fix(discord): preserve stack hints for empty gateway type errors

extensions/discord/src/monitor/gateway-supervisor.test.ts

@@ -8,6 +8,8 @@ import {
 
 describe("classifyDiscordGatewayEvent", () => {
   it("maps current Carbon gateway errors onto domain events", () => {
+    const transientTypeError = new TypeError();
+    transientTypeError.stack = "TypeError\n    at gatewayCrash (discord-gateway.js:12:34)";
     const reconnectEvent = classifyDiscordGatewayEvent({
       err: new Error("Max reconnect attempts (0) reached after close code 1006"),
       isDisallowedIntentsError: () => false,
@@ -21,7 +23,7 @@ describe("classifyDiscordGatewayEvent", () => {
       isDisallowedIntentsError: (err) => String(err).includes("4014"),
     });
     const transientEvent = classifyDiscordGatewayEvent({
-      err: new TypeError(),
+      err: transientTypeError,
       isDisallowedIntentsError: () => false,
     });
 
@@ -30,20 +32,24 @@ describe("classifyDiscordGatewayEvent", () => {
     expect(fatalEvent.type).toBe("fatal");
     expect(disallowedEvent.type).toBe("disallowed-intents");
     expect(transientEvent.type).toBe("fatal");
-    expect(transientEvent.message).toBe("TypeError");
+    expect(transientEvent.message).toBe("TypeError @ gatewayCrash (discord-gateway.js:12:34)");
     expect(transientEvent.shouldStopLifecycle).toBe(true);
   });
 
   it("wraps fatal lifecycle stops with discord-specific context", () => {
+    const transientTypeError = new TypeError();
+    transientTypeError.stack = "TypeError\n    at gatewayCrash (discord-gateway.js:12:34)";
     const event = classifyDiscordGatewayEvent({
-      err: new TypeError(),
+      err: transientTypeError,
       isDisallowedIntentsError: () => false,
     });
 
     const wrapped = new DiscordGatewayLifecycleError(event);
 
     expect(wrapped.name).toBe("DiscordGatewayLifecycleError");
-    expect(wrapped.message).toBe("discord gateway fatal: TypeError");
+    expect(wrapped.message).toBe(
+      "discord gateway fatal: TypeError @ gatewayCrash (discord-gateway.js:12:34)",
+    );
     expect(wrapped.eventType).toBe("fatal");
     expect(wrapped.cause).toBeInstanceOf(TypeError);
   });
@@ -127,12 +133,18 @@ describe("createDiscordGatewaySupervisor", () => {
     });
 
     supervisor.dispose();
-    emitter.emit("error", new TypeError());
-    emitter.emit("error", new TypeError());
+    const first = new TypeError();
+    first.stack = "TypeError\n    at gatewayCrash (discord-gateway.js:12:34)";
+    const second = new TypeError();
+    second.stack = "TypeError\n    at gatewayCrash (discord-gateway.js:12:34)";
+    emitter.emit("error", first);
+    emitter.emit("error", second);
 
     expect(runtime.error).toHaveBeenCalledTimes(1);
     expect(runtime.error).toHaveBeenCalledWith(
-      expect.stringContaining("suppressed late gateway fatal error after dispose: TypeError"),
+      expect.stringContaining(
+        "suppressed late gateway fatal error after dispose: TypeError @ gatewayCrash (discord-gateway.js:12:34)",
+      ),
     );
   });
 });

extensions/discord/src/monitor/gateway-supervisor.ts

@@ -41,16 +41,40 @@ export type DiscordGatewaySupervisor = {
 
 type GatewaySupervisorPhase = "active" | "buffering" | "disposed" | "teardown";
 
+function readFirstStackFrame(err: Error): string | undefined {
+  const stack = err.stack;
+  if (!stack) {
+    return undefined;
+  }
+  const frame = stack
+    .split("\n")
+    .slice(1)
+    .map((line) => line.trim())
+    .find(Boolean);
+  return frame ? frame.replace(/^at\s+/, "") : undefined;
+}
+
+function formatDiscordGatewayErrorMessage(err: unknown): string {
+  if (!(err instanceof Error)) {
+    return formatErrorMessage(err);
+  }
+  if (err.message) {
+    const detail = formatErrorMessage(err);
+    return err.name ? `${err.name}: ${detail}` : detail;
+  }
+  const detail = formatErrorMessage(err);
+  const firstFrame = readFirstStackFrame(err);
+  if (firstFrame && detail === (err.name || "Error")) {
+    return `${detail} @ ${firstFrame}`;
+  }
+  return detail;
+}
+
 export function classifyDiscordGatewayEvent(params: {
   err: unknown;
   isDisallowedIntentsError: (err: unknown) => boolean;
 }): DiscordGatewayEvent {
-  const message =
-    params.err instanceof Error
-      ? params.err.message
-        ? `${params.err.name}: ${params.err.message}`
-        : params.err.name || "Error"
-      : formatErrorMessage(params.err);
+  const message = formatDiscordGatewayErrorMessage(params.err);
   if (params.isDisallowedIntentsError(params.err)) {
     return {
       type: "disallowed-intents",