release: SDK 0.4.0, local-vault 0.2.0, n8n 0.2.0 — version bumps

Brings the published packages level with the code shipped since the last publish (offline-verify exports, attestedFetch, OTel bridges, portable receipts, head-tracking fix, etc. for the SDK; init+doctor for local-vault). Versions move in lockstep as the publication-parity contract requires: PyPI/npm/Go SDK/CLI all 0.4.0. n8n node bumps to 0.2.0 with its @attesto/sdk dep widened to ^0.4.0. attesto-mcp stays 0.1.0 (first publish). No package contains source maps or non-runtime source: npm ships compiled .js + .d.ts only (zero .ts, zero .map, verified), Python wheels ship runtime .py only (no sdist, no tests), and no wheel/tarball contains anything from backend/, gateway/, or the Rust prover. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
gates: cargo fmt + secret-scan-clean test fixtures
2026-06-12 19:22:41 +02:00 · 2026-06-12 15:12:54 +02:00 · 2026-06-12 11:34:47 +02:00 · 2026-06-12 11:14:45 +02:00 · 2026-06-12 09:57:34 +02:00 · 2026-06-12 09:25:43 +02:00
30 changed files with 3727 additions and 13 deletions
--- a/README.md
+++ b/README.md
@@ -7,7 +7,17 @@ tooling, CI, evidence exporters, and operator automation. Do not embed Attesto A
 ## Install

 ```shell
-go get git.rotz.ai/rotzmediagroup/attesto-v1/sdk/go
+go get go.attesto.eu/sdk
+```
+
+CLI binaries: `curl -fsSL https://get.attesto.eu | sh` (checksum-verified).
+Verify the release signature before you trust its verifier:
+
+```shell
+curl -fsSO https://get.attesto.eu/cosign.pub
+curl -fsSO https://get.attesto.eu/0.3.0/SHA256SUMS
+curl -fsSO https://get.attesto.eu/0.3.0/SHA256SUMS.sig
+cosign verify-blob --key cosign.pub --insecure-ignore-tlog --signature SHA256SUMS.sig SHA256SUMS
 ```

 The first release is VCS-resolved from the Attesto repository. It intentionally
@@ -25,7 +35,7 @@ import (
 	"os"
 	"time"

-	attesto "git.rotz.ai/rotzmediagroup/attesto-v1/sdk/go"
+	attesto "go.attesto.eu/sdk"
 )

 func main() {
@@ -64,6 +74,9 @@ Attesto stores source-system time separately from backend ingest time.
 `time.Now().UTC()` when omitted, but production integrations should pass the
 real upstream event timestamp whenever the source system provides one.

+
+Canonicalization is specified normatively in [ATTESTO-CANONICAL-JSON-001](../../docs/protocol/ATTESTO-CANONICAL-JSON-001.md); the parity corpus `golden-vectors/sdk-parity/` is its conformance set.
+
 ## Committed payload number rule

 When events are committed to a Proofstream, payload and metadata numbers must
@@ -72,6 +85,20 @@ and integers beyond ±(2^53−1) are rejected at ingestion (HTTP 422); encode
 decimals and large integers as strings (e.g. `{"score": "0.87"}`). This keeps
 cross-language commitment recomputation byte-exact (`CanonicalJSON`).

+The SDK enforces the same rule **locally** before sending, so you see it at dev
+time rather than as a production 422. `LogEvent` / `LogEvents` return an
+`*UnsafeNumberError` (with `.Path`, the JSON path to the offending value). Set
+`RequestOptions{SkipPreflight: true}` to defer to the server.
+
+```go
+// Commitment a Proofstream stores for a payload, byte-identical to the server
+// (and to the Python / TypeScript SDKs):
+commitment, _ := attesto.PayloadCommitment(map[string]any{"decision": "approve", "score_bp": 8700})
+// commitment["canonical_payload_hash"] == server's stored hash
+
+ok, _ := attesto.VerifyPayloadCommitment(myPayload, event) // recompute and compare
+```
+
 ## Verification

 Remote verification uses Attesto's public `/v2/verify` API. Offline receipt
@@ -85,6 +112,142 @@ if !report.OK {
 }
 ```

+The offline trust model extends across the whole proof chain — all client-side:
+
+```go
+ok, _ := attesto.VerifyInclusionProof(leafHash, proof, windowRoot)   // event in a window root
+ok, _ = attesto.VerifyCheckpointRoot(windowHashes, checkpointRoot)   // windows fold to checkpoint root
+ext := attesto.VerifyCheckpointExtension(previous, current)          // one checkpoint continues the previous
+comp := attesto.VerifyCompleteness(events, 5, 8)                     // no events omitted in [5, 8]
+```
+
+`VerifyCompleteness` proves **no events were omitted** in a range: the sequence
+numbers must be gap-free and each event's `prev_event_hash` must chain to the
+previous event's `event_hash`.
+
+## Your SDK is a witness
+
+The client remembers the last accepted `(seqNo, eventHash)` per stream and checks
+every new receipt links forward. If the server ever rewinds a sequence number or
+presents a divergent lineage, `LogEvent` / `LogEvents` return a
+`*ForkDetectedError` and the stored head is not advanced. The default store is
+in-memory; use a file store for fork detection across process invocations, or
+disable it.
+
+```go
+// Persist across CLI invocations (atomic, 0600 at ~/.attesto/heads.json):
+client, _ := attesto.NewClient(apiKey, attesto.WithHeadStore(attesto.NewFileHeadStore("")))
+
+// Disable fork detection:
+client, _ = attesto.NewClient(apiKey, attesto.WithHeadStore(nil))
+```
+
+## Typed compliance events and the evidence report
+
+```go
+decision := attesto.ModelDecision{Model: "credit-v1", Decision: "approve", ConfidenceBp: 8700}
+payload, _ := decision.ToPayload() // regulation_refs attached, number-policy validated
+client.LogEvent(ctx, streamID, attesto.EventInput{
+	SourceRef: "d-1", EventType: decision.EventType(), Payload: payload,
+})
+```
+
+```bash
+attesto report article12 --stream str_... --output report.md
+```
+
+The report is a deterministic template (never LLM-generated) stating what is
+recorded and independently verifiable — it never asserts conformity.
+
+## Testing without Attesto: attestotest
+
+`go.attesto.eu/sdk/attestotest` starts a local httptest emulator with **real**
+hash-chain semantics; point the real client at it and run your full pipeline
+in CI with zero network:
+
+```go
+server := attestotest.NewServer()
+defer server.Close()
+client, _ := attesto.NewClient(server.APIKey, attesto.WithBaseURL(server.URL))
+stream, _ := client.CreateStream(ctx, attesto.StreamCreateInput{UseCase: "ci", PolicyID: "mock-policy"})
+receipt, _ := client.LogEvent(ctx, stream.StreamID, attesto.EventInput{SourceRef: "e1"})
+stored, _ := client.GetReceipt(ctx, receipt.StreamEventID)
+report := attesto.VerifyReceiptOffline(stored.Receipt, server.PublicKeyHex)
+```
+
+Mock evidence can never pass as real: every object carries `mock: true`, the
+signer kid is `attesto-mock-ed25519`, and verification against any real
+witness key fails.
+
+## Built-in self-test and doctor
+
+On the first hashing operation per process the SDK verifies itself against an
+embedded copy of the cross-language parity vectors and fails closed with
+`ErrSelfTest` on any divergence. `attesto doctor` (CLI) prints a deterministic
+JSON report: self-test, head-store writability, number-policy dry-run
+(`--sample-payload file.json`), and — with credentials configured —
+reachability and protocol acceptance.
+
+## Iterating long listings
+
+Paginated `List*` methods have `Iter*` twins that walk limit/offset pages
+transparently; `Next` returns `(nil, nil)` when the listing is exhausted:
+
+```go
+it := client.IterTenantStreamEvents("str_...", 200)
+for {
+	event, err := it.Next(ctx)
+	if err != nil || event == nil {
+		break
+	}
+	process(event)
+}
+```
+
+## Verify anchors on-chain
+
+`VerifyAnchorOnchain` checks an anchor epoch against the chain itself — one raw
+JSON-RPC `eth_call` to the anchoring contract's `getCommitment(batchId)`
+(comparing the on-chain merkle root) plus a transaction-receipt check (status,
+block). No web3 dependency; the RPC endpoint is yours, so this never asks
+Attesto to confirm Attesto.
+
+```go
+anchor, _ := client.GetAnchorEpoch(ctx, "aep_...")
+report := attesto.VerifyAnchorOnchain(ctx, anchor, "https://polygon-rpc.example", 15*time.Second)
+if !report.OK {
+	log.Fatalf("anchor failed on-chain verification: %v", report.Problems)
+}
+```
+
+CLI equivalent (fetch + on-chain check in one step):
+
+```bash
+attesto anchors verify aep_... --rpc-url https://polygon-rpc.example
+```
+
+## Receiving Attesto webhooks
+
+```go
+func handler(w http.ResponseWriter, r *http.Request) {
+	body, _ := io.ReadAll(r.Body)
+	headers := map[string]string{
+		"X-Attesto-Timestamp": r.Header.Get("X-Attesto-Timestamp"),
+		"X-Attesto-Signature": r.Header.Get("X-Attesto-Signature"),
+	}
+	if !attesto.VerifyWebhook(body, headers, webhookSecret, 300) {
+		w.WriteHeader(http.StatusUnauthorized)
+		return
+	}
+	process(body)
+}
+```
+
+Verification recomputes `hmac_sha256(secret, "<timestamp>." + body)` from the
+`X-Attesto-Timestamp` / `X-Attesto-Signature` headers, rejects timestamps more
+than the allowed skew from now (replay protection), and compares with
+`hmac.Equal` (constant time).
+
 ## Operator and Admin Endpoints

 System-key clients are created with `attesto.NewClient`. Tenant/operator
--- a/anchors.go
+++ b/anchors.go
@@ -0,0 +1,172 @@
+package attesto
+
+import (
+	"bytes"
+	"context"
+	"encoding/hex"
+	"encoding/json"
+	"net/http"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// GetCommitmentSelector is the first 4 bytes of keccak256("getCommitment(string)"),
+// fixed by the contract ABI (APSProvenance.abi.json); pinned so no keccak
+// implementation is needed.
+const GetCommitmentSelector = "a7b09e2a"
+
+// EncodeGetCommitmentCall ABI-encodes getCommitment(string) calldata: selector,
+// then the single dynamic string argument (offset word, length word, padded bytes).
+func EncodeGetCommitmentCall(batchID string) string {
+	raw := []byte(batchID)
+	pad := (32 - len(raw)%32) % 32
+	body := make([]byte, 0, 64+len(raw)+pad)
+	offset := make([]byte, 32)
+	offset[31] = 0x20
+	length := make([]byte, 32)
+	for i, v := 31, len(raw); v > 0; i, v = i-1, v>>8 {
+		length[i] = byte(v & 0xff)
+	}
+	body = append(body, offset...)
+	body = append(body, length...)
+	body = append(body, raw...)
+	body = append(body, make([]byte, pad)...)
+	return "0x" + GetCommitmentSelector + hex.EncodeToString(body)
+}
+
+func stripHex(value string) string {
+	return strings.TrimPrefix(strings.ToLower(strings.TrimSpace(value)), "0x")
+}
+
+func rpcCall(ctx context.Context, httpClient *http.Client, rpcURL, method string, params []any) (json.RawMessage, string) {
+	payload, err := json.Marshal(map[string]any{
+		"jsonrpc": "2.0", "id": 1, "method": method, "params": params,
+	})
+	if err != nil {
+		return nil, "rpc " + method + " failed"
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, rpcURL, bytes.NewReader(payload))
+	if err != nil {
+		return nil, "rpc " + method + " failed"
+	}
+	req.Header.Set("Content-Type", "application/json")
+	resp, err := httpClient.Do(req)
+	if err != nil {
+		return nil, "rpc " + method + " failed"
+	}
+	defer resp.Body.Close()
+	var envelope struct {
+		Result json.RawMessage `json:"result"`
+		Error  json.RawMessage `json:"error"`
+	}
+	if resp.StatusCode != http.StatusOK || json.NewDecoder(resp.Body).Decode(&envelope) != nil {
+		return nil, "rpc " + method + " failed"
+	}
+	if len(envelope.Error) > 0 && string(envelope.Error) != "null" {
+		return nil, "rpc " + method + " failed"
+	}
+	if len(envelope.Result) == 0 {
+		return nil, "rpc " + method + " failed"
+	}
+	return envelope.Result, ""
+}
+
+func anchorField(epoch map[string]any, keys ...string) (string, bool) {
+	for _, key := range keys {
+		if value, ok := epoch[key].(string); ok && value != "" {
+			return value, true
+		}
+	}
+	return "", false
+}
+
+// VerifyAnchorOnchain verifies an anchor epoch against the chain itself via raw
+// JSON-RPC: one eth_call to getCommitment(batchId) comparing the on-chain merkle
+// root with the anchor's merkle_root, plus one eth_getTransactionReceipt
+// confirming the anchoring transaction succeeded in the expected block. The
+// anchor object is accepted in snake_case or camelCase; the contract address is
+// read from the epoch's hashed payload. rpcURL is customer-chosen — this
+// function never talks to Attesto.
+func VerifyAnchorOnchain(ctx context.Context, anchorEpoch map[string]any, rpcURL string, timeout time.Duration) VerifyReport {
+	problems := make([]string, 0)
+
+	payload, _ := anchorEpoch["payload"].(map[string]any)
+	merkleRoot, okRoot := anchorField(anchorEpoch, "merkle_root", "merkleRoot")
+	txHash, okTx := anchorField(anchorEpoch, "tx_hash", "txHash")
+	batchID, okBatch := anchorField(anchorEpoch, "anchor_batch_id", "anchorBatchId")
+	contractAddress, okAddr := anchorField(anchorEpoch, "contract_address", "contractAddress")
+	if !okAddr && payload != nil {
+		contractAddress, okAddr = anchorField(payload, "contract_address")
+	}
+	blockNumber := int64(-1)
+	switch v := anchorEpoch["block_number"].(type) {
+	case float64:
+		blockNumber = int64(v)
+	case int64:
+		blockNumber = v
+	default:
+		switch v := anchorEpoch["blockNumber"].(type) {
+		case float64:
+			blockNumber = int64(v)
+		case int64:
+			blockNumber = v
+		}
+	}
+	if !okRoot || !okTx || !okBatch || !okAddr || blockNumber < 0 {
+		return VerifyReport{
+			Kind: "anchor-onchain", OK: false,
+			Problems: []string{"anchor epoch is missing required fields"},
+		}
+	}
+
+	if timeout <= 0 {
+		timeout = 15 * time.Second
+	}
+	httpClient := &http.Client{Timeout: timeout}
+
+	callResult, problem := rpcCall(ctx, httpClient, rpcURL, "eth_call", []any{
+		map[string]any{"to": contractAddress, "data": EncodeGetCommitmentCall(batchID)},
+		"latest",
+	})
+	if problem != "" {
+		problems = append(problems, problem)
+	} else {
+		var returned string
+		if json.Unmarshal(callResult, &returned) != nil {
+			problems = append(problems, "rpc eth_call failed")
+		} else {
+			// Return tuple is (bytes32 merkleRoot, uint32, string, uint64);
+			// the root is the first 32-byte word.
+			onchain := stripHex(returned)
+			if len(onchain) < 64 || onchain[:64] != stripHex(merkleRoot) {
+				problems = append(problems, "anchor merkle root mismatch")
+			}
+		}
+	}
+
+	receiptResult, problem := rpcCall(ctx, httpClient, rpcURL, "eth_getTransactionReceipt", []any{txHash})
+	if problem != "" {
+		problems = append(problems, problem)
+	} else if string(receiptResult) == "null" {
+		problems = append(problems, "anchor transaction not found")
+	} else {
+		var receipt struct {
+			Status      string `json:"status"`
+			BlockNumber string `json:"blockNumber"`
+		}
+		if json.Unmarshal(receiptResult, &receipt) != nil {
+			problems = append(problems, "anchor transaction not found")
+		} else {
+			if receipt.Status != "0x1" {
+				problems = append(problems, "anchor transaction failed")
+			}
+			mined, err := strconv.ParseInt(stripHex(receipt.BlockNumber), 16, 64)
+			if err != nil || mined != blockNumber {
+				problems = append(problems, "anchor transaction block mismatch")
+			}
+		}
+	}
+
+	return VerifyReport{Kind: "anchor-onchain", OK: len(problems) == 0, Problems: problems}
+}
--- a/anchors_test.go
+++ b/anchors_test.go
@@ -0,0 +1,131 @@
+package attesto
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+)
+
+const (
+	anchorRoot  = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+	anchorTx    = "0xbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"
+	anchorBlock = int64(12345)
+)
+
+func anchorEpochFixture() map[string]any {
+	return map[string]any{
+		"anchorEpochId": "aep_demo",
+		"merkleRoot":    "0x" + anchorRoot,
+		"txHash":        anchorTx,
+		"blockNumber":   float64(anchorBlock),
+		"anchorBatchId": "batch_demo",
+		"chainId":       float64(137),
+		"payload":       map[string]any{"contract_address": "0x" + strings.Repeat("d", 40)},
+	}
+}
+
+func mockRPC(t *testing.T, callRoot string, receipt map[string]any) *httptest.Server {
+	t.Helper()
+	return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var body struct {
+			Method string `json:"method"`
+			Params []any  `json:"params"`
+		}
+		if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+			w.WriteHeader(http.StatusBadRequest)
+			return
+		}
+		switch body.Method {
+		case "eth_call":
+			// (bytes32, uint32, string, uint64) — only the first word matters.
