feat: add RegradeResource RPC — re-apply tier connection caps to live Postgres roles

internal/backend/postgres/backend.go

@@ -37,6 +37,25 @@ type Backend interface {
 	Provision(ctx context.Context, token, tier string) (*Credentials, error)
 	StorageBytes(ctx context.Context, token, providerResourceID string) (int64, error)
 	Deprovision(ctx context.Context, token, providerResourceID string) error
+	// Regrade re-applies the tier's per-role CONNECTION LIMIT to an already
+	// provisioned resource (e.g. after a plan upgrade). Idempotent.
+	//
+	// connLimit is the connection cap to apply (-1 = unlimited). Backends that
+	// own a dedicated pod per resource (k8s) ALTER ROLE in place. The shared
+	// local/dedicated/neon backends set no per-role cap at provision time, so
+	// they return RegradeResult{Applied:false, SkipReason:"..."} without error.
+	//
+	// A non-error RegradeResult{Applied:false} means "nothing to do / not
+	// reachable" — the caller can safely retry on the next sweep. An error is
+	// reserved for unexpected failures.
+	Regrade(ctx context.Context, token, providerResourceID string, connLimit int) (RegradeResult, error)
+}
+
+// RegradeResult is the outcome of a Backend.Regrade call.
+type RegradeResult struct {
+	Applied          bool   // true if the new connection cap was applied
+	AppliedConnLimit int    // the cap that is now in effect (-1 = unlimited)
+	SkipReason       string // populated when Applied is false
 }
 
 // Credentials returned by Provision.

internal/backend/postgres/dedicated.go

@@ -77,6 +77,14 @@ func (p *DedicatedProvider) Deprovision(ctx context.Context, token, providerReso
 	return p.deprovisionLocal(ctx, token)
 }
 
+// Regrade is a no-op for the dedicated provider. The Neon path manages
+// connection limits through the Neon project plan, not a per-role
+// CONNECTION LIMIT; the local-admin path sets no per-role cap at provision
+// time. Either way there is no cap to re-apply, so a skip result is returned.
+func (p *DedicatedProvider) Regrade(ctx context.Context, token, providerResourceID string, connLimit int) (RegradeResult, error) {
+	return RegradeResult{Applied: false, SkipReason: "backend has no per-role connection cap"}, nil
+}
+
 // --- Neon API path ---
 
 func (p *DedicatedProvider) provisionNeon(ctx context.Context, token, tier string) (*Credentials, error) {

internal/backend/postgres/k8s.go

@@ -373,6 +373,65 @@ func (b *K8sBackend) Deprovision(ctx context.Context, token, providerResourceID
 	return nil
 }
 
