tools: support anyOf types

afaik gpt-oss is the first model that meaningfully transforms tool
function definitions in its template. We found that relatively common
definitions that include `anyOf` were not working because the template
was assuming that types were always defined via a `type` field.

anyOf allows for fully recursive types, so I exposed a
`toTypeScriptType()` function to handle this recursive logic in go and
keep the templates cleaner. The gpt-oss templates will need to be
updated to use this.

We should keep building out our function definition support to more
fully support the parts of json schema that make sense for this use
case, but in the meantime this will unblock some users (e.g., zed's
ollama integration w/ gpt-oss). Probably the most urgent is proper array
support

api/types.go

@@ -225,20 +225,68 @@ func (pt PropertyType) String() string {
 	return fmt.Sprintf("%v", []string(pt))
 }
 
+type ToolProperty struct {
+	AnyOf       []ToolProperty `json:"anyOf,omitempty"`
+	Type        PropertyType   `json:"type"`
+	Items       any            `json:"items,omitempty"`
+	Description string         `json:"description"`
+	Enum        []any          `json:"enum,omitempty"`
+}
+
+// ToTypeScriptType converts a ToolProperty to a TypeScript type string
+func (tp ToolProperty) ToTypeScriptType() string {
+	if len(tp.AnyOf) > 0 {
+		var types []string
+		for _, anyOf := range tp.AnyOf {
+			types = append(types, anyOf.ToTypeScriptType())
+		}
+		return strings.Join(types, " | ")
+	}
+
+	if len(tp.Type) == 0 {
+		return "any"
+	}
+
+	if len(tp.Type) == 1 {
+		return mapToTypeScriptType(tp.Type[0])
+	}
+
+	var types []string
+	for _, t := range tp.Type {
+		types = append(types, mapToTypeScriptType(t))
+	}
+	return strings.Join(types, " | ")
+}
+
+// mapToTypeScriptType maps JSON Schema types to TypeScript types
+func mapToTypeScriptType(jsonType string) string {
+	switch jsonType {
+	case "string":
+		return "string"
+	case "number", "integer":
+		return "number"
+	case "boolean":
+		return "boolean"
+	case "array":
+		return "any[]"
+	case "object":
+		return "Record<string, any>"
+	case "null":
+		return "null"
+	default:
+		return "any"
+	}
+}
+
 type ToolFunction struct {
 	Name        string `json:"name"`
 	Description string `json:"description"`
 	Parameters  struct {
-		Type       string   `json:"type"`
-		Defs       any      `json:"$defs,omitempty"`
-		Items      any      `json:"items,omitempty"`
-		Required   []string `json:"required"`
-		Properties map[string]struct {
-			Type        PropertyType `json:"type"`
-			Items       any          `json:"items,omitempty"`
-			Description string       `json:"description"`
-			Enum        []any        `json:"enum,omitempty"`
-		} `json:"properties"`
+		Type       string                  `json:"type"`
+		Defs       any                     `json:"$defs,omitempty"`
+		Items      any                     `json:"items,omitempty"`
+		Required   []string                `json:"required"`
+		Properties map[string]ToolProperty `json:"properties"`
 	} `json:"parameters"`
 }