Bump Ministack to 1.4.15; adopt typed duplicate-instance fault match

docs/testing.md

@@ -205,11 +205,11 @@ password rotation last. Each subtest pins one AWS seam:
   discovery → `dbconn` connect → PG-major assertion → DDL smoke;
 - **control-plane error contract** — unknown identifiers and duplicate
   creations surface as the AWS SDK's typed RDS faults, matched with
-  `errors.As`. One documented emulator divergence: Ministack emits the
-  duplicate-instance wire code with a `Fault` suffix real AWS omits, so
-  the SDK leaves it a generic API error. The test pins the divergent code
-  exactly — it fails the day the emulator is fixed, forcing the
-  workaround's removal in favor of the typed match production code uses;
+  `errors.As` — exactly the match production code uses. (An earlier
+  emulator divergence — a `Fault` suffix on the duplicate-instance wire
+  code that real AWS omits — was fixed upstream in Ministack v1.4.14 at
+  pg-sprite's request; the pinned image carries the fix, so no divergence
+  workaround remains);
 - **password rotation** — what a rotation does to a running schema change
   (see below), plus pg-sprite's contract that the resulting auth failure
   is terminal, not retryable.

internal/testutil/ministack.go

@@ -88,30 +88,33 @@ func ministackImage() string {
 	if img := os.Getenv("MINISTACK_IMAGE"); img != "" {
 		return img
 	}
-	return "ministackorg/ministack:1.4.13-full"
+	return "ministackorg/ministack:1.4.15-full"
 }
 
 // auroraEngineVersion returns a real aurora-postgresql engine version for
-// the requested major. Real RDS requires a full version string ("16.6"),
-// not a bare major — Ministack is lenient, but this tier exists to
-// rehearse calls the way the real control plane requires, so the request
-// is constructed as AWS would accept it. The exact minor is immaterial:
-// Ministack derives the sibling database image from the major, and the
-// test asserts the running server's major independently.
+// the requested major. Real RDS requires a full version string ("16.14"),
+// not a bare major, and Ministack validates the version against its
+// creatable catalog at create time — an unknown version fails with the
+// AWS-exact InvalidParameterCombination, so each entry here must be a
+// version the pinned image advertises via DescribeDBEngineVersions. The
+// exact minor is immaterial beyond that: Ministack derives the sibling
+// database image from the major, and the test asserts the running
+// server's major independently.
 func auroraEngineVersion(major int) string {
 	versions := map[int]string{
-		14: "14.15",
-		15: "15.10",
-		16: "16.6",
-		17: "17.4",
-		18: "18.3",
+		14: "14.23",
+		15: "15.18",
+		16: "16.14",
+		17: "17.10",
+		18: "18.4",
 	}
 	if v, ok := versions[major]; ok {
 		return v
 	}
-	// A major newer than this map: fall back to "<major>.1" so the call
-	// still carries a full version string.
-	return fmt.Sprintf("%d.1", major)
+	// A major newer than this map: fall back to the bare major, which the
+	// emulator's validator accepts as a dot-boundary prefix of any
+	// catalog entry for that major.
+	return strconv.Itoa(major)
 }
 
 // AuroraCluster is a provisioned Ministack aurora-postgresql cluster and

internal/testutil/ministack_integration_test.go

@@ -10,7 +10,6 @@ import (
 	"github.com/aws/aws-sdk-go-v2/aws"
 	"github.com/aws/aws-sdk-go-v2/service/rds"
 	"github.com/aws/aws-sdk-go-v2/service/rds/types"
-	"github.com/aws/smithy-go"
 	"github.com/jackc/pgx/v5/pgconn"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -98,18 +97,9 @@ func errorContract(t *testing.T, cluster *testutil.AuroraCluster) {
 		Engine:               aws.String("aurora-postgresql"),
 		DBInstanceClass:      aws.String("db.t3.medium"),
 	})
-	// Real AWS emits wire code "DBInstanceAlreadyExists", which the SDK
-	// maps to types.DBInstanceAlreadyExistsFault — production code must
-	// match that typed fault with errors.As, exactly like the two cases
-	// above. Ministack diverges: it emits "DBInstanceAlreadyExistsFault",
-	// which the SDK leaves as a generic API error. Pin the divergent code
-	// exactly so this assertion fails the day the emulator is fixed, and
-	// this workaround is replaced by the typed errors.As match.
-	var apiErr smithy.APIError
-	require.ErrorAs(t, err, &apiErr,
-		"creating a duplicate instance must surface an RDS API error")
-	require.Equal(t, "DBInstanceAlreadyExistsFault", apiErr.ErrorCode(),
-		"emulator no longer emits its divergent duplicate-instance code — assert types.DBInstanceAlreadyExistsFault with errors.As instead of this pin")
+	var instanceExists *types.DBInstanceAlreadyExistsFault
+	require.ErrorAs(t, err, &instanceExists,
+		"creating a duplicate instance must surface the typed already-exists fault")
 }
 
 // passwordRotation proves what a master-password rotation does to a