fix(gateway): distinguish disconnected from stuck in health-monitor restart reason

resolveChannelRestartReason did not handle the "disconnected" evaluation
reason explicitly, so it fell through to "stuck". This conflates a clean
WebSocket drop (e.g. Discord 1006) with a genuinely stuck channel, making
logs misleading and preventing future policy differentiation.

Add "disconnected" to ChannelRestartReason and handle it before the
catch-all "stuck" return.

Closes #36404

src/gateway/channel-health-policy.test.ts

@@ -234,4 +234,17 @@ describe("resolveChannelRestartReason", () => {
     );
     expect(reason).toBe("gave-up");
   });
+
+  it("maps disconnected to disconnected instead of stuck", () => {
+    const reason = resolveChannelRestartReason(
+      {
+        running: true,
+        connected: false,
+        enabled: true,
+        configured: true,
+      },
+      { healthy: false, reason: "disconnected" },
+    );
+    expect(reason).toBe("disconnected");
+  });
 });

src/gateway/channel-health-policy.ts

@@ -36,7 +36,7 @@ export type ChannelHealthPolicy = {
   channelConnectGraceMs: number;
 };
 
-export type ChannelRestartReason = "gave-up" | "stopped" | "stale-socket" | "stuck";
+export type ChannelRestartReason = "gave-up" | "stopped" | "stale-socket" | "stuck" | "disconnected";
 
 function isManagedAccount(snapshot: ChannelHealthSnapshot): boolean {
   return snapshot.enabled !== false && snapshot.configured !== false;
@@ -133,5 +133,8 @@ export function resolveChannelRestartReason(
   if (evaluation.reason === "not-running") {
     return snapshot.reconnectAttempts && snapshot.reconnectAttempts >= 10 ? "gave-up" : "stopped";
   }
+  if (evaluation.reason === "disconnected") {
+    return "disconnected";
+  }
   return "stuck";
 }