fix(translator): strip errorMessage and other non-standard schema keywords from Gemini tool schemas

open-sse/translator/formats/gemini.js

@@ -32,7 +32,14 @@ export const UNSUPPORTED_SCHEMA_CONSTRAINTS = [
   "title", "optional", "deprecated", "if", "then", "else", "contentMediaType", "contentEncoding",
   // UI/Styling properties (from Cursor tools - NOT JSON Schema standard)
   "cornerRadius", "fillColor", "fontFamily", "fontSize", "fontWeight",
-  "gap", "padding", "strokeColor", "strokeThickness", "textColor"
+  "gap", "padding", "strokeColor", "strokeThickness", "textColor",
+  // Non-standard annotation/error keywords used by some MCP tool schemas (#4283).
+  // Gemini's schema proto has no field for these and rejects the whole request with
+  // "Unknown name X: Cannot find field" if any nested schema node carries them.
+  "errorMessage", "errorMessages", "x-errorMessage", "x-errorMessages",
+  "markdownDescription", "x-intellij-html-description",
+  "x-taplo-info", "x-taplo", "doNotSuggest", "suggestSortText",
+  "minProperties", "maxProperties"
 ];
 
 // Default safety settings

tests/unit/gemini-unknown-schema-fields.test.js

@@ -0,0 +1,105 @@
+/**
+ * Regression test for #4283
+ *
+ * Gemini Antigravity rejects tool schemas that contain unknown JSON Schema
+ * keywords with: "Unknown name X: Cannot find field."
+ *
+ * The UNSUPPORTED_SCHEMA_CONSTRAINTS list in gemini.js did not include
+ * "errorMessage" (and similar non-standard annotation keywords used by some
+ * MCP tool schemas), causing 400 INVALID_ARGUMENT errors on tools with error
+ * documentation fields.
+ *
+ * Fix: add errorMessage, errorMessages, markdownDescription, and other
+ * non-standard annotation keywords to the strip list.
+ */
+
+import { describe, it, expect } from "vitest";
+import { cleanJSONSchemaForAntigravity, UNSUPPORTED_SCHEMA_CONSTRAINTS } from "../../open-sse/translator/formats/gemini.js";
+
+describe("UNSUPPORTED_SCHEMA_CONSTRAINTS includes non-standard annotation keywords (#4283)", () => {
+  it("includes errorMessage", () => {
+    expect(UNSUPPORTED_SCHEMA_CONSTRAINTS).toContain("errorMessage");
+  });
+  it("includes errorMessages", () => {
+    expect(UNSUPPORTED_SCHEMA_CONSTRAINTS).toContain("errorMessages");
+  });
+  it("includes markdownDescription", () => {
+    expect(UNSUPPORTED_SCHEMA_CONSTRAINTS).toContain("markdownDescription");
+  });
+  it("includes minProperties", () => {
+    expect(UNSUPPORTED_SCHEMA_CONSTRAINTS).toContain("minProperties");
+  });
+  it("includes maxProperties", () => {
+    expect(UNSUPPORTED_SCHEMA_CONSTRAINTS).toContain("maxProperties");
+  });
+});
+
+describe("cleanJSONSchemaForAntigravity strips errorMessage recursively (#4283)", () => {
+  it("strips top-level errorMessage", () => {
+    const schema = {
+      type: "object",
+      properties: {
+        code: { type: "integer" }
+      },
+      errorMessage: "Invalid input"
+    };
+    const result = cleanJSONSchemaForAntigravity(structuredClone(schema));
+    expect(result).not.toHaveProperty("errorMessage");
+  });
+
+  it("strips errorMessage nested inside array items", () => {
+    const schema = {
+      type: "object",
+      properties: {
+        tags: {
+          type: "array",
+          items: {
+            type: "string",
+            errorMessage: "Must be a non-empty string"
+          }
+        }
+      }
+    };
+    const result = cleanJSONSchemaForAntigravity(structuredClone(schema));
+    expect(result.properties.tags.items).not.toHaveProperty("errorMessage");
+  });
+
+  it("strips markdownDescription from nested property", () => {
+    const schema = {
+      type: "object",
+      properties: {
+        name: {
+          type: "string",
+          markdownDescription: "The **name** of the resource"
+        }
+      }
+    };
+    const result = cleanJSONSchemaForAntigravity(structuredClone(schema));
+    expect(result.properties.name).not.toHaveProperty("markdownDescription");
+  });
+
+  it("strips minProperties / maxProperties", () => {
+    const schema = {
+      type: "object",
+      minProperties: 1,
+      maxProperties: 10,
+      properties: { x: { type: "string" } }
+    };
+    const result = cleanJSONSchemaForAntigravity(structuredClone(schema));
+    expect(result).not.toHaveProperty("minProperties");
+    expect(result).not.toHaveProperty("maxProperties");
+  });
+
+  it("leaves other valid fields intact", () => {
+    const schema = {
+      type: "object",
+      description: "A valid tool",
+      properties: {
+        n: { type: "number", description: "A number" }
+      }
+    };
+    const result = cleanJSONSchemaForAntigravity(structuredClone(schema));
+    expect(result.description).toBe("A valid tool");
+    expect(result.properties.n.description).toBe("A number");
+  });
+});