From 710f0fb3527ea9f0f2a2e02994b45e1c52e46e80 Mon Sep 17 00:00:00 2001
From: Cristian Magherusan-Stanciu <cristi.magherusan@gmail.com>
Date: Fri, 9 Oct 2026 10:48:17 +0200
Subject: [PATCH] fix(config): map invalid ladder amendments to
 ErrLadderAmendInvalid

- AmendLadderTranche returned the plain Validate() error, so callers
  other than the HTTP handler could not tell a bad amendment from a
  server fault. The error now matches ErrLadderAmendInvalid via
  errors.Is while keeping the specific validation message (the
  sentinel text is about the run total and cap, which would mislead).
- Unit test covers the mapping without a database and fails without it.

Refs #668
---
 internal/config/ladder_amend.go               |  8 ++++++++
 .../config/store_postgres_ladder_amend.go     |  2 +-
 .../store_postgres_ladder_amend_test.go       | 20 +++++++++++++++++++
 3 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 internal/config/store_postgres_ladder_amend_test.go

diff --git a/internal/config/ladder_amend.go b/internal/config/ladder_amend.go
index 35e085882..f80a0614f 100644
--- a/internal/config/ladder_amend.go
+++ b/internal/config/ladder_amend.go
@@ -15,6 +15,14 @@ var (
 	ladderAmountPattern    = regexp.MustCompile(`^(0|[1-9]\d{0,13})(\.\d{1,6})?$`)
 )
 
+// ladderAmendValidationError keeps the Validate message for the caller while
+// matching ErrLadderAmendInvalid, so store callers can map every invalid
+// amendment to a client error with errors.Is.
+type ladderAmendValidationError struct{ err error }
+
+func (e ladderAmendValidationError) Error() string   { return e.err.Error() }
+func (e ladderAmendValidationError) Unwrap() []error { return []error{ErrLadderAmendInvalid, e.err} }
+
 type LadderAmendment struct {
 	ExpectedRevision *int64    `json:"expected_revision"`
 	ScheduledDate    time.Time `json:"scheduled_date"`
diff --git a/internal/config/store_postgres_ladder_amend.go b/internal/config/store_postgres_ladder_amend.go
index 0c71a534b..1995a4f43 100644
--- a/internal/config/store_postgres_ladder_amend.go
+++ b/internal/config/store_postgres_ladder_amend.go
@@ -24,7 +24,7 @@ func (s *PostgresStore) LadderTrancheScope(ctx context.Context, id string) (acco
 
 func (s *PostgresStore) AmendLadderTranche(ctx context.Context, id, accountID, provider, actor string, amendment LadderAmendment) (*LadderAmendmentResult, error) {
 	if err := amendment.Validate(); err != nil {
-		return nil, err
+		return nil, ladderAmendValidationError{err}
 	}
 	if actor == "" {
 		return nil, errors.New("ladder amendment actor is required")
diff --git a/internal/config/store_postgres_ladder_amend_test.go b/internal/config/store_postgres_ladder_amend_test.go
new file mode 100644
index 000000000..d6226b921
--- /dev/null
+++ b/internal/config/store_postgres_ladder_amend_test.go
@@ -0,0 +1,20 @@
+package config
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestAmendLadderTranche_InvalidAmendmentMatchesErrLadderAmendInvalid(t *testing.T) {
+	zero := int64(0)
+	store := &PostgresStore{} // validation fails before the database is used
+	_, err := store.AmendLadderTranche(context.Background(), "id", "account", "aws", "actor",
+		LadderAmendment{ExpectedRevision: &zero, ScheduledDate: time.Now(), AmountUSDHr: "0"})
+	require.ErrorIs(t, err, ErrLadderAmendInvalid)
+	assert.Contains(t, err.Error(), "amount_usd_hr must be a positive decimal")
+	assert.NotContains(t, err.Error(), "per-run cap")
+}