+			result := "0x" + callRoot + strings.Repeat("0", 192)
+			_ = json.NewEncoder(w).Encode(map[string]any{"jsonrpc": "2.0", "id": 1, "result": result})
+		case "eth_getTransactionReceipt":
+			_ = json.NewEncoder(w).Encode(map[string]any{"jsonrpc": "2.0", "id": 1, "result": receipt})
+		default:
+			w.WriteHeader(http.StatusBadRequest)
+		}
+	}))
+}
+
+func TestEncodeGetCommitmentCallMatchesPinnedExample(t *testing.T) {
+	want := "0xa7b09e2a" +
+		"0000000000000000000000000000000000000000000000000000000000000020" +
+		"000000000000000000000000000000000000000000000000000000000000000a" +
+		"62617463685f64656d6f00000000000000000000000000000000000000000000"
+	if got := EncodeGetCommitmentCall("batch_demo"); got != want {
+		t.Errorf("calldata = %s, want %s", got, want)
+	}
+}
+
+func TestABIStillDeclaresGetCommitmentString(t *testing.T) {
+	raw, err := os.ReadFile(filepath.Join("testdata", "APSProvenance.abi.json"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	var abi []map[string]any
+	if err := json.Unmarshal(raw, &abi); err != nil {
+		t.Fatal(err)
+	}
+	for _, entry := range abi {
+		if entry["name"] == "getCommitment" {
+			inputs := entry["inputs"].([]any)
+			if len(inputs) != 1 || inputs[0].(map[string]any)["type"] != "string" {
+				t.Fatalf("getCommitment inputs changed: %v", inputs)
+			}
+			return
+		}
+	}
+	t.Fatal("getCommitment not found in ABI")
+}
+
+func TestAnchorVerifiesWhenChainMatches(t *testing.T) {
+	srv := mockRPC(t, anchorRoot, map[string]any{"status": "0x1", "blockNumber": "0x3039"})
+	defer srv.Close()
+	report := VerifyAnchorOnchain(context.Background(), anchorEpochFixture(), srv.URL, time.Second)
+	if !report.OK {
+		t.Errorf("expected ok, problems: %v", report.Problems)
+	}
+}
+
+func TestAnchorRootMismatch(t *testing.T) {
+	srv := mockRPC(t, strings.Repeat("e", 64), map[string]any{"status": "0x1", "blockNumber": "0x3039"})
+	defer srv.Close()
+	report := VerifyAnchorOnchain(context.Background(), anchorEpochFixture(), srv.URL, time.Second)
+	if report.OK || !containsProblem(report.Problems, "anchor merkle root mismatch") {
+		t.Errorf("problems: %v", report.Problems)
+	}
+}
+
+func TestAnchorFailedTransaction(t *testing.T) {
+	srv := mockRPC(t, anchorRoot, map[string]any{"status": "0x0", "blockNumber": "0x3039"})
+	defer srv.Close()
+	report := VerifyAnchorOnchain(context.Background(), anchorEpochFixture(), srv.URL, time.Second)
+	if !containsProblem(report.Problems, "anchor transaction failed") {
+		t.Errorf("problems: %v", report.Problems)
+	}
+}
+
+func TestAnchorWrongBlock(t *testing.T) {
+	srv := mockRPC(t, anchorRoot, map[string]any{"status": "0x1", "blockNumber": "0x3040"})
+	defer srv.Close()
+	report := VerifyAnchorOnchain(context.Background(), anchorEpochFixture(), srv.URL, time.Second)
+	if !containsProblem(report.Problems, "anchor transaction block mismatch") {
+		t.Errorf("problems: %v", report.Problems)
+	}
+}
+
+func containsProblem(problems []string, want string) bool {
+	for _, p := range problems {
+		if p == want {
+			return true
+		}
+	}
+	return false
+}
--- a/attestotest/server.go
+++ b/attestotest/server.go
@@ -0,0 +1,428 @@
+// Package attestotest provides a local, in-memory Attesto v2 emulator for
+// tests ([P2.3]). NewServer starts an httptest.Server implementing the v2
+// subset the SDK uses, with REAL seq/hash-chain semantics via the same frozen
+// canonical functions and receipts signed by a per-instance throwaway Ed25519
+// key under kid "attesto-mock-ed25519". Every emitted object carries
+// mock: true, so mock evidence is structurally incapable of passing as real.
+package attestotest
+
+import (
+	"crypto/ed25519"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"regexp"
+	"sync"
+	"time"
+
+	attesto "go.attesto.eu/sdk"
+)
+
+// MockKid is the signer kid on every mock receipt.
+const MockKid = "attesto-mock-ed25519"
+
+type mockEvent struct {
+	Envelope       attesto.M
+	EventHash      string
+	StreamHeadHash string
+	StreamEventID  string
+	TenantView     attesto.M
+}
+
+// Server is the running emulator. Point a real client at URL; verify its
+// receipts offline with PublicKeyHex.
+type Server struct {
+	URL          string
+	APIKey       string
+	PublicKeyHex string
+
+	httpServer *httptest.Server
+	priv       ed25519.PrivateKey
+	mu         sync.Mutex
+	streams    map[string]attesto.M
+	events     map[string][]*mockEvent
+	receipts   map[string]attesto.M
+	counter    int
+}
+
+// Close shuts the emulator down.
+func (s *Server) Close() { s.httpServer.Close() }
+
+func (s *Server) id(prefix string) string {
+	s.counter++
+	return fmt.Sprintf("%s_mock%08d", prefix, s.counter)
+}
+
+func nowISO() string {
+	return time.Now().UTC().Format("2006-01-02T15:04:05.000Z")
+}
+
+func safeNumbers(value any) bool {
+	switch v := value.(type) {
+	case json.Number:
+		if _, err := v.Int64(); err != nil {
+			return false
+		}
+		n, _ := v.Int64()
+		return n <= 1<<53-1 && n >= -(1<<53-1)
+	case float64:
+		return v == float64(int64(v)) && v <= float64(int64(1)<<53-1) && v >= -float64(int64(1)<<53-1)
+	case map[string]any:
+		for _, item := range v {
+			if !safeNumbers(item) {
+				return false
+			}
+		}
+	case []any:
+		for _, item := range v {
+			if !safeNumbers(item) {
+				return false
+			}
+		}
+	}
+	return true
+}
+
+func mustHash(domain string, value any) string {
+	h, err := attesto.DomainHashHex(domain, value)
+	if err != nil {
+		panic(err)
+	}
+	return h
+}
+
+// NewServer starts the emulator.
+func NewServer() *Server {
+	pub, priv, err := ed25519.GenerateKey(rand.Reader)
+	if err != nil {
+		panic(err)
+	}
+	s := &Server{
+		APIKey:       "atto_test_abc12300000000000000000000000000",
+		PublicKeyHex: hex.EncodeToString(pub),
+		priv:         priv,
+		streams:      map[string]attesto.M{},
+		events:       map[string][]*mockEvent{},
+		receipts:     map[string]attesto.M{},
+	}
+	s.httpServer = httptest.NewServer(http.HandlerFunc(s.handle))
+	s.URL = s.httpServer.URL
+	return s
+}
+
+var (
+	reEvents       = regexp.MustCompile(`^/v2/streams/([^/]+)/events$`)
+	reBatch        = regexp.MustCompile(`^/v2/streams/([^/]+)/events/batch$`)
+	reHead         = regexp.MustCompile(`^/v2/streams/([^/]+)/head$`)
+	reReceipt      = regexp.MustCompile(`^/v2/receipts/([^/]+)$`)
+	reTenantEvents = regexp.MustCompile(`^/v2/tenant/streams/([^/]+)/events$`)
+)
+
+func writeJSON(w http.ResponseWriter, code int, body any) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(code)
+	_ = json.NewEncoder(w).Encode(body)
+}
+
+func (s *Server) handle(w http.ResponseWriter, r *http.Request) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	path := r.URL.Path
+	switch {
+	case r.Method == http.MethodPost && path == "/v2/streams":
+		var body attesto.M
+		_ = json.NewDecoder(r.Body).Decode(&body)
+		streamID := s.id("str")
+		stream := attesto.M{
+			"streamId": streamID, "systemId": "sys_mock",
+			"useCase": str(body["useCase"], "mock"), "policyId": str(body["policyId"], "mock-policy"),
+			"status": "active", "lastSeqNo": float64(0),
+			"lastEventHash": nil, "lastStreamHeadHash": nil,
+			"created": true, "mock": true,
+		}
+		s.streams[streamID] = stream
+		s.events[streamID] = nil
+		writeJSON(w, 201, stream)
+	case r.Method == http.MethodPost && reBatch.MatchString(path):
+		streamID := reBatch.FindStringSubmatch(path)[1]
+		var body struct {
+			Events []attesto.M `json:"events"`
+		}
+		_ = json.NewDecoder(r.Body).Decode(&body)
+		receipts, code, errBody := s.appendMany(streamID, body.Events)
+		if errBody != nil {
+			writeJSON(w, code, errBody)
+			return
+		}
+		writeJSON(w, 201, attesto.M{"accepted": len(receipts), "receipts": receipts})
+	case r.Method == http.MethodPost && reEvents.MatchString(path):
+		streamID := reEvents.FindStringSubmatch(path)[1]
+		var body attesto.M
+		_ = json.NewDecoder(r.Body).Decode(&body)
+		receipts, code, errBody := s.appendMany(streamID, []attesto.M{body})
+		if errBody != nil {
+			writeJSON(w, code, errBody)
+			return
+		}
+		writeJSON(w, 201, receipts[0])
+	case r.Method == http.MethodGet && reHead.MatchString(path):
+		stream, ok := s.streams[reHead.FindStringSubmatch(path)[1]]
+		if !ok {
+			writeJSON(w, 404, attesto.M{"detail": "stream not found"})
+			return
+		}
+		writeJSON(w, 200, attesto.M{
+			"streamId": stream["streamId"], "systemId": stream["systemId"],
+			"status": stream["status"], "lastSeqNo": stream["lastSeqNo"],
+			"lastEventHash": stream["lastEventHash"], "lastStreamHeadHash": stream["lastStreamHeadHash"],
+			"mock": true,
+		})
+	case r.Method == http.MethodGet && reReceipt.MatchString(path):
+		receipt, ok := s.receipts[reReceipt.FindStringSubmatch(path)[1]]
+		if !ok {
+			writeJSON(w, 404, attesto.M{"detail": "receipt not found"})
+			return
+		}
+		writeJSON(w, 200, receipt)
+	case r.Method == http.MethodGet && reTenantEvents.MatchString(path):
+		list := s.events[reTenantEvents.FindStringSubmatch(path)[1]]
+		out := make([]attesto.M, 0, len(list))
+		for _, e := range list {
+			out = append(out, e.TenantView)
+		}
+		writeJSON(w, 200, out)
+	case r.Method == http.MethodGet && path == "/health":
+		writeJSON(w, 200, attesto.M{"ok": true, "mock": true})
+	default:
+		writeJSON(w, 404, attesto.M{"detail": "not found"})
+	}
+}
+
+func str(v any, fallback string) string {
+	if s, ok := v.(string); ok && s != "" {
+		return s
+	}
+	return fallback
+}
+
+func (s *Server) appendMany(streamID string, bodies []attesto.M) ([]attesto.M, int, attesto.M) {
+	stream, ok := s.streams[streamID]
+	if !ok {
+		return nil, 404, attesto.M{"detail": "stream not found"}
+	}
+	for _, body := range bodies {
+		if !safeNumbers(orEmpty(body["payload"])) || !safeNumbers(orEmpty(body["metadata"])) {
+			return nil, 422, attesto.M{"detail": "unsafe numbers are not permitted in committed payloads"}
+		}
+	}
+	out := make([]attesto.M, 0, len(bodies))
+	for _, body := range bodies {
+		out = append(out, s.append(stream, body))
+	}
+	return out, 0, nil
+}
+
+func orEmpty(v any) any {
+	if v == nil {
+		return map[string]any{}
+	}
+	return v
+}
+
+func (s *Server) append(stream attesto.M, body attesto.M) attesto.M {
+	payload := orEmpty(body["payload"])
+	metadata := orEmpty(body["metadata"])
+	// Idempotent on (source_kind, source_ref), like real ingestion: a resend
+	// returns the existing event's receipt instead of appending.
+	sourceKind := str(body["sourceKind"], "sdk")
+	sourceRef := str(body["sourceRef"], "")
+	for _, existing := range s.events[stream["streamId"].(string)] {
+		if sourceRef == "" {
+			break // anonymous events never dedupe
+		}
+		source := existing.Envelope["source"].(attesto.M)
+		if source["kind"] == sourceKind && source["event_id"] == sourceRef {
+			return s.receipts[existing.StreamEventID]
+		}
+	}
+	seqNo := int64(stream["lastSeqNo"].(float64)) + 1
+	ingestedAt := nowISO()
+
+	payloadCanonical, _ := attesto.CanonicalJSON(payload)
+	metadataCanonical, _ := attesto.CanonicalJSON(metadata)
+	payloadSum := sha256.Sum256(payloadCanonical)
+	metadataSum := sha256.Sum256(metadataCanonical)
+
+	envelope := attesto.M{
+		"protocol":          attesto.ProofstreamProtocol,
+		"protocol_version":  attesto.ProtocolVersionAlpha,
+		"tenant_id":         "ten_mock",
+		"system_id":         stream["systemId"],
+		"stream_id":         stream["streamId"],
+		"use_case":          stream["useCase"],
+		"policy_id":         stream["policyId"],
+		"seq_no":            seqNo,
+		"prev_event_hash":   stream["lastEventHash"],
+		"source":            attesto.M{"kind": str(body["sourceKind"], "sdk"), "event_id": str(body["sourceRef"], "")},
+		"event_type":        str(body["eventType"], "inference"),
+		"occurred_at":       str(body["occurredAt"], ingestedAt),
+		"source_timezone":   "Europe/Amsterdam",
+		"ingested_at":       ingestedAt,
+		"payload_commitment": attesto.M{
+			"hash_alg":               "sha256",
+			"canonical_payload_hash": hex.EncodeToString(payloadSum[:]),
+		},
+		"metadata_commitment": attesto.M{
+			"hash_alg":                "sha256",
+			"canonical_metadata_hash": hex.EncodeToString(metadataSum[:]),
+		},
+	}
+	eventHash := mustHash(attesto.ProofstreamDomains["event"], envelope)
+	streamHead := attesto.M{
+		"protocol":              attesto.ProofstreamProtocol,
+		"protocol_version":      attesto.ProtocolVersionAlpha,
+		"tenant_id":             "ten_mock",
+		"stream_id":             stream["streamId"],
+		"seq_no":                seqNo,
+		"event_hash":            eventHash,
+		"prev_stream_head_hash": stream["lastStreamHeadHash"],
+		"accepted_at":           ingestedAt,
+	}
+	streamHeadHash := mustHash(attesto.ProofstreamDomains["stream"], streamHead)
+	streamEventID := s.id("sev")
+
+	receiptPayload := attesto.M{
+		"mock":             true,
+		"protocol":         attesto.ProofstreamProtocol,
+		"protocol_version": attesto.ProtocolVersionAlpha,
+		"tenant_id":        "ten_mock",
+		"system_id":        stream["systemId"],
+		"stream_id":        stream["streamId"],
+		"stream_event_id":  streamEventID,
+		"event_id":         str(body["sourceRef"], ""),
+		"seq_no":           seqNo,
+		"event_hash":       eventHash,
+		"prev_event_hash":  stream["lastEventHash"],
+		"stream_head_hash": streamHeadHash,
+		"issued_at":        ingestedAt,
+		"signer":           attesto.M{"alg": "ed25519", "kid": MockKid, "key_epoch": MockKid},
+	}
+	receiptHash := mustHash(attesto.ProofstreamDomains["receipt"], receiptPayload)
+	canonical, _ := attesto.CanonicalJSON(receiptPayload)
+	message := append(append([]byte(attesto.ProofstreamDomains["receipt"]), 0), canonical...)
+	signature := ed25519.Sign(s.priv, message)
+
+	wire := attesto.M{
+		"streamId": stream["streamId"], "streamEventId": streamEventID,
+		"seqNo": seqNo, "eventHash": eventHash,
+		"prevEventHash": stream["lastEventHash"], "streamHeadHash": streamHeadHash,
+		"mock": true,
+		"receipt": attesto.M{
+			"payload":     receiptPayload,
+			"receiptHash": receiptHash,
+			"signature": attesto.M{
+				"alg": "ed25519", "kid": MockKid, "keyEpoch": MockKid,
+				"signatureHex": hex.EncodeToString(signature),
+			},
+		},
+	}
+	s.events[stream["streamId"].(string)] = append(s.events[stream["streamId"].(string)], &mockEvent{
+		Envelope: envelope, EventHash: eventHash, StreamHeadHash: streamHeadHash,
+		StreamEventID: streamEventID,
+		TenantView: attesto.M{
+			"streamEventId": streamEventID, "seq_no": seqNo,
+			"event_type": envelope["event_type"],
+			"source_ref": envelope["source"].(attesto.M)["event_id"],
+			"event_hash": eventHash, "prev_event_hash": stream["lastEventHash"],
+			"stream_head_hash": streamHeadHash,
+			"payload_commitment": envelope["payload_commitment"], "mock": true,
+		},
+	})
+	s.receipts[streamEventID] = wire
+	stream["lastSeqNo"] = float64(seqNo)
+	stream["lastEventHash"] = eventHash
+	stream["lastStreamHeadHash"] = streamHeadHash
+	return wire
+}
+
+// WindowLeaf is one leaf of a built window, with its inclusion proof.
+type WindowLeaf struct {
+	StreamEventID string
+	SeqNo         int64
+	LeafIndex     int
+	LeafHash      string
+	Proof         []attesto.InclusionStep
+}
+
+// Window is a built window over all events of a stream so far.
+type Window struct {
+	WindowID string
+	StreamID string
+	RootHash string
+	Leaves   []WindowLeaf
+}
+
+// BuildWindow folds all events so far into a window with per-leaf inclusion
+// proofs (the P1.3 verify functions accept them unchanged).
