fix(v2): coerce string-encoded numbers/bools in tool arguments

LLMs occasionally return numeric or boolean tool-call fields as JSON
strings (e.g. "3" instead of 3, "true" instead of true), which Go's
strict json.Unmarshal rejects. The strict unmarshal stays as the happy
path; on failure we retry with a coercion pass that walks the target
struct (recursing into nested structs, slices, maps, and pointer fields)
and converts strings to the appropriate kind. Returns the original error
if coercion can't recover.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

v2/tool_coerce.go

@@ -0,0 +1,134 @@
+package llm
+
+import (
+	"encoding/json"
+	"reflect"
+	"strconv"
+	"strings"
+)
+
+// coerceArgsToType reparses argsJSON with leniency: where the target struct
+// expects a numeric or boolean field but the JSON value is a string, it
+// converts the string to the target kind. Recurses into nested structs,
+// slices, maps, and pointer fields.
+//
+// Returns a freshly marshaled JSON byte slice that can be unmarshaled into
+// the target type with strict json.Unmarshal.
+func coerceArgsToType(argsJSON []byte, target reflect.Type) ([]byte, error) {
+	var raw any
+	if err := json.Unmarshal(argsJSON, &raw); err != nil {
+		return nil, err
+	}
+	raw = coerceValue(raw, target)
+	return json.Marshal(raw)
+}
+
+func coerceValue(v any, t reflect.Type) any {
+	if t == nil {
+		return v
+	}
+	for t.Kind() == reflect.Ptr {
+		t = t.Elem()
+	}
+
+	switch t.Kind() {
+	case reflect.Struct:
+		m, ok := v.(map[string]any)
+		if !ok {
+			return v
+		}
+		for i := 0; i < t.NumField(); i++ {
+			f := t.Field(i)
+			if !f.IsExported() {
+				continue
+			}
+			name := jsonFieldName(f)
+			if name == "-" {
+				continue
+			}
+			if val, present := m[name]; present {
+				m[name] = coerceValue(val, f.Type)
+			}
+		}
+		return m
+
+	case reflect.Slice, reflect.Array:
+		arr, ok := v.([]any)
+		if !ok {
+			return v
+		}
+		elemType := t.Elem()
+		for i := range arr {
+			arr[i] = coerceValue(arr[i], elemType)
+		}
+		return arr
+
+	case reflect.Map:
+		m, ok := v.(map[string]any)
+		if !ok {
+			return v
+		}
+		valType := t.Elem()
+		for k := range m {
+			m[k] = coerceValue(m[k], valType)
+		}
+		return m
+
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		if s, ok := v.(string); ok {
+			s = strings.TrimSpace(s)
+			s = strings.TrimPrefix(s, "+")
+			if n, err := strconv.ParseInt(s, 10, 64); err == nil {
+				return n
+			}
+			if f, err := strconv.ParseFloat(s, 64); err == nil {
+				return int64(f)
+			}
+		}
+
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		if s, ok := v.(string); ok {
+			s = strings.TrimSpace(s)
+			s = strings.TrimPrefix(s, "+")
+			if n, err := strconv.ParseUint(s, 10, 64); err == nil {
+				return n
+			}
+			if f, err := strconv.ParseFloat(s, 64); err == nil && f >= 0 {
+				return uint64(f)
+			}
+		}
+
+	case reflect.Float32, reflect.Float64:
+		if s, ok := v.(string); ok {
+			s = strings.TrimSpace(s)
+			if f, err := strconv.ParseFloat(s, 64); err == nil {
+				return f
+			}
+		}
+
+	case reflect.Bool:
+		if s, ok := v.(string); ok {
+			if b, err := strconv.ParseBool(strings.TrimSpace(s)); err == nil {
+				return b
+			}
+		}
+	}
+	return v
+}
+
+func jsonFieldName(f reflect.StructField) string {
+	tag := f.Tag.Get("json")
+	if tag == "" {
+		return f.Name
+	}
+	if idx := strings.Index(tag, ","); idx >= 0 {
+		tag = tag[:idx]
+	}
+	if tag == "-" {
+		return "-"
+	}
+	if tag == "" {
+		return f.Name
+	}
+	return tag
+}