test(core-realtime): unit cover registerChannel + listChannels

- Add 4 new test cases to RealtimeHandlerRegistry test suite
- registerChannel stores outbound-only descriptors distinct from inbound
- listChannels() includes both inbound (from register) and outbound-only channels
- Validates backward-compat guarantee and re-registration behavior

Test count: 4 → 8 in realtime-handler-registry.test.ts
All 35 tests in core-realtime pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/core-realtime/src/realtime-handler-registry.test.ts

@@ -41,4 +41,51 @@ describe("RealtimeHandlerRegistry", () => {
     expect(reg.getInboundDescriptor("test.ch")!.handler).toBe(h2);
     expect(reg.list()).toHaveLength(1);
   });
+
+  it("registerChannel stores a descriptor that appears in listChannels() but not in list()", () => {
+    const reg = new RealtimeHandlerRegistry();
+    const outboundCh = defineRealtimeChannel(
+      "test.outbound",
+      z.object({ y: z.string() }).strict(),
+      { scope: "authenticated" },
+    );
+    reg.registerChannel(outboundCh);
+    expect(reg.listChannels()).toHaveLength(1);
+    expect(reg.listChannels()[0]!.name).toBe("test.outbound");
+    expect(reg.list()).toHaveLength(0);
+  });
+
+  it("register auto-populates listChannels()", () => {
+    const reg = new RealtimeHandlerRegistry();
+    reg.register({ descriptor: ch, handler: vi.fn() });
+    expect(reg.listChannels()).toHaveLength(1);
+    expect(reg.listChannels()[0]!.name).toBe("test.ch");
+  });
+
+  it("listChannels() returns both inbound and outbound-only channels when both are registered", () => {
+    const reg = new RealtimeHandlerRegistry();
+    const outboundCh = defineRealtimeChannel(
+      "test.outbound",
+      z.object({ y: z.string() }).strict(),
+      { scope: "authenticated" },
+    );
+    reg.register({ descriptor: ch, handler: vi.fn() });
+    reg.registerChannel(outboundCh);
+    expect(reg.listChannels()).toHaveLength(2);
+    const names = reg.listChannels().map((c) => c.name).sort();
+    expect(names).toEqual(["test.ch", "test.outbound"]);
+  });
+
+  it("re-registering an outbound-only channel via registerChannel replaces the previous entry", () => {
+    const reg = new RealtimeHandlerRegistry();
+    const outboundCh = defineRealtimeChannel(
+      "test.outbound",
+      z.object({ y: z.string() }).strict(),
+      { scope: "authenticated" },
+    );
+    reg.registerChannel(outboundCh);
+    reg.registerChannel(outboundCh);
+    expect(reg.listChannels()).toHaveLength(1);
+    expect(reg.listChannels()[0]!.name).toBe("test.outbound");
+  });
 });