battery: send alerts on channel "testowy" (index 2), not the pinned send channel

Owner request. BatteryAlertService reads new env BATTERY_ALERT_CHANNEL
(default 2) at construction and passes it through MeshService.sendText,
which gains an optional trailing channel argument defaulting to the
pinned MESH_SEND_CHANNEL — every other sender is untouched. Threshold,
cooldown, merged one-message-per-cycle format and @mentions unchanged.

src/battery/battery.service.spec.ts

@@ -33,9 +33,10 @@ function makeService(
 }
 
 beforeEach(() => {
-  // defaults under test: threshold 20, cooldown 6 h
+  // defaults under test: threshold 20, cooldown 6 h, channel 2 ("testowy")
   delete process.env.BATTERY_ALERT_THRESHOLD;
   delete process.env.BATTERY_ALERT_COOLDOWN_MS;
+  delete process.env.BATTERY_ALERT_CHANNEL;
 });
 
 describe('mention', () => {
@@ -79,11 +80,13 @@ describe('BatteryAlertService check threshold', () => {
 
     await svc.check();
 
-    // <= choice: exactly 20 qualifies too — both in ONE batched message
+    // <= choice: exactly 20 qualifies too — both in ONE batched message, on the default channel 2
     expect(sendText).toHaveBeenCalledTimes(1);
     expect(sendText).toHaveBeenCalledWith(
       BROADCAST_ADDR,
       '⚠️ battery low: @!00000001 19%, @!00000002 20%',
+      undefined,
+      2,
     );
   });
 
@@ -99,6 +102,8 @@ describe('BatteryAlertService check threshold', () => {
       expect(sendText).toHaveBeenCalledWith(
         BROADCAST_ADDR,
         '⚠️ battery low: @!00000001 50%',
+        undefined,
+        2,
       );
     } finally {
       delete process.env.BATTERY_ALERT_THRESHOLD;
@@ -127,9 +132,31 @@ describe('BatteryAlertService check threshold', () => {
     expect(sendText.mock.calls[0]).toEqual([
       BROADCAST_ADDR,
       '⚠️ battery low: @!00000abc (A) 5%, @!00000def (B) 3%',
+      undefined,
+      2, // default channel "testowy" — not the pinned send channel (3)
     ]);
   });
 
+  it('sends on a custom BATTERY_ALERT_CHANNEL when set', async () => {
+    process.env.BATTERY_ALERT_CHANNEL = '5';
+    const sendText = vi.fn(async (..._args: unknown[]) => 1);
+    try {
+      const svc = makeService([node(0xabc, 5)], sendText);
+
+      await svc.check();
+
+      expect(sendText).toHaveBeenCalledTimes(1);
+      expect(sendText.mock.calls[0]).toEqual([
+        BROADCAST_ADDR,
+        '⚠️ battery low: @!00000abc 5%',
+        undefined,
+        5,
+      ]);
+    } finally {
+      delete process.env.BATTERY_ALERT_CHANNEL;
+    }
+  });
+
   it('never throws when a send fails', async () => {
     const svc = makeService(
       [node(1, 5)],
@@ -197,11 +224,11 @@ describe('BatteryAlertService check cooldown', () => {
 });
 
 describe('BatteryAlertService check end-to-end (real MeshService)', () => {
-  it('broadcasts the alert on the pinned send channel (index 3 by default)', async () => {
+  it('broadcasts the alert on "testowy" (channel index 2), not the pinned send channel', async () => {
     const bridge = await startBridge();
     process.env.MESH_HOST = '127.0.0.1';
     process.env.MESH_PORT = String(bridge.port);
-    delete process.env.MESH_SEND_CHANNEL; // default path: "test" (index 3)
+    delete process.env.MESH_SEND_CHANNEL; // default pinned send channel is 3 — the alert must NOT ride it
     const mesh = new RealMeshService();
     try {
       mesh.onModuleInit();
@@ -241,7 +268,7 @@ describe('BatteryAlertService check end-to-end (real MeshService)', () => {
 
       await waitFor(() => readOutbound().length === 1);
       const pkt = readOutbound()[0];
-      expect(pkt.channel).toBe(3); // "test" — never the primary channel (0)
+      expect(pkt.channel).toBe(2); // "testowy" — not the pinned send channel (3) or primary (0)
       const data =
         pkt.payloadVariant?.case === 'decoded'
           ? pkt.payloadVariant.value