refactor: extract getFetchInputUrl helper to deduplicate URL extraction

The OpenAI/Codex and Copilot fetch wrappers each contained an identical
15-line IIFE that extracted a URL string from the `fetch` `input`
argument (handling string, URL, and Request-like shapes). Extract the
logic into a single `getFetchInputUrl` helper so both wrappers share
one implementation.

Behavior-preserving: the helper returns the same empty-string fallback
on unrecognized inputs, so callers continue to fall through to normal
fetch behavior without throwing.

Author: mux-bot[bot]

src/node/services/providerModelFactory.ts

@@ -665,6 +665,33 @@ const CODEX_ALLOWED_PARAMS = new Set([
   "text", // structured output via Output.object -> text.format
 ]);
 
+// ---------------------------------------------------------------------------
+// Fetch input helpers
+// ---------------------------------------------------------------------------
+
+/**
+ * Extract a URL string from the `input` argument of a `fetch`-compatible call.
+ * Handles the three shapes AI SDK providers pass through: plain string, `URL`,
+ * and `Request`-like objects that expose a `url` property. Returns an empty
+ * string when the URL cannot be determined so callers can fall through to
+ * normal fetch behavior without throwing.
+ */
+function getFetchInputUrl(input: Parameters<typeof fetch>[0]): string {
+  if (typeof input === "string") {
+    return input;
+  }
+  if (input instanceof URL) {
+    return input.toString();
+  }
+  if (typeof input === "object" && input !== null && "url" in input) {
+    const possibleUrl = (input as { url?: unknown }).url;
+    if (typeof possibleUrl === "string") {
+      return possibleUrl;
+    }
+  }
+  return "";
+}
+
 // ---------------------------------------------------------------------------
 // Content extraction
 // ---------------------------------------------------------------------------
@@ -1193,21 +1220,7 @@ export class ProviderModelFactory {
             init?: Parameters<typeof fetch>[1]
           ): Promise<Response> => {
             try {
-              const urlString = (() => {
-                if (typeof input === "string") {
-                  return input;
-                }
-                if (input instanceof URL) {
-                  return input.toString();
-                }
-                if (typeof input === "object" && input !== null && "url" in input) {
-                  const possibleUrl = (input as { url?: unknown }).url;
-                  if (typeof possibleUrl === "string") {
-                    return possibleUrl;
-                  }
-                }
-                return "";
-              })();
+              const urlString = getFetchInputUrl(input);
 
               const method = (init?.method ?? "GET").toUpperCase();
               const isOpenAIResponses = /\/v1\/responses(\?|$)/.test(urlString);
@@ -1667,21 +1680,7 @@ export class ProviderModelFactory {
           headers.set("Authorization", `Bearer ${resolvedApiKey ?? ""}`);
           headers.set("Openai-Intent", "conversation-edits");
 
-          const urlString = (() => {
-            if (typeof input === "string") {
-              return input;
-            }
-            if (input instanceof URL) {
-              return input.toString();
-            }
-            if (typeof input === "object" && input !== null && "url" in input) {
-              const possibleUrl = (input as { url?: unknown }).url;
-              if (typeof possibleUrl === "string") {
-                return possibleUrl;
-              }
-            }
-            return "";
-          })();
+          const urlString = getFetchInputUrl(input);
 
           const method = (
             init?.method ?? (input instanceof Request ? input.method : "GET")