## Problem/Motivation Agents using tools with a free-form multiple map input (e.g. `tool_belt_field_set_value`'s `value`) fail on Anthropic with: ``` Error invoking model response: tools.N.custom.input_schema: JSON schema is invalid. It must match JSON Schema draft 2020-12 ``` The tool serializer emits an empty map's `properties` member as `\ArrayObject` so it JSON-encodes as `{}`. `SchemaToolsPropertyConverter::arrayObjectsToArrays()` casts every `\ArrayObject` to a plain PHP array, and an empty one loses its `{}` vs `[]` identity. Top-level property schemas are rebuilt into AI module property objects, but an `items` schema passes through to the provider payload untouched, so the mangled member re-encodes as: ```json "items": { "type": "object", "properties": [] } ``` `properties` must be a JSON object, so strict draft 2020-12 validation (Anthropic, both native and OpenAI-compatible endpoints) rejects the whole tools payload. MCP is unaffected because it encodes the serializer's schema directly, with the `\ArrayObject` intact. Confirmed by bisection against the live API: the identical payload is accepted once `items.properties` is `{}` or absent. ## Steps to reproduce 1. Configure an agent whose tools include `tool:tool_belt:field_set_value` (e.g. the content agent). 2. Run it against an Anthropic provider. 3. The request is rejected with the `tools.N.custom.input_schema` error above; `N` is the tool's index in the agent's tool list. ## Proposed resolution Drop empty `properties` members while casting `\ArrayObject` values in `SchemaToolsPropertyConverter`: an empty `properties` member constrains nothing, so removing it is semantically identical and keeps every passthrough schema draft 2020-12-valid. A scan of all rendered function schemas on a site with tool_belt/tool_shop enabled shows `properties` is the only member affected (both serializer emission sites use `\ArrayObject` only for `properties`). ### AI usage (if applicable) * [x] AI Assisted Issue: This issue was generated with AI assistance, but was reviewed and refined by the creator. * [x] AI Assisted Code: This code was mainly generated by a human, with AI autocompleting or parts AI generated, but under full human supervision. * [ ] AI Generated Code: This code was mainly generated by an AI with human guidance, and reviewed, tested, and refined by a human. * [ ] Vibe Coded: This code was generated by an AI and has only been functionally tested.