fix(opencode): avoid gemini combiner schema sibling injection (#15318)

2 files changed, 130 insertions, 5 deletions

diff --git a/packages/opencode/src/provider/transform.ts b/packages/opencode/src/provider/transform.ts
index b659799c1..4be3035ab 100644
--- a/packages/opencode/src/provider/transform.ts
+++ b/packages/opencode/src/provider/transform.ts
@@ -897,6 +897,32 @@ export namespace ProviderTransform {
 
     // Convert integer enums to string enums for Google/Gemini
     if (model.providerID === "google" || model.api.id.includes("gemini")) {
+      const isPlainObject = (node: unknown): node is Record<string, any> =>
+        typeof node === "object" && node !== null && !Array.isArray(node)
+      const hasCombiner = (node: unknown) =>
+        isPlainObject(node) &&
+        (Array.isArray(node.anyOf) || Array.isArray(node.oneOf) || Array.isArray(node.allOf))
+      const hasSchemaIntent = (node: unknown) => {
+        if (!isPlainObject(node)) return false
+        if (hasCombiner(node)) return true
+        return [
+          "type",
+          "properties",
+          "items",
+          "prefixItems",
+          "enum",
+          "const",
+          "$ref",
+          "additionalProperties",
+          "patternProperties",
+          "required",
+          "not",
+          "if",
+          "then",
+          "else",
+        ].some((key) => key in node)
+      }
+
       const sanitizeGemini = (obj: any): any => {
         if (obj === null || typeof obj !== "object") {
           return obj
@@ -927,19 +953,18 @@ export namespace ProviderTransform {
           result.required = result.required.filter((field: any) => field in result.properties)
         }
 
-        if (result.type === "array") {
+        if (result.type === "array" && !hasCombiner(result)) {
           if (result.items == null) {
             result.items = {}
           }
-          // Ensure items has at least a type if it's an empty object
-          // This handles nested arrays like { type: "array", items: { type: "array", items: {} } }
-          if (typeof result.items === "object" && !Array.isArray(result.items) && !result.items.type) {
+          // Ensure items has a type only when it's still schema-empty.
+          if (isPlainObject(result.items) && !hasSchemaIntent(result.items)) {
             result.items.type = "string"
           }
         }
 
         // Remove properties/required from non-object types (Gemini rejects these)
-        if (result.type && result.type !== "object") {
+        if (result.type && result.type !== "object" && !hasCombiner(result)) {
           delete result.properties
           delete result.required
         }
diff --git a/packages/opencode/test/provider/transform.test.ts b/packages/opencode/test/provider/transform.test.ts
index 189bdfd32..232984635 100644
--- a/packages/opencode/test/provider/transform.test.ts
+++ b/packages/opencode/test/provider/transform.test.ts
@@ -510,6 +510,106 @@ describe("ProviderTransform.schema - gemini nested array items", () => {
   })
 })
 
+describe("ProviderTransform.schema - gemini combiner nodes", () => {
+  const geminiModel = {
+    providerID: "google",
+    api: {
+      id: "gemini-3-pro",
+    },
+  } as any
+
+  const walk = (node: any, cb: (node: any, path: (string | number)[]) => void, path: (string | number)[] = []) => {
+    if (node === null || typeof node !== "object") {
+      return
+    }
+    if (Array.isArray(node)) {
+      node.forEach((item, i) => walk(item, cb, [...path, i]))
+      return
+    }
+    cb(node, path)
+    Object.entries(node).forEach(([key, value]) => walk(value, cb, [...path, key]))
+  }
+
+  test("keeps edits.items.anyOf without adding type", () => {
+    const schema = {
+      type: "object",
+      properties: {
+        edits: {
+          type: "array",
+          items: {
+            anyOf: [
+              {
+                type: "object",
+                properties: {
+                  old_string: { type: "string" },
+                  new_string: { type: "string" },
+                },
+                required: ["old_string", "new_string"],
+              },
+              {
+                type: "object",
+                properties: {
+                  old_string: { type: "string" },
+                  new_string: { type: "string" },
+                  replace_all: { type: "boolean" },
+                },
+                required: ["old_string", "new_string"],
+              },
+            ],
+          },
+        },
+      },
+      required: ["edits"],
+    } as any
+
+    const result = ProviderTransform.schema(geminiModel, schema) as any
+
+    expect(Array.isArray(result.properties.edits.items.anyOf)).toBe(true)
+    expect(result.properties.edits.items.type).toBeUndefined()
+  })
+
+  test("does not add sibling keys to combiner nodes during sanitize", () => {
+    const schema = {
+      type: "object",
+      properties: {
+        edits: {
+          type: "array",
+          items: {
+            anyOf: [{ type: "string" }, { type: "number" }],
+          },
+        },
+        value: {
+          oneOf: [{ type: "string" }, { type: "boolean" }],
+        },
+        meta: {
+          allOf: [
+            {
+              type: "object",
+              properties: { a: { type: "string" } },
+            },
+            {
+              type: "object",
+              properties: { b: { type: "string" } },
+            },
+          ],
+        },
+      },
+    } as any
+    const input = JSON.parse(JSON.stringify(schema))
+    const result = ProviderTransform.schema(geminiModel, schema) as any
+
+    walk(result, (node, path) => {
+      const hasCombiner = Array.isArray(node.anyOf) || Array.isArray(node.oneOf) || Array.isArray(node.allOf)
+      if (!hasCombiner) {
+        return
+      }
+      const before = path.reduce((acc: any, key) => acc?.[key], input)
+      const added = Object.keys(node).filter((key) => !(key in before))
+      expect(added).toEqual([])
+    })
+  })
+})
+
 describe("ProviderTransform.schema - gemini non-object properties removal", () => {
   const geminiModel = {
     providerID: "google",