@effect/ai-google: Gemini rejects primitive tool results (requires object)

[lucas-barake]

What version of Effect is running?

• @effect/ai-google: 0.12.1
• effect: 3.19.15

What steps can reproduce the bug?

Define a tool with a primitive success or failure schema (e.g., Schema.String, Schema.Number):

const SearchTool = Tool.make("search", {
  description: "Search for items",
  parameters: { query: Schema.String },
  success: Schema.String, // or failure: Schema.String with failureMode: "return"
})

When the tool executes and returns a primitive value, the agentic loop fails on iteration 2 (when the tool result is sent back to Gemini) with:

Invalid value at 'contents[2].parts[0].function_response.response' (type.googleapis.com/google.protobuf.Struct), "Found 5 results"

What is the expected behavior?

Primitive tool results should work with Gemini.

What do you see instead?

Gemini's function_response.response field requires a Struct (object), but primitive values are sent directly, causing a 400 error when the tool result is sent back on iteration 2.