diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index 24475b5..85fd7d8 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -1,6 +1,6 @@
 # Shared reporting and PromptKit v0.20.0 implementation plan
 
-Status: ready for implementation; no stages completed.
+Status: implementation in progress; Stage 1 complete.
 
 ## Scope, authority, and execution
 
@@ -61,6 +61,10 @@ writer, or upstream-domain correctness guarantee is added by this plan.
 
 ## Stage 1: Shared report representation and safe YAML conversion
 
+**Complete.** JSON normalization and safe YAML conversion are implemented.
+Focused conversion tests and the root workspace suite (`GOTOOLCHAIN=local go
+test ./...` with Go 1.27.0) passed.
+
 Start in the root package beside [reporter.go](../../reporter.go). Add private
 report normalization using `encoding/json`: marshal the original report value,
 then decode with `UseNumber` into maps, sequences, scalars, null, and
diff --git a/report_value.go b/report_value.go
new file mode 100644
index 0000000..61fe775
--- /dev/null
+++ b/report_value.go
@@ -0,0 +1,229 @@
+package commandkit
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"math/big"
+	"regexp"
+	"sort"
+	"strconv"
+	"strings"
+
+	"go.yaml.in/yaml/v4"
+)
+
+// normalizeReport applies the JSON representation selected by the report's
+// author while retaining numeric tokens for subsequent rendering.
+func normalizeReport(value any) (any, error) {
+	data, err := json.Marshal(value)
+	if err != nil {
+		return nil, err
+	}
+	decoder := json.NewDecoder(bytes.NewReader(data))
+	decoder.UseNumber()
+	var normalized any
+	if err := decoder.Decode(&normalized); err != nil {
+		return nil, err
+	}
+	return normalized, nil
+}
+
+// DecodeYAMLReport decodes one YAML document from safe inspection output into
+// JSON-compatible values. Unsupported YAML meanings return an error; the result
+// is not a lossless representation of the input document.
+func DecodeYAMLReport(reader io.Reader) (any, error) {
+	decoder := yaml.NewDecoder(reader)
+	var doc yaml.Node
+	if err := decoder.Decode(&doc); err != nil {
+		return nil, err
+	}
+	var extra yaml.Node
+	if err := decoder.Decode(&extra); err != io.EOF {
+		if err != nil {
+			return nil, err
+		}
+		return nil, errors.New("multiple YAML documents")
+	}
+	return yamlReportValue(&doc, make(map[*yaml.Node]bool))
+}
+
+func yamlReportValue(node *yaml.Node, visiting map[*yaml.Node]bool) (any, error) {
+	if node == nil || visiting[node] {
+		return nil, errors.New("invalid or cyclic YAML alias")
+	}
+	visiting[node] = true
+	defer delete(visiting, node)
+	switch node.Kind {
+	case yaml.DocumentNode:
+		if len(node.Content) != 1 {
+			return nil, errors.New("invalid YAML document")
+		}
+		return yamlReportValue(node.Content[0], visiting)
+	case yaml.AliasNode:
+		return yamlReportValue(node.Alias, visiting)
+	case yaml.MappingNode:
+		if node.ShortTag() != "!!map" {
+			return nil, fmt.Errorf("unsupported YAML tag %s", node.Tag)
+		}
+		result := make(map[string]any, len(node.Content)/2)
+		for i := 0; i < len(node.Content); i += 2 {
+			key, err := yamlReportValue(node.Content[i], visiting)
+			if err != nil {
+				return nil, err
+			}
+			name, ok := key.(string)
+			if !ok {
+				return nil, errors.New("YAML mapping key is not a string")
+			}
+			if _, exists := result[name]; exists {
+				return nil, fmt.Errorf("duplicate YAML mapping key %q", name)
+			}
+			value, err := yamlReportValue(node.Content[i+1], visiting)
+			if err != nil {
+				return nil, err
+			}
+			result[name] = value
+		}
+		return result, nil
+	case yaml.SequenceNode:
+		if node.ShortTag() != "!!seq" {
+			return nil, fmt.Errorf("unsupported YAML tag %s", node.Tag)
+		}
+		result := make([]any, 0, len(node.Content))
+		for _, child := range node.Content {
+			value, err := yamlReportValue(child, visiting)
+			if err != nil {
+				return nil, err
+			}
+			result = append(result, value)
+		}
+		return result, nil