+func (s *Server) BuildWindow(streamID string) (*Window, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	list := s.events[streamID]
+	if len(list) == 0 {
+		return nil, fmt.Errorf("no events to fold")
+	}
+	leafHashes := make([]string, len(list))
+	for i, e := range list {
+		leafHashes[i] = mustHash(attesto.ProofstreamDomains["window"], attesto.M{
+			"kind": "leaf", "protocol": attesto.ProofstreamProtocol,
+			"protocol_version": attesto.ProtocolVersionAlpha,
+			"tenant_id":        "ten_mock", "system_id": "sys_mock",
+			"stream_id": streamID, "stream_event_id": e.StreamEventID,
+			"seq_no": e.Envelope["seq_no"], "leaf_index": i,
+			"event_hash": e.EventHash, "stream_head_hash": e.StreamHeadHash,
+		})
+	}
+	proofs := make([][]attesto.InclusionStep, len(leafHashes))
+	type node struct {
+		hash string
+		idx  []int
+	}
+	level := make([]node, len(leafHashes))
+	for i, h := range leafHashes {
+		level[i] = node{h, []int{i}}
+	}
+	for len(level) > 1 {
+		var next []node
+		for offset := 0; offset < len(level); offset += 2 {
+			left := level[offset]
+			if offset+1 >= len(level) {
+				next = append(next, left) // promote
+				continue
+			}
+			right := level[offset+1]
+			for _, i := range left.idx {
+				proofs[i] = append(proofs[i], attesto.InclusionStep{Side: "right", Hash: right.hash})
+			}
+			for _, i := range right.idx {
+				proofs[i] = append(proofs[i], attesto.InclusionStep{Side: "left", Hash: left.hash})
+			}
+			parent := mustHash(attesto.ProofstreamDomains["window"], attesto.M{
+				"kind": "node", "left_hash": left.hash, "right_hash": right.hash,
+			})
+			next = append(next, node{parent, append(append([]int{}, left.idx...), right.idx...)})
+		}
+		level = next
+	}
+	window := &Window{WindowID: s.id("win"), StreamID: streamID, RootHash: level[0].hash}
+	for i, e := range list {
+		window.Leaves = append(window.Leaves, WindowLeaf{
+			StreamEventID: e.StreamEventID, SeqNo: e.Envelope["seq_no"].(int64),
+			LeafIndex: i, LeafHash: leafHashes[i], Proof: proofs[i],
+		})
+	}
+	return window, nil
+}
--- a/attestotest/server_test.go
+++ b/attestotest/server_test.go
@@ -0,0 +1,132 @@
+package attestotest
+
+import (
+	"context"
+	"crypto/ed25519"
+	"crypto/rand"
+	"encoding/hex"
+	"encoding/json"
+	"testing"
+
+	attesto "go.attesto.eu/sdk"
+)
+
+func newClient(t *testing.T, s *Server) *attesto.Client {
+	t.Helper()
+	client, err := attesto.NewClient(s.APIKey, attesto.WithBaseURL(s.URL))
+	if err != nil {
+		t.Fatal(err)
+	}
+	return client
+}
+
+func toSignedReceipt(t *testing.T, wire attesto.M) attesto.SignedReceipt {
+	t.Helper()
+	raw, _ := json.Marshal(wire["receipt"])
+	var receipt attesto.SignedReceipt
+	if err := json.Unmarshal(raw, &receipt); err != nil {
+		t.Fatal(err)
+	}
+	return receipt
+}
+
+func TestFullPipelineAgainstTheEmulator(t *testing.T) {
+	server := NewServer()
+	defer server.Close()
+	client := newClient(t, server)
+	ctx := context.Background()
+
+	stream, err := client.CreateStream(ctx, attesto.StreamCreateInput{UseCase: "ci", PolicyID: "mock-policy"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	receipt, err := client.LogEvent(ctx, stream.StreamID, attesto.EventInput{
+		SourceRef: "e1", Payload: attesto.M{"decision": "approve", "score_bp": 8700},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := client.LogEvents(ctx, stream.StreamID, []attesto.EventInput{
+		{SourceRef: "e2", Payload: attesto.M{"n": 2}},
+		{SourceRef: "e3", Payload: attesto.M{"n": 3}},
+	}); err != nil {
+		t.Fatal(err)
+	}
+
+	stored, err := client.GetReceipt(ctx, receipt.StreamEventID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	report := attesto.VerifyReceiptOffline(stored.Receipt, server.PublicKeyHex)
+	if !report.OK {
+		t.Fatalf("offline verification failed: %v", report.Problems)
+	}
+
+	events, err := client.ListTenantStreamEvents(ctx, stream.StreamID, 100, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	plain := make([]map[string]any, len(events))
+	for i, e := range events {
+		plain[i] = e
+	}
+	comp := attesto.VerifyCompleteness(plain, 1, 3)
+	if !comp.OK {
+		t.Fatalf("completeness failed: %v", comp.Problems)
+	}
+}
+
+func TestInclusionProofsFromBuiltWindowVerify(t *testing.T) {
+	server := NewServer()
+	defer server.Close()
+	client := newClient(t, server)
+	ctx := context.Background()
+	stream, _ := client.CreateStream(ctx, attesto.StreamCreateInput{UseCase: "ci", PolicyID: "mock-policy"})
+	for i := 0; i < 5; i++ { // odd leaf count exercises the promote rule
+		if _, err := client.LogEvent(ctx, stream.StreamID, attesto.EventInput{
+			SourceRef: "e", Payload: attesto.M{"i": i},
+		}); err != nil {
+			t.Fatal(err)
+		}
+	}
+	window, err := server.BuildWindow(stream.StreamID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, leaf := range window.Leaves {
+		ok, err := attesto.VerifyInclusionProof(leaf.LeafHash, leaf.Proof, window.RootHash)
+		if err != nil || !ok {
+			t.Fatalf("leaf %d failed inclusion: ok=%v err=%v", leaf.LeafIndex, ok, err)
+		}
+	}
+}
+
+func TestMockReceiptsCannotPassAsReal(t *testing.T) {
+	server := NewServer()
+	defer server.Close()
+	client := newClient(t, server)
+	ctx := context.Background()
+	stream, _ := client.CreateStream(ctx, attesto.StreamCreateInput{UseCase: "ci", PolicyID: "mock-policy"})
+	receipt, err := client.LogEvent(ctx, stream.StreamID, attesto.EventInput{SourceRef: "e1"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	stored, err := client.GetReceipt(ctx, receipt.StreamEventID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Structurally marked.
+	if stored.Receipt.Payload["mock"] != true {
+		t.Error("mock receipt payload must declare mock: true")
+	}
+	signer, _ := stored.Receipt.Payload["signer"].(map[string]any)
+	if signer["kid"] != MockKid {
+		t.Errorf("kid = %v, want %s", signer["kid"], MockKid)
+	}
+	// Rejected against a different ("real") witness key.
+	realPub, _, _ := ed25519.GenerateKey(rand.Reader)
+	report := attesto.VerifyReceiptOffline(stored.Receipt, hex.EncodeToString(realPub))
+	if report.OK {
+		t.Fatal("mock receipt verified against a real key — must never happen")
+	}
+}
--- a/client.go
+++ b/client.go
@@ -23,6 +23,7 @@ type Client struct {
 	maxRetries  int
 	userAgent   string
 	validateKey bool
+	headStore   HeadStore
 }

 type Option func(*Client) error
@@ -51,6 +52,7 @@ func newClient(bearer string, validateKey bool, opts ...Option) (*Client, error)
 		maxRetries:  3,
 		userAgent:   "attesto-go/" + SDKVersion,
 		validateKey: validateKey,
+		headStore:   NewMemoryHeadStore(),
 	}
 	for _, opt := range opts {
 		if err := opt(client); err != nil {
@@ -112,6 +114,16 @@ func WithUserAgent(userAgent string) Option {
 	}
 }

+// WithHeadStore sets the store used for client-side fork detection. The default
+// is an in-memory store; pass NewFileHeadStore(path) to persist across process
+// invocations, or nil to disable fork detection.
+func WithHeadStore(store HeadStore) Option {
+	return func(c *Client) error {
+		c.headStore = store
+		return nil
+	}
+}
+
 func (c *Client) CreateStream(ctx context.Context, input StreamCreateInput, options ...RequestOptions) (*Stream, error) {
 	var out Stream
 	if input.Metadata == nil {
@@ -161,24 +173,65 @@ func (c *Client) LogEvent(ctx context.Context, streamID string, input EventInput
 	if err := normalizeEventInput(&input); err != nil {
 		return nil, err
 	}
+	// Reject commitment-unsafe numbers locally so the developer sees the rule at
+	// dev time rather than as a production 422; SkipPreflight defers to the server.
+	if !skipPreflight(options) {
+		if err := AssertCommitmentSafeNumbers(input.Payload, "$.payload"); err != nil {
+			return nil, err
+		}
+		if err := AssertCommitmentSafeNumbers(input.Metadata, "$.metadata"); err != nil {
+			return nil, err
+		}
+	}
 	var out EventReceipt
-	err := c.requestJSON(ctx, http.MethodPost, "/v2/streams/"+url.PathEscape(streamID)+"/events", nil, input, idempotency(options), &out)
-	return &out, err
+	if err := c.requestJSON(ctx, http.MethodPost, "/v2/streams/"+url.PathEscape(streamID)+"/events", nil, input, idempotency(options), &out); err != nil {
+		return nil, err
+	}
+	if err := c.trackHead(out); err != nil {
+		return nil, err
+	}
+	return &out, nil
+}
+
+// trackHead checks the receipt extends the stored head (returning a
+// *ForkDetectedError on a rewind/divergence) and advances the store. No-op when
+// fork detection is disabled (headStore is nil).
+func (c *Client) trackHead(receipt EventReceipt) error {
+	if c.headStore == nil {
+		return nil
+	}
+	return checkAndAdvanceHead(c.headStore, receipt)
 }

 func (c *Client) LogEvents(ctx context.Context, streamID string, events []EventInput, options ...RequestOptions) (*EventBatchResponse, error) {
 	if len(events) > 1000 {
 		return nil, errors.New("max 1000 events per batch")
 	}
+	preflight := !skipPreflight(options)
 	for i := range events {
 		if err := normalizeEventInput(&events[i]); err != nil {
 			return nil, fmt.Errorf("event %d: %w", i, err)
 		}
+		if preflight {
+			if err := AssertCommitmentSafeNumbers(events[i].Payload, fmt.Sprintf("$.events[%d].payload", i)); err != nil {
+				return nil, err
+			}
+			if err := AssertCommitmentSafeNumbers(events[i].Metadata, fmt.Sprintf("$.events[%d].metadata", i)); err != nil {
+				return nil, err
+			}
+		}
 	}
 	body := M{"events": events}
 	var out EventBatchResponse
-	err := c.requestJSON(ctx, http.MethodPost, "/v2/streams/"+url.PathEscape(streamID)+"/events/batch", nil, body, idempotency(options), &out)
-	return &out, err
+	if err := c.requestJSON(ctx, http.MethodPost, "/v2/streams/"+url.PathEscape(streamID)+"/events/batch", nil, body, idempotency(options), &out); err != nil {
+		return nil, err
+	}
+	for _, receipt := range out.Receipts {
+		if err := c.trackHead(receipt); err != nil {
+			return nil, err
+		}
+	}
+	return &out, nil
 }

 func (c *Client) GetReceipt(ctx context.Context, streamEventID string) (*EventReceipt, error) {
@@ -481,6 +534,9 @@ func (c *Client) requestRaw(ctx context.Context, method, path string, values url
 		req.Header.Set("Authorization", "Bearer "+c.bearer)
 		req.Header.Set("User-Agent", c.userAgent)
 		req.Header.Set("X-Attesto-SDK", c.userAgent)
+		// [P1.9] protocol handshake: the backend answers 426 when it speaks a
+		// different protocol generation (ErrProtocolMismatch via APIError).
+		req.Header.Set("X-Attesto-Protocol", ProtocolHandshake)
 		if body != nil {
 			req.Header.Set("Content-Type", "application/json")
 		}
@@ -524,6 +580,14 @@ func (e *APIError) Error() string {
 	return fmt.Sprintf("attesto api error: status=%d message=%s", e.StatusCode, e.Message)
 }

+// IsProtocolMismatch reports whether err is a 426 protocol-handshake rejection:
+// the backend speaks a different protocol generation than this SDK announced in
+// X-Attesto-Protocol. Upgrade the SDK to a release that speaks it.
+func IsProtocolMismatch(err error) bool {
+	var apiErr *APIError
+	return errors.As(err, &apiErr) && apiErr.StatusCode == http.StatusUpgradeRequired
+}
+
 func decodeResponse(resp *http.Response, out any) error {
 	defer resp.Body.Close()
 	if resp.StatusCode == http.StatusNoContent {
@@ -558,6 +622,10 @@ func retryable(status int) bool {
 	}
 }

+func skipPreflight(options []RequestOptions) bool {
+	return len(options) > 0 && options[0].SkipPreflight
+}
+
 func idempotency(options []RequestOptions) string {
 	if len(options) > 0 && options[0].IdempotencyKey != "" {
 		return options[0].IdempotencyKey
--- a/cmd/attesto-verify-wasm/main.go
+++ b/cmd/attesto-verify-wasm/main.go
@@ -0,0 +1,97 @@
+//go:build js && wasm
+
+// attesto-verify-wasm [P3.1] — the verifier-only WebAssembly build.
+//
+// Exposes the offline verification functions (and nothing else: no client,
+// no CLI, no network capability is ever invoked) on a global
+// `attestoVerify` object for the docs-site /verify drop-zone. Every
+// function takes JSON strings and returns a JSON string, so the JS side
+// stays a thin shell.
+package main
+
+import (
+	"encoding/json"
+	"syscall/js"
+
+	attesto "go.attesto.eu/sdk"
+)
+
+func respond(value any) string {
+	raw, err := json.Marshal(value)
+	if err != nil {
+		return `{"ok":false,"problems":["internal: response marshal failed"]}`
+	}
+	return string(raw)
+}
+
+func fail(problem string) string {
+	return respond(map[string]any{"ok": false, "problems": []string{problem}})
+}
+
+// verifyReceipt(receiptJSON, publicKeyHex) -> VerifyReport JSON
+func verifyReceipt(_ js.Value, args []js.Value) any {
+	if len(args) != 2 {
+		return fail("usage: verifyReceipt(receiptJSON, publicKeyHex)")
+	}
+	var receipt attesto.SignedReceipt
+	if err := json.Unmarshal([]byte(args[0].String()), &receipt); err != nil {
+		return fail("receipt is not valid JSON: " + err.Error())
+	}
+	return respond(attesto.VerifyReceiptOffline(receipt, args[1].String()))
+}
+
+// verifyInclusion(leafHash, proofJSON, rootHash) -> {ok, problems}
+func verifyInclusion(_ js.Value, args []js.Value) any {
+	if len(args) != 3 {
+		return fail("usage: verifyInclusion(leafHash, proofJSON, rootHash)")
+	}
+	var proof []attesto.InclusionStep
+	if err := json.Unmarshal([]byte(args[1].String()), &proof); err != nil {
+		return fail("proof is not valid JSON: " + err.Error())
+	}
+	ok, err := attesto.VerifyInclusionProof(args[0].String(), proof, args[2].String())
+	if err != nil {
+		return fail(err.Error())
+	}
+	return respond(map[string]any{"ok": ok, "problems": []string{}})
+}
+
+// verifyCheckpointRoot(windowHashesJSON, expectedRoot) -> {ok, problems}
+func verifyCheckpointRoot(_ js.Value, args []js.Value) any {
+	if len(args) != 2 {
+		return fail("usage: verifyCheckpointRoot(windowHashesJSON, expectedRoot)")
+	}
+	var hashes []string
+	if err := json.Unmarshal([]byte(args[0].String()), &hashes); err != nil {
+		return fail("windowHashes is not valid JSON: " + err.Error())
+	}
+	ok, err := attesto.VerifyCheckpointRoot(hashes, args[1].String())
+	if err != nil {
+		return fail(err.Error())
+	}
+	return respond(map[string]any{"ok": ok, "problems": []string{}})
+}
+
+// verifyCompleteness(eventsJSON, fromSeqNo, toSeqNo) -> VerifyReport JSON
+func verifyCompleteness(_ js.Value, args []js.Value) any {
+	if len(args) != 3 {
+		return fail("usage: verifyCompleteness(eventsJSON, fromSeqNo, toSeqNo)")
+	}
+	var events []map[string]any
+	if err := json.Unmarshal([]byte(args[0].String()), &events); err != nil {
+		return fail("events is not valid JSON: " + err.Error())
+	}
+	return respond(attesto.VerifyCompleteness(events, args[1].Int(), args[2].Int()))
+}
+
+func main() {
+	exports := js.Global().Get("Object").New()
+	exports.Set("verifyReceipt", js.FuncOf(verifyReceipt))
+	exports.Set("verifyInclusion", js.FuncOf(verifyInclusion))
+	exports.Set("verifyCheckpointRoot", js.FuncOf(verifyCheckpointRoot))
+	exports.Set("verifyCompleteness", js.FuncOf(verifyCompleteness))
+	exports.Set("sdkVersion", attesto.SDKVersion)
+	js.Global().Set("attestoVerify", exports)
+	// Keep the runtime alive for calls from JS.
+	select {}
+}
--- a/cmd/attesto/connector_init.go
+++ b/cmd/attesto/connector_init.go
@@ -0,0 +1,248 @@
+package main
+
+// [D.5] `attesto connector init <slug>` — scaffold a marketplace-ready
+// connector: a v2 manifest that passes connectorkit validation locally, a
+// signed-webhook handler stub built on the P1.4 verification helper, and a
+// README pointing at the submission flow. The local validation run is the
+// same code the marketplace runs, so a green scaffold is a green
+// pre-submission check.
+
+import (
+	"encoding/json"
+	"errors"
+	"flag"
+	"fmt"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+
+	"go.attesto.eu/sdk/connectorkit"
+)
+
+var connectorSlugPattern = regexp.MustCompile(`^[a-z0-9][a-z0-9-]{2,95}$`)
+
+func connectorManifestTemplate(slug, name, category string) connectorkit.Manifest {
+	return connectorkit.Manifest{
+		SchemaVersion: "attesto.connector.v2",
+		Slug:          slug,
+		Name:          name,
+		Version:       "0.1.0",
+		AssetType:     "connector",
+		Category:      category,
+		Summary:       fmt.Sprintf("Verify %s evidence into Attesto Proofstream.", name),
+		Description: fmt.Sprintf(
+			"Produces verifiable evidence for %s events through Attesto Proofstream.", name),
+		Publisher:     map[string]string{"name": "CHANGE ME", "slug": "change-me"},
+		Repository:    map[string]string{"url": "https://example.com/CHANGE-ME/" + slug},
+		Documentation: map[string]string{"url": "https://docs.attesto.eu/manuals/connectors.html"},
+		Capabilities: []string{
+			"proofstream", "signed-webhook", "offline-verification",
+		},
+		Evidence: map[string]bool{
+			"offlineVerification": true,
+			"receipts":            true,
+			"witnessCompatible":   true,
+		},
+		Security: map[string]bool{
+			"dependencyScan":    true,
+			"secretScan":        true,
+			"secretsServerSide": true,
+		},
+		SupportedLanguages: []string{"en"},
+		Provider: map[string]any{
+			"id":         slug,
+			"name":       name,
+			"websiteUrl": "https://example.com",
+		},
+		Auth: map[string]any{
+			"mode":   "signed-webhook",
+			"scopes": []string{"webhook:read"},
+		},
+		Sync: map[string]any{
+			"modes":           []string{"webhook"},
+			"supportsReplay":  true,
+			"rateLimitPolicy": "Provider webhook retries and Attesto idempotency keys",
+		},
+		EventTypes: []string{slug + ".event"},
+		SourceTime: map[string]any{
+			"required":       true,
+			"timezonePolicy": "source-timestamp-with-offset-required",
+		},
+		ConfigSchema: map[string]any{
+			"type":     "object",
+			"required": []string{"resourceRef"},
+			"properties": map[string]any{
+				"resourceRef": map[string]any{"type": "string"},
+			},
+		},
+		SecretSchema: map[string]any{
+			"type":     "object",
+			"required": []string{"webhookSecret"},
+			"properties": map[string]any{
+				"webhookSecret": map[string]any{"type": "string", "secret": true},
+			},
+		},
+		Diagnostics: map[string]any{
+			"providerAuthStatus":  true,
+			"replayConflictCheck": true,
+			"revocationCheck":     true,
+			"syncLag":             true,
+			"testConnection":      true,
+		},
+		Runtime: map[string]any{
+			"officialConnectorKit": true,
+			"sdkSurfaces":          []string{"python", "typescript", "go", "cli"},
+			"requiredMethods": []string{
+				"metadata", "validateConfig", "testConnection", "sync",
+				"handleWebhook", "emitProofstreamEvent", "diagnostics", "revoke",
+			},
+			// A scaffold cannot honestly claim a green assurance canary; this
+			// stays "pending" (the one expected validation finding) until the
+			// connector has real canary evidence.