+// Regrade re-applies a connection cap to the customer's app Postgres role.
+// Used after a plan upgrade: the role's CONNECTION LIMIT was set at provision
+// time from the old (lower) tier and nothing re-applies the new cap.
+//
+// It resolves the resource → its namespace/Service/admin Secret the same way
+// StorageBytes does, then runs ALTER ROLE on the customer DB. Re-applying the
+// same value is a harmless no-op (idempotent).
+//
+// When the pod is unreachable (paused, terminating, legacy row without the
+// modern Secret/Service) this returns RegradeResult{Applied:false} with a
+// skip reason and no error — the caller retries on the next sweep.
+func (b *K8sBackend) Regrade(ctx context.Context, token, providerResourceID string, connLimit int) (RegradeResult, error) {
+	ns := providerResourceID
+	if ns == "" {
+		ns = k8sNsPrefix + token
+	}
+
+	// Resolve admin connection — identical pattern to StorageBytes. Legacy rows
+	// whose pods are gone (missing Secret/Service) are non-actionable: skip,
+	// don't error, so the caller doesn't retry forever.
+	secret, err := b.cs.CoreV1().Secrets(ns).Get(ctx, "postgres-admin", metav1.GetOptions{})
+	if err != nil {
+		if k8serrors.IsNotFound(err) {
+			return RegradeResult{Applied: false, SkipReason: "resource not reachable: postgres-admin secret not found"}, nil
+		}
+		return RegradeResult{Applied: false, SkipReason: fmt.Sprintf("resource not reachable: get secret: %v", err)}, nil
+	}
+	svc, err := b.cs.CoreV1().Services(ns).Get(ctx, "postgres", metav1.GetOptions{})
+	if err != nil {
+		if k8serrors.IsNotFound(err) {
+			return RegradeResult{Applied: false, SkipReason: "resource not reachable: postgres service not found"}, nil
+		}
+		return RegradeResult{Applied: false, SkipReason: fmt.Sprintf("resource not reachable: get service: %v", err)}, nil
+	}
+
+	adminUser := string(secret.Data["POSTGRES_USER"])
+	adminPass := string(secret.Data["POSTGRES_PASSWORD"])
+	// The app role is derived from the token exactly as in Provision.
+	appUser := "usr_" + k8sShort(token)
+
+	dsn := fmt.Sprintf("postgres://%s:%s@%s:5432/postgres?sslmode=disable", adminUser, adminPass, svc.Spec.ClusterIP)
+	conn, err := pgx.Connect(ctx, dsn)
+	if err != nil {
+		return RegradeResult{Applied: false, SkipReason: fmt.Sprintf("resource not reachable: connect: %v", err)}, nil
+	}
+	defer conn.Close(ctx)
+
+	// ALTER ROLE re-applies the tier's connection cap. -1 = unlimited (passed
+	// through verbatim). Identifier quoted with %q, mirroring the CREATE USER
+	// path in initDatabase.
+	stmt := fmt.Sprintf(`ALTER ROLE %q CONNECTION LIMIT %d`, appUser, connLimit)
+	if _, err := conn.Exec(ctx, stmt); err != nil {
+		// Role missing on a live pod is non-actionable too — treat as skip.
+		return RegradeResult{Applied: false, SkipReason: fmt.Sprintf("resource not reachable: alter role: %v", err)}, nil
+	}
+
+	return RegradeResult{Applied: true, AppliedConnLimit: connLimit}, nil
+}
+
 // --- private resource creators ---
 
 func (b *K8sBackend) applyNamespace(ctx context.Context, ns string) error {

internal/backend/postgres/local.go

@@ -217,6 +217,13 @@ func (b *LocalBackend) Deprovision(ctx context.Context, token, providerResourceI
 	return nil
 }
 
+// Regrade is a no-op for the shared local backend: Provision sets no per-role
+// CONNECTION LIMIT on the shared cluster, so there is no cap to re-apply on a
+// plan upgrade. Returns a skip result without error.
+func (b *LocalBackend) Regrade(ctx context.Context, token, providerResourceID string, connLimit int) (RegradeResult, error) {
+	return RegradeResult{Applied: false, SkipReason: "backend has no per-role connection cap"}, nil
+}
+
 // buildDBURL constructs the user-facing connection URL for the provisioned database.
 // sslmode=disable is explicit because the shared postgres-customers cluster does not
 // have SSL configured. Without it, lib/pq defaults to sslmode=prefer and fails with

internal/backend/postgres/neon.go

@@ -178,3 +178,10 @@ func (b *NeonBackend) Deprovision(ctx context.Context, token, providerResourceID
 	slog.Info("db.neon.Deprovision: deprovisioned", "token", token, "project_id", providerResourceID)
 	return nil
 }
+
+// Regrade is a no-op for the Neon backend: connection limits are governed by
+// the Neon project plan, not a per-role CONNECTION LIMIT, so there is nothing
+// to re-apply on a plan upgrade.
+func (b *NeonBackend) Regrade(ctx context.Context, token, providerResourceID string, connLimit int) (RegradeResult, error) {
+	return RegradeResult{Applied: false, SkipReason: "backend has no per-role connection cap"}, nil
+}

internal/server/server.go

@@ -13,6 +13,7 @@ import (
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/status"
 
