diff --git a/Server/api/auth_characterization_test.go b/Server/api/auth_characterization_test.go
index 859b6a62..cffb1259 100644
--- a/Server/api/auth_characterization_test.go
+++ b/Server/api/auth_characterization_test.go
@@ -449,23 +449,22 @@ func TestAuthCharacterization_RegisterPolicyAndFailurePaths(t *testing.T) {
 			t.Error("user row exists after a failed insert")
 		}
 	})
-	t.Run("session insert fails after the user is committed -> 500", func(t *testing.T) {
+	t.Run("session insert fails -> 500, nothing committed", func(t *testing.T) {
 		database := newAuthTestDB(t)
 		router := buildAuthRouter(database, auth.NewRateLimiter())
 		code := seedInvite(t, database)
 		failWrite(t, database, "INSERT", "sessions")
 		rr := send(t, router, http.MethodPost, "/api/v1/auth/register", "", "", "", body(code))
-		wantErr(t, rr, http.StatusInternalServerError, "INTERNAL_ERROR", "failed to create session")
-		// known: the account and the invite use are already committed when the
-		// session insert fails, so the caller sees a 500 for a registration
-		// that succeeded — a retry gets "invalid invite or credentials" while
-		// a login with the same password works (ledger OC-0376).
-		if userByName(t, database, "fresh") == nil {
-			t.Error("user row missing: this row pins the partial-success behaviour, which has changed")
+		// OC-0376 (fixed in B3-9): the first session is inserted inside the
+		// registration transaction, so a store fault leaves no half-registered
+		// account and does not burn the invite — the caller simply retries.
+		if userByName(t, database, "fresh") != nil {
+			t.Error("user row exists after the session insert failed")
 		}
-		if n := inviteUseCount(t, database, code); n != 1 {
-			t.Errorf("invite use_count = %d, want 1 (pinned partial success)", n)
+		if n := inviteUseCount(t, database, code); n != 0 {
+			t.Errorf("invite use_count = %d, want 0 (transaction rolled back)", n)
 		}
+		wantErr(t, rr, http.StatusInternalServerError, "INTERNAL_ERROR", "registration failed — please try again")
 	})
 }
 
diff --git a/Server/db/auth_queries.go b/Server/db/auth_queries.go
index a06b9325..94fab803 100644
--- a/Server/db/auth_queries.go
+++ b/Server/db/auth_queries.go
@@ -71,9 +71,13 @@ func (d *DB) CreateOwnerIfEmpty(ctx context.Context, username, passwordHash stri
 	return uid, nil
 }
 
-// CreateUserWithInvite atomically consumes an invite and creates the user in
-// the same transaction so a failed registration does not burn the invite.
-func (d *DB) CreateUserWithInvite(ctx context.Context, username, passwordHash string, roleID int, inviteCode string) (int64, error) {
+// CreateUserWithInvite atomically consumes an invite, creates the user and
+// inserts the account's first session in one transaction, so a failure at any
+// step — the session insert included (OC-0376) — leaves no half-registered
+// account and does not burn the invite. sessionTokenHash must already be
+// hashed. The H-6 session cap needs no eviction here: the user has no sessions
+// yet.
+func (d *DB) CreateUserWithInvite(ctx context.Context, username, passwordHash string, roleID int, inviteCode, sessionTokenHash, device, ip string) (int64, error) {
 	tx, err := d.writer.BeginTx(ctx, nil)
 	if err != nil {
 		return 0, fmt.Errorf("CreateUserWithInvite begin: %w", err)
@@ -114,6 +118,9 @@ func (d *DB) CreateUserWithInvite(ctx context.Context, username, passwordHash st
 	if err != nil {
 		return 0, fmt.Errorf("CreateUserWithInvite last insert id: %w", err)
 	}
+	if _, err := insertSession(ctx, d.q.WithTx(tx), uid, sessionTokenHash, device, ip); err != nil {
+		return 0, fmt.Errorf("CreateUserWithInvite create session: %w", err)
+	}
 	if err := tx.Commit(); err != nil {
 		return 0, fmt.Errorf("CreateUserWithInvite commit: %w", err)
 	}
@@ -254,9 +261,15 @@ func (d *DB) CreateSession(ctx context.Context, userID int64, tokenHash, device,
 			"user_id", userID, "err", err)
 	}
 
+	return insertSession(ctx, d.q, userID, tokenHash, device, ip)
+}
+
+// insertSession inserts one session row through q — d.q, or d.q.WithTx(tx)
+// when the row must commit with other writes (CreateUserWithInvite).
+func insertSession(ctx context.Context, q *dbgen.Queries, userID int64, tokenHash, device, ip string) (int64, error) {
 	expiresAt := time.Now().Add(sessionTTL).UTC().Format(sessionTimeLayout)
 	deviceCopy, ipCopy := device, ip
-	res, err := d.q.InsertSession(ctx, dbgen.InsertSessionParams{
+	res, err := q.InsertSession(ctx, dbgen.InsertSessionParams{
 		UserID:    userID,
 		Token:     tokenHash,
 		Device:    &deviceCopy,
diff --git a/Server/db/coverage_boost_test.go b/Server/db/coverage_boost_test.go
index 34ef4b17..6c1733ac 100644
--- a/Server/db/coverage_boost_test.go
+++ b/Server/db/coverage_boost_test.go
@@ -756,7 +756,7 @@ func TestCreateUserWithInvite_Success(t *testing.T) {
 		t.Fatalf("CreateInvite: %v", err)
 	}
 