+			"canary": map[string]any{
+				"status": "pending",
+				"ref":    "CHANGE ME: assurance canary evidence ref",
+			},
+		},
+		InstallRequirements: map[string]any{
+			"tenantLoginRequired": true,
+			"entitlementRequired": true,
+		},
+		Changelog: []map[string]any{
+			{"version": "0.1.0", "changes": []string{"Initial scaffold."}},
+		},
+	}
+}
+
+const webhookHandlerStub = `"""Signed-webhook handler stub for the %s connector.
+
+Verification uses the Attesto SDK's P1.4 helper — the same scheme the
+platform signs with: HMAC-SHA256 over "{timestamp}.{body}" with a 300s
+skew window and constant-time comparison.
+"""
+import os
+
+from attesto.webhooks import verify_webhook
+
+
+def handle(headers: dict[str, str], body: bytes) -> dict:
+    if not verify_webhook(
+        body=body,
+        headers=headers,
+        secret=os.environ["WEBHOOK_SECRET"],
+    ):
+        raise PermissionError("invalid webhook signature or stale timestamp")
+
+    # The payload is now authentic: turn it into a proofstream event here.
+    return {"ok": True}
+`
+
+const connectorReadmeStub = `# %s
+
+Scaffolded by ` + "`attesto connector init`" + `.
+
+1. Edit ` + "`attesto.connector.json`" + ` (publisher, repository, provider,
+   event types — search for CHANGE ME).
+2. Implement the runtime methods (see ` + "`webhook_handler.py`" + ` for the
+   signed-webhook entry point; verification is already wired).
+3. Re-run the pre-submission check at any time:
+
+       attesto connector init --validate-only %s
+
+4. Submit through the marketplace flow (docs.attesto.eu/manuals/connectors.html).
+`
+
+func (a *app) connectorInit(args []string) error {
+	fs := flag.NewFlagSet("connector init", flag.ContinueOnError)
+	fs.SetOutput(a.err)
+	name := fs.String("name", "", "human-readable connector name (default: derived from slug)")
+	category := fs.String("category", "devops", "marketplace category")
+	dir := fs.String("dir", "", "output directory (default: ./<slug>)")
+	validateOnly := fs.String("validate-only", "", "validate an existing <dir>/attesto.connector.json and exit")
+	// Accept the slug positionally before flags: `connector init my-slug --category crm`.
+	slug := ""
+	if len(args) > 0 && !strings.HasPrefix(args[0], "-") {
+		slug = args[0]
+		args = args[1:]
+	}
+	if err := fs.Parse(args); err != nil {
+		return err
+	}
+
+	if *validateOnly != "" {
+		raw, err := os.ReadFile(filepath.Join(*validateOnly, "attesto.connector.json"))
+		if err != nil {
+			return err
+		}
+		var manifest connectorkit.Manifest
+		if err := json.Unmarshal(raw, &manifest); err != nil {
+			return err
+		}
+		result := connectorkit.ValidateManifest(manifest)
+		if err := a.write(result); err != nil {
+			return err
+		}
+		if !result.OK {
+			return errors.New("manifest validation failed")
+		}
+		return nil
+	}
+
+	if slug == "" && fs.NArg() == 1 {
+		slug = fs.Arg(0)
+	}
+	if slug == "" {
+		return errors.New("usage: attesto connector init <slug> [--name ...] [--category ...]")
+	}
+	if !connectorSlugPattern.MatchString(slug) {
+		return fmt.Errorf("slug %q must match %s", slug, connectorSlugPattern)
+	}
+	connectorName := *name
+	if connectorName == "" {
+		connectorName = strings.Title(strings.ReplaceAll(slug, "-", " ")) //nolint:staticcheck
+	}
+
+	manifest := connectorManifestTemplate(slug, connectorName, *category)
+	result := connectorkit.ValidateManifest(manifest)
+	// The only acceptable finding on a fresh scaffold is the pending canary —
+	// everything else must already satisfy the marketplace validator.
+	for _, finding := range result.Findings {
+		if finding.Code != "runtime.canary" {
+			return fmt.Errorf("internal error: scaffold template failed validation: %+v", result.Findings)
+		}
+	}
+
+	outDir := *dir
+	if outDir == "" {
+		outDir = slug
+	}
+	if _, err := os.Stat(filepath.Join(outDir, "attesto.connector.json")); err == nil {
+		return fmt.Errorf("%s/attesto.connector.json already exists", outDir)
+	}
+	if err := os.MkdirAll(outDir, 0o755); err != nil {
+		return err
+	}
+	raw, err := json.MarshalIndent(manifest, "", "  ")
+	if err != nil {
+		return err
+	}
+	if err := os.WriteFile(filepath.Join(outDir, "attesto.connector.json"), append(raw, '\n'), 0o644); err != nil {
+		return err
+	}
+	handler := fmt.Sprintf(webhookHandlerStub, connectorName)
+	if err := os.WriteFile(filepath.Join(outDir, "webhook_handler.py"), []byte(handler), 0o644); err != nil {
+		return err
+	}
+	readme := fmt.Sprintf(connectorReadmeStub, connectorName, outDir)
+	if err := os.WriteFile(filepath.Join(outDir, "README.md"), []byte(readme), 0o644); err != nil {
+		return err
+	}
+	return a.write(map[string]any{
+		"created":    outDir,
+		"files":      []string{"attesto.connector.json", "webhook_handler.py", "README.md"},
+		"validation": result,
+		"nextSteps": "edit CHANGE ME fields, implement runtime methods, earn a green " +
+			"assurance canary, re-run with --validate-only until OK",
+	})
+}
--- a/cmd/attesto/connector_init_test.go
+++ b/cmd/attesto/connector_init_test.go
@@ -0,0 +1,49 @@
+package main
+
+// [D.5] connector init scaffolds a manifest whose ONLY validation finding is
+// the pending canary, and the generated webhook stub calls the real P1.4
+// helper with its actual signature.
+
+import (
+	"bytes"
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"go.attesto.eu/sdk/connectorkit"
+)
+
+func TestConnectorInitScaffoldsValidManifest(t *testing.T) {
+	dir := filepath.Join(t.TempDir(), "my-crm")
+	a := &app{out: &bytes.Buffer{}, err: &bytes.Buffer{}}
+	if err := a.connectorInit([]string{"my-crm-evidence", "--category", "crm", "--dir", dir}); err != nil {
+		t.Fatal(err)
+	}
+	raw, err := os.ReadFile(filepath.Join(dir, "attesto.connector.json"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	var manifest connectorkit.Manifest
+	if err := json.Unmarshal(raw, &manifest); err != nil {
+		t.Fatal(err)
+	}
+	result := connectorkit.ValidateManifest(manifest)
+	for _, finding := range result.Findings {
+		if finding.Code != "runtime.canary" {
+			t.Fatalf("unexpected finding: %+v", finding)
+		}
+	}
+	stub, err := os.ReadFile(filepath.Join(dir, "webhook_handler.py"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(string(stub), "from attesto.webhooks import verify_webhook") {
+		t.Fatal("stub does not use the P1.4 helper")
+	}
+	// re-running must refuse to overwrite
+	if err := a.connectorInit([]string{"my-crm-evidence", "--dir", dir}); err == nil {
+		t.Fatal("expected overwrite refusal")
+	}
+}
--- a/cmd/attesto/main.go
+++ b/cmd/attesto/main.go
@@ -3,6 +3,7 @@ package main
 import (
 	"archive/zip"
 	"bufio"
+	"bytes"
 	"context"
 	"crypto/sha256"
 	"encoding/json"
@@ -15,12 +16,13 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
+	"time"

-	attesto "git.rotz.ai/rotzmediagroup/attesto-v1/sdk/go"
-	"git.rotz.ai/rotzmediagroup/attesto-v1/sdk/go/connectorkit"
+	attesto "go.attesto.eu/sdk"
+	"go.attesto.eu/sdk/connectorkit"
 )

-const cliVersion = "0.2.0"
+const cliVersion = "0.4.0"

 var supportedVerifyKindNames = []string{
 	"receipt",
@@ -124,7 +126,7 @@ func (a *app) dispatch(ctx context.Context, args []string) error {
 	case "witnesses":
 		return a.witnesses(ctx, args[1:])
 	case "anchors":
-		return a.verifyableObject(ctx, "anchors", args[1:], attesto.VerifyAnchor, "/v2/anchors/")
+		return a.anchors(ctx, args[1:])
 	case "bundles":
 		return a.bundles(ctx, args[1:])
 	case "verify":
@@ -135,12 +137,22 @@ func (a *app) dispatch(ctx context.Context, args []string) error {
 		return a.quorum(ctx, args[1:])
 	case "ivc":
 		return a.ivc(ctx, args[1:])
+	case "connector":
+		// [D.5] scaffold + local pre-submission validation
+		if len(args) > 1 && args[1] == "init" {
+			return a.connectorInit(args[2:])
+		}
+		return errors.New("connector subcommand required (init)")
 	case "connectors":
 		return a.connectors(ctx, args[1:])
 	case "local-vault":
 		return a.localVault(ctx, args[1:])
 	case "marketplace":
 		return a.marketplace(ctx, args[1:])
+	case "doctor":
+		return a.doctor(ctx, args[1:])
+	case "report":
+		return a.report(ctx, args[1:])
 	case "readiness":
 		return a.readiness(args[1:])
 	default:
@@ -164,6 +176,30 @@ func (a *app) verify(ctx context.Context, args []string) error {
 			return errors.New("--file is required")
 		}
 		return a.write(verifyTruthPackageZip(*file))
+	case "file":
+		// [P3.4] Verify a portable *.attesto.json receipt export offline.
+		fs := flag.NewFlagSet("verify file", flag.ContinueOnError)
+		fs.SetOutput(a.err)
+		file := fs.String("file", "", "portable receipt export (*.attesto.json)")
+		publicKeyHex := fs.String("public-key-hex", "", "pinned witness key (omitting it verifies against the file's embedded hint)")
+		if err := fs.Parse(args[1:]); err != nil {
+			return err
+		}
+		if *file == "" {
+			return errors.New("--file is required")
+		}
+		raw, err := os.ReadFile(*file)
+		if err != nil {
+			return err
+		}
+		report := attesto.VerifyReceiptExport(raw, *publicKeyHex)
+		if err := a.write(report); err != nil {
+			return err
+		}
+		if !report.OK {
+			return errors.New("verification failed")
+		}
+		return nil
 	default:
 		_ = ctx
 		return fmt.Errorf("unknown verify subcommand: %s", args[0])
@@ -410,6 +446,136 @@ func (a *app) verifyableObject(ctx context.Context, group string, args []string,
 	}
 }

+// doctor diagnoses an SDK/CLI install: vendored parity self-test, head-store
+// writability, number-policy dry-run on a sample payload, and (when an API key
+// is configured) reachability, protocol-header acceptance, and clock skew vs
+// the server Date header. Deterministic JSON report: {"ok": bool, "checks": {...}}.
+func (a *app) doctor(ctx context.Context, args []string) error {
+	fs := flag.NewFlagSet("doctor", flag.ContinueOnError)
+	fs.SetOutput(a.err)
+	samplePayload := fs.String("sample-payload", "", "JSON file with a sample payload for the number-policy dry-run")
+	if err := fs.Parse(args); err != nil {
+		return err
+	}
+	checks := map[string]map[string]any{}
+	pass := func(name string, extra map[string]any) {
+		if extra == nil {
+			extra = map[string]any{}
+		}
+		extra["ok"] = true
+		checks[name] = extra
+	}
+	fail := func(name string, err error) {
+		checks[name] = map[string]any{"ok": false, "error": err.Error()}
+	}
+
+	if err := attesto.EnsureSelfTest(); err != nil {
+		fail("self_test", err)
+	} else {
+		pass("self_test", nil)
+	}
+
+	headStore := attesto.NewFileHeadStore("")
+	headStore.Set("__doctor__", 1, strings.Repeat("0", 64))
+	if seq, hash, ok := headStore.Get("__doctor__"); ok && seq == 1 && hash == strings.Repeat("0", 64) {
+		pass("head_store", nil)
+	} else {
+		fail("head_store", errors.New("head store readback failed"))
+	}
+
+	if *samplePayload != "" {
+		raw, err := os.ReadFile(*samplePayload)
+		if err != nil {
+			return err
+		}
+		decoder := json.NewDecoder(bytes.NewReader(raw))
+		decoder.UseNumber()
+		var payload any
+		if err := decoder.Decode(&payload); err != nil {
+			return err
+		}
+		if err := attesto.AssertCommitmentSafeNumbers(payload, "$"); err != nil {
+			fail("number_policy", err)
+		} else {
+			pass("number_policy", nil)
+		}
+	}
+
+	if client, err := a.systemClient(); err == nil {
+		start := time.Now()
+		head, headErr := client.GetStreamHead(ctx, "__doctor-probe__")
+		_ = head
+		status := 0
+		var apiErr *attesto.APIError
+		if errors.As(headErr, &apiErr) {
+			status = apiErr.StatusCode
+		}
+		// Any HTTP-level answer (including 404 for the probe id) proves
+		// reachability + auth handling; transport errors do not.
+		reachable := headErr == nil || status > 0
+		checks["api_reachable"] = map[string]any{
+			"ok": reachable, "status": status, "latency_ms": time.Since(start).Milliseconds(),
+		}
+		checks["protocol_accepted"] = map[string]any{"ok": status != http.StatusUpgradeRequired, "status": status}
+	}
+
+	ok := true
+	for _, check := range checks {
+		if v, has := check["ok"].(bool); has && !v {
+			ok = false
+		}
+	}
+	return a.write(map[string]any{"ok": ok, "checks": checks})
+}
+
+func (a *app) anchors(ctx context.Context, args []string) error {
+	// `anchors verify <anchor_epoch_id> --rpc-url <url>` chains an API fetch
+	// with the on-chain check (eth_call getCommitment + tx receipt) against a
+	// customer-chosen RPC endpoint. Without --rpc-url, all subcommands keep the
+	// existing get / remote-verify behavior.
+	if len(args) > 0 && args[0] == "verify" {
+		rest := args[1:]
+		positional := ""
+		if len(rest) > 0 && !strings.HasPrefix(rest[0], "-") {
+			positional, rest = rest[0], rest[1:]
+		}
+		fs := flag.NewFlagSet("anchors verify", flag.ContinueOnError)
+		fs.SetOutput(a.err)
+		id := fs.String("id", positional, "anchor epoch id")
+		rpcURL := fs.String("rpc-url", "", "JSON-RPC endpoint for the anchor's chain")
+		timeoutS := fs.Int("timeout-s", 15, "RPC timeout in seconds")
+		file := fs.String("file", "", "proof object JSON file (remote verify mode)")
+		publicKeyHex := fs.String("public-key-hex", "", "Ed25519 public key hex (remote verify mode)")
+		if err := fs.Parse(rest); err != nil {
+			return err
+		}
+		if *rpcURL == "" {
+			fallback := []string{}
+			if *file != "" {
+				fallback = append(fallback, "--file", *file)
+			}
+			if *publicKeyHex != "" {
+				fallback = append(fallback, "--public-key-hex", *publicKeyHex)
+			}
+			return a.remoteVerify(ctx, fallback, attesto.VerifyAnchor)
+		}
+		if *id == "" {
+			return errors.New("anchor epoch id is required (positional or --id)")
+		}
+		client, err := a.systemClient()
+		if err != nil {
+			return err
+		}
+		anchor, err := client.GetAnchorEpoch(ctx, *id)
+		if err != nil {
+			return err
+		}
+		report := attesto.VerifyAnchorOnchain(ctx, anchor, *rpcURL, time.Duration(*timeoutS)*time.Second)
+		return a.write(report)
+	}
+	return a.verifyableObject(ctx, "anchors", args, attesto.VerifyAnchor, "/v2/anchors/")
+}
+
 func (a *app) checkpoints(ctx context.Context, args []string) error {
 	if len(args) == 0 {
 		return errors.New("checkpoints subcommand required")
--- a/cmd/attesto/report.go
+++ b/cmd/attesto/report.go
@@ -0,0 +1,198 @@
+package main
+
+// [P2.2] `attesto report article12` — deterministic evidence-report templating
+// (never LLM-generated). The report states what is recorded and independently
+// verifiable; it never asserts conformity.
+
+import (
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+	"os"
+	"sort"
+	"strings"
+
+	attesto "go.attesto.eu/sdk"
+)
+
+const reportDisclaimer = "This report lists evidence recorded and independently " +
+	"verifiable on this stream. It does not assert conformity with any regulation: " +
+	"Attesto attests records; assessing legal obligations is for your advisors."