+	"instant.dev/common/plans"
 	commonv1 "instant.dev/proto/common/v1"
 	provisionerv1 "instant.dev/proto/provisioner/v1"
 
@@ -546,6 +547,94 @@ func (s *Server) GetStorageBytes(ctx context.Context, req *provisionerv1.Storage
 	}
 }
 
+// regradeConnLimits is the source of truth for per-tier Postgres connection
+// caps used by RegradeResource. It is the shared plans registry — the same
+// source the agent API uses via plans.Registry.ConnectionsLimit(tier,
+// "postgres") — so the cap re-applied here stays platform-consistent.
+var regradeConnLimits = plans.Default()
+
+// RegradeResource re-applies the tier's per-role connection cap to an
+// already-provisioned resource. It exists because a plan upgrade does not, on
+// its own, re-apply the higher CONNECTION LIMIT to the customer's Postgres
+// role — the role keeps the old (lower) cap until this RPC runs.
+//
+// Phase 1 is Postgres-only. Non-Postgres resource types and backends with no
+// per-role connection cap (the shared local/dedicated/neon backends) return
+// {applied:false} with a skip reason rather than an error.
+func (s *Server) RegradeResource(ctx context.Context, req *provisionerv1.RegradeRequest) (*provisionerv1.RegradeResponse, error) {
+	if req.Token == "" {
+		return nil, status.Error(codes.InvalidArgument, "token is required")
+	}
+
+	ctx, span := otel.Tracer("instant.dev/provisioner").Start(ctx, "RegradeResource",
+		trace.WithAttributes(
+			attribute.String("resource_type", req.ResourceType.String()),
+			attribute.String("tier", req.Tier),
+			attribute.String("resource.token", req.Token),
+		),
+	)
+	defer span.End()
+
+	// Phase 1: Postgres only.
+	if req.ResourceType != commonv1.ResourceType_RESOURCE_TYPE_POSTGRES {
+		slog.Info("server.RegradeResource",
+			"token", req.Token, "tier", req.Tier,
+			"applied", false, "skip_reason", "unsupported resource type for regrade",
+			"request_id", req.RequestId)
+		return &provisionerv1.RegradeResponse{
+			Applied:    false,
+			SkipReason: "unsupported resource type for regrade",
+		}, nil
+	}
+
+	// Select the backend that actually owns this resource. k8s namespace IDs
+	// (prefix "instant-customer-") go through the regular postgresBackend,
+	// matching the routing DeprovisionResource uses.
+	backend := s.postgresBackend
+	if s.dedicatedPostgresBackend != nil && req.ProviderResourceId != "" &&
+		!strings.HasPrefix(req.ProviderResourceId, "instant-customer-") {
+		backend = s.dedicatedPostgresBackend
+	}
+
+	// Only the k8s backend applies a per-role CONNECTION LIMIT at provision
+	// time. Every other backend would return the same skip via Regrade, but
+	// checking here keeps the contract explicit and avoids a needless k8s/DB
+	// round-trip.
+	if _, ok := backend.(*postgres.K8sBackend); !ok {
+		slog.Info("server.RegradeResource",
+			"token", req.Token, "tier", req.Tier,
+			"applied", false, "skip_reason", "backend has no per-role connection cap",
+			"request_id", req.RequestId)
+		return &provisionerv1.RegradeResponse{
+			Applied:    false,
+			SkipReason: "backend has no per-role connection cap",
+		}, nil
+	}
+
+	// Connection cap comes from the shared plans registry, keeping it
+	// consistent with the cap the agent API reports and the k8s backend
+	// applies at provision time. -1 = unlimited; passed through verbatim.
+	connLimit := regradeConnLimits.ConnectionsLimit(req.Tier, "postgres")
+
+	result, err := backend.Regrade(ctx, req.Token, req.ProviderResourceId, connLimit)
+	if err != nil {
+		return nil, mapError("RegradeResource.postgres", err)
+	}
+
+	slog.Info("server.RegradeResource",
+		"token", req.Token, "tier", req.Tier,
+		"applied", result.Applied,
+		"applied_conn_limit", result.AppliedConnLimit,
+		"skip_reason", result.SkipReason,
+		"request_id", req.RequestId)
+
+	return &provisionerv1.RegradeResponse{
+		Applied:          result.Applied,
+		AppliedConnLimit: int32(result.AppliedConnLimit),
+		SkipReason:       result.SkipReason,
+	}, nil
+}
+
 // mapError converts backend errors to appropriate gRPC status codes.
 func mapError(op string, err error) error {
 	if err == nil {

