Add account balance anchors

internal/app/app_test.go

@@ -60,6 +60,64 @@ func seed(t *testing.T, a *App, s State) State {
 	return result.State
 }
 
+func TestSaveAccountClearsStaleBalanceAnchorOnIdentityChange(t *testing.T) {
+	cases := []struct {
+		name   string
+		change func(*domain.Account)
+		clear  bool
+	}{
+		{
+			name: "currency",
+			change: func(account *domain.Account) {
+				account.Currency = "USD"
+			},
+			clear: true,
+		},
+		{
+			name: "external account",
+			change: func(account *domain.Account) {
+				account.ExternalAccountID = "new_uid"
+			},
+			clear: true,
+		},
+		{
+			name: "display name",
+			change: func(account *domain.Account) {
+				account.DisplayName = "Renamed"
+			},
+			clear: false,
+		},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			a, s := testApp(t)
+			anchored := s.Data.Accounts[0]
+			anchored.ExternalAccountID = "old_uid"
+			anchored.AnchorBalance = "100.00"
+			anchored.AnchorDate = "2026-09-10"
+			var err error
+			s, err = a.Mutate(context.Background(), s.Revision, func(d *domain.Dataset) error {
+				return SaveAccount(d, anchored)
+			})
+			if err != nil {
+				t.Fatal(err)
+			}
+			changed := anchored
+			tc.change(&changed)
+			s, err = a.Mutate(context.Background(), s.Revision, func(d *domain.Dataset) error {
+				return SaveAccount(d, changed)
+			})
+			if err != nil {
+				t.Fatal(err)
+			}
+			got := s.Data.Accounts[0]
+			if tc.clear != (got.AnchorBalance == "" && got.AnchorDate == "") {
+				t.Fatalf("anchor after %s change: balance=%q date=%q", tc.name, got.AnchorBalance, got.AnchorDate)
+			}
+		})
+	}
+}
+
 // A released binary wrote include_amount into config.toml. Refusing it on
 // startup made every upgraded deployment crash-loop against its own settings
 // file, so a retired key must load and then disappear on the next save.

internal/app/import.go

@@ -882,6 +882,7 @@ func (a *App) Sync(ctx context.Context) (State, error) {
 		}
 		s = result.State
 		a.ops.AccountSync[account.ID] = now.Format(time.RFC3339)
+		s = a.anchorAccount(ctx, s, account, to)
 	}
 	a.ops.SyncError = strings.Join(failures, "; ")
 	a.ops.SyncRetryAt = ""
@@ -897,6 +898,66 @@ func (a *App) Sync(ctx context.Context) (State, error) {
 	return a.snapshot(ctx)
 }
 
+// anchorAccount fixes a connected cash account's start balance after its first
+// successful sync: the bank's booked (CLBD) balance is captured once, verbatim,
+// with the day it was true, so a date-windowed history still yields the real
+// balance — the money from before the window is derived as the anchor less
+// every movement booked through the anchor date, and an older import later
+// corrects that derivation by itself. The balance is fetched after the
+// transactions to minimize the gap between the two reads. Banks supply booking
+// dates rather than exact times, so the anchor day is deliberately treated as
+// one completed booked state. Every failure leaves the anchor unset for the
+// next sync to retry; a missing CLBD figure is such a failure, because an
+// available or expected balance includes pending amounts that have no booked
+// fact to subtract.
+func (a *App) anchorAccount(ctx context.Context, s State, account domain.Account, today string) State {
+	if account.Investing() || account.AnchorDate != "" || account.ExternalAccountID == "" {
+		return s
+	}
+	balances, err := a.bank.Balances(ctx, account.ExternalAccountID)
+	if err != nil {
+		return s
+	}
+	var selected banking.Balance
+	anchorDate := ""
+	for _, balance := range balances {
+		if balance.Type != "CLBD" || balance.Currency != account.Currency {
+			continue
+		}
+		date := balance.ReferenceDate
+		if date == "" {
+			date = today
+		} else if _, e := time.Parse("2006-01-02", date); e != nil || date > today {
+			continue
+		}
+		if date < anchorDate {
+			continue
+		}
+		// Two different booked figures for the same account, currency and
+		// reference day are ambiguous. Do not let response order decide money.
+		if date == anchorDate && anchorDate != "" && balance.Amount != selected.Amount {
+			return s
+		}
+		selected, anchorDate = balance, date
+	}
+	if anchorDate == "" {
+		return s
+	}
+	data := domain.Clone(s.Data)
+	for i := range data.Accounts {
+		if data.Accounts[i].ID != account.ID {
+			continue
+		}
+		data.Accounts[i].AnchorBalance = selected.Amount
+		data.Accounts[i].AnchorDate = anchorDate
+		if next, e := a.commit(ctx, s.Revision, data); e == nil {
+			return next
+		}
+		return s
+	}
+	return s
+}
+
 // syncInterval is how often connected accounts synchronize on their own. Twice
 // a day halves how long a booking can sit unseen while staying inside Enable
 // Banking's documented background allowance of roughly four fetches per day per