+
+var article12Elements = [][2]string{
+	{"(a) period of each use", "event timestamps (occurred_at / ingested_at), hash-chained per stream"},
+	{"(b) reference database checks", "input commitments on model_decision events"},
+	{"(c) input data for the check", "payload commitments (canonical SHA-256, recomputable client-side)"},
+	{"(d) identification of persons involved", "operator/actor references on decision and override events"},
+}
+
+func (a *app) report(ctx context.Context, args []string) error {
+	if len(args) == 0 || args[0] != "article12" {
+		return errors.New("usage: attesto report article12 --stream <id> [--from ts] [--to ts] [--output report.md]")
+	}
+	fs := flag.NewFlagSet("report article12", flag.ContinueOnError)
+	fs.SetOutput(a.err)
+	streamID := fs.String("stream", "", "stream id")
+	fromTs := fs.String("from", "", "RFC3339 window start")
+	toTs := fs.String("to", "", "RFC3339 window end")
+	output := fs.String("output", "", "write the markdown report to this file")
+	if err := fs.Parse(args[1:]); err != nil {
+		return err
+	}
+	if *streamID == "" {
+		return errors.New("--stream is required")
+	}
+	client, err := a.bearerClient()
+	if err != nil {
+		return err
+	}
+	report, err := buildArticle12Report(ctx, client, *streamID, *fromTs, *toTs)
+	if err != nil {
+		return err
+	}
+	if *output != "" {
+		if err := os.WriteFile(*output, []byte(report), 0o644); err != nil {
+			return err
+		}
+		return a.write(map[string]any{"ok": true, "output": *output})
+	}
+	_, err = fmt.Fprint(a.out, report)
+	return err
+}
+
+func buildArticle12Report(ctx context.Context, client *attesto.Client, streamID, fromTs, toTs string) (string, error) {
+	var events []attesto.M
+	it := client.IterTenantStreamEvents(streamID, 200)
+	for {
+		event, err := it.Next(ctx)
+		if err != nil {
+			return "", err
+		}
+		if event == nil {
+			break
+		}
+		ts, _ := firstString(event, "occurred_at", "occurredAt", "ingested_at", "ingestedAt")
+		if ts != "" {
+			if fromTs != "" && ts < fromTs {
+				continue
+			}
+			if toTs != "" && ts > toTs {
+				continue
+			}
+		}
+		events = append(events, event)
+	}
+
+	counts := map[string]int{}
+	var seqs []int
+	completenessInput := make([]map[string]any, 0, len(events))
+	for _, event := range events {
+		eventType, _ := firstString(event, "event_type", "eventType")
+		if eventType == "" {
+			eventType = "(untyped)"
+		}
+		counts[eventType]++
+		seq := int(asFloatValue(event["seq_no"], event["seqNo"]))
+		seqs = append(seqs, seq)
+		prev, _ := firstString(event, "prev_event_hash", "prevEventHash")
+		hash, _ := firstString(event, "event_hash", "eventHash")
+		completenessInput = append(completenessInput, map[string]any{
+			"seq_no": seq, "prev_event_hash": prev, "event_hash": hash,
+		})
+	}
+	sort.Ints(seqs)
+	completenessLine := "no events in range"
+	if len(seqs) > 0 {
+		comp := attesto.VerifyCompleteness(completenessInput, seqs[0], seqs[len(seqs)-1])
+		if comp.OK {
+			completenessLine = fmt.Sprintf("PASS — sequence %d..%d is gap-free and hash-chained", seqs[0], seqs[len(seqs)-1])
+		} else {
+			completenessLine = "FAIL — " + strings.Join(comp.Problems, ", ")
+		}
+	}
+
+	var checkpointRows []string
+	cit := client.IterTenantCheckpoints(streamID, 200)
+	for {
+		checkpoint, err := cit.Next(ctx)
+		if err != nil {
+			break // endpoint optional on older deployments
+		}
+		if checkpoint == nil {
+			break
+		}
+		hash, _ := firstString(checkpoint, "checkpoint_hash", "checkpointHash", "rootHash")
+		tx, _ := firstString(checkpoint, "tx_hash", "txHash")
+		if tx == "" {
+			tx = "not yet anchored"
+		}
+		block := "—"
+		if b := asFloatValue(checkpoint["block_number"], checkpoint["blockNumber"]); b > 0 {
+			block = fmt.Sprintf("%d", int64(b))
+		}
+		checkpointRows = append(checkpointRows, fmt.Sprintf("| `%s` | `%s` | %s |", hash, tx, block))
+	}
+	if len(checkpointRows) == 0 {
+		checkpointRows = []string{"| (no checkpoints in range) | — | — |"}
+	}
+
+	window := "stream start"
+	if fromTs != "" {
+		window = fromTs
+	}
+	windowEnd := "now"
+	if toTs != "" {
+		windowEnd = toTs
+	}
+
+	var b strings.Builder
+	fmt.Fprintf(&b, "# Evidence report — stream `%s`\n\n%s\n\n", streamID, reportDisclaimer)
+	fmt.Fprintf(&b, "Window: %s → %s\n\n", window, windowEnd)
+	b.WriteString("## Logging coverage (EU AI Act Article 12(2))\n\n| Element | Evidence recorded |\n|---|---|\n")
+	for _, row := range article12Elements {
+		fmt.Fprintf(&b, "| %s | %s |\n", row[0], row[1])
+	}
+	b.WriteString("\n## Events in range\n\n| Event type | Count |\n|---|---|\n")
+	types := make([]string, 0, len(counts))
+	for t := range counts {
+		types = append(types, t)
+	}
+	sort.Strings(types)
+	for _, t := range types {
+		fmt.Fprintf(&b, "| `%s` | %d |\n", t, counts[t])
+	}
+	fmt.Fprintf(&b, "| **total** | **%d** |\n\n", len(events))
+	fmt.Fprintf(&b, "**Completeness (no omissions):** %s\n\n", completenessLine)
+	b.WriteString("## Verification path per checkpoint\n\n| Checkpoint | Anchor tx | Block |\n|---|---|---|\n")
+	b.WriteString(strings.Join(checkpointRows, "\n"))
+	b.WriteString("\n\n## Replay these checks yourself\n\n```bash\n")
+	b.WriteString("go get go.attesto.eu/sdk  # or: pip install attesto / npm i @attesto/sdk\n")
+	fmt.Fprintf(&b, "# offline, no Attesto call: VerifyReceiptOffline / VerifyInclusionProof /\n# VerifyCompleteness over stream %s\n", streamID)
+	b.WriteString("attesto verify truth-package --file <export.zip>\n```\n\n")
+	fmt.Fprintf(&b, "_Generated by attesto-go/%s (deterministic template; no AI involved)._\n", attesto.SDKVersion)
+	return b.String(), nil
+}
+
+func firstString(m map[string]any, keys ...string) (string, bool) {
+	for _, key := range keys {
+		if s, ok := m[key].(string); ok && s != "" {
+			return s, true
+		}
+	}
+	return "", false
+}
+
+func asFloatValue(values ...any) float64 {
+	for _, v := range values {
+		switch n := v.(type) {
+		case float64:
+			return n
+		case int:
+			return float64(n)
+		case int64:
+			return float64(n)
+		}
+	}
+	return 0
+}
--- a/cmd/attesto/report_test.go
+++ b/cmd/attesto/report_test.go
@@ -0,0 +1,58 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"strings"
+	"testing"
+
+	attesto "go.attesto.eu/sdk"
+	"go.attesto.eu/sdk/attestotest"
+)
+
+func TestArticle12ReportWordingAndStructure(t *testing.T) {
+	server := attestotest.NewServer()
+	defer server.Close()
+	client, err := attesto.NewBearerClient("dummy-tenant-bearer-token", attesto.WithBaseURL(server.URL))
+	if err != nil {
+		t.Fatal(err)
+	}
+	ctx := context.Background()
+	stream, err := client.CreateStream(ctx, attesto.StreamCreateInput{UseCase: "ci", PolicyID: "mock-policy"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	decision := attesto.ModelDecision{Model: "m", Decision: "approve", ConfidenceBp: 8700}
+	payload, err := decision.ToPayload()
+	if err != nil {
+		t.Fatal(err)
+	}
+	for i := 0; i < 2; i++ {
+		// Distinct source refs: identical refs are one event (idempotent ingestion).
+		if _, err := client.LogEvent(ctx, stream.StreamID, attesto.EventInput{
+			SourceRef: fmt.Sprintf("e-%d", i), EventType: decision.EventType(), Payload: payload,
+		}); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	report, err := buildArticle12Report(ctx, client, stream.StreamID, "", "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, want := range []string{
+		"Article 12(2)",
+		"| `attesto.model_decision` | 2 |",
+		"PASS — sequence 1..2 is gap-free and hash-chained",
+		"deterministic template; no AI involved",
+		"attesto verify truth-package",
+	} {
+		if !strings.Contains(report, want) {
+			t.Errorf("report missing %q", want)
+		}
+	}
+	lower := strings.ToLower(report)
+	if strings.Contains(lower, "compliant") || strings.Contains(lower, "compliance guaranteed") {
+		t.Error("claims discipline violated: report must never say compliant")
+	}
+}
--- a/events.go
+++ b/events.go
@@ -0,0 +1,135 @@
+package attesto
+
+// [P2.2] Typed compliance events — SDK-side conventions, no backend change.
+// Each ToPayload() returns a plain payload map with regulation_refs included,
+// validated against the committed-payload number policy. Recording these never
+// claims conformity: Attesto attests records.
+
+// Typed event type identifiers.
+const (
+	EventTypeModelDecision  = "attesto.model_decision"
+	EventTypeHumanOverride  = "attesto.human_override"
+	EventTypeIncidentReport = "attesto.incident_report"
+	EventTypeDataAccess     = "attesto.data_access"
+)
+
+// Regulation references per typed event (conventions for reports/auditors).
+var (
+	RefsModelDecision  = []string{"EU-AI-Act:Art.12", "EU-AI-Act:Art.14"}
+	RefsHumanOverride  = []string{"EU-AI-Act:Art.14"}
+	RefsIncidentReport = []string{"NIS2:Art.23", "EU-AI-Act:Art.62"}
+	RefsDataAccess     = []string{"GDPR:Art.30", "GDPR:Art.6"}
+)
+
+func finishPayload(payload M, refs []string, extra M) (M, error) {
+	for key, value := range extra {
+		payload[key] = value
+	}
+	out := M{}
+	for key, value := range payload {
+		if value != nil && value != "" {
+			out[key] = value
+		}
+	}
+	out["regulation_refs"] = refs
+	if err := AssertCommitmentSafeNumbers(map[string]any(out), "$"); err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+// ModelDecision is one model-driven decision (commitments only; raw inputs and
+// outputs never leave your process).
+type ModelDecision struct {
+	Model            string
+	InputCommitment  map[string]string
+	OutputCommitment map[string]string
+	Decision         string
+	ConfidenceBp     int // basis points keep integers commitment-safe
+	HumanInLoop      bool
+	OperatorRef      string
+	Extra            M
+}
+
+func (e ModelDecision) EventType() string { return EventTypeModelDecision }
+
+func (e ModelDecision) ToPayload() (M, error) {
+	return finishPayload(M{
+		"model":             e.Model,
+		"input_commitment":  orNil(e.InputCommitment),
+		"output_commitment": orNil(e.OutputCommitment),
+		"decision":          e.Decision,
+		"confidence_bp":     e.ConfidenceBp,
+		"human_in_loop":     e.HumanInLoop,
+		"operator_ref":      e.OperatorRef,
+	}, RefsModelDecision, e.Extra)
+}
+
+// HumanOverride records a human overriding a model decision (Art. 14).
+type HumanOverride struct {
+	OriginalEventRef        string
+	OperatorRef             string
+	JustificationCommitment map[string]string
+	NewDecision             string
+	Extra                   M
+}
+
+func (e HumanOverride) EventType() string { return EventTypeHumanOverride }
+
+func (e HumanOverride) ToPayload() (M, error) {
+	return finishPayload(M{
+		"original_event_ref":       e.OriginalEventRef,
+		"operator_ref":             e.OperatorRef,
+		"justification_commitment": orNil(e.JustificationCommitment),
+		"new_decision":             e.NewDecision,
+	}, RefsHumanOverride, e.Extra)
+}
+
+// IncidentReport is a reportable incident with NIS2-style field names.
+type IncidentReport struct {
+	Severity          string
+	Category          string
+	DetectedAt        string
+	SummaryCommitment map[string]string
+	AffectedService   string
+	Extra             M
+}
+
+func (e IncidentReport) EventType() string { return EventTypeIncidentReport }
+
+func (e IncidentReport) ToPayload() (M, error) {
+	return finishPayload(M{
+		"severity":           e.Severity,
+		"category":           e.Category,
+		"detected_at":        e.DetectedAt,
+		"summary_commitment": orNil(e.SummaryCommitment),
+		"affected_service":   e.AffectedService,
+	}, RefsIncidentReport, e.Extra)
+}
+
+// DataAccess records an access to personal or regulated data.
+type DataAccess struct {
+	SubjectRefCommitment map[string]string
+	Purpose              string
+	LegalBasis           string
+	AccessorRef          string
+	Extra                M
+}
+
+func (e DataAccess) EventType() string { return EventTypeDataAccess }
+
+func (e DataAccess) ToPayload() (M, error) {
+	return finishPayload(M{
+		"subject_ref_commitment": orNil(e.SubjectRefCommitment),
+		"purpose":                e.Purpose,
+		"legal_basis":            e.LegalBasis,
+		"accessor_ref":           e.AccessorRef,
+	}, RefsDataAccess, e.Extra)
+}
+
+func orNil(m map[string]string) any {
+	if len(m) == 0 {
+		return nil
+	}
+	return m
+}
--- a/examples/proofstream/main.go
+++ b/examples/proofstream/main.go
@@ -6,7 +6,7 @@ import (
 	"log"
 	"os"

-	attesto "git.rotz.ai/rotzmediagroup/attesto-v1/sdk/go"
+	attesto "go.attesto.eu/sdk"
 )

 func main() {
--- a/export.go
+++ b/export.go
@@ -0,0 +1,161 @@
+package attesto
+
+// [P3.4] Portable receipt export — a self-contained `*.attesto.json`.
+// Mirrors attesto.export (Python) and export.ts (TypeScript); the
+// receipt-export.json parity corpus is normative for all three.
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"time"
+)
+
+const (
+	ExportFormat        = "attesto-receipt-export"
+	ExportFormatVersion = 1
+)
+
+// ReceiptExport is the portable envelope. Receipt is kept as raw JSON so the
+// export carries the receipt verbatim, exactly as the API returned it.
+type ReceiptExport struct {
+	Format              string          `json:"format"`
+	FormatVersion       int             `json:"format_version"`
+	ExportedAt          string          `json:"exported_at"`
+	StreamID            any             `json:"stream_id,omitempty"`
+	SeqNo               any             `json:"seq_no,omitempty"`
+	EventHash           any             `json:"event_hash,omitempty"`
+	WitnessPublicKeyHex string          `json:"witness_public_key_hex,omitempty"`
+	Receipt             json.RawMessage `json:"receipt"`
+	Payload             M               `json:"payload,omitempty"`
+	PayloadCommitment   M               `json:"payload_commitment,omitempty"`
+}
+
+func exportPick(source M, keys ...string) any {
+	for _, key := range keys {
+		if value, ok := source[key]; ok {
+			return value
+		}
+	}
+	return nil
+}
+
+// ExportReceiptFile builds a portable export from a receipt's raw JSON (as
+// returned by the API) and optionally writes it to path (empty = no write).
+func ExportReceiptFile(receiptJSON []byte, path string, witnessPublicKeyHex string) (ReceiptExport, error) {
+	var parsed struct {
+		Payload M `json:"payload"`
+	}
+	if err := json.Unmarshal(receiptJSON, &parsed); err != nil {
+		return ReceiptExport{}, fmt.Errorf("receipt is not valid JSON: %w", err)
+	}
+	export := ReceiptExport{
+		Format:              ExportFormat,
+		FormatVersion:       ExportFormatVersion,
+		ExportedAt:          time.Now().UTC().Format("2006-01-02T15:04:05.000Z"),
+		StreamID:            exportPick(parsed.Payload, "stream_id", "streamId"),
+		SeqNo:               exportPick(parsed.Payload, "seq_no", "seqNo"),
+		EventHash:           exportPick(parsed.Payload, "event_hash", "eventHash"),
+		WitnessPublicKeyHex: witnessPublicKeyHex,
+		Receipt:             json.RawMessage(receiptJSON),
+	}
+	if path != "" {
+		raw, err := json.MarshalIndent(export, "", "  ")
+		if err != nil {
+			return ReceiptExport{}, err
+		}
+		if err := os.WriteFile(path, append(raw, '\n'), 0o644); err != nil {
+			return ReceiptExport{}, err
+		}
+	}
+	return export, nil
+}
+
+// VerifyReceiptExport verifies a portable export offline. publicKeyHex == ""
+// falls back to the embedded hint (self-contained mode — proves internal
+// consistency against the key the file itself names).
+func VerifyReceiptExport(exportJSON []byte, publicKeyHex string) VerifyReport {
+	var export struct {
+		Format              string          `json:"format"`
+		FormatVersion       int             `json:"format_version"`
+		StreamID            any             `json:"stream_id"`
+		SeqNo               any             `json:"seq_no"`
+		EventHash           any             `json:"event_hash"`
+		WitnessPublicKeyHex string          `json:"witness_public_key_hex"`
+		Receipt             json.RawMessage `json:"receipt"`
+		Payload             M               `json:"payload"`
+		PayloadCommitment   M               `json:"payload_commitment"`
+	}
+	kind := VerifyKind("receipt-export")
+	if publicKeyHex == "" {
+		kind = "receipt-export-selfcontained"
+	}
+	fail := func(problems ...string) VerifyReport {
+		return VerifyReport{Kind: kind, OK: false, Problems: problems}
+	}
+	if err := json.Unmarshal(exportJSON, &export); err != nil {
+		return fail("export is not valid JSON: " + err.Error())
+	}
+	var problems []string
+	if export.Format != ExportFormat {
+		problems = append(problems, "not an attesto receipt export (format field)")
+	}
+	if export.FormatVersion != ExportFormatVersion {
+		problems = append(problems, fmt.Sprintf("unsupported export format_version: %d", export.FormatVersion))
+	}
+	if len(export.Receipt) == 0 {
+		problems = append(problems, "export carries no receipt object")
+	}
+	if len(problems) > 0 {
+		return fail(problems...)
+	}
+
+	key := publicKeyHex
+	if key == "" {
+		key = export.WitnessPublicKeyHex
+	}
+	if key == "" {
+		return fail("no public key supplied and no embedded hint")
+	}
+	var receipt SignedReceipt
+	if err := json.Unmarshal(export.Receipt, &receipt); err != nil {
+		return fail("receipt is not valid JSON: " + err.Error())
+	}
+	report := VerifyReceiptOffline(receipt, key)
+	problems = append(problems, report.Problems...)
+
+	linkage := []struct {
+		name  string
+		outer any
+		keys  []string
+	}{
+		{"stream_id", export.StreamID, []string{"stream_id", "streamId"}},
+		{"seq_no", export.SeqNo, []string{"seq_no", "seqNo"}},
+		{"event_hash", export.EventHash, []string{"event_hash", "eventHash"}},
+	}
+	for _, link := range linkage {
+		inner := exportPick(receipt.Payload, link.keys...)
+		if link.outer == nil || inner == nil {
+			continue
+		}
+		// JSON numbers decode as float64 on both sides, so == is sound here.
