[aisdk] Allow passing of provider metadata in tool definitions (#579)

## Summary
We need it so that we can specify whether the tool schema validation
should be strict or not.

## How was it tested?
Used with testpilot and its custom tools. I'll send a PR on axiom to
show its usage too.

## Community Contribution License

All community contributions in this pull request are licensed to the
project maintainers under the terms of the [Apache 2
License](https://www.apache.org/licenses/LICENSE-2.0).

By creating this pull request I represent that I have the right to
license the contributions to the project maintainers under the Apache 2
License as stated in the [Community Contribution
License](https://github.com/jetify-com/opensource/blob/main/CONTRIBUTING.md#community-contribution-license).

Author: ipince

aisdk/ai/api/llm_tool.go

@@ -30,7 +30,7 @@ type ToolDefinition interface {
 }
 
 // For the equivalent of ToolDefinition in MCP, see the Tool struct in:
-// https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/protocol.go#L854
+// https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/protocol.go#L901
 
 // FunctionTool represents a tool that has a name, description, and set of input arguments.
 // Note: this is not the user-facing tool definition. The AI SDK methods will
@@ -47,6 +47,11 @@ type FunctionTool struct {
 	// the tool's input requirements and provide matching suggestions.
 	// InputSchema should be defined using a JSON schema.
 	InputSchema *jsonschema.Schema `json:"input_schema,omitzero"`
+
+	// ProviderMetadata contains additional provider-specific metadata.
+	// They are passed through to the provider from the AI SDK and enable
+	// provider-specific functionality that can be fully encapsulated in the provider.
+	ProviderMetadata *ProviderMetadata `json:"provider_metadata,omitzero"`
 }
 
 var _ ToolDefinition = &FunctionTool{}
@@ -57,6 +62,9 @@ func (t *FunctionTool) Type() string { return "function" }
 // isToolDefinition is a marker method to satisfy the ToolDefinition interface
 func (t *FunctionTool) isToolDefinition() bool { return true }
 
+// GetProviderMetadata returns the provider-specific metadata for the function tool
+func (t FunctionTool) GetProviderMetadata() *ProviderMetadata { return t.ProviderMetadata }
+
 // FunctionTool JSON marshaling - automatically includes "type" field
 func (t *FunctionTool) MarshalJSON() ([]byte, error) {
 	type Alias FunctionTool

aisdk/ai/provider/openai/internal/codec/encode_tools.go

@@ -93,11 +93,16 @@ func encodeFunctionTool(tool api.FunctionTool) (*responses.ToolUnionParam, []api
 		return nil, nil, fmt.Errorf("failed to convert tool parameters: %w", err)
 	}
 
+	strict := true // Default to true
+	md := GetMetadata(tool)
+	if md != nil && md.StrictSchemas != nil {
+		strict = *md.StrictSchemas
+	}
+
 	result := responses.ToolParamOfFunction(
 		name,
 		props,
-		// TODO: allow passing the strict flag to the function
-		true, // strict mode enabled
+		strict,
 	)
 
 	// Add description if provided