test(ladder): pin netted-row float fields and rate rounding guards

internal/config/ladder_provenance_test.go

@@ -3,6 +3,7 @@ package config
 import (
 	"math"
 	"math/big"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -80,3 +81,31 @@ func TestAssumeOnDemandIfUnknown_OnlyForUnprovenBasis(t *testing.T) {
 	_, err := nettingOnDemand("1", &LadderTrancheDB{})
 	require.Error(t, err, "netting still refuses an unknown basis")
 }
+
+func TestNewLadderInFlightRow_FloatFieldsFeedAllocate(t *testing.T) {
+	od, native := LadderAmountOnDemand, LadderAmountCommitment
+	legacy, err := newLadderInFlightRow("12.5", &LadderTrancheDB{AmountBasis: &od})
+	require.NoError(t, err)
+	require.Equal(t, 1.0, legacy.Rate)
+	require.Equal(t, 12.5, legacy.CommitmentUSDPerHour)
+
+	// Tight bound: the rate is the largest float not above the exact rate.
+	for _, text := range []string{"1/10", "1/3", "1/2"} {
+		exact, ok := new(big.Rat).SetString(text)
+		require.True(t, ok)
+		row, rowErr := newLadderInFlightRow("1", &LadderTrancheDB{AmountBasis: &native, CommitmentRate: &text})
+		require.NoError(t, rowErr, text)
+		require.LessOrEqual(t, new(big.Rat).SetFloat64(row.Rate).Cmp(exact), 0, text)
+		require.Greater(t, new(big.Rat).SetFloat64(math.Nextafter(row.Rate, 2)).Cmp(exact), 0, text)
+	}
+
+	one := "1"
+	row, err := newLadderInFlightRow("3", &LadderTrancheDB{AmountBasis: &native, CommitmentRate: &one})
+	require.NoError(t, err)
+	require.Equal(t, 1.0, row.Rate)
+
+	tiny := "1/1" + strings.Repeat("0", 400)
+	row, err = newLadderInFlightRow("1", &LadderTrancheDB{AmountBasis: &native, CommitmentRate: &tiny})
+	require.NoError(t, err)
+	require.Equal(t, math.SmallestNonzeroFloat64, row.Rate, "a rate below float range must not become 0")
+}

internal/config/store_postgres_ladder_basis_integration_test.go

@@ -99,7 +99,12 @@ func TestLadderNetting_LegacyOnlyRowsKeepTheExactTotalBitForBit(t *testing.T) {
 	}
 	want, err := nettingFloat(exact)
 	require.NoError(t, err)
-	got := mustOnDemand(t, plannedRows(t, f))
+	rows := plannedRows(t, f)
+	require.Len(t, rows, len(amounts))
+	for _, r := range rows {
+		require.Equal(t, 1.0, r.Rate, "legacy on-demand rows carry rate 1")
+	}
+	got := mustOnDemand(t, rows)
 	require.Equal(t, math.Float64bits(want), math.Float64bits(got))
 }
 

internal/config/store_postgres_ladder_lock.go

@@ -99,7 +99,7 @@ func acquireLadderConfigLock(ctx context.Context, tx pgx.Tx, configID string) er
 // runs' windows never overlap.
 const ladderSettleSkewMargin = time.Minute
 
-// ladderSettleAnchor is the anchor every caller passes to settledLadderCommit
+// ladderSettleAnchor is the anchor every caller passes to settledLadderRows
 // for an existing-commitment read taken at or after asOf.
 func ladderSettleAnchor(asOf time.Time) time.Time { return asOf.Add(-ladderSettleSkewMargin) }
 

internal/config/store_postgres_ladder_settled_integration_test.go

@@ -21,7 +21,7 @@ import (
 
 // TestPostgresStoreDB_LadderSettledAt covers the stamp written by
 // TransitionLadderTrancheTx, the CHECK that rejects an unstamped completed
-// row, and the boundaries of settledLadderCommit. Migration behavior is in
+// row, and the boundaries of settledLadderRows. Migration behavior is in
 // the migrations package (000117). Set LADDER_SETTLED_TEST_DATABASE_URL to a
 // dedicated pr842a_* database to run it without Docker.
 func TestPostgresStoreDB_LadderSettledAt(t *testing.T) {
@@ -85,7 +85,7 @@ func TestPostgresStoreDB_LadderSettledAt(t *testing.T) {
 		requireCheckViolation(t, err)
 	})
 
-	t.Run("settledLadderCommit boundaries", func(t *testing.T) {
+	t.Run("settledLadderRows boundaries", func(t *testing.T) {
 		otherCfg := seedLadderConfigWithExtID(ctx, t, store, "333333333333")
 		anchor := time.Now().UTC().Truncate(time.Microsecond)
 		add := func(status ladder.TrancheStatus, amount float64, settled *time.Time) {