From 70f94685e6bec059ca2e0f62037f0dacd8b5fef9 Mon Sep 17 00:00:00 2001
From: Sahil Singh <iffcogc34@gmail.com>
Date: Tue, 18 Aug 2026 19:22:56 +0530
Subject: [PATCH] fix(gemini): inject missing items schema for array typed mcp
 tools (#10578) (#10605)

---
 open-sse/translator/helpers/geminiHelper.ts | 28 ++++++++++++
 tests/unit/gemini-array-items.test.ts       | 47 +++++++++++++++++++++
 2 files changed, 75 insertions(+)
 create mode 100644 tests/unit/gemini-array-items.test.ts

diff --git a/open-sse/translator/helpers/geminiHelper.ts b/open-sse/translator/helpers/geminiHelper.ts
index 623e39cba3..8a67b07bc5 100644
--- a/open-sse/translator/helpers/geminiHelper.ts
+++ b/open-sse/translator/helpers/geminiHelper.ts
@@ -727,5 +727,33 @@ export function cleanJSONSchemaForAntigravity(schema: unknown): unknown {
 
   injectObjectType(cleaned);
 
+  // Phase 8: Ensure array types have an items schema (#10578).
+  // Gemini strictly requires array parameters to define their `items` schema.
+  // If an MCP tool defines an array but forgets the items, inject a safe default.
+  function ensureArrayItems(obj: unknown): void {
+    if (!obj || typeof obj !== "object") return;
+
+    if (Array.isArray(obj)) {
+      for (const item of obj) {
+        ensureArrayItems(item);
+      }
+      return;
+    }
+
+    const record = obj as JsonRecord;
+    if (record.type === "array" && !record.items) {
+      record.items = { type: "string" };
+    }
+
+    // Recurse into remaining values.
+    for (const value of Object.values(record)) {
+      if (value && typeof value === "object") {
+        ensureArrayItems(value);
+      }
+    }
+  }
+
+  ensureArrayItems(cleaned);
+
   return cleaned;
 }
diff --git a/tests/unit/gemini-array-items.test.ts b/tests/unit/gemini-array-items.test.ts
new file mode 100644
index 0000000000..52db074c6f
--- /dev/null
+++ b/tests/unit/gemini-array-items.test.ts
@@ -0,0 +1,47 @@
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import { cleanJSONSchemaForAntigravity } from "../../open-sse/translator/helpers/geminiHelper";
+
+type SchemaNode = {
+  type?: string;
+  properties?: Record<string, SchemaNode>;
+  items?: SchemaNode;
+  required?: string[];
+  [key: string]: unknown;
+};
+
+describe("Gemini array items sanitizer (#10578)", () => {
+  it("should inject a string items schema for array types that are missing it", () => {
+    const sloppySchema = {
+      type: "object",
+      properties: {
+        emails: {
+          type: "array",
+        },
+      },
+      required: ["emails"],
+    };
+
+    const cleanedSchema = cleanJSONSchemaForAntigravity(sloppySchema as unknown) as SchemaNode;
+
+    assert.equal(cleanedSchema.properties?.emails?.type, "array");
+    assert.ok(cleanedSchema.properties?.emails?.items, "items should be injected");
+    assert.equal(cleanedSchema.properties?.emails?.items?.type, "string");
+  });
+
+  it("should safely ignore arrays that already have valid items", () => {
+    const goodSchema = {
+      type: "object",
+      properties: {
+        tags: {
+          type: "array",
+          items: { type: "number" },
+        },
+      },
+    };
+
+    const cleanedSchema = cleanJSONSchemaForAntigravity(goodSchema as unknown) as SchemaNode;
+
+    assert.equal(cleanedSchema.properties?.tags?.items?.type, "number");
+  });
+});