Carry additionalProperties through the Anthropic tool input_schema so it matches functool strict validation

[PratikDhanave (PratikDhanave)]

What

The Anthropic provider builds anthropic.ToolInputSchemaParam from a func tool's schema by copying only the properties and required keywords and discarding everything else. In particular it drops additionalProperties:false, which functool's strict schema always emits.

This change copies the remaining schema keywords into ToolInputSchemaParam.ExtraFields (which the anthropic-sdk-go marshals via MarshalWithExtras), so the model-facing schema stays in sync with the Go-side validation.

Why

funcTool.Call runs handler -> inputFormat.Unmarshal -> applySchema -> validate -> resolved.Validate, and the resolved schema rejects extra properties. Because the Anthropic path told the model nothing about additionalProperties, a hallucinated extra argument would pass the model but then fail functool validation on the Go side — an asymmetry that only affected Anthropic.

This restores cross-SDK parity: the OpenAI provider forwards the whole schema map (schemaToMap returns the full map) and the Gemini provider sets decl.ParametersJsonSchema = schema. Only Anthropic was stripping keywords. Matching the other providers keeps behavior aligned with the .NET/Python semantics where the declared tool schema and the validated schema are the same.

How it is tested

Added TestToolInputSchemaCarriesAdditionalProperties in agent_test.go. It builds a tool via functool.MustNew over a struct argument, runs the agent through the existing fake-transport harness, captures the request body, and asserts tools[0].input_schema.additionalProperties == false. The test fails before the fix (keyword omitted) and passes after.

[Copilot]

Pull request overview

This PR updates the Anthropic provider’s tool schema construction to preserve full JSON Schema semantics (notably additionalProperties: false) so the schema sent to the model matches the stricter Go-side functool validation behavior, aligning Anthropic with the existing OpenAI/Gemini providers.

Changes:

• Forward non-properties/required JSON Schema keywords into anthropic.ToolInputSchemaParam.ExtraFields so they are included in the serialized input_schema.
• Add a regression test that captures the outbound Anthropic request and asserts tools[0].input_schema.additionalProperties == false.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
provider/anthropicprovider/agent.go	Preserves additional JSON Schema keywords by copying them into ToolInputSchemaParam.ExtraFields when building Anthropic tool params.
provider/anthropicprovider/agent_test.go	Adds a request-capture test asserting additionalProperties: false is present in the tool input_schema.

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[github-actions]

Parity Review — No Issues Found

This PR is a bug fix to the Anthropic provider's tool schema serialization (buildMessageParams). It carries remaining JSON Schema keywords (e.g. additionalProperties: false) through ExtraFields so the model-facing schema matches the schema that functool.Call validates against.

Public API impact: No exported symbols were added, changed, or removed. The change is confined to internal implementation inside buildMessageParams.

Cross-SDK parity: The fix restores parity rather than diverging from it. Upstream .NET and Python semantics require that the declared tool schema and the server-side validated schema are the same object. The OpenAI and Gemini Go providers already forward the full schema map; this PR brings Anthropic into alignment. No equivalent gap was identified in the upstream .NET (Microsoft.Agents.AI.Anthropic) or Python Anthropic provider.

public-api-change label is not warranted. parity-approved label is appropriate and already present.

Generated by Go API Consistency Review Agent · sonnet46 · 21 AIC · ⌖ 4.99 AIC · ⊞ 6K · ◷