🤖 fix: handle null citations in Anthropic API proxy responses

Some AI bridge proxies (e.g., Coder's aibridge) normalize Anthropic API
responses and incorrectly set 'citations: null' on all content blocks.
The Vercel AI SDK's Anthropic provider has strict validation that expects
citations to be an array when present, causing validation errors:
  'Invalid input: expected array, received null'

This adds a fetch wrapper that intercepts responses and removes null
citations fields from content blocks before the SDK validates them.

The fix is applied only to the Anthropic provider since that's where
the validation issue occurs.

Author: ibetitsmike

src/node/services/aiService.ts

@@ -169,6 +169,83 @@ function wrapFetchWithAnthropicCacheControl(baseFetch: typeof fetch): typeof fet
   return Object.assign(cachingFetch, baseFetch) as typeof fetch;
 }
 
+/**
+ * Wrap fetch to fix Anthropic API responses from proxies that incorrectly
+ * return `citations: null` instead of omitting the field or returning an array.
+ *
+ * The Vercel AI SDK's Anthropic provider has strict validation that expects
+ * `citations` to be an array when present. Some AI bridge proxies (e.g., Coder's
+ * aibridge) normalize the response and set `citations: null` on all content blocks,
+ * which causes validation errors like:
+ *   "Invalid input: expected array, received null"
+ *
+ * This wrapper intercepts the response, parses the JSON, removes null citations
+ * fields from content blocks, and returns a fixed response.
+ */
+function wrapFetchWithCitationsNullFix(baseFetch: typeof fetch): typeof fetch {
+  const fixingFetch = async (
+    input: Parameters<typeof fetch>[0],
+    init?: Parameters<typeof fetch>[1]
+  ): Promise<Response> => {
+    const response = await baseFetch(input, init);
+
+    // Only fix successful JSON responses
+    const contentType = response.headers.get("content-type") ?? "";
+    if (!response.ok || !contentType.includes("application/json")) {
+      return response;
+    }
+
+    try {
+      const json = (await response.json()) as {
+        content?: Array<{ citations?: unknown }>;
+      };
+
+      // Fix citations: null in content blocks
+      if (Array.isArray(json.content)) {
+        let modified = false;
+        for (const block of json.content) {
+          if (
+            block &&
+            typeof block === "object" &&
+            "citations" in block &&
+            block.citations === null
+          ) {
+            delete block.citations;
+            modified = true;
+          }
+        }
+
+        if (modified) {
+          const fixedBody = JSON.stringify(json);
+          const fixedHeaders = new Headers(response.headers);
+          fixedHeaders.set("content-length", String(fixedBody.length));
+          return new Response(fixedBody, {
+            status: response.status,
+            statusText: response.statusText,
+            headers: fixedHeaders,
+          });
+        }
+      }
+
+      // No fix needed, but we already consumed the body - reconstruct
+      return new Response(JSON.stringify(json), {
+        status: response.status,
+        statusText: response.statusText,
+        headers: response.headers,
+      });
+    } catch {
+      // Can't fix - response body was consumed but failed to parse
+      // This shouldn't happen for valid JSON, but return a failed response
+      return new Response(null, {
+        status: 500,
+        statusText: "Failed to parse response JSON",
+      });
+    }
+  };
+
+  return Object.assign(fixingFetch, baseFetch) as typeof fetch;
+}
+
 /**
  * Get fetch function for provider - use custom if provided, otherwise unlimited timeout default
  */
@@ -429,11 +506,13 @@ export class AIService extends EventEmitter {
 
         // Lazy-load Anthropic provider to reduce startup time
         const { createAnthropic } = await PROVIDER_REGISTRY.anthropic();
-        // Wrap fetch to inject cache_control on tools and messages
-        // (SDK doesn't translate providerOptions to cache_control for these)
         // Use getProviderFetch to preserve any user-configured custom fetch (e.g., proxies)
+        // Then chain wrappers:
+        // 1. citationsFix: removes `citations: null` from API proxy responses (breaks SDK validation)
+        // 2. cacheControl: injects cache_control on tools/messages (SDK doesn't translate providerOptions)
         const baseFetch = getProviderFetch(providerConfig);
-        const fetchWithCacheControl = wrapFetchWithAnthropicCacheControl(baseFetch);
+        const fetchWithCitationsFix = wrapFetchWithCitationsNullFix(baseFetch);
+        const fetchWithCacheControl = wrapFetchWithAnthropicCacheControl(fetchWithCitationsFix);
         const provider = createAnthropic({
           ...normalizedConfig,
           headers,