internal/app/manage.go

@@ -61,6 +61,12 @@ func SaveAccount(d *domain.Dataset, v domain.Account) error {
 	}
 	for i, x := range d.Accounts {
 		if x.ID == v.ID {
+			// A balance belongs to the account identity and currency that the
+			// bank reported. Changing either makes the captured figure stale;
+			// clear it so the next connected sync can capture a matching one.
+			if x.Currency != v.Currency || x.ExternalAccountID != v.ExternalAccountID {
+				v.AnchorBalance, v.AnchorDate = "", ""
+			}
 			d.Accounts[i] = v
 			return nil
 		}

internal/app/sync_test.go

@@ -17,8 +17,9 @@ import (
 )
 
 type bankScenario struct {
-	session banking.Session
-	fail    bool
+	session  banking.Session
+	fail     bool
+	balances []banking.Balance
 }
 
 func (b *bankScenario) Authorize(context.Context, string, string, string, string) (string, error) {
@@ -41,6 +42,9 @@ func (b *bankScenario) Status(context.Context, string) (banking.SessionStatus, e
 	return status, nil
 }
 func (b *bankScenario) Balances(context.Context, string) ([]banking.Balance, error) {
+	if b.balances != nil {
+		return b.balances, nil
+	}
 	return []banking.Balance{{Amount: "100.00", Currency: "EUR", Type: "CLBD"}}, nil
 }
 func (b *bankScenario) Transactions(_ context.Context, a domain.Account, from, to string, _ bool) ([]domain.Facts, error) {
@@ -83,6 +87,53 @@ func TestSyncRestoresSavedConsentBindingsAndDoesNotDuplicateFacts(t *testing.T)
 		t.Fatal("provider failure was not isolated from canonical data")
 	}
 }
+
+// The first successful sync fixes the start balance from the bank's booked
+// figure only: an available balance includes pending amounts with no booked
+// fact to subtract, and a later balance change must never move an anchor that
+// has been set — the anchor is the day a figure was true, not a mirror.
+func TestSyncAnchorsBalanceOnceFromBookedFigureOnly(t *testing.T) {
+	a, s := testApp(t)
+	account := s.Data.Accounts[0]
+	account.ExternalAccountID = "provider_uid"
+	provider := &bankScenario{
+		session:  banking.Session{ID: "session", ValidUntil: time.Now().Add(24 * time.Hour).Format(time.RFC3339), Accounts: []domain.Account{account}},
+		balances: []banking.Balance{{Amount: "999.99", Currency: "EUR", Type: "ITAV"}},
+	}
+	a.bank = provider
+	a.ops.Sessions = []banking.Session{provider.session}
+	if err := a.saveOps(); err != nil {
+		t.Fatal(err)
+	}
+	unbooked, err := a.Sync(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := unbooked.Data.Accounts[0]; got.AnchorBalance != "" || got.AnchorDate != "" {
+		t.Fatalf("available-only balance was anchored: %+v", got)
+	}
+	yesterday := time.Now().UTC().AddDate(0, 0, -1).Format("2006-01-02")
+	older := time.Now().UTC().AddDate(0, 0, -2).Format("2006-01-02")
+	provider.balances = append(provider.balances,
+		banking.Balance{Amount: "240.00", Currency: "EUR", Type: "CLBD", ReferenceDate: older},
+		banking.Balance{Amount: "250.00", Currency: "EUR", Type: "CLBD", ReferenceDate: yesterday},
