fix(provider): drop top-level schema composition for Anthropic MCP tools

packages/opencode/src/provider/transform.ts

@@ -1521,6 +1521,18 @@ export function schema(model: Provider.Model, schema: JSONSchema7): JSONSchema7
     // Codex also applies lossy compaction above 4 KB; defer that until OpenCode needs the same schema budget.
   }
 
+  if (model.api.npm === "@ai-sdk/anthropic" || model.api.npm === "@ai-sdk/google-vertex/anthropic") {
+    // Anthropic's input_schema does not support oneOf, allOf, or anyOf at the top
+    // level (nested composition inside properties is fine). MCP servers can still
+    // emit these, e.g. `anyOf: [{ required: ["route"] }, { required: ["file"] }]`.
+    if (isPlainObject(schema)) {
+      const dropped = ["oneOf", "allOf", "anyOf"]
+      schema = Object.fromEntries(
+        Object.entries(schema as JsonRecord).filter(([key]) => !dropped.includes(key)),
+      ) as JSONSchema7
+    }
+  }
+
   if (model.providerID === "moonshotai" || model.api.id.toLowerCase().includes("kimi")) {
     const sanitizeMoonshot = (obj: unknown): unknown => {
       if (obj === null || typeof obj !== "object") return obj

packages/opencode/test/provider/transform.test.ts

@@ -1629,6 +1629,94 @@ describe("ProviderTransform.schema - openai supported schema subset", () => {
   })
 })
 
+describe("ProviderTransform.schema - anthropic top-level composition removal", () => {
+  const anthropicModel = {
+    providerID: "anthropic",
+    api: {
+      id: "claude-sonnet-4",
+      npm: "@ai-sdk/anthropic",
+    },
+  } as any
+
+  const vertexAnthropicModel = {
+    providerID: "google-vertex",
+    api: {
+      id: "claude-sonnet-4",
+      npm: "@ai-sdk/google-vertex/anthropic",
+    },
+  } as any
+
+  test("drops anyOf at the schema root", () => {
+    const result = ProviderTransform.schema(anthropicModel, {
+      type: "object",
+      properties: {
+        route: { type: "string" },
+        file: { type: "string" },
+      },
+      anyOf: [{ required: ["route"] }, { required: ["file"] }],
+    } as any) as any
+
+    expect(result).toEqual({
+      type: "object",
+      properties: {
+        route: { type: "string" },
+        file: { type: "string" },
+      },
+    })
+  })
+
+  test("drops oneOf and allOf at the schema root", () => {
+    const result = ProviderTransform.schema(anthropicModel, {
+      type: "object",
+      properties: { query: { type: "string" } },
+      oneOf: [{ required: ["query"] }],
+      allOf: [{ required: ["query"] }],
+    } as any) as any
+
+    expect(result).toEqual({
+      type: "object",
+      properties: { query: { type: "string" } },
+    })
+  })
+
+  test("keeps nested anyOf inside properties", () => {
+    const result = ProviderTransform.schema(anthropicModel, {
+      type: "object",
+      properties: {
+        value: {
+          anyOf: [{ type: "string" }, { type: "number" }],
+        },
+      },
+    } as any) as any
+
+    expect(result.properties.value.anyOf).toEqual([{ type: "string" }, { type: "number" }])
+  })
+
+  test("sanitizes Claude models served through Vertex AI", () => {
+    const result = ProviderTransform.schema(vertexAnthropicModel, {
+      type: "object",
+      anyOf: [{ required: ["route"] }, { required: ["file"] }],
+    } as any) as any
+
+    expect(result).toEqual({ type: "object" })
+  })
+
+  test("does not affect providers without anthropic-specific sanitization", () => {
+    const result = ProviderTransform.schema(
+      {
+        providerID: "mistral",
+        api: { id: "mistral-large", npm: "@ai-sdk/mistral" },
+      } as any,
+      {
+        type: "object",
+        anyOf: [{ required: ["route"] }, { required: ["file"] }],
+      } as any,
+    ) as any
+
+    expect(result.anyOf).toEqual([{ required: ["route"] }, { required: ["file"] }])
+  })
+})
+
 describe("ProviderTransform.schema - moonshot $ref siblings", () => {
   const moonshotModel = {
     providerID: "moonshotai",