fix(proxy): keep password-only proxy credentials (#10720) (#10752)

Co-authored-by: Markus Hartung <mail@hartmark.se>

tests/unit/probe-10720-proxy-password-only-auth.test.ts

@@ -0,0 +1,36 @@
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import { proxyConfigToUrl } from "../../open-sse/utils/proxyDispatcher.ts";
+
+describe("#10720 — proxyConfigToUrl drops password-only auth (no username)", () => {
+  it("keeps a password-only credential in the built proxy URL", () => {
+    const url = proxyConfigToUrl({
+      type: "http",
+      host: "127.0.0.1",
+      port: 20130,
+      username: "",
+      password: "s3cret",
+    });
+    assert.ok(url.includes(":s3cret@"), `expected password in URL, got: ${url}`);
+  });
+
+  it("still builds a normal username:password URL", () => {
+    const url = proxyConfigToUrl({
+      type: "http",
+      host: "127.0.0.1",
+      port: 20130,
+      username: "user",
+      password: "s3cret",
+    });
+    assert.ok(url.includes("user:s3cret@"), `expected user:pass in URL, got: ${url}`);
+  });
+
+  it("builds no auth segment when neither username nor password is set", () => {
+    const url = proxyConfigToUrl({
+      type: "http",
+      host: "127.0.0.1",
+      port: 20130,
+    });
+    assert.ok(!url.includes("@"), `expected no auth segment, got: ${url}`);
+  });
+});