Phase 6: Radio config + path hash mode

frontend/src/components/settings/SettingsRadioSection.tsx

@@ -47,6 +47,7 @@ export function SettingsRadioSection({
   const [bw, setBw] = useState('');
   const [sf, setSf] = useState('');
   const [cr, setCr] = useState('');
+  const [pathHashMode, setPathHashMode] = useState('0');
   const [gettingLocation, setGettingLocation] = useState(false);
   const [busy, setBusy] = useState(false);
   const [rebooting, setRebooting] = useState(false);
@@ -77,6 +78,7 @@ export function SettingsRadioSection({
     setBw(String(config.radio.bw));
     setSf(String(config.radio.sf));
     setCr(String(config.radio.cr));
+    setPathHashMode(String(config.path_hash_mode));
   }, [config]);
 
   useEffect(() => {
@@ -159,6 +161,8 @@ export function SettingsRadioSection({
       return null;
     }
 
+    const parsedPathHashMode = parseInt(pathHashMode, 10);
+
     return {
       name,
       lat: parsedLat,
@@ -170,6 +174,11 @@ export function SettingsRadioSection({
         sf: parsedSf,
         cr: parsedCr,
       },
+      ...(config.path_hash_mode_supported &&
+      !isNaN(parsedPathHashMode) &&
+      parsedPathHashMode !== config.path_hash_mode
+        ? { path_hash_mode: parsedPathHashMode }
+        : {}),
     };
   };
 
@@ -427,6 +436,33 @@ export function SettingsRadioSection({
         </div>
       </div>
 
+      {config.path_hash_mode_supported && (
+        <>
+          <Separator />
+          <div className="space-y-2">
+            <Label htmlFor="path-hash-mode">Path Hash Mode</Label>
+            <select
+              id="path-hash-mode"
+              value={pathHashMode}
+              onChange={(e) => setPathHashMode(e.target.value)}
+              className="w-full h-10 px-3 rounded-md border border-input bg-background text-sm ring-offset-background focus:outline-none focus:ring-2 focus:ring-ring focus:ring-offset-2"
+            >
+              <option value="0">1 byte (default)</option>
+              <option value="1">2 bytes</option>
+              <option value="2">3 bytes</option>
+            </select>
+            <div className="rounded-md border border-amber-500/50 bg-amber-500/10 p-3 text-xs text-amber-200">
+              <p className="font-semibold mb-1">Compatibility Warning</p>
+              <p>
+                ALL nodes along a message&apos;s route &mdash; your radio, every repeater, and the
+                recipient &mdash; must be running firmware that supports the selected mode. Messages
+                sent with 2-byte or 3-byte hops will be dropped by any node on older firmware.
+              </p>
+            </div>
+          </div>
+        </>
+      )}
+
       {error && (
         <div className="text-sm text-destructive" role="alert">
           {error}

frontend/src/test/appFavorites.test.tsx

@@ -174,6 +174,8 @@ const baseConfig = {
   tx_power: 17,
   max_tx_power: 22,
   radio: { freq: 910.525, bw: 62.5, sf: 7, cr: 5 },
+  path_hash_mode: 0,
+  path_hash_mode_supported: false,
 };
 
 const baseSettings = {

frontend/src/test/appSearchJump.test.tsx

@@ -202,6 +202,8 @@ describe('App search jump target handling', () => {
       tx_power: 17,
       max_tx_power: 22,
       radio: { freq: 910.525, bw: 62.5, sf: 7, cr: 5 },
+      path_hash_mode: 0,
+      path_hash_mode_supported: false,
     });
     mocks.api.getSettings.mockResolvedValue({
       max_radio_contacts: 200,

frontend/src/test/appStartupHash.test.tsx

@@ -158,6 +158,8 @@ describe('App startup hash resolution', () => {
       tx_power: 17,
       max_tx_power: 22,
       radio: { freq: 910.525, bw: 62.5, sf: 7, cr: 5 },
+      path_hash_mode: 0,
+      path_hash_mode_supported: false,
     });
     mocks.api.getSettings.mockResolvedValue({
       max_radio_contacts: 200,

frontend/src/test/pathUtils.test.ts

@@ -41,6 +41,8 @@ function createConfig(overrides: Partial<RadioConfig> = {}): RadioConfig {
     tx_power: 10,
     max_tx_power: 20,
     radio: { freq: 915, bw: 250, sf: 10, cr: 8 },
+    path_hash_mode: 0,
+    path_hash_mode_supported: false,
     ...overrides,
   };
 }

frontend/src/test/settingsModal.test.tsx

@@ -30,6 +30,8 @@ const baseConfig: RadioConfig = {
     sf: 7,
     cr: 5,
   },
+  path_hash_mode: 0,
+  path_hash_mode_supported: false,
 };
 
 const baseHealth: HealthStatus = {

frontend/src/types.ts

@@ -13,6 +13,8 @@ export interface RadioConfig {
   tx_power: number;
   max_tx_power: number;
   radio: RadioSettings;
+  path_hash_mode: number;
+  path_hash_mode_supported: boolean;
 }
 
 export interface RadioConfigUpdate {
@@ -21,6 +23,7 @@ export interface RadioConfigUpdate {
   lon?: number;
   tx_power?: number;
   radio?: RadioSettings;
+  path_hash_mode?: number;
 }
 
 export interface FanoutStatusEntry {