+	case yaml.ScalarNode:
+		switch node.ShortTag() {
+		case "!!str":
+			// The YAML resolver falls back to a string when a numeric scalar is
+			// outside its machine-number range. Preserve explicit and quoted
+			// strings, but do not silently turn a plain numeric scalar into text.
+			if node.Style == 0 {
+				plain := strings.ReplaceAll(node.Value, "_", "")
+				if yamlInteger.MatchString(plain) {
+					return yamlReportNumber(node.Value, "!!int")
+				}
+				if yamlNumericPlain.MatchString(plain) {
+					return yamlReportNumber(node.Value, "!!float")
+				}
+			}
+			return node.Value, nil
+		case "!!null":
+			return nil, nil
+		case "!!bool":
+			return strings.EqualFold(node.Value, "true"), nil
+		case "!!int", "!!float":
+			return yamlReportNumber(node.Value, node.ShortTag())
+		}
+	}
+	return nil, fmt.Errorf("unsupported YAML value with tag %s", node.Tag)
+}
+
+var yamlDecimal = regexp.MustCompile(`^([+-]?)([0-9]*)(?:\.([0-9]*))?([eE][+-]?[0-9]+)?$`)
+var yamlInteger = regexp.MustCompile(`^[+-]?(?:0[bB][01]+|0[oO][0-7]+|0[xX][0-9a-fA-F]+|[0-9]+)$`)
+var yamlNumericPlain = regexp.MustCompile(`^[+-]?(?:[0-9]+(?:\.[0-9]*)?|\.[0-9]+)(?:[eE][+-]?[0-9]+)?$`)
+var jsonNumberPattern = regexp.MustCompile(`^-?(?:0|[1-9][0-9]*)(?:\.[0-9]+)?(?:[eE][+-]?[0-9]+)?$`)
+
+func yamlReportNumber(value, tag string) (json.Number, error) {
+	original := value
+	value = strings.ReplaceAll(value, "_", "")
+	if tag == "!!int" {
+		n, ok := new(big.Int).SetString(value, 0)
+		if ok {
+			return json.Number(n.String()), nil
+		}
+		if !yamlNumericPlain.MatchString(value) {
+			return "", fmt.Errorf("unsupported YAML number %q", original)
+		}
+	}
+	match := yamlDecimal.FindStringSubmatch(value)
+	if match == nil || (match[2] == "" && match[3] == "") {
+		return "", fmt.Errorf("unsupported YAML number %q", original)
+	}
+	integer := strings.TrimLeft(match[2], "0")
+	if integer == "" {
+		integer = "0"
+	}
+	sign := match[1]
+	if sign == "+" {
+		sign = ""
+	}
+	result := sign + integer
+	if strings.Contains(value, ".") {
+		fraction := match[3]
+		if fraction == "" {
+			fraction = "0"
+		}
+		result += "." + fraction
+	}
+	result += match[4]
+	if !json.Valid([]byte(result)) {
+		return "", fmt.Errorf("unsupported YAML number %q", original)
+	}
+	return json.Number(result), nil
+}
+
+func reportYAMLNode(value any) (*yaml.Node, error) {
+	switch v := value.(type) {
+	case nil:
+		return &yaml.Node{Kind: yaml.ScalarNode, Tag: "!!null", Value: "null"}, nil
+	case bool:
+		return &yaml.Node{Kind: yaml.ScalarNode, Tag: "!!bool", Value: strconv.FormatBool(v)}, nil
+	case string:
+		return reportYAMLString(v), nil
+	case json.Number:
+		if !jsonNumberPattern.MatchString(string(v)) {
+			return nil, fmt.Errorf("invalid JSON number %q", v)
+		}
+		tag := "!!int"
+		if strings.ContainsAny(string(v), ".eE") {
+			tag = "!!float"
+		}
+		return &yaml.Node{Kind: yaml.ScalarNode, Tag: tag, Value: string(v)}, nil
+	case []any:
+		node := &yaml.Node{Kind: yaml.SequenceNode, Tag: "!!seq"}
+		for _, item := range v {
+			child, err := reportYAMLNode(item)
+			if err != nil {
+				return nil, err
+			}
+			node.Content = append(node.Content, child)
+		}
+		return node, nil
+	case map[string]any:
+		node := &yaml.Node{Kind: yaml.MappingNode, Tag: "!!map"}
+		keys := make([]string, 0, len(v))
+		for key := range v {
+			keys = append(keys, key)
+		}
+		sort.Strings(keys)
+		for _, key := range keys {
+			child, err := reportYAMLNode(v[key])
+			if err != nil {
+				return nil, err
+			}
+			node.Content = append(node.Content, reportYAMLString(key), child)
+		}
+		return node, nil
+	default:
+		return nil, fmt.Errorf("unsupported normalized report value %T", value)
+	}
+}
+
+func reportYAMLString(value string) *yaml.Node {
+	node := &yaml.Node{Kind: yaml.ScalarNode, Tag: "!!str", Value: value}
+	plain := strings.ReplaceAll(value, "_", "")
+	if yamlInteger.MatchString(plain) || yamlNumericPlain.MatchString(plain) {