+	)
+	anchored, err := a.Sync(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := anchored.Data.Accounts[0]; got.AnchorBalance != "250.00" || got.AnchorDate != yesterday {
+		t.Fatalf("booked balance was not anchored at its reference day: %+v", got)
+	}
+	provider.balances = []banking.Balance{{Amount: "300.00", Currency: "EUR", Type: "CLBD", ReferenceDate: yesterday}}
+	retained, err := a.Sync(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !reflect.DeepEqual(anchored.Data, retained.Data) {
+		t.Fatal("a later balance moved an existing anchor")
+	}
+}
 func TestReconnectReplacesOldConsentWithoutDuplicatingLocalAccount(t *testing.T) {
 	a, s := testApp(t)
 	account := s.Data.Accounts[0]
@@ -196,9 +247,16 @@ func TestSyncSessionRateLimitPreservesBindingsAndRecovers(t *testing.T) {
 		failures: map[string]error{},
 	}
 	a.bank = b
+	first, err := a.Sync(ctx)
+	if err != nil || len(first.Data.Transactions) != 4 {
+		t.Fatalf("initial sync: transactions=%d, error=%v, sync error=%s", len(first.Data.Transactions), err, first.Status.SyncError)
+	}
+	// The first successful sync also anchors each account's balance; a second
+	// sync reaches the steady state where the session bindings have absorbed
+	// the anchored accounts and nothing changes any more.
 	before, err := a.Sync(ctx)
-	if err != nil || len(before.Data.Transactions) != 4 {
-		t.Fatalf("initial sync: transactions=%d, error=%v, sync error=%s", len(before.Data.Transactions), err, before.Status.SyncError)
+	if err != nil || !reflect.DeepEqual(first.Data, before.Data) {
+		t.Fatalf("steady-state sync changed canonical data: %v", err)
 	}
 	old := time.Now().Add(-48 * time.Hour).UTC().Format(time.RFC3339)
 	a.ops.LastSync = old
@@ -267,9 +325,19 @@ func TestSyncMissingMembershipStillRejectsAccount(t *testing.T) {
 	if len(b.accounts) != 1 || b.accounts[0].ID != "other" || a.ops.AccountSync[s.Data.Accounts[0].ID] != last || a.ops.LastSync != last {
 		t.Fatal("missing member was fetched or advanced its cursor, or valid member was skipped")
 	}
-	if !reflect.DeepEqual(before.Accounts, after.Data.Accounts) || len(after.Data.Transactions) != 1 || after.Data.Transactions[0].Facts.AccountID != "other" {
+	if !reflect.DeepEqual(before.Accounts[0], after.Data.Accounts[0]) || len(after.Data.Transactions) != 1 || after.Data.Transactions[0].Facts.AccountID != "other" {
 		t.Fatal("missing membership changed bindings or imported unauthorized facts")
 	}
+	// The authorized member's first successful sync anchors its balance from
+	// the bank's booked figure; the rejected member must not gain one.
+	anchored := after.Data.Accounts[1]
+	if anchored.AnchorBalance != "100.00" || anchored.AnchorDate == "" {
+		t.Fatalf("authorized member was not anchored: %+v", anchored)
+	}
+	anchored.AnchorBalance, anchored.AnchorDate = "", ""
+	if !reflect.DeepEqual(before.Accounts[1], anchored) {
+		t.Fatal("anchoring changed more than the anchor on the authorized member")
+	}
 }
 
