Gemini provider: tool schema emits unsupported 'additionalProperties' field (12 tools rejected, all exec calls fail)

[FerasMahmoud]

Bug Description

Running any zero exec command against the Google/Gemini provider fails because Zero emits OpenAI-style JSON Schema tool declarations that Google's function_declarations API rejects.

Reproduction

1. Install Zero 0.1.0 (npm install -g)
2. zero providers setup google (configure API key)
3. zero providers use google
4. zero exec "say hi" --model gemini-2.5-pro

Error (exact)

All 12 tool declarations are rejected with:

Invalid JSON payload received. Unknown name "additionalProperties" at "tools[0].function_declarations[N].parameters": Cannot find field

This repeats for every tool in the payload. The exec call never reaches the model.

Root Cause

Zero serializes tool schemas using OpenAI's JSON Schema format, which includes fields like additionalProperties. Google's Generative AI API (GoogleGenAI v1alpha OpenAPI spec) uses function_declarations[].parameters and only supports a subset of JSON Schema — additionalProperties is not a recognized field and causes a 400 rejection.

Environment

• Zero 0.1.0 (npm install)
• WSL2 Ubuntu 24.04
• Model: gemini-2.5-pro
• Provider: Google (via zero providers setup google)

Suggested Fix

Strip OpenAI-only JSON Schema fields (additionalProperties, $schema, $id, patternProperties, etc.) from tool parameter schemas when transport=google before sending to the Gemini API. Alternatively, map to Google's parameters_schema using only the supported subset (type, description, properties, required, items, enum, nullable).

[gnanam1990]

Thanks for the detailed report — the exact error, repro, and root-cause analysis made this quick to confirm and fix.

Confirmed. Zero serializes tool parameter schemas in OpenAI's JSON Schema dialect and always emits additionalProperties, which Google's functionDeclarations schema rejects, 400-ing every tool declaration before the request reaches the model.

Fix in #374:

• Sanitizes tool parameters in the Gemini mapper only — additionalProperties stays for OpenAI (needed for strict mode) and is harmless for Anthropic, so it is not stripped globally.
• Uses an allowlist of the keywords Google's Schema type supports (type, description, enum, properties, required, items, anyOf, default, nullable, format, and the min/max/length constraints), so any other OpenAI-only or MCP-supplied field is dropped too — not just additionalProperties. This also covers the $schema/patternProperties cases you flagged as alternatives.
• Recurses through properties, items, and anyOf, so nested schemas are cleaned at every depth.

Covered by a unit test on the sanitizer plus an end-to-end test that asserts the outgoing request body carries no additionalProperties while the real schema survives (red-green against the reported payload). Will land once #374 is reviewed and merged.