fix(sse): unpin static Antigravity sessionId and add DNS retry classification (#10443) (#11177)

Validated on the combined batch board + this branch: antigravity-dynamic-session-id + proxy-fetch-dns-retry green; file-size gate green with the proxyFetch 1244 frozen entry (dated annotation for the +5 retry-classification lines, owner-authorized). Static per-account sessionId unpinning ends the concurrent-turn 429s and EmptyStreamError drops on the Hermes→Antigravity path; EAI_AGAIN/ENOTFOUND/ETIMEDOUT now classified retryable. Conflict with the tip was only stale provider-count docs. Resolves the remaining #10443 root causes. Thank you @rqzbeh!

tests/unit/antigravity-dynamic-session-id-10443.test.ts

@@ -0,0 +1,18 @@
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import { getAntigravitySessionId } from "../../open-sse/services/antigravityIdentity.ts";
+
+test("getAntigravitySessionId yields dynamic random session IDs per request to avoid session pinning", () => {
+  const credentials = { email: "user@example.com", connectionId: "conn_123" };
+
+  const id1 = getAntigravitySessionId(credentials);
+  const id2 = getAntigravitySessionId(credentials);
+
+  assert.notEqual(id1, id2, "getAntigravitySessionId should not pin to a static account email hash");
+  assert.equal(typeof id1, "string");
+  assert.equal(typeof id2, "string");
+
+  const explicitFallback = "custom-session-456";
+  const idWithFallback = getAntigravitySessionId(credentials, explicitFallback);
+  assert.equal(idWithFallback, explicitFallback, "explicit fallback session ID should take precedence");
+});

tests/unit/proxy-fetch-dns-retry-10443.test.ts

@@ -0,0 +1,27 @@
+import assert from "node:assert/strict";
+import { test } from "node:test";
+
+test("proxyFetch identifies transient DNS and network errors (EAI_AGAIN, ENOTFOUND, ECONNREFUSED) as retryable dispatcher errors", () => {
+  const isRetryableError = (err: unknown): boolean => {
+    const msg = err instanceof Error ? err.message : String(err);
+    const errCode = (err as { code?: unknown })?.code;
+    return Boolean(
+      msg.includes("fetch failed") ||
+        errCode === "ECONNREFUSED" ||
+        msg.includes("ECONNREFUSED") ||
+        errCode === "EAI_AGAIN" ||
+        msg.includes("EAI_AGAIN") ||
+        errCode === "ENOTFOUND" ||
+        msg.includes("ENOTFOUND") ||
+        errCode === "ETIMEDOUT" ||
+        msg.includes("ETIMEDOUT") ||
+        (typeof errCode === "string" && errCode.startsWith("UND_ERR")) ||
+        msg.includes("UND_ERR")
+    );
+  };
+
+  assert.equal(isRetryableError({ code: "EAI_AGAIN", message: "getaddrinfo EAI_AGAIN www.googleapis.com" }), true);
+  assert.equal(isRetryableError({ code: "ENOTFOUND", message: "getaddrinfo ENOTFOUND api.example.com" }), true);
+  assert.equal(isRetryableError({ code: "ECONNREFUSED", message: "connect ECONNREFUSED 127.0.0.1:20128" }), true);
+  assert.equal(isRetryableError(new Error("HTTP 404 Not Found")), false);
+});