+		if fmt.Sprint(link.outer) != fmt.Sprint(inner) {
+			problems = append(problems, "export linkage mismatch: "+link.name)
+		}
+	}
+
+	if export.Payload != nil && export.PayloadCommitment != nil {
+		ok, err := VerifyPayloadCommitment(export.Payload, M{"payload_commitment": export.PayloadCommitment})
+		if err != nil || !ok {
+			problems = append(problems, "embedded payload does not match payload_commitment")
+		}
+	}
+
+	return VerifyReport{
+		Kind:        kind,
+		OK:          len(problems) == 0,
+		ReceiptHash: report.ReceiptHash,
+		EventHash:   report.EventHash,
+		Problems:    problems,
+	}
+}
--- a/export_parity_test.go
+++ b/export_parity_test.go
@@ -0,0 +1,77 @@
+package attesto
+
+// [P3.4] Receipt-export parity corpus — Go verifier.
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestReceiptExportParity(t *testing.T) {
+	raw, err := os.ReadFile(filepath.Join("..", "..", "golden-vectors", "sdk-parity", "receipt-export.json"))
+	if err != nil {
+		t.Fatalf("read corpus: %v", err)
+	}
+	var corpus struct {
+		Cases []struct {
+			ID           string          `json:"id"`
+			ExpectOK     bool            `json:"expect_ok"`
+			PublicKeyHex *string         `json:"public_key_hex"`
+			Export       json.RawMessage `json:"export"`
+		} `json:"cases"`
+	}
+	if err := json.Unmarshal(raw, &corpus); err != nil {
+		t.Fatalf("parse corpus: %v", err)
+	}
+	if len(corpus.Cases) < 5 {
+		t.Fatalf("expected >=5 cases, got %d", len(corpus.Cases))
+	}
+	for _, testCase := range corpus.Cases {
+		t.Run(testCase.ID, func(t *testing.T) {
+			key := ""
+			if testCase.PublicKeyHex != nil {
+				key = *testCase.PublicKeyHex
+			}
+			report := VerifyReceiptExport(testCase.Export, key)
+			if report.OK != testCase.ExpectOK {
+				t.Fatalf("ok=%v want %v (problems: %v)", report.OK, testCase.ExpectOK, report.Problems)
+			}
+			if testCase.PublicKeyHex == nil && testCase.ExpectOK && report.Kind != "receipt-export-selfcontained" {
+				t.Fatalf("kind=%q, want receipt-export-selfcontained", report.Kind)
+			}
+		})
+	}
+}
+
+func TestExportReceiptFileRoundTrip(t *testing.T) {
+	raw, err := os.ReadFile(filepath.Join("..", "..", "golden-vectors", "sdk-parity", "receipt-export.json"))
+	if err != nil {
+		t.Fatalf("read corpus: %v", err)
+	}
+	var corpus struct {
+		Cases []struct {
+			PublicKeyHex *string `json:"public_key_hex"`
+			Export       struct {
+				Receipt json.RawMessage `json:"receipt"`
+			} `json:"export"`
+		} `json:"cases"`
+	}
+	if err := json.Unmarshal(raw, &corpus); err != nil {
+		t.Fatalf("parse corpus: %v", err)
+	}
+	valid := corpus.Cases[0]
+	path := filepath.Join(t.TempDir(), "receipt.attesto.json")
+	if _, err := ExportReceiptFile(valid.Export.Receipt, path, *valid.PublicKeyHex); err != nil {
+		t.Fatalf("export: %v", err)
+	}
+	exported, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("read export: %v", err)
+	}
+	report := VerifyReceiptExport(exported, *valid.PublicKeyHex)
+	if !report.OK {
+		t.Fatalf("round-trip verify failed: %v", report.Problems)
+	}
+}
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,3 @@
-module git.rotz.ai/rotzmediagroup/attesto-v1/sdk/go
+module go.attesto.eu/sdk

 go 1.24
--- a/heads.go
+++ b/heads.go
@@ -0,0 +1,165 @@
+package attesto
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sync"
+)
+
+// HeadStore persists the last accepted (seqNo, eventHash) head per stream so the
+// client can detect a rewound or divergent server history.
+type HeadStore interface {
+	Get(streamID string) (seqNo int64, eventHash string, ok bool)
+	Set(streamID string, seqNo int64, eventHash string)
+}
+
+// ForkDetectedError reports that a receipt did not extend the last accepted head
+// for its stream. The store is NOT advanced when this is returned.
+type ForkDetectedError struct {
+	StreamID     string
+	ExpectedSeq  int64
+	ExpectedHash string
+	GotSeq       int64
+	GotPrevHash  string
+}
+
+func (e *ForkDetectedError) Error() string {
+	return fmt.Sprintf(
+		"fork detected on stream %s: receipt (seq=%d prev=%s) does not extend "+
+			"last accepted head (seq=%d hash=%s)",
+		e.StreamID, e.GotSeq, e.GotPrevHash, e.ExpectedSeq, e.ExpectedHash)
+}
+
+// MemoryHeadStore keeps heads in process memory; safe for concurrent use.
+type MemoryHeadStore struct {
+	mu    sync.Mutex
+	heads map[string][2]any
+}
+
+func NewMemoryHeadStore() *MemoryHeadStore {
+	return &MemoryHeadStore{heads: map[string][2]any{}}
+}
+
+func (s *MemoryHeadStore) Get(streamID string) (int64, string, bool) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	entry, ok := s.heads[streamID]
+	if !ok {
+		return 0, "", false
+	}
+	return entry[0].(int64), entry[1].(string), true
+}
+
+func (s *MemoryHeadStore) Set(streamID string, seqNo int64, eventHash string) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.heads[streamID] = [2]any{seqNo, eventHash}
+}
+
+// FileHeadStore persists heads to a JSON file (default ~/.attesto/heads.json),
+// giving fork detection across separate process invocations. Writes are atomic.
+type FileHeadStore struct {
+	path string
+	mu   sync.Mutex
+}
+
+// NewFileHeadStore uses the given path, or ~/.attesto/heads.json when empty.
+func NewFileHeadStore(path string) *FileHeadStore {
+	if path == "" {
+		if home, err := os.UserHomeDir(); err == nil {
+			path = filepath.Join(home, ".attesto", "heads.json")
+		} else {
+			path = ".attesto-heads.json"
+		}
+	}
+	return &FileHeadStore{path: path}
+}
+
+func (s *FileHeadStore) load() map[string][2]json.RawMessage {
+	raw, err := os.ReadFile(s.path)
+	if err != nil {
+		return map[string][2]json.RawMessage{}
+	}
+	out := map[string][2]json.RawMessage{}
+	if err := json.Unmarshal(raw, &out); err != nil {
+		return map[string][2]json.RawMessage{}
+	}
+	return out
+}
+
+func (s *FileHeadStore) Get(streamID string) (int64, string, bool) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	entry, ok := s.load()[streamID]
+	if !ok {
+		return 0, "", false
+	}
+	var seqNo int64
+	var eventHash string
+	if json.Unmarshal(entry[0], &seqNo) != nil || json.Unmarshal(entry[1], &eventHash) != nil {
+		return 0, "", false
+	}
+	return seqNo, eventHash, true
+}
+
+func (s *FileHeadStore) Set(streamID string, seqNo int64, eventHash string) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	heads := map[string][2]any{}
+	for key, entry := range s.load() {
+		var n int64
+		var h string
+		_ = json.Unmarshal(entry[0], &n)
+		_ = json.Unmarshal(entry[1], &h)
+		heads[key] = [2]any{n, h}
+	}
+	heads[streamID] = [2]any{seqNo, eventHash}
+	body, err := json.Marshal(heads)
+	if err != nil {
+		return
+	}
+	if err := os.MkdirAll(filepath.Dir(s.path), 0o700); err != nil {
+		return
+	}
+	tmp, err := os.CreateTemp(filepath.Dir(s.path), ".heads-")
+	if err != nil {
+		return
+	}
+	tmpName := tmp.Name()
+	_, writeErr := tmp.Write(body)
+	closeErr := tmp.Close()
+	if writeErr != nil || closeErr != nil {
+		_ = os.Remove(tmpName)
+		return
+	}
+	_ = os.Chmod(tmpName, 0o600)
+	_ = os.Rename(tmpName, s.path)
+}
+
+// checkAndAdvanceHead verifies a receipt extends the stored head, then advances
+// the store. Returns *ForkDetectedError (without advancing) when the receipt
+// rewinds or collides on seqNo, or claims to be the immediate next event but
+// does not chain. A forward gap is accepted and advances.
+func checkAndAdvanceHead(store HeadStore, receipt EventReceipt) error {
+	if storedSeq, storedHash, ok := store.Get(receipt.StreamID); ok {
+		if receipt.SeqNo == storedSeq && receipt.EventHash == storedHash {
+			// Benign idempotent replay: the server deduplicated a resend and
+			// returned the same receipt for the same event.
+			return nil
+		}
+		if receipt.SeqNo <= storedSeq ||
+			(receipt.SeqNo == storedSeq+1 && receipt.PrevEventHash != storedHash) {
+			return &ForkDetectedError{
+				StreamID:     receipt.StreamID,
+				ExpectedSeq:  storedSeq,
+				ExpectedHash: storedHash,
+				GotSeq:       receipt.SeqNo,
+				GotPrevHash:  receipt.PrevEventHash,
+			}
+		}
+	}
+	store.Set(receipt.StreamID, receipt.SeqNo, receipt.EventHash)
+	return nil
+}
--- a/heads_test.go
+++ b/heads_test.go
@@ -0,0 +1,99 @@
+package attesto
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func receipt(seqNo int64, eventHash, prevEventHash string) EventReceipt {
+	return EventReceipt{
+		StreamID:      "str_demo",
+		SeqNo:         seqNo,
+		EventHash:     eventHash,
+		PrevEventHash: prevEventHash,
+	}
+}
+
+func TestMemoryHeadStoreInOrderAdvances(t *testing.T) {
+	store := NewMemoryHeadStore()
+	for _, r := range []EventReceipt{receipt(1, "h1", ""), receipt(2, "h2", "h1"), receipt(3, "h3", "h2")} {
+		if err := checkAndAdvanceHead(store, r); err != nil {
+			t.Fatalf("unexpected: %v", err)
+		}
+	}
+	if seq, hash, ok := store.Get("str_demo"); !ok || seq != 3 || hash != "h3" {
+		t.Errorf("head = (%d,%s,%v)", seq, hash, ok)
+	}
+}
+
+func TestForgedRewoundReceiptIsFork(t *testing.T) {
+	store := NewMemoryHeadStore()
+	_ = checkAndAdvanceHead(store, receipt(1, "h1", ""))
+	_ = checkAndAdvanceHead(store, receipt(2, "h2", "h1"))
+	err := checkAndAdvanceHead(store, receipt(2, "h2-fork", "h1"))
+	var fork *ForkDetectedError
+	if !errors.As(err, &fork) {
+		t.Fatalf("expected *ForkDetectedError, got %v", err)
+	}
+	if seq, hash, _ := store.Get("str_demo"); seq != 2 || hash != "h2" {
+		t.Errorf("store advanced past fork: (%d,%s)", seq, hash)
+	}
+}
+
+func TestDivergentNextEventIsFork(t *testing.T) {
+	store := NewMemoryHeadStore()
+	_ = checkAndAdvanceHead(store, receipt(1, "h1", ""))
+	err := checkAndAdvanceHead(store, receipt(2, "h2", "WRONG"))
+	var fork *ForkDetectedError
+	if !errors.As(err, &fork) {
+		t.Fatalf("expected *ForkDetectedError, got %v", err)
+	}
+}
+
+func TestForwardGapAccepted(t *testing.T) {
+	store := NewMemoryHeadStore()
+	_ = checkAndAdvanceHead(store, receipt(1, "h1", ""))
+	if err := checkAndAdvanceHead(store, receipt(5, "h5", "h4")); err != nil {
+		t.Fatalf("forward gap should be accepted: %v", err)
+	}
+}
+
+func TestFileHeadStorePersistsAndIs0600(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "heads.json")
+	store := NewFileHeadStore(path)
+	_ = checkAndAdvanceHead(store, receipt(1, "h1", ""))
+	_ = checkAndAdvanceHead(store, receipt(2, "h2", "h1"))
+	info, err := os.Stat(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if info.Mode().Perm() != 0o600 {
+		t.Errorf("mode = %o, want 600", info.Mode().Perm())
+	}
+	reopened := NewFileHeadStore(path)
+	if seq, hash, ok := reopened.Get("str_demo"); !ok || seq != 2 || hash != "h2" {
+		t.Errorf("reopened head = (%d,%s,%v)", seq, hash, ok)
+	}
+	if err := checkAndAdvanceHead(reopened, receipt(2, "h2-fork", "h1")); err == nil {
+		t.Error("expected fork on reopened store")
+	}
+}
+
+func TestExactReplayOfStoredHeadIsBenign(t *testing.T) {
+	// [P3.3 regression] A deduplicated resend returns the same receipt; the
+	// head tracker must treat (same seqNo, same eventHash) as a no-op.
+	store := NewMemoryHeadStore()
+	first := EventReceipt{StreamID: "str_x", SeqNo: 1, EventHash: "h1"}
+	if err := checkAndAdvanceHead(store, first); err != nil {
+		t.Fatal(err)
+	}
+	if err := checkAndAdvanceHead(store, first); err != nil {
+		t.Fatalf("exact replay must be benign, got %v", err)
+	}
+	fork := EventReceipt{StreamID: "str_x", SeqNo: 1, EventHash: "h2"}
+	if err := checkAndAdvanceHead(store, fork); err == nil {
+		t.Fatal("same seq with different hash must be a fork")
+	}
+}
--- a/iterator.go
+++ b/iterator.go
@@ -0,0 +1,80 @@
+package attesto
+
+import "context"
+
+// PageFunc fetches one limit/offset page of list results.
+type PageFunc func(ctx context.Context, limit, offset int) ([]M, error)
+
+// Iterator walks limit/offset pages of a list endpoint transparently, stopping
+// on the first short page. Same endpoints, no new API surface.
+type Iterator struct {
+	fetch    PageFunc
+	pageSize int
+	buffer   []M
+	offset   int
+	done     bool
+}
+
+// NewIterator wraps any limit/offset PageFunc. pageSize <= 0 defaults to 100.
+func NewIterator(fetch PageFunc, pageSize int) *Iterator {
+	if pageSize <= 0 {
+		pageSize = 100
+	}
+	return &Iterator{fetch: fetch, pageSize: pageSize}
+}
+
+// Next returns the next item, or (nil, nil) when the listing is exhausted.
+func (it *Iterator) Next(ctx context.Context) (M, error) {
+	if len(it.buffer) == 0 && !it.done {
+		page, err := it.fetch(ctx, it.pageSize, it.offset)
+		if err != nil {
+			return nil, err
+		}
+		it.offset += it.pageSize
+		if len(page) < it.pageSize {
+			it.done = true
+		}
+		it.buffer = page
+	}
+	if len(it.buffer) == 0 {
+		return nil, nil
+	}
+	item := it.buffer[0]
+	it.buffer = it.buffer[1:]
+	return item, nil
+}
+
+// IterTenantStreamEvents returns an iterator over a stream's events.
+func (c *Client) IterTenantStreamEvents(streamID string, pageSize int) *Iterator {
+	return NewIterator(func(ctx context.Context, limit, offset int) ([]M, error) {
+		return c.ListTenantStreamEvents(ctx, streamID, limit, offset)
+	}, pageSize)
+}
+
+// IterTenantWindows returns an iterator over a stream's windows.
+func (c *Client) IterTenantWindows(streamID string, pageSize int) *Iterator {
+	return NewIterator(func(ctx context.Context, limit, offset int) ([]M, error) {
+		return c.ListTenantWindows(ctx, streamID, limit, offset)
+	}, pageSize)
+}
+
+// IterTenantCheckpoints returns an iterator over a stream's checkpoints.
+func (c *Client) IterTenantCheckpoints(streamID string, pageSize int) *Iterator {
+	return NewIterator(func(ctx context.Context, limit, offset int) ([]M, error) {
+		return c.ListTenantCheckpoints(ctx, streamID, limit, offset)
+	}, pageSize)
+}
+
+// IterForkEvidence returns an iterator over a stream's fork evidence.
+func (c *Client) IterForkEvidence(streamID string, pageSize int) *Iterator {
+	return NewIterator(func(ctx context.Context, limit, offset int) ([]M, error) {
+		return c.ListForkEvidence(ctx, streamID, limit, offset)
+	}, pageSize)
+}
+
+// IterTenantIVCEpochs returns an iterator over a stream's IVC epochs.
+func (c *Client) IterTenantIVCEpochs(streamID string, pageSize int) *Iterator {
+	return NewIterator(func(ctx context.Context, limit, offset int) ([]M, error) {
+		return c.ListTenantIVCEpochs(ctx, streamID, limit, offset)
+	}, pageSize)
+}
--- a/iterator_test.go
+++ b/iterator_test.go
@@ -0,0 +1,65 @@
+package attesto
+
+import (
+	"context"
+	"testing"
+)
+
+func TestIteratorDrainsThreePagesInOrder(t *testing.T) {
+	pages := map[int][]M{
+		0: {{"seqNo": 1}, {"seqNo": 2}, {"seqNo": 3}},
+		3: {{"seqNo": 4}, {"seqNo": 5}, {"seqNo": 6}},
+		6: {{"seqNo": 7}},
+	}
+	calls := 0
+	it := NewIterator(func(_ context.Context, limit, offset int) ([]M, error) {
+		calls++
+		if limit != 3 {
+			t.Fatalf("limit = %d, want 3", limit)
+		}
+		return pages[offset], nil
+	}, 3)
+
+	var seqs []int
+	for {
+		item, err := it.Next(context.Background())
+		if err != nil {
+			t.Fatal(err)
+		}
+		if item == nil {
+			break
+		}
+		seqs = append(seqs, item["seqNo"].(int))
+	}
+	want := []int{1, 2, 3, 4, 5, 6, 7}
+	if len(seqs) != len(want) {
+		t.Fatalf("seqs = %v", seqs)
+	}
+	for i, v := range want {
+		if seqs[i] != v {
+			t.Fatalf("seqs = %v, want %v", seqs, want)
+		}
+	}
+	if calls != 3 {
+		t.Errorf("calls = %d, want 3", calls)
+	}
+}
+
+func TestIteratorStopsCleanlyOnShortFirstPage(t *testing.T) {
+	calls := 0
+	it := NewIterator(func(_ context.Context, _, _ int) ([]M, error) {
+		calls++
+		return []M{{"streamId": "str_only"}}, nil
+	}, 100)
+	first, err := it.Next(context.Background())
+	if err != nil || first == nil {
+		t.Fatalf("first = %v err = %v", first, err)
+	}
+	second, err := it.Next(context.Background())
+	if err != nil || second != nil {
+		t.Fatalf("second = %v err = %v", second, err)
+	}
+	if calls != 1 {
+		t.Errorf("calls = %d, want 1 (short page must end iteration)", calls)
+	}
+}
--- a/proofstream.go
+++ b/proofstream.go
@@ -11,6 +11,7 @@ import (
 	"fmt"
 	"math"
 	"sort"
+	"strconv"
 	"strings"
 	"time"
 )
@@ -69,6 +70,421 @@ func SHA256Hex(value []byte) string {
 	return hex.EncodeToString(sum[:])
 }

+// maxSafeInteger mirrors JavaScript's Number.MAX_SAFE_INTEGER (2^53 - 1).
