Restructure refimpl into go-lang and python subdirectories

Move Go reference implementation to refimpl/go-lang/ and add new
Python reference implementation in refimpl/python/. Update build.sh
with renamed draft and simplified tool paths.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

refimpl/go-lang/ect/create.go

@@ -0,0 +1,152 @@
+package ect
+
+import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"encoding/json"
+	"errors"
+	"time"
+
+	"github.com/go-jose/go-jose/v4"
+)
+
+// CreateOptions configures ECT creation.
+type CreateOptions struct {
+	// KeyID is the kid header value (references public key from WIT).
+	KeyID string
+	// IATMaxAge caps how far in the past iat may be (recommended 15 min).
+	IATMaxAge time.Duration
+	// DefaultExpiry is added to time.Now() for exp when zero (recommended 5–15 min).
+	DefaultExpiry time.Duration
+	// ValidateUUIDs when true requires jti and wid (if set) to be UUID format (RFC 9562).
+	ValidateUUIDs bool
+	// MaxParLength is the max number of parent references (0 = no limit; recommended 100).
+	MaxParLength int
+}
+
+// DefaultCreateOptions returns recommended defaults.
+func DefaultCreateOptions() CreateOptions {
+	return CreateOptions{
+		IATMaxAge:     15 * time.Minute,
+		DefaultExpiry: 10 * time.Minute,
+	}
+}
+
+// Create builds and signs an ECT. Payload must have required claims set;
+// Iat/Exp can be zero to use defaults (now, now+DefaultExpiry).
+// Create may modify the payload in place (Iat, Exp, Sub, Par) when filling defaults; pass a copy if the original must stay unchanged.
+func Create(payload *Payload, privateKey *ecdsa.PrivateKey, opts CreateOptions) (compact string, err error) {
+	if payload == nil || privateKey == nil {
+		return "", ErrPayloadRequired
+	}
+	if opts.KeyID == "" {
+		return "", ErrKeyIDRequired
+	}
+	now := time.Now()
+	if payload.Iat == 0 {
+		payload.Iat = now.Unix()
+	}
+	if payload.Exp == 0 {
+		if opts.DefaultExpiry == 0 {
+			opts.DefaultExpiry = 10 * time.Minute
+		}
+		payload.Exp = now.Add(opts.DefaultExpiry).Unix()
+	}
+	if payload.Sub == "" {
+		payload.Sub = payload.Iss
+	}
+	if payload.Par == nil {
+		payload.Par = []string{}
+	}
+
+	if err := validatePayloadForCreate(payload, opts); err != nil {
+		return "", err
+	}
+
+	payloadBytes, err := json.Marshal(payload)
+	if err != nil {
+		return "", err
+	}
+
+	sig := jose.SigningKey{Algorithm: jose.ES256, Key: privateKey}
+	options := &jose.SignerOptions{
+		ExtraHeaders: map[jose.HeaderKey]interface{}{
+			jose.HeaderType: ECTType,
+			jose.HeaderKey("kid"): opts.KeyID,
+		},
+	}
+	signer, err := jose.NewSigner(sig, options)
+	if err != nil {
+		return "", err
+	}
+
+	jws, err := signer.Sign(payloadBytes)
+	if err != nil {
+		return "", err
+	}
+
+	return jws.CompactSerialize()
+}
+
+func validatePayloadForCreate(p *Payload, opts CreateOptions) error {
+	if p.Iss == "" {
+		return errors.New("ect: iss required")
+	}
+	if len(p.Aud) == 0 {
+		return errors.New("ect: aud required")
+	}
+	if p.Jti == "" {
+		return errors.New("ect: jti required")
+	}
+	if p.ExecAct == "" {
+		return errors.New("ect: exec_act required")
+	}
+	if opts.ValidateUUIDs {
+		if !ValidUUID(p.Jti) {
+			return ErrInvalidJTI
+		}
+		if p.Wid != "" && !ValidUUID(p.Wid) {
+			return ErrInvalidWID
+		}
+	}
+	if opts.MaxParLength > 0 && len(p.Par) > opts.MaxParLength {
+		return ErrParLength
+	}
+	if p.InpHash != "" {
+		if err := ValidateHashFormat(p.InpHash); err != nil {
+			return err
+		}
+	}
+	if p.OutHash != "" {
+		if err := ValidateHashFormat(p.OutHash); err != nil {
+			return err
+		}
+	}
+	if err := ValidateExt(p.Ext); err != nil {
+		return err
+	}
+	// pol/pol_decision are OPTIONAL; if either is set, both must be present and valid
+	if p.Pol != "" || p.PolDecision != "" {
+		if p.Pol == "" || p.PolDecision == "" {
+			return ErrPolPolDecisionPair
+		}
+		if !ValidPolDecision(p.PolDecision) {
+			return ErrInvalidPolDecision
+		}
+	}
+	// compensation_* live in ext per spec
+	if p.Ext != nil {
+		if _, hasReason := p.Ext["compensation_reason"]; hasReason {
+			if v, _ := p.Ext["compensation_required"].(bool); !v {
+				return errors.New("ect: ext.compensation_reason requires ext.compensation_required true")
+			}
+		}
+	}
+	return nil
+}
+
+// GenerateKey creates an ECDSA P-256 key for ES256 (for testing/demo).
+func GenerateKey() (*ecdsa.PrivateKey, error) {
+	return ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+}