internal/server/server_test.go

@@ -25,6 +25,7 @@ type mockPostgresBackend struct {
 	provision    func(ctx context.Context, token, tier string) (*postgres.Credentials, error)
 	storageBytes func(ctx context.Context, token, providerResourceID string) (int64, error)
 	deprovision  func(ctx context.Context, token, providerResourceID string) error
+	regrade      func(ctx context.Context, token, providerResourceID string, connLimit int) (postgres.RegradeResult, error)
 }
 
 func (m *mockPostgresBackend) Provision(ctx context.Context, token, tier string) (*postgres.Credentials, error) {
@@ -52,6 +53,13 @@ func (m *mockPostgresBackend) Deprovision(ctx context.Context, token, id string)
 	return nil
 }
 
+func (m *mockPostgresBackend) Regrade(ctx context.Context, token, id string, connLimit int) (postgres.RegradeResult, error) {
+	if m.regrade != nil {
+		return m.regrade(ctx, token, id, connLimit)
+	}
+	return postgres.RegradeResult{Applied: false, SkipReason: "backend has no per-role connection cap"}, nil
+}
+
 type mockRedisBackend struct {
 	provision    func(ctx context.Context, token, tier string) (*redis.Credentials, error)
 	storageBytes func(ctx context.Context, token, providerResourceID string) (int64, error)
@@ -357,6 +365,55 @@ func TestGetStorageBytes_Storage_NilMinIOBackend_ReturnsZero(t *testing.T) {
 	}
 }
 
+// --- RegradeResource tests ---
+
+func TestRegradeResource_EmptyToken_ReturnsInvalidArgument(t *testing.T) {
+	srv := newTestServer()
+	_, err := srv.RegradeResource(context.Background(), &provisionerv1.RegradeRequest{
+		ResourceType: commonv1.ResourceType_RESOURCE_TYPE_POSTGRES,
+		Tier:         "pro",
+	})
+	assertCode(t, err, codes.InvalidArgument)
+}
+
+func TestRegradeResource_NonPostgres_SkipsWithReason(t *testing.T) {
+	srv := newTestServer()
+	resp, err := srv.RegradeResource(context.Background(), &provisionerv1.RegradeRequest{
+		Token:        "tok-123",
+		ResourceType: commonv1.ResourceType_RESOURCE_TYPE_REDIS,
+		Tier:         "pro",
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if resp.Applied {
+		t.Fatal("expected applied=false for non-postgres resource")
+	}
+	if resp.SkipReason != "unsupported resource type for regrade" {
+		t.Fatalf("unexpected skip_reason: %q", resp.SkipReason)
+	}
+}
+
+func TestRegradeResource_NonK8sBackend_SkipsWithReason(t *testing.T) {
+	// newTestServer wires the shared mockPostgresBackend, which is not a
+	// *postgres.K8sBackend — the server should skip without touching it.
+	srv := newTestServer()
+	resp, err := srv.RegradeResource(context.Background(), &provisionerv1.RegradeRequest{
+		Token:        "tok-123",
+		ResourceType: commonv1.ResourceType_RESOURCE_TYPE_POSTGRES,
+		Tier:         "pro",
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if resp.Applied {
+		t.Fatal("expected applied=false for non-k8s backend")
+	}
+	if resp.SkipReason != "backend has no per-role connection cap" {
+		t.Fatalf("unexpected skip_reason: %q", resp.SkipReason)
+	}
+}
+
 // --- helper ---
 
 func assertCode(t *testing.T, err error, want codes.Code) {