diff --git a/attestotest/server.go b/attestotest/server.go
index d9ccf16..246627c 100644
--- a/attestotest/server.go
+++ b/attestotest/server.go
@@ -236,6 +236,19 @@ func orEmpty(v any) any {
 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()
 
@@ -323,6 +336,7 @@ func (s *Server) append(stream attesto.M, body attesto.M) attesto.M {
 		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,
diff --git a/cmd/attesto/report_test.go b/cmd/attesto/report_test.go
index 780b2ae..fedc420 100644
--- a/cmd/attesto/report_test.go
+++ b/cmd/attesto/report_test.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+	"fmt"
 	"strings"
 	"testing"
 
@@ -27,8 +28,9 @@ func TestArticle12ReportWordingAndStructure(t *testing.T) {
 		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: "e", EventType: decision.EventType(), Payload: payload,
+			SourceRef: fmt.Sprintf("e-%d", i), EventType: decision.EventType(), Payload: payload,
 		}); err != nil {
 			t.Fatal(err)
 		}
diff --git a/heads.go b/heads.go
index 27d4332..6464281 100644
--- a/heads.go
+++ b/heads.go
@@ -144,6 +144,11 @@ func (s *FileHeadStore) Set(streamID string, seqNo int64, eventHash string) {
 // 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{
diff --git a/heads_test.go b/heads_test.go
index a6137e3..f50e0ca 100644
--- a/heads_test.go
+++ b/heads_test.go
@@ -80,3 +80,20 @@ func TestFileHeadStorePersistsAndIs0600(t *testing.T) {
 		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")
+	}
+}