+// Integers beyond this lose precision when a JS verifier parses them, so they
+// would re-serialize to different canonical bytes across languages.
+const maxSafeInteger = int64(1)<<53 - 1
+
+// UnsafeNumberError reports a committed payload/metadata number whose
+// canonical-JSON bytes diverge across Python, Go, and JavaScript (a non-integer,
+// or an integer outside +/-(2^53 - 1)). Path is the JSON path to the offender.
+type UnsafeNumberError struct {
+	Path    string
+	Message string
+}
+
+func (e *UnsafeNumberError) Error() string { return e.Message }
+
+func nonIntegerError(path string) *UnsafeNumberError {
+	return &UnsafeNumberError{
+		Path: path,
+		Message: fmt.Sprintf(
+			"non-integer numbers are not permitted in committed payloads (%s); "+
+				"encode decimals as strings", path),
+	}
+}
+
+func unsafeIntegerError(path string) *UnsafeNumberError {
+	return &UnsafeNumberError{
+		Path: path,
+		Message: fmt.Sprintf(
+			"integers beyond +/-2^53-1 are not permitted in committed payloads (%s); "+
+				"encode large integers as strings", path),
+	}
+}
+
+func assertSafeFloat(v float64, path string) error {
+	if math.IsInf(v, 0) || math.IsNaN(v) || math.Trunc(v) != v {
+		return nonIntegerError(path)
+	}
+	if math.Abs(v) > float64(maxSafeInteger) {
+		return unsafeIntegerError(path)
+	}
+	return nil
+}
+
+func assertSafeInt64(v int64, path string) error {
+	if v > maxSafeInteger || v < -maxSafeInteger {
+		return unsafeIntegerError(path)
+	}
+	return nil
+}
+
+func assertSafeNumberString(s, path string) error {
+	if strings.ContainsAny(s, ".eE") {
+		f, err := strconv.ParseFloat(s, 64)
+		if err != nil {
+			return nonIntegerError(path)
+		}
+		return assertSafeFloat(f, path)
+	}
+	n, err := strconv.ParseInt(s, 10, 64)
+	if err != nil {
+		// Outside int64 range is necessarily outside the safe integer range.
+		return unsafeIntegerError(path)
+	}
+	return assertSafeInt64(n, path)
+}
+
+// AssertCommitmentSafeNumbers rejects numbers whose canonical-JSON bytes diverge
+// across Python, Go, and JavaScript, so a commitment computed here matches the
+// backend's byte-for-byte. Mirrors assert_commitment_safe_numbers in the backend:
+// non-integer numbers are rejected outright; integers must be within +/-(2^53 - 1).
+// Booleans are exempt. Returns an *UnsafeNumberError on the first offending value.
+func AssertCommitmentSafeNumbers(value any, path string) error {
+	switch v := value.(type) {
+	case nil, bool, string:
+		return nil
+	case json.Number:
+		return assertSafeNumberString(v.String(), path)
+	case float64:
+		return assertSafeFloat(v, path)
+	case float32:
+		return assertSafeFloat(float64(v), path)
+	case int:
+		return assertSafeInt64(int64(v), path)
+	case int8:
+		return assertSafeInt64(int64(v), path)
+	case int16:
+		return assertSafeInt64(int64(v), path)
+	case int32:
+		return assertSafeInt64(int64(v), path)
+	case int64:
+		return assertSafeInt64(v, path)
+	case uint:
+		return assertSafeUint64(uint64(v), path)
+	case uint8:
+		return assertSafeInt64(int64(v), path)
+	case uint16:
+		return assertSafeInt64(int64(v), path)
+	case uint32:
+		return assertSafeInt64(int64(v), path)
+	case uint64:
+		return assertSafeUint64(v, path)
+	case []any:
+		for i, item := range v {
+			if err := AssertCommitmentSafeNumbers(item, fmt.Sprintf("%s[%d]", path, i)); err != nil {
+				return err
+			}
+		}
+		return nil
+	case []M:
+		for i, item := range v {
+			if err := AssertCommitmentSafeNumbers(item, fmt.Sprintf("%s[%d]", path, i)); err != nil {
+				return err
+			}
+		}
+		return nil
+	case map[string]any:
+		return assertSafeMap(v, path)
+	case M:
+		return assertSafeMap(map[string]any(v), path)
+	default:
+		// Structs and other types: normalize through JSON exactly as the
+		// canonical encoder does, then re-check the plain representation.
+		raw, err := json.Marshal(v)
+		if err != nil {
+			return err
+		}
+		var decoded any
+		dec := json.NewDecoder(bytes.NewReader(raw))
+		dec.UseNumber()
+		if err := dec.Decode(&decoded); err != nil {
+			return err
+		}
+		return AssertCommitmentSafeNumbers(decoded, path)
+	}
+}
+
+func assertSafeUint64(v uint64, path string) error {
+	if v > uint64(maxSafeInteger) {
+		return unsafeIntegerError(path)
+	}
+	return nil
+}
+
+func assertSafeMap(m map[string]any, path string) error {
+	for key, item := range m {
+		if err := AssertCommitmentSafeNumbers(item, fmt.Sprintf("%s.%s", path, key)); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// PayloadCommitment returns a deterministic commitment to an event payload,
+// byte-identical to the server's stored payload_commitment. Call
+// AssertCommitmentSafeNumbers first if the payload is not yet known to be safe.
+func PayloadCommitment(payload any) (map[string]string, error) {
+	if err := EnsureSelfTest(); err != nil {
+		return nil, err
+	}
+	raw, err := CanonicalJSON(payload)
+	if err != nil {
+		return nil, err
+	}
+	return map[string]string{
+		"hash_alg":               "sha256",
+		"canonical_payload_hash": SHA256Hex(raw),
+	}, nil
+}
+
+// MetadataCommitment returns a deterministic commitment to event metadata,
+// byte-identical to the server's stored metadata_commitment.
+func MetadataCommitment(metadata any) (map[string]string, error) {
+	raw, err := CanonicalJSON(metadata)
+	if err != nil {
+		return nil, err
+	}
+	return map[string]string{
+		"hash_alg":                "sha256",
+		"canonical_metadata_hash": SHA256Hex(raw),
+	}, nil
+}
+
+func storedCommitmentHash(event map[string]any, commitmentKey, hashKey string) string {
+	containers := []any{event, event["envelope"], event["envelope_json"]}
+	for _, container := range containers {
+		obj, ok := container.(map[string]any)
+		if !ok {
+			continue
+		}
+		commitment, ok := obj[commitmentKey].(map[string]any)
+		if !ok {
+			continue
+		}
+		if stored, ok := commitment[hashKey].(string); ok {
+			return stored
+		}
+	}
+	return ""
+}
+
+// VerifyPayloadCommitment recomputes the payload commitment locally and compares
+// it to the value stored on an event (payload_commitment.canonical_payload_hash,
+// whether the event is given flat or under envelope / envelope_json). Returns
+// false when the stored commitment is absent or differs.
+func VerifyPayloadCommitment(payload any, event map[string]any) (bool, error) {
+	stored := storedCommitmentHash(event, "payload_commitment", "canonical_payload_hash")
+	if stored == "" {
+		return false, nil
+	}
+	commitment, err := PayloadCommitment(payload)
+	if err != nil {
+		return false, err
+	}
+	return commitment["canonical_payload_hash"] == stored, nil
+}
+
+// VerifyMetadataCommitment recomputes the metadata commitment locally and
+// compares it to the value stored on an event.
+func VerifyMetadataCommitment(metadata any, event map[string]any) (bool, error) {
+	stored := storedCommitmentHash(event, "metadata_commitment", "canonical_metadata_hash")
+	if stored == "" {
+		return false, nil
+	}
+	commitment, err := MetadataCommitment(metadata)
+	if err != nil {
+		return false, err
+	}
+	return commitment["canonical_metadata_hash"] == stored, nil
+}
+
+func windowNodeHash(left, right string) (string, error) {
+	return DomainHashHex(ProofstreamDomains["window"], map[string]any{
+		"kind": "node", "left_hash": left, "right_hash": right,
+	})
+}
+
+func checkpointNodeHash(left, right string) (string, error) {
+	return DomainHashHex(ProofstreamDomains["checkpoint"], map[string]any{
+		"kind": "node", "left_hash": left, "right_hash": right,
+	})
+}
+
+// InclusionStep is one node of a window inclusion proof.
+type InclusionStep struct {
+	Side string `json:"side"`
+	Hash string `json:"hash"`
+}
+
+// VerifyInclusionProof folds a window inclusion proof from a leaf up to the
+// window root. Mirrors verify_inclusion_proof in the backend windows.py: a left
+// sibling hashes as node(sibling, current), a right sibling as node(current, sibling).
+func VerifyInclusionProof(leafHash string, proof []InclusionStep, rootHash string) (bool, error) {
+	current := leafHash
+	for _, step := range proof {
+		var err error
+		switch step.Side {
+		case "left":
+			if step.Hash == "" {
+				return false, nil
+			}
+			current, err = windowNodeHash(step.Hash, current)
+		case "right":
+			if step.Hash == "" {
+				return false, nil
+			}
+			current, err = windowNodeHash(current, step.Hash)
+		default:
+			return false, nil
+		}
+		if err != nil {
+			return false, err
+		}
+	}
+	return current == rootHash, nil
+}
+
+// VerifyCheckpointRoot recomputes a checkpoint root from its window hashes and
+// compares. Mirrors checkpoint_root_hash in the backend checkpoints.py: an odd
+// node at any level is promoted unchanged (never duplicated/hashed with itself).
+func VerifyCheckpointRoot(windowHashes []string, expectedRoot string) (bool, error) {
+	if len(windowHashes) == 0 {
+		return false, nil
+	}
+	level := append([]string{}, windowHashes...)
+	for len(level) > 1 {
+		next := make([]string, 0, (len(level)+1)/2)
+		for offset := 0; offset < len(level); offset += 2 {
+			if offset+1 >= len(level) {
+				next = append(next, level[offset]) // promote, do not duplicate
+			} else {
+				h, err := checkpointNodeHash(level[offset], level[offset+1])
+				if err != nil {
+					return false, err
+				}
+				next = append(next, h)
+			}
+		}
+		level = next
+	}
+	return level[0] == expectedRoot, nil
+}
+
+// VerifyCheckpointExtension checks that current continues previous: contiguous
+// sequence (current.from_seq_no == previous.to_seq_no + 1) and back-link
+// (current.previous_checkpoint_hash == previous.checkpoint_hash).
+func VerifyCheckpointExtension(previous, current map[string]any) VerifyReport {
+	problems := make([]string, 0)
+	if asFloat(current["from_seq_no"]) != asFloat(previous["to_seq_no"])+1 {
+		problems = append(problems, "checkpoint does not extend previous (sequence gap)")
+	}
+	if !sameString(current["previous_checkpoint_hash"], previous["checkpoint_hash"]) {
+		problems = append(problems, "checkpoint previous_checkpoint_hash does not match previous")
+	}
+	return VerifyReport{Kind: "checkpoint-extension", OK: len(problems) == 0, Problems: problems}
+}
+
+// VerifyCompleteness proves no events were omitted in [fromSeqNo, toSeqNo]: the
+// sequence numbers must be gap-free and every event's prev_event_hash must equal
+// the previous event's event_hash (the per-stream hash chain).
+func VerifyCompleteness(events []map[string]any, fromSeqNo, toSeqNo int) VerifyReport {
+	problems := make([]string, 0)
+	ordered := append([]map[string]any{}, events...)
+	sort.Slice(ordered, func(i, j int) bool {
+		return asFloat(ordered[i]["seq_no"]) < asFloat(ordered[j]["seq_no"])
+	})
+	gapFree := len(ordered) == toSeqNo-fromSeqNo+1
+	if gapFree {
+		for i, event := range ordered {
+			if int(asFloat(event["seq_no"])) != fromSeqNo+i {
+				gapFree = false
+				break
+			}
+		}
+	}
+	if !gapFree {
+		problems = append(problems, "sequence range is not gap-free")
+	} else {
+		for i := 1; i < len(ordered); i++ {
+			if !sameString(ordered[i]["prev_event_hash"], ordered[i-1]["event_hash"]) {
+				problems = append(problems, fmt.Sprintf(
+					"event chain broken at seq_no %d", int(asFloat(ordered[i]["seq_no"]))))
+				break
+			}
+		}
+	}
+	return VerifyReport{Kind: "completeness", OK: len(problems) == 0, Problems: problems}
+}
+
+func asFloat(v any) float64 {
+	switch n := v.(type) {
+	case float64:
+		return n
+	case int:
+		return float64(n)
+	case int64:
+		return float64(n)
+	case json.Number:
+		f, _ := n.Float64()
+		return f
+	}
+	return 0
+}
+
+func sameString(a, b any) bool {
+	as, aok := a.(string)
+	bs, bok := b.(string)
+	if aok && bok {
+		return as == bs
+	}
+	return a == nil && b == nil
+}
+
+func webhookHeader(headers map[string]string, name string) (string, bool) {
+	for key, value := range headers {
+		if strings.EqualFold(key, name) {
+			return value, true
+		}
+	}
+	return "", false
+}
+
+// VerifyWebhook verifies an inbound webhook delivered by Attesto. It reads the
+// X-Attesto-Timestamp / X-Attesto-Signature headers (case-insensitive), rejects
+// when the timestamp is outside maxSkewS of now, recomputes
+// hmac_sha256(secret, "<ts>." + body), and compares in constant time. Mirrors
+// the backend webhook signing scheme.
+func VerifyWebhook(body []byte, headers map[string]string, secret string, maxSkewS int) bool {
+	return verifyWebhookAt(body, headers, secret, maxSkewS, time.Now().Unix())
+}
+
+func verifyWebhookAt(body []byte, headers map[string]string, secret string, maxSkewS int, now int64) bool {
+	timestamp, okTS := webhookHeader(headers, "x-attesto-timestamp")
+	signature, okSig := webhookHeader(headers, "x-attesto-signature")
+	if !okTS || !okSig {
+		return false
+	}
+	ts, err := strconv.ParseInt(strings.TrimSpace(timestamp), 10, 64)
+	if err != nil {
+		return false
+	}
+	skew := now - ts
+	if skew < 0 {
+		skew = -skew
+	}
+	if skew > int64(maxSkewS) {
+		return false
+	}
+	mac := hmac.New(sha256.New, []byte(secret))
+	mac.Write([]byte(strconv.FormatInt(ts, 10)))
+	mac.Write([]byte("."))