 func TestSyncTransactionFailuresPreserveProgressAndSafeErrors(t *testing.T) {

internal/app/wealth.go

@@ -49,9 +49,11 @@ type WealthAccount struct {
 	Records      int    `json:"records"`
 	FirstBooking string `json:"first_booking,omitempty"`
 	LastBooking  string `json:"last_booking,omitempty"`
-	// Cash is every recorded movement summed. It equals the account's real
-	// balance only when the journal holds that account's complete history,
-	// which a broker export does and a date-windowed bank statement does not.
+	// Cash is every recorded movement summed — plus, when the account carries a
+	// balance anchor, the derived start balance. Without an anchor it equals
+	// the account's real balance only when the journal holds that account's
+	// complete history, which a broker export does and a date-windowed bank
+	// statement does not.
 	Cash domain.Money `json:"cash"`
 	// Positions is the market value of every priced holding, and Wealth the two
 	// together: the number this page exists to show. Unpriced counts the
@@ -192,6 +194,13 @@ func WealthOf(data domain.Dataset) Wealth {
 		unappliedFee, unappliedTax   int64
 		unappliedRows                int
 		unmatchedCash, unmatchedRows int64
+		// anchored accounts carry the bank's booked balance on anchorDate.
+		// residual is that figure less every movement booked through the
+		// anchor day: the money from before the recorded history, and the
+		// account's derived start balance.
+		anchored   bool
+		anchorDate string
+		residual   int64
 	}
 	states := map[string]*accountState{}
 	state := func(id string) *accountState {
@@ -200,15 +209,42 @@ func WealthOf(data domain.Dataset) Wealth {
 		}
 		return states[id]
 	}
+	// An anchored account's balance is the bank's own figure plus what moved
+	// after the anchor day. The residue is order-independent, so it is settled
+	// before the chronological pass that judges running balances.
+	for _, account := range data.Accounts {
+		if account.AnchorDate == "" {
+			continue
+		}
+		anchor, err := account.AnchorBalance.Minor()
+		if err != nil {
+			continue
+		}
+		st := state(account.ID)
+		st.anchored, st.anchorDate, st.residual = true, account.AnchorDate, anchor
+		for _, t := range data.Transactions {
+			if t.Facts.AccountID != account.ID || t.Facts.BookingDate > account.AnchorDate {
+				continue
+			}
+			if minor, e := t.Facts.Amount.Minor(); e == nil {
+				st.residual -= minor
+			}
+		}
+	}
 	// A day's rows are applied together before any low-water mark is taken.
 	// Order within a day is not knowable: a broker export states a booking date
 	// and a clock time, the time is local and crosses midnight, so only the
 	// date is imported. A purchase funded by a sale nine seconds earlier then
 	// arrives in an arbitrary order, and checking row by row reports a dip
 	// that never happened.
+	// Days on or before an anchor are not judged at all: the history before
+	// the anchor is incomplete by definition, so a running balance there is
+	// not observable.
 	closeDay := func(st *accountState) {
-		if st.cash < st.lowestCash {
-			st.lowestCash, st.lowestCashDate = st.cash, st.day
+		if !st.anchored || st.day > st.anchorDate {
+			if effective := st.cash + st.residual; effective < st.lowestCash {
+				st.lowestCash, st.lowestCashDate = effective, st.day
+			}
 		}
 		for _, held := range st.holdings {
 			if held.units < held.lowest {
@@ -317,13 +353,22 @@ func WealthOf(data domain.Dataset) Wealth {
 		if kind == "" {
 			kind = domain.AccountCash
 		}
+		cash := st.cash + st.residual
 		entry := WealthAccount{
 			AccountID: account.ID, DisplayName: account.DisplayName, Institution: account.Institution,
 			Currency: account.Currency, Kind: kind, Active: account.Active,
 			Records: st.records, FirstBooking: st.first, LastBooking: st.last,
-			Cash: domain.FormatMoney(st.cash), Flows: []WealthFlow{},
+			Cash: domain.FormatMoney(cash), Flows: []WealthFlow{},
 			Holdings: []WealthHolding{}, Checks: []WealthCheck{},
 		}
+		// The start balance reads first, like the carried-over line on a paper
+		// statement, and keeps the invariant that the flows sum to the balance.
+		if st.anchored {
+			entry.Flows = append(entry.Flows, WealthFlow{
+				Event: "anchor", Label: "Start balance (before the recorded rows)",
+				Cash: domain.FormatMoney(st.residual),
+			})
+		}
 		for _, flow := range flowLabels {
 			if moved := st.flows[flow.event]; moved != nil {
 				entry.Flows = append(entry.Flows, WealthFlow{
@@ -333,7 +378,7 @@ func WealthOf(data domain.Dataset) Wealth {
 			}
 		}
 		seen(account.Currency)
-		totals[account.Currency] += st.cash
+		totals[account.Currency] += cash
 		positions, unpriced, stale := int64(0), 0, []string{}
 		for _, id := range st.order {
 			held := st.holdings[id]
@@ -372,7 +417,7 @@ func WealthOf(data domain.Dataset) Wealth {
 		}
 		slices.SortFunc(entry.Holdings, func(x, y WealthHolding) int { return strings.Compare(x.Name, y.Name) })
 		entry.Positions, entry.Unpriced = domain.FormatMoney(positions), unpriced
-		entry.Wealth = domain.FormatMoney(st.cash + positions)
+		entry.Wealth = domain.FormatMoney(cash + positions)
 		positionTotals[account.Currency] += positions
 		unpricedTotals[account.Currency] += unpriced
 