+		node.Style = yaml.DoubleQuotedStyle
+	}
+	return node
+}
diff --git a/report_value_test.go b/report_value_test.go
new file mode 100644
index 0000000..1fba8fe
--- /dev/null
+++ b/report_value_test.go
@@ -0,0 +1,135 @@
+package commandkit
+
+import (
+	"bytes"
+	"encoding/json"
+	"reflect"
+	"strings"
+	"testing"
+
+	"go.yaml.in/yaml/v4"
+)
+
+type reportJSONValue struct{}
+
+func (reportJSONValue) MarshalJSON() ([]byte, error) {
+	return []byte(`{"selected":123456789012345678901234567890,"text":"false"}`), nil
+}
+
+func TestNormalizeReport(t *testing.T) {
+	value := struct {
+		Visible any    `json:"visible"`
+		Hidden  string `json:"-"`
+		Empty   string `json:"empty,omitempty"`
+	}{Visible: reportJSONValue{}, Hidden: "secret"}
+	got, err := normalizeReport(value)
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := map[string]any{"visible": map[string]any{
+		"selected": json.Number("123456789012345678901234567890"),
+		"text":     "false",
+	}}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("got %#v, want %#v", got, want)
+	}
+	if _, err := normalizeReport(make(chan int)); err == nil {
+		t.Fatal("unsupported value should fail")
+	}
+}
+
+func TestYAMLReportValues(t *testing.T) {
+	input := `large: 123456789012345678901234567890
+hex: 0xff
+fraction: .125
+text: "false"
+redacted: "[REDACTED]"
+zero: 0
+no: false
+nothing: null
+empty_map: {}
+empty_list: []
+items: [one, "2", null]
+`
+	got, err := DecodeYAMLReport(strings.NewReader(input))
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := map[string]any{
+		"large": json.Number("123456789012345678901234567890"),
+		"hex":   json.Number("255"), "fraction": json.Number("0.125"),
+		"text": "false", "redacted": "[REDACTED]", "zero": json.Number("0"),
+		"no": false, "nothing": nil, "empty_map": map[string]any{},
+		"empty_list": []any{}, "items": []any{"one", "2", nil},
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("got %#v, want %#v", got, want)
+	}
+	node, err := reportYAMLNode(got)
+	if err != nil {
+		t.Fatal(err)
+	}
+	data, err := yaml.Marshal(node)
+	if err != nil {
+		t.Fatal(err)
+	}
+	roundtrip, err := DecodeYAMLReport(bytes.NewReader(data))
+	if err != nil {
+		t.Fatalf("decode %s: %v", data, err)
+	}
+	if !reflect.DeepEqual(roundtrip, want) {
+		t.Fatalf("roundtrip %s: got %#v, want %#v", data, roundtrip, want)
+	}
+}
+
+func TestDecodeYAMLReportRejectsUnsupportedValues(t *testing.T) {
+	for _, input := range []string{"1: value", "a: .inf", "a: !custom value", "a: 1\n---\nb: 2", "a: &a [*a]", "a: 1\na: 2"} {
+		t.Run(input, func(t *testing.T) {
+			if _, err := DecodeYAMLReport(strings.NewReader(input)); err == nil {
+				t.Fatal("expected conversion error")
+			}
+		})
+	}
+}
+
+func TestYAMLReportLargeNumericScalars(t *testing.T) {
+	for _, tc := range []struct{ input, want string }{
+		{"1e9999", "1e9999"}, {"0x100000000000000000000", "1208925819614629174706176"},
+		{"+01.2500e+9999", "1.2500e+9999"},
+	} {
+		t.Run(tc.input, func(t *testing.T) {
+			got, err := DecodeYAMLReport(strings.NewReader(tc.input))
+			if err != nil || got != json.Number(tc.want) {
+				t.Fatalf("got %#v, %v; want %s", got, err, tc.want)
+			}
+		})
+	}
+	for _, input := range []string{`"1e9999"`, `!!str 1e9999`, `.`, `hello`} {
+		got, err := DecodeYAMLReport(strings.NewReader(input))
+		if err != nil {
+			t.Fatal(err)
+		}
+		if _, ok := got.(string); !ok {
+			t.Fatalf("%q became %#v", input, got)
+		}
+	}
+}
+
+func TestReportYAMLNodePreservesNumericLookingStrings(t *testing.T) {
+	value := map[string]any{"1e9999": "0x100000000000000000000", "number": json.Number("1e9999")}
+	node, err := reportYAMLNode(value)
+	if err != nil {
+		t.Fatal(err)
+	}
+	data, err := yaml.Marshal(node)
+	if err != nil {
+		t.Fatal(err)
+	}
+	got, err := DecodeYAMLReport(bytes.NewReader(data))
+	if err != nil {
+		t.Fatalf("%s: %v", data, err)
+	}
+	if !reflect.DeepEqual(got, value) {
+		t.Fatalf("%s: got %#v, want %#v", data, got, value)
+	}
+}