-	uid, err := database.CreateUserWithInvite(context.Background(), "newuser", "hash", 4, code)
+	uid, err := database.CreateUserWithInvite(context.Background(), "newuser", "hash", 4, code, "sess-newuser", "test", "127.0.0.1")
 	if err != nil {
 		t.Fatalf("CreateUserWithInvite: %v", err)
 	}
@@ -769,12 +769,16 @@ func TestCreateUserWithInvite_Success(t *testing.T) {
 	if inv == nil || inv.Uses != 1 {
 		t.Errorf("invite uses = %v, want 1", inv)
 	}
+	// The first session commits with the account (OC-0376).
+	if sess, err := database.GetSessionByTokenHash(context.Background(), "sess-newuser"); err != nil || sess == nil || sess.UserID != uid {
+		t.Errorf("session = %+v, %v; want a session for user %d", sess, err, uid)
+	}
 }
 
 func TestCreateUserWithInvite_InvalidCode(t *testing.T) {
 	database := openMigratedMemory(t)
 
-	_, err := database.CreateUserWithInvite(context.Background(), "baduser", "hash", 4, "nonexistent-code")
+	_, err := database.CreateUserWithInvite(context.Background(), "baduser", "hash", 4, "nonexistent-code", "sess-bad", "test", "127.0.0.1")
 	if err == nil {
 		t.Error("expected error for invalid invite code")
 	}
@@ -787,7 +791,7 @@ func TestCreateUserWithInvite_RevokedInvite(t *testing.T) {
 	code, _ := database.CreateInvite(context.Background(), creatorID, 0, nil)
 	_ = database.RevokeInvite(context.Background(), code)
 
-	_, err := database.CreateUserWithInvite(context.Background(), "revokeduser", "hash", 4, code)
+	_, err := database.CreateUserWithInvite(context.Background(), "revokeduser", "hash", 4, code, "sess-revoked", "test", "127.0.0.1")
 	if err == nil {
 		t.Error("expected error for revoked invite")
 	}
@@ -801,7 +805,7 @@ func TestCreateUserWithInvite_ExpiredInvite(t *testing.T) {
 	pastTime := time.Now().Add(-1 * time.Hour)
 	code, _ := database.CreateInvite(context.Background(), creatorID, 0, &pastTime)
 
-	_, err := database.CreateUserWithInvite(context.Background(), "expireduser", "hash", 4, code)
+	_, err := database.CreateUserWithInvite(context.Background(), "expireduser", "hash", 4, code, "sess-expired", "test", "127.0.0.1")
 	if err == nil {
 		t.Error("expected error for expired invite")
 	}
diff --git a/Server/service/auth.go b/Server/service/auth.go
index c64a275b..6ab5f41b 100644
--- a/Server/service/auth.go
+++ b/Server/service/auth.go
@@ -296,9 +296,16 @@ func (s *AuthService) Register(ctx context.Context, in RegisterInput) (*AuthResu
 		return nil, ErrPasswordHash
 	}
 
-	// Atomically consume the invite and create the user so failed
-	// registrations do not burn a valid invite code.
-	uid, err := s.st.CreateUserWithInvite(ctx, in.Username, hash, int(permissions.MemberRoleID), in.InviteCode)
+	// The session token exists before the transaction so the account, the
+	// invite use and the first session commit together: a fault at any step
+	// — the session insert included — rolls the whole registration back and
+	// burns nothing (OC-0376).
+	token, err := auth.GenerateToken()
+	if err != nil {
+		return nil, ErrSessionIssue
+	}
+	uid, err := s.st.CreateUserWithInvite(ctx, in.Username, hash, int(permissions.MemberRoleID), in.InviteCode,
+		auth.HashToken(token), in.Device, in.IP)
 	if err != nil {
 		// UNIQUE constraint violation → duplicate username → 400.
 		// Any other DB error → 500.
@@ -317,12 +324,6 @@ func (s *AuthService) Register(ctx context.Context, in RegisterInput) (*AuthResu
 	db.WriteAudit(context.WithoutCancel(ctx), s.st, uid, "user_register", "user", uid,
 		"new account created via invite")
 
-	// Issue session.
-	token, err := issueSession(ctx, s.st, uid, in.Device, in.IP)
-	if err != nil {
-		return nil, ErrSessionIssue
-	}
-
 	user, err := s.st.GetUserByID(ctx, uid)
 	if err != nil || user == nil {
 		slog.Error("failed to fetch user after registration", "user_id", uid, "error", err)
diff --git a/Server/service/datastore.go b/Server/service/datastore.go
index 5cb1ab52..e06057ed 100644
--- a/Server/service/datastore.go
+++ b/Server/service/datastore.go
@@ -81,7 +81,7 @@ type Store interface {
 	GetUserByUsername(ctx context.Context, username string) (*db.User, error)
 	CreateUser(ctx context.Context, username, passwordHash string, roleID int) (int64, error)
 	CreateOwnerIfEmpty(ctx context.Context, username, passwordHash string, roleID int) (int64, error)
-	CreateUserWithInvite(ctx context.Context, username, passwordHash string, roleID int, inviteCode string) (int64, error)
+	CreateUserWithInvite(ctx context.Context, username, passwordHash string, roleID int, inviteCode, sessionTokenHash, device, ip string) (int64, error)
 	UpdateUserProfile(ctx context.Context, userID int64, username string, avatar, displayName, about *string) error
 	UpdateUserCustomStatus(ctx context.Context, userID int64, customStatus *string) error
 	UpdateUserPassword(ctx context.Context, userID int64, newPasswordHash string) error