@@ -384,8 +429,15 @@ func WealthOf(data domain.Dataset) Wealth {
 		} else {
 			check("Row arithmetic", "every record agrees with its own gross, fee, tax, quantity and price", false)
 		}
+		if st.anchored {
+			check("Balance anchored", fmt.Sprintf("cash is the bank's own booked balance %s on %s plus every movement after that day; the start balance line, %s, is that figure less the movements booked through it", account.AnchorBalance, st.anchorDate, domain.FormatMoney(st.residual)), false)
+		} else if !account.Investing() && account.ExternalAccountID != "" {
+			check("Balance not anchored", "cash is the recorded movements only; the next successful synchronization captures the bank's booked balance and fixes the start balance", false)
+		}
 		if st.lowestCash < 0 {
 			check("Cash never negative", fmt.Sprintf("balance reached %s on %s, so the history is incomplete or a movement is misread", domain.FormatMoney(st.lowestCash), st.lowestCashDate), true)
+		} else if st.anchored {
+			check("Cash never negative", "the running balance stays at or above zero from the anchor day onward; earlier days are not judged against an incomplete window", false)
 		} else {
 			check("Cash never negative", "the running balance stays at or above zero throughout", false)
 		}

internal/app/wealth_test.go

@@ -416,3 +416,71 @@ func TestWealthCountsHandValuedAssets(t *testing.T) {
 		t.Errorf("assets not echoed sorted by name with their dates: %+v", report.Assets)
 	}
 }
+
+// A bank's date-windowed history starts mid-life, so an anchored account
+// derives its start balance: the bank's booked figure on the anchor day less
+// everything booked through it. The derived line keeps the flows summing to
+// the balance, and the pre-anchor window is never judged as an overdraft —
+// the history there is incomplete by definition.
+func TestAnchoredAccountDerivesStartBalance(t *testing.T) {
+	data := domain.NewDataset()
+	data.Accounts = []domain.Account{
+		{ID: "acc_anchored", DisplayName: "Checking", Currency: "EUR", Active: true, ExternalAccountID: "uid_one", AnchorBalance: "2450.00", AnchorDate: "2026-09-10"},
+		{ID: "acc_plain", DisplayName: "Connected", Currency: "EUR", Active: true, ExternalAccountID: "uid_two"},
+	}
+	row := func(id, account, date string, amount domain.Money) domain.Transaction {
+		f := domain.Facts{ID: id, Source: "enablebanking", AccountID: account, BookingDate: date, Amount: amount, Currency: "EUR", RawDescription: id, Fingerprint: "fp_" + id}
+		return domain.Transaction{Facts: f, Enrichment: domain.Fallback(f)}
+	}
+	data.Transactions = []domain.Transaction{
+		// The recorded window alone would dip to −900 before the anchor day.
+		row("tx_pre", "acc_anchored", "2026-09-01", "-900.00"),
+		row("tx_on", "acc_anchored", "2026-09-10", "50.00"),
+		row("tx_post", "acc_anchored", "2026-09-12", "-100.00"),
+		row("tx_other", "acc_plain", "2026-09-12", "10.00"),
+	}
+	if err := domain.Validate(data); err != nil {
+		t.Fatal(err)
+	}
+	report := WealthOf(data)
+	anchored := report.Accounts[0]
+	// 2450.00 on 2026-09-10 less the −850.00 booked through that day puts
+	// 3300.00 before the window; the balance is 2450.00 − 100.00 booked after.
+	if anchored.Cash != "2350.00" || anchored.Wealth != "2350.00" {
+		t.Errorf("anchored cash %s wealth %s, want 2350.00", anchored.Cash, anchored.Wealth)
+	}
+	if len(anchored.Flows) == 0 || anchored.Flows[0].Event != "anchor" || anchored.Flows[0].Cash != "3300.00" {
+		t.Errorf("start balance line missing or wrong: %+v", anchored.Flows)
+	}
+	total := int64(0)
+	for _, flow := range anchored.Flows {
+		cash, err := flow.Cash.Minor()
+		if err != nil {
+			t.Fatal(err)
+		}
+		total += cash
+	}
+	if domain.FormatMoney(total) != anchored.Cash {
+		t.Errorf("flows sum to %s, balance is %s", domain.FormatMoney(total), anchored.Cash)
+	}
+	checks := map[string]WealthCheck{}
+	for _, check := range anchored.Checks {
+		checks[check.Name] = check
+	}
+	if _, ok := checks["Balance anchored"]; !ok {
+		t.Errorf("no anchor note: %+v", anchored.Checks)
+	}
+	if check := checks["Cash never negative"]; check.Failed {
+		t.Errorf("pre-anchor window judged as an overdraft: %s", check.Detail)
+	}
+	note := false
+	for _, check := range report.Accounts[1].Checks {
+		note = note || check.Name == "Balance not anchored"
+	}
+	if !note {
+		t.Errorf("connected account without an anchor carries no note: %+v", report.Accounts[1].Checks)
+	}
+	if report.Totals[0].Cash != "2360.00" {
+		t.Errorf("total cash %s, want 2360.00", report.Totals[0].Cash)
+	}
+}