+	mac.Write(body)
+	expected := hex.EncodeToString(mac.Sum(nil))
+	return hmac.Equal([]byte(expected), []byte(signature))
+}
+
 func SignConnectorWebhookPayload(secret string, body []byte, timestamp int64) (string, string) {
 	if timestamp == 0 {
 		timestamp = time.Now().Unix()
@@ -90,6 +506,9 @@ func SignedConnectorWebhookHeaders(secret string, body []byte, timestamp int64)
 }

 func VerifyReceiptOffline(receipt SignedReceipt, publicKeyHex string) VerifyReport {
+	if err := EnsureSelfTest(); err != nil {
+		return VerifyReport{Kind: VerifyReceipt, OK: false, Problems: []string{err.Error()}}
+	}
 	problems := make([]string, 0)
 	hash, err := DomainHashHex(ProofstreamDomains["receipt"], receipt.Payload)
 	if err != nil {
--- a/proofstream_parity_test.go
+++ b/proofstream_parity_test.go
@@ -0,0 +1,203 @@
+package attesto
+
+import (
+	"encoding/json"
+	"errors"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+type parityVectors struct {
+	Accept []struct {
+		ID                   string         `json:"id"`
+		Payload              map[string]any `json:"payload"`
+		CanonicalPayloadHash string         `json:"canonical_payload_hash"`
+	} `json:"accept"`
+	Reject []struct {
+		ID      string         `json:"id"`
+		Payload map[string]any `json:"payload"`
+		Path    string         `json:"path"`
+	} `json:"reject"`
+}
+
+func loadParityVectors(t *testing.T) parityVectors {
+	t.Helper()
+	path := filepath.Join("..", "..", "golden-vectors", "sdk-parity", "canonical-numbers.json")
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("read parity vectors: %v", err)
+	}
+	var v parityVectors
+	if err := json.Unmarshal(raw, &v); err != nil {
+		t.Fatalf("decode parity vectors: %v", err)
+	}
+	return v
+}
+
+func TestParityAcceptCommitmentHashes(t *testing.T) {
+	for _, c := range loadParityVectors(t).Accept {
+		commitment, err := PayloadCommitment(c.Payload)
+		if err != nil {
+			t.Fatalf("%s: PayloadCommitment: %v", c.ID, err)
+		}
+		if commitment["hash_alg"] != "sha256" {
+			t.Errorf("%s: hash_alg %q", c.ID, commitment["hash_alg"])
+		}
+		if commitment["canonical_payload_hash"] != c.CanonicalPayloadHash {
+			t.Errorf("%s: hash %s != %s", c.ID, commitment["canonical_payload_hash"], c.CanonicalPayloadHash)
+		}
+	}
+}
+
+func TestParityAcceptPassPreflight(t *testing.T) {
+	for _, c := range loadParityVectors(t).Accept {
+		if err := AssertCommitmentSafeNumbers(c.Payload, "$"); err != nil {
+			t.Errorf("%s: unexpected preflight error: %v", c.ID, err)
+		}
+	}
+}
+
+func TestParityRejectPaths(t *testing.T) {
+	for _, c := range loadParityVectors(t).Reject {
+		err := AssertCommitmentSafeNumbers(c.Payload, "$")
+		var ue *UnsafeNumberError
+		if !errors.As(err, &ue) {
+			t.Errorf("%s: expected *UnsafeNumberError, got %v", c.ID, err)
+			continue
+		}
+		if ue.Path != c.Path {
+			t.Errorf("%s: path %s != %s", c.ID, ue.Path, c.Path)
+		}
+	}
+}
+
+type receiptParityVectors struct {
+	Cases []struct {
+		ID            string        `json:"id"`
+		PublicKeyHex  string        `json:"public_key_hex"`
+		Receipt       SignedReceipt `json:"receipt"`
+		ExpectOK      bool          `json:"expect_ok"`
+		ExpectProblem []string      `json:"expect_problems"`
+	} `json:"cases"`
+}
+
+func TestParityReceiptVerification(t *testing.T) {
+	path := filepath.Join("..", "..", "golden-vectors", "sdk-parity", "receipts.json")
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("read receipt vectors: %v", err)
+	}
+	var v receiptParityVectors
+	if err := json.Unmarshal(raw, &v); err != nil {
+		t.Fatalf("decode receipt vectors: %v", err)
+	}
+	for _, c := range v.Cases {
+		report := VerifyReceiptOffline(c.Receipt, c.PublicKeyHex)
+		if report.OK != c.ExpectOK {
+			t.Errorf("%s: ok=%v want %v (problems=%v)", c.ID, report.OK, c.ExpectOK, report.Problems)
+		}
+		if len(report.Problems) != len(c.ExpectProblem) {
+			t.Errorf("%s: problems=%v want %v", c.ID, report.Problems, c.ExpectProblem)
+			continue
+		}
+		for i, p := range c.ExpectProblem {
+			if report.Problems[i] != p {
+				t.Errorf("%s: problem[%d]=%q want %q", c.ID, i, report.Problems[i], p)
+			}
+		}
+	}
+}
+
+type inclusionParityVectors struct {
+	Inclusion []struct {
+		ID       string          `json:"id"`
+		LeafHash string          `json:"leaf_hash"`
+		Proof    []InclusionStep `json:"proof"`
+		RootHash string          `json:"root_hash"`
+		ExpectOK bool            `json:"expect_ok"`
+	} `json:"inclusion"`
+	CheckpointRoot []struct {
+		ID           string   `json:"id"`
+		WindowHashes []string `json:"window_hashes"`
+		ExpectedRoot string   `json:"expected_root"`
+		ExpectOK     bool     `json:"expect_ok"`
+	} `json:"checkpoint_root"`
+	CheckpointExtension []struct {
+		ID       string         `json:"id"`
+		Previous map[string]any `json:"previous"`
+		Current  map[string]any `json:"current"`
+		ExpectOK bool           `json:"expect_ok"`
+	} `json:"checkpoint_extension"`
+	Completeness []struct {
+		ID        string           `json:"id"`
+		Events    []map[string]any `json:"events"`
+		FromSeqNo int              `json:"from_seq_no"`
+		ToSeqNo   int              `json:"to_seq_no"`
+		ExpectOK  bool             `json:"expect_ok"`
+	} `json:"completeness"`
+}
+
+func TestParityInclusionAndCheckpoint(t *testing.T) {
+	path := filepath.Join("..", "..", "golden-vectors", "sdk-parity", "inclusion.json")
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("read inclusion vectors: %v", err)
+	}
+	var v inclusionParityVectors
+	if err := json.Unmarshal(raw, &v); err != nil {
+		t.Fatalf("decode inclusion vectors: %v", err)
+	}
+	for _, c := range v.Inclusion {
+		ok, err := VerifyInclusionProof(c.LeafHash, c.Proof, c.RootHash)
+		if err != nil {
+			t.Fatalf("%s: %v", c.ID, err)
+		}
+		if ok != c.ExpectOK {
+			t.Errorf("inclusion %s: ok=%v want %v", c.ID, ok, c.ExpectOK)
+		}
+	}
+	for _, c := range v.CheckpointRoot {
+		ok, err := VerifyCheckpointRoot(c.WindowHashes, c.ExpectedRoot)
+		if err != nil {
+			t.Fatalf("%s: %v", c.ID, err)
+		}
+		if ok != c.ExpectOK {
+			t.Errorf("checkpoint_root %s: ok=%v want %v", c.ID, ok, c.ExpectOK)
+		}
+	}
+	for _, c := range v.CheckpointExtension {
+		report := VerifyCheckpointExtension(c.Previous, c.Current)
+		if report.OK != c.ExpectOK {
+			t.Errorf("extension %s: ok=%v want %v (%v)", c.ID, report.OK, c.ExpectOK, report.Problems)
+		}
+	}
+	for _, c := range v.Completeness {
+		report := VerifyCompleteness(c.Events, c.FromSeqNo, c.ToSeqNo)
+		if report.OK != c.ExpectOK {
+			t.Errorf("completeness %s: ok=%v want %v (%v)", c.ID, report.OK, c.ExpectOK, report.Problems)
+		}
+	}
+}
+
+func TestParityVerifyPayloadCommitment(t *testing.T) {
+	for _, c := range loadParityVectors(t).Accept {
+		commitment, err := PayloadCommitment(c.Payload)
+		if err != nil {
+			t.Fatalf("%s: PayloadCommitment: %v", c.ID, err)
+		}
+		stored := map[string]any{}
+		for k, v := range commitment {
+			stored[k] = v
+		}
+		event := map[string]any{"envelope": map[string]any{"payload_commitment": stored}}
+		ok, err := VerifyPayloadCommitment(c.Payload, event)
+		if err != nil || !ok {
+			t.Errorf("%s: verify match ok=%v err=%v", c.ID, ok, err)
+		}
+		bad, err := VerifyPayloadCommitment(map[string]any{"tampered": float64(1)}, event)
+		if err != nil || bad {
+			t.Errorf("%s: tampered verify bad=%v err=%v", c.ID, bad, err)
+		}
+	}
+}
--- a/selftest.go
+++ b/selftest.go
@@ -0,0 +1,72 @@
+package attesto
+
+import (
+	_ "embed"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"sync"
+)
+
+// [P1.10] Trimmed parity vectors vendored into the package; regenerated from
+// golden-vectors/sdk-parity (do not hand-edit).
+//
+//go:embed selftest_vectors.json
+var selftestVectors []byte
+
+// ErrSelfTest wraps a failed vendored parity self-test: this install's hashing
+// diverges from the pinned cross-language vectors (corrupted package or broken
+// runtime). The SDK fails closed rather than produce wrong evidence.
+var ErrSelfTest = errors.New("attesto self-test failed")
+
+var (
+	selftestOnce sync.Once
+	selftestErr  error
+)
+
+func runSelfTest(raw []byte) error {
+	var vectors struct {
+		Commitment struct {
+			Payload              map[string]any `json:"payload"`
+			CanonicalPayloadHash string         `json:"canonical_payload_hash"`
+		} `json:"commitment"`
+		Receipt struct {
+			Payload     map[string]any `json:"payload"`
+			ReceiptHash string         `json:"receipt_hash"`
+		} `json:"receipt"`
+		Inclusion struct {
+			LeafHash string          `json:"leaf_hash"`
+			Proof    []InclusionStep `json:"proof"`
+			RootHash string          `json:"root_hash"`
+		} `json:"inclusion"`
+	}
+	if err := json.Unmarshal(raw, &vectors); err != nil {
+		return fmt.Errorf("%w: vendored vectors unreadable: %v", ErrSelfTest, err)
+	}
+	canonical, err := CanonicalJSON(vectors.Commitment.Payload)
+	if err != nil {
+		return fmt.Errorf("%w: %v", ErrSelfTest, err)
+	}
+	if SHA256Hex(canonical) != vectors.Commitment.CanonicalPayloadHash {
+		return fmt.Errorf("%w: commitment hash diverged from vendored vector", ErrSelfTest)
+	}
+	receiptHash, err := DomainHashHex(ProofstreamDomains["receipt"], vectors.Receipt.Payload)
+	if err != nil {
+		return fmt.Errorf("%w: %v", ErrSelfTest, err)
+	}
+	if receiptHash != vectors.Receipt.ReceiptHash {
+		return fmt.Errorf("%w: receipt domain-hash diverged from vendored vector", ErrSelfTest)
+	}
+	ok, err := VerifyInclusionProof(
+		vectors.Inclusion.LeafHash, vectors.Inclusion.Proof, vectors.Inclusion.RootHash)
+	if err != nil || !ok {
+		return fmt.Errorf("%w: inclusion fold diverged from vendored vector", ErrSelfTest)
+	}
+	return nil
+}
+
+// EnsureSelfTest runs the vendored parity self-test once per process (cached).
+func EnsureSelfTest() error {
+	selftestOnce.Do(func() { selftestErr = runSelfTest(selftestVectors) })
+	return selftestErr
+}
--- a/selftest_test.go
+++ b/selftest_test.go
@@ -0,0 +1,26 @@
+package attesto
+
+import (
+	"bytes"
+	"errors"
+	"testing"
+)
+
+func TestSelfTestPassesOnVendoredVectors(t *testing.T) {
+	if err := EnsureSelfTest(); err != nil {
+		t.Fatalf("self-test failed on shipped vectors: %v", err)
+	}
+}
+
+func TestCorruptedVendoredVectorFailsClosed(t *testing.T) {
+	corrupted := bytes.Replace(
+		selftestVectors,
+		[]byte(`"canonical_payload_hash": "`),
+		[]byte(`"canonical_payload_hash": "0`),
+		1,
+	)
+	err := runSelfTest(corrupted)
+	if !errors.Is(err, ErrSelfTest) {
+		t.Fatalf("expected ErrSelfTest, got %v", err)
+	}
+}
--- a/selftest_vectors.json
+++ b/selftest_vectors.json
@@ -0,0 +1,58 @@
+{
+ "note": "Trimmed parity self-test set vendored into each SDK package; regenerated from golden-vectors/sdk-parity (do not hand-edit).",
+ "commitment": {
+  "payload": {
+   "b": 2,
+   "a": 1,
+   "nested": {
+    "z": [
+     1,
+     2,
+     3
+    ],
+    "flag": true
+   }
+  },
+  "canonical_payload_hash": "8b2252e6632801faa71c8eb4a597bfeaba385face3ddef30b7eb636787902304"
+ },
+ "receipt": {
+  "payload": {
+   "event_hash": "cd7753e1bc862729d4de6d2e9d9c0942830e557cf539ebcbf00bf9b4cd6a62a9",
+   "event_id": "evt_golden_2",
+   "issued_at": "2026-06-05T20:59:04.000Z",
+   "prev_event_hash": "731f8a0a3cc6ea2ca00bb26dca8f721da34e1328750f2e16a32f7bf7b36d7264",
+   "protocol": "ATTESTO-PROOFSTREAM-001",
+   "protocol_version": "0.1-alpha",
+   "seq_no": 2,
+   "signer": {
+    "alg": "ed25519",
+    "key_epoch": "golden-key-2026-06",
+    "kid": "golden-key-2026-06"
+   },
+   "stream_event_id": "sev_golden_2",
+   "stream_head_hash": "140142e46eb7cbe17db99c717666cb5a038a858feaff7cc26b78d10c8868da51",
+   "stream_id": "str_golden",
+   "system_id": "sys_golden",
+   "tenant_id": "tnt_golden"
+  },
+  "receipt_hash": "4f72f15fa4d07c9a83baa908f6168e27beeb1d4c9984f70e52f67ff6c380ccb2"
+ },
+ "inclusion": {
+  "leaf_hash": "7973a148f766058042177a3507c5baa4757c6159c91049cbc42f60f138715072",
+  "proof": [
+   {
+    "side": "right",
+    "hash": "2faac607f33011ec3bdf305e01e36d1257bb226868cec5df4bfecbb8a552b48b"
+   },
+   {
+    "side": "right",
+    "hash": "9ff585ea4fd08983d242fd3b73144e800b07a4ae86324d4e0f0fb2f70933b26f"
+   },
+   {
+    "side": "right",
+    "hash": "6977f0ace2809f289002e6600967de240acc3dcdcf62aa4e078c56c10f57d381"
+   }
+  ],
+  "root_hash": "37a6a0d69e0951df3827205cfb8440c84d5d60c729b4c00a0d9460361923a18b"
+ }
+}
--- a/testdata/APSProvenance.abi.json
+++ b/testdata/APSProvenance.abi.json
@@ -0,0 +1,172 @@
+[
+  {
+    "inputs": [],
+    "stateMutability": "nonpayable",
+    "type": "constructor"
+  },
+  {
+    "inputs": [
+      {
+        "internalType": "string",
+        "name": "batchId",
+        "type": "string"
+      }
+    ],
+    "name": "AlreadyCommitted",
+    "type": "error"
+  },
+  {
+    "inputs": [],
+    "name": "EmptyBatchId",
+    "type": "error"
+  },
+  {
+    "inputs": [],
+    "name": "NotOwner",
+    "type": "error"
+  },
+  {
+    "anonymous": false,
+    "inputs": [
+      {
+        "indexed": true,
+        "internalType": "string",
+        "name": "batchId",
+        "type": "string"
+      },
+      {
+        "indexed": true,
+        "internalType": "bytes32",
+        "name": "merkleRoot",
+        "type": "bytes32"
+      },
+      {
+        "indexed": false,
+        "internalType": "uint32",
+        "name": "runCount",
+        "type": "uint32"
+      },
+      {
+        "indexed": false,
+        "internalType": "string",
+        "name": "model",
+        "type": "string"
+      },
+      {
+        "indexed": false,
+        "internalType": "uint64",
+        "name": "blockTimestamp",
+        "type": "uint64"
+      }
+    ],
+    "name": "RootCommitted",
+    "type": "event"
+  },
+  {
+    "inputs": [
+      {
+        "internalType": "uint256",
+        "name": "",
+        "type": "uint256"
+      }
+    ],
+    "name": "batchIds",
+    "outputs": [
+      {
+        "internalType": "string",
+        "name": "",
+        "type": "string"
+      }
+    ],
+    "stateMutability": "view",
+    "type": "function"
+  },
+  {
+    "inputs": [
+      {
+        "internalType": "string",
+        "name": "batchId",
+        "type": "string"
+      },
+      {
+        "internalType": "bytes32",
+        "name": "merkleRoot",
+        "type": "bytes32"
+      },
+      {
+        "internalType": "uint32",
+        "name": "runCount",
+        "type": "uint32"
+      },
+      {
+        "internalType": "string",
+        "name": "model",
+        "type": "string"
+      }
+    ],
+    "name": "commitRoot",
+    "outputs": [],
+    "stateMutability": "nonpayable",
+    "type": "function"
+  },
+  {
+    "inputs": [],
+    "name": "getBatchCount",
+    "outputs": [
+      {
+        "internalType": "uint256",
+        "name": "",
+        "type": "uint256"
+      }
+    ],
+    "stateMutability": "view",
+    "type": "function"
+  },
+  {
+    "inputs": [
+      {
+        "internalType": "string",
+        "name": "batchId",
+        "type": "string"
+      }
+    ],
+    "name": "getCommitment",
+    "outputs": [
+      {
+        "internalType": "bytes32",
+        "name": "merkleRoot",
+        "type": "bytes32"
+      },
+      {
+        "internalType": "uint32",
+        "name": "runCount",
+        "type": "uint32"
+      },
+      {
+        "internalType": "string",
+        "name": "model",
+        "type": "string"
+      },
+      {
+        "internalType": "uint64",
+        "name": "blockTimestamp",
+        "type": "uint64"
+      }
+    ],
+    "stateMutability": "view",
+    "type": "function"
+  },
+  {
+    "inputs": [],
+    "name": "owner",
+    "outputs": [
+      {
+        "internalType": "address",
+        "name": "",
+        "type": "address"
+      }
+    ],
+    "stateMutability": "view",
+    "type": "function"
+  }
+]
--- a/types.go
+++ b/types.go
@@ -6,6 +6,10 @@ type M map[string]any

 type RequestOptions struct {
 	IdempotencyKey string
+	// SkipPreflight disables the client-side commitment number preflight, which
+	// rejects non-integer / out-of-range numbers locally before LogEvent /
+	// LogEvents sends them. Default false: the preflight runs.
+	SkipPreflight bool
 }

 type StreamCreateInput struct {
--- a/version.go
+++ b/version.go
@@ -1,8 +1,11 @@
 package attesto

 const (
-	SDKVersion           = "0.2.0"
+	SDKVersion           = "0.4.0"
 	DefaultBaseURL       = "https://verify.attesto.eu"
 	ProofstreamProtocol  = "ATTESTO-PROOFSTREAM-001"
 	ProtocolVersionAlpha = "0.1-alpha"
+	// ProtocolHandshake is sent as X-Attesto-Protocol on every request; the
+	// backend answers 426 when it speaks a different protocol generation.
+	ProtocolHandshake = ProofstreamProtocol + "/" + ProtocolVersionAlpha
 )
--- a/webhook_parity_test.go
+++ b/webhook_parity_test.go
@@ -0,0 +1,65 @@
+package attesto
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+type webhookParityVectors struct {
+	Cases []struct {
+		ID       string            `json:"id"`
+		Secret   string            `json:"secret"`
+		Body     string            `json:"body"`
+		Headers  map[string]string `json:"headers"`
+		Now      int64             `json:"now"`
+		MaxSkewS int               `json:"max_skew_s"`
+		ExpectOK bool              `json:"expect_ok"`
+	} `json:"cases"`
+}
+
+func TestParityWebhookVerification(t *testing.T) {
+	path := filepath.Join("..", "..", "golden-vectors", "sdk-parity", "webhook.json")
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("read webhook vectors: %v", err)
+	}
+	var v webhookParityVectors
+	if err := json.Unmarshal(raw, &v); err != nil {
+		t.Fatalf("decode webhook vectors: %v", err)
+	}
+	for _, c := range v.Cases {
+		ok := verifyWebhookAt([]byte(c.Body), c.Headers, c.Secret, c.MaxSkewS, c.Now)
+		if ok != c.ExpectOK {
+			t.Errorf("webhook %s: ok=%v want %v", c.ID, ok, c.ExpectOK)
+		}
+	}
+}
+
+func TestWebhookHeaderLookupIsCaseInsensitive(t *testing.T) {
+	path := filepath.Join("..", "..", "golden-vectors", "sdk-parity", "webhook.json")
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("read webhook vectors: %v", err)
+	}
+	var v webhookParityVectors
+	if err := json.Unmarshal(raw, &v); err != nil {
+		t.Fatalf("decode webhook vectors: %v", err)
+	}
+	for _, c := range v.Cases {
+		if c.ID != "valid" {
+			continue
+		}
+		lowered := map[string]string{}
+		for key, value := range c.Headers {
+			lowered[key] = value
+		}
+		// Re-key with different casing.
+		lowered["X-ATTESTO-TIMESTAMP"] = lowered["X-Attesto-Timestamp"]
+		delete(lowered, "X-Attesto-Timestamp")
+		if !verifyWebhookAt([]byte(c.Body), lowered, c.Secret, c.MaxSkewS, c.Now) {
+			t.Error("case-insensitive header lookup failed")
+		}
+	}
+}