bug: Nullable type arrays in tool schemas cause 400 error on Antigravity/Droid Factory

[stondy0103]

Bug Description

When using Antigravity (Droid Factory) with Gemini models via the OpenAI Responses API, requests fail with:

400 Invalid value at 'request.tools[0].function_declarations[19].parameters.properties[3].value.type'
(type.googleapis.com/google.cloud.aiplatform.master.Type), "["STRING","NULL"]"

This happens when tool schemas include nullable types like "type": ["string", "null"] (which Claude Code and other OpenAI-compatible tools commonly send).

Root Cause

In internal/translator/gemini/openai/responses/gemini_openai-responses_request.go, lines 333-348:

if propType := value.Get("type"); propType.Exists() {
    upperType := strings.ToUpper(propType.String())
    cleaned, _ = sjson.Set(cleaned, "properties."+key.String()+".type", upperType)
}

When type is a JSON array ["string", "null"]:

1. gjson.Result.String() returns raw text ["string","null"]
2. strings.ToUpper() → ["STRING","NULL"]
3. sjson.Set() stores it as a JSON string "[\"STRING\",\"NULL\"]" — not a JSON array
4. Downstream flattenTypeArrays() skips it because IsArray() returns false on a string
5. Gemini API rejects the invalid type value

Additionally, this code only iterates top-level properties — nested schemas with type arrays are not processed at all.

Suggested Fix

Remove the type uppercasing block (lines 333-348) and pass the raw schema directly:

if params := tool.Get("parameters"); params.Exists() {
    funcDecl, _ = sjson.SetRaw(funcDecl, "parametersJsonSchema", params.Raw)
}

This is safe because:

• Antigravity executor already runs CleanJSONSchemaForGemini() which properly handles type arrays, nullable fields, and all schema cleanup
• Gemini/Vertex executors use parametersJsonSchema which accepts raw JSON Schema directly (no uppercasing needed)
• The uppercasing logic was redundant and incomplete (top-level only)
• No impact on other models or executors

Verified

Built and deployed the fix locally. Tested with Droid Factory (Antigravity) Gemini models — the error no longer occurs.

Fix PR

#205

Environment

• Client: Claude Code (OpenAI Responses API format)
• Provider: Antigravity / Droid Factory
• Models: Gemini models via Antigravity