internal/domain/domain.go

@@ -291,6 +291,20 @@ func Validate(d Dataset) error {
 		if a.Kind != "" && a.Kind != AccountCash && a.Kind != AccountInvestment {
 			return fmt.Errorf("account %q: kind must be %q or %q", a.ID, AccountCash, AccountInvestment)
 		}
+		// An anchor is one figure and the day it was true: neither half means
+		// anything alone, and anchoring an investment account would mask an
+		// incomplete broker history instead of exposing it.
+		if (a.AnchorBalance == "") != (a.AnchorDate == "") {
+			return fmt.Errorf("account %q: an anchor needs both a balance and its date", a.ID)
+		}
+		if a.AnchorDate != "" {
+			if a.Investing() {
+				return fmt.Errorf("account %q: a balance anchor belongs to a cash account; a broker export carries its complete history", a.ID)
+			}
+			if _, err := a.AnchorBalance.Minor(); err != nil || !validDate(a.AnchorDate) {
+				return fmt.Errorf("account %q: invalid anchor balance or date", a.ID)
+			}
+		}
 		accounts[a.ID] = a
 	}
 	for _, c := range d.Categories {

internal/domain/domain_test.go

@@ -77,6 +77,18 @@ func TestDomainRejectsBrokenReferencesAndTaxonomy(t *testing.T) {
 		{"nonleaf merchant default", func(d *Dataset) { d.Merchants[0].DefaultCategoryID = "cat_food" }},
 		{"oversized tag name", func(d *Dataset) { d.Tags[0].Name = strings.Repeat("x", 201) }},
 		{"oversized category name", func(d *Dataset) { d.Categories[2].Name = strings.Repeat("x", 201) }},
+		{"anchor balance without its date", func(d *Dataset) { d.Accounts[1].AnchorBalance = "100.00" }},
+		{"anchor date without its balance", func(d *Dataset) { d.Accounts[1].AnchorDate = "2026-01-01" }},
+		{"anchored investment account", func(d *Dataset) {
+			d.Accounts[1].Kind = AccountInvestment
+			d.Accounts[1].AnchorBalance, d.Accounts[1].AnchorDate = "100.00", "2026-01-01"
+		}},
+		{"invalid anchor date", func(d *Dataset) {
+			d.Accounts[1].AnchorBalance, d.Accounts[1].AnchorDate = "100.00", "2026-02-30"
+		}},
+		{"invalid anchor balance", func(d *Dataset) {
+			d.Accounts[1].AnchorBalance, d.Accounts[1].AnchorDate = "1e2", "2026-01-01"
+		}},
 	}
 	for _, tc := range cases {
 		t.Run(tc.name, func(t *testing.T) {

internal/domain/model.go

@@ -31,6 +31,16 @@ type Account struct {
 	// broker exports no counterparty column, so deposits and withdrawals carry
 	// this IBAN instead and pair with the funding account like any transfer.
 	ReferenceIBAN string `json:"reference_iban,omitempty"`
+	// AnchorBalance is the bank's booked (CLBD) balance on AnchorDate, captured
+	// once from open banking after a sync. It fixes the start balance of a
+	// date-windowed history: the money that existed before the recorded rows is
+	// AnchorBalance less every movement booked through AnchorDate, so the
+	// account's real balance is computable without complete history. The bank's
+	// figure is stored verbatim — the start balance is derived, never stored —
+	// so importing older history later corrects the derivation by itself.
+	// Cash accounts only: a broker export carries its complete history.
+	AnchorBalance Money  `json:"anchor_balance,omitempty"`
+	AnchorDate    string `json:"anchor_date,omitempty"`
 	Active        bool   `json:"active"`
 }