[bug] Gemini schema sanitization misses properties/required when type is undefined

[ChickenBreast-ky]

Bug Description

sanitizeGemini in transform.ts strips properties and required from non-object types, but misses the case where type is entirely undefined.

This is a follow-up edge case from #11889 / PR #11888.

Root Cause

The current check:

if (result.type && result.type !== "object") {
  delete result.properties
  delete result.required
}

When type is undefined, result.type && ... short-circuits to false, so properties/required are not removed.

Reproduction

MCP tools like Notion MCP define schemas where type is omitted but properties/required are present:

{
  "data": {
    "description": "The data required for updating a page",
    "properties": { "page_id": { "type": "string" } },
    "required": ["page_id"]
  }
}

This causes:

Bad Request: GenerateContentRequest.tools[0].function_declarations[90].parameters.properties[data].properties: only allowed for OBJECT type

Expected Behavior

Schemas with properties/required but no type should be treated as implicit objects (per JSON Schema spec) and have type: "object" added.

Proposed Fix

// Add type "object" for schemas with properties/required but missing type
if (!result.type && (result.properties || result.required)) {
  result.type = "object"
}

Environment

• OpenCode v1.1.56
• Notion MCP Server
• Gemini model (google provider)

[R44VC0RP]

Confirmed — good catch. PR #11888 fixed the case where type is explicitly non-object, but missed when type is undefined.

Your proposed fix is correct. Per JSON Schema spec, a schema with properties/required but no explicit type should be treated as an implicit object. Adding type: "object" in that case fixes the issue.

The relevant code is in packages/opencode/src/provider/transform.ts:796:

if (result.type && result.type !== "object") {
  delete result.properties
  delete result.required
}

Should add before this:

if (!result.type && (result.properties || result.required)) {
  result.type = "object"
}

Feel free to open a PR with tests.