fix(sse): default crash-guard logger to console.warn, not console (#12042)

Real production incident (2026-08-29): the crash guard #11556 introduced defaulted its logger to `log ?? console` — console is an object, not a function, so a burst of client aborts (ECONNRESET) reaching the process-level guard threw TypeError inside the uncaughtException handler itself and killed the server, twice in three minutes. Fix: default to console.warn.bind(console).

Bug-injection round trip confirms the new test fails on the old default and passes on the fix. Existing guard suite stays green: 9/9 (verified together with the new test).

src/shared/utils/httpClientAbortGuard.mjs

@@ -117,7 +117,10 @@ export function installProcessCrashGuard(log) {
   if (crashGuardInstalled) return;
   crashGuardInstalled = true;
 
-  const logger = log ?? console;
+  // `console` is an object, not a callable: `log ?? console` followed by
+  // `logger("warn", ...)` throws TypeError and kills the process on the very
+  // abort the guard exists to swallow. Default to console.warn as a function.
+  const logger = typeof log === "function" ? log : console.warn.bind(console);
 
   process.on("uncaughtException", (err, origin) => {
     if (shouldSwallowUncaught(err, origin)) {

tests/unit/httpClientAbortGuard-default-logger.test.mjs

@@ -0,0 +1,33 @@
+"use strict";
+
+import assert from "node:assert";
+import { test } from "node:test";
+
+// Production calls installProcessCrashGuard() with NO argument in
+// apiBridgeServer.ts / liveServer.ts / embedWsProxy.ts. The default logger
+// must be callable; this file runs in its own node:test process, so the
+// module-level installed flag starts unset and the no-arg path is exercised
+// for real. Emitting "uncaughtException" through process.emit would trip the
+// test runner's own listener, so the guard handler is invoked directly.
+import { installProcessCrashGuard } from "../../src/shared/utils/httpClientAbortGuard.mjs";
+
+test("installProcessCrashGuard() with no argument swallows a client abort without throwing", () => {
+  const warnings = [];
+  const originalWarn = console.warn;
+  console.warn = (...args) => warnings.push(args);
+  try {
+    installProcessCrashGuard();
+    const handlers = process
+      .listeners("uncaughtException")
+      .filter((fn) => fn.toString().includes("swallowed client-abort"));
+    assert.ok(handlers.length > 0, "guard handler must be registered");
+    const abortErr = Object.assign(new Error("aborted"), { code: "ECONNRESET" });
+    // A broken default logger (console is an object, not a function) throws
+    // TypeError here — that is what took the production process down.
+    assert.doesNotThrow(() => handlers[0](abortErr, "uncaughtException"));
+    assert.equal(warnings.length, 1, "the swallowed abort must be logged once");
+    assert.ok(String(warnings[0][1]).includes("swallowed client-abort"));
+  } finally {
+    console.warn = originalWarn;
+  }
+});