGateway> {
   const form = new FormData()
   form.append('file', file)

frontend/src/components/GatewaysPanel.tsx

@@ -1,8 +1,8 @@
 import { useEffect, useState } from 'react'
-import { Plus, Wifi, WifiOff, Upload, Loader2 } from 'lucide-react'
+import { Plus, Wifi, WifiOff, Upload, Loader2, Trash2 } from 'lucide-react'
 import type { Zone, MhiGateway } from '../types'
 import {
-  fetchMhiGateways, createMhiGateway, testMhiGatewayConnection, importMhiRegisterMap, assignMhiUnit,
+  fetchMhiGateways, createMhiGateway, testMhiGatewayConnection, importMhiRegisterMap, assignMhiUnit, deleteMhiGateway,
 } from '../api'
 
 // Gateway configuration + MAPS register-map import for MHI aircon units (manual
@@ -65,6 +65,22 @@ export default function GatewaysPanel({ zones, onAssigned }: { zones: Zone[]; on
     }
   }
 
+  async function handleDelete(gw: MhiGateway) {
+    if (!confirm(
+      `Delete gateway "${gw.name}"? This removes its connection config and register-map import.` +
+      (gw.assigned_count > 0 ? ` ${gw.assigned_count} assigned device(s) will be unlinked from it (not deleted) — ` +
+        'if this gateway was switched to native MQTT, remove those Modbus device rows separately in Devices.' : '')
+    )) return
+    setError(''); setMsg('')
+    try {
+      await deleteMhiGateway(gw.id)
+      setMsg('Gateway deleted.')
+      load()
+    } catch (e) {
+      setError(e instanceof Error ? e.message : 'Delete failed')
+    }
+  }
+
   async function handleImport(id: number, file: File | undefined) {
     if (!file) return
     setImportingId(id); setError(''); setMsg('')
@@ -170,6 +186,9 @@ export default function GatewaysPanel({ zones, onAssigned }: { zones: Zone[]; on
                       onChange={e => { handleImport(gw.id, e.target.files?.[0]); e.target.value = '' }}
                     />
                   </label>
+                  <button className="btn btn-sm btn-danger" onClick={() => handleDelete(gw)}>
+                    <Trash2 size={13} strokeWidth={1.75} /> Delete gateway
+                  </button>
                 </div>
               </div>