feat(server): central audited chokepoint for customer-data drops + CI guard

Addresses the OPEN truehomie-db DROP incident root-cause class: an active
customer's DB+role were dropped by an unidentified path with NO audit trail.
The provisioner was a dumb executor — DeprovisionResource dropped whatever
token it was handed and kept no record of its own.

- guardedDrop (drop_chokepoint.go): the single sanctioned wrapper for a
  customer-data destruction. Every backend Deprovision dispatch in
  DeprovisionResource now routes through it. Emits a structured
  `event=provisioner.drop` audit log line (token, provider_resource_id,
  resource_type, backend, request_id, caller from gRPC peer) BEFORE the drop
  + instant_provisioner_drop_total{resource_type,backend,outcome}. This is the
  always-on, app-layer equivalent of the cluster's log_statement='ddl' trap.

- drop_guard_test.go: AST-iterating CI guard (rule 18) that FAILS the build if
  any DROP DATABASE/ROLE/USER SQL literal, ACL DELUSER, mongo dropDatabase, or
  Database().Drop() call appears outside a sanctioned deprovision function
  reached through guardedDrop. A new un-audited drop path cannot merge. Proven
  non-vacuous: a synthetic un-sanctioned DROP is flagged; a commented DROP and
  a Collection.Drop (not customer data) are not.

Behaviour of WHAT gets purged in the TTL reaper / team-deletion / user-DELETE
flows is unchanged — the chokepoint only ADDs the audit line + metric around
the existing dispatch. The larger deletion-intent proto field + terminality
enforcement (needs platform-DB read, flag-gated) is designed + filed in
docs/ci/DATA-INTEGRITY-DROP-PATH-AUDIT.md.

make gate: green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: Manas Srivastava

internal/server/drop_chokepoint.go

@@ -0,0 +1,145 @@
+package server
+
+// drop_chokepoint.go — the SINGLE sanctioned wrapper for a customer-data
+// destruction (DROP DATABASE / DROP USER / dropDatabase / ACL DELUSER / namespace
+// teardown) on the provisioner.
+//
+// # WHY THIS EXISTS (truehomie-db DROP incident, 2026-06-03)
+//
+// An active Pro customer's Postgres database + role were dropped on the shared
+// postgres-customers cluster by an unidentified path, leaving NO audit_log row.
+// The provisioner is a "dumb executor": DeprovisionResource drops whatever
+// (token, provider_resource_id, resource_type) it is handed, and — critically —
+// it kept no record of its own. So even a drop that *did* go through the gRPC
+// funnel produced no provisioner-side trail to attribute it.
+//
+// guardedDrop closes that gap on the funnel: every backend Deprovision dispatch
+// in DeprovisionResource routes through here, which emits a structured DDL-audit
+// log line + Prometheus counter BEFORE invoking the backend. This is the
+// application-layer analogue of the postgres-customers `log_statement='ddl'` trap
+// set during the incident — but always-on, in the provisioner's own log stream,
+// and independent of the platform audit_log (which the provisioner cannot write,
+// having no platform-DB access).
+//
+// guardedDrop is the ONLY sanctioned customer-data drop wrapper. The CI guard in
+// drop_guard_test.go fails the build if a raw DROP DATABASE / DROP ROLE /
+// DROP USER / dropDatabase / ACL DELUSER literal appears in a provisioner backend
+// file that is NOT one of the sanctioned deprovision files reached through here —
+// so a NEW un-audited drop call site cannot be merged.
+//
+// SCOPE NOTE: guardedDrop does NOT (yet) refuse a drop based on resource
+// terminality / paid-tier — that requires the provisioner to read the platform
+// DB (resources.status/tier), a larger change designed + filed in
+// docs/ci/DATA-INTEGRITY-DROP-PATH-AUDIT.md (deletion-intent proto field +
+// terminality guard, flag-gated). guardedDrop is the always-safe, zero-behaviour-
+// change first layer: it makes every sanctioned drop auditable and a new
+// un-audited path unmergeable.
+
+import (
+	"context"
+	"log/slog"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+	"google.golang.org/grpc/peer"
+
+	provisionerv1 "instant.dev/proto/provisioner/v1"
+
+	"instant.dev/provisioner/internal/circuit"
+)
+
+// dropTotal counts every customer-data drop the provisioner performs through the
+// sanctioned chokepoint, labelled by resource_type, backend (shared|dedicated),
+// and outcome (ok|error|breaker_open). A spike in this counter is the alertable
+// signal that drops are happening at an abnormal rate (the truehomie incident
+// class). Eager-registered (NewCounterVec via promauto on the default registry)
+// so the series exists at /metrics before the first drop — but only label
+// combinations actually observed appear (standard *Vec behaviour). Rule 25:
+// alert + dashboard tile + catalog row ship alongside this metric.
+var dropTotal = promauto.NewCounterVec(prometheus.CounterOpts{
+	Name: "instant_provisioner_drop_total",
+	Help: "Customer-data drops performed by the provisioner via the sanctioned chokepoint, by resource_type, backend, and outcome.",
+}, []string{"resource_type", "backend", "outcome"})
+
+// dropBackend distinguishes the shared multi-tenant backend from a dedicated
+// (per-tenant pod / Neon project) backend in the audit line + metric.
+type dropBackend string
+
+const (
+	dropBackendShared    dropBackend = "shared"
+	dropBackendDedicated dropBackend = "dedicated"
+)
+
+// callerFromContext returns a best-effort identifier for the gRPC peer that
+// issued the request (e.g. "10.109.3.201:54422"), or "unknown" when the peer is
+// not available. This is the provisioner-side attribution that was MISSING in the
+// truehomie incident — every sanctioned drop now records who asked for it.
+func callerFromContext(ctx context.Context) string {
+	if p, ok := peer.FromContext(ctx); ok && p.Addr != nil {
+		return p.Addr.String()
+	}
+	return "unknown"
+}
+
+// guardedDrop is the single sanctioned wrapper for a customer-data destruction.
+// It emits the DDL-audit log line + metric, then invokes fn (the backend
+// Deprovision) inside the supplied circuit breaker. Every Deprovision dispatch in
+// DeprovisionResource MUST call this rather than callBackendVoid directly.
+//
+// The audit line is emitted BEFORE the drop so a backend that hangs or crashes
+// the process mid-drop still leaves the "we are about to drop X" record — exactly
+// the trail that was absent in the incident.
+func (s *Server) guardedDrop(
+	ctx context.Context,
+	req *provisionerv1.DeprovisionRequest,
+	backend dropBackend,
+	breaker *circuit.Breaker,
+	fn func() error,
+) error {
+	resType := req.ResourceType.String()
+	caller := callerFromContext(ctx)
+
+	// DDL-audit: the always-on, provisioner-side record of the drop. This is the
+	// in-app equivalent of the cluster's log_statement='ddl' trap.
+	slog.Info("provisioner.drop",
+		"event", "provisioner.drop",
+		"token", req.Token,
+		"provider_resource_id", req.ProviderResourceId,
+		"resource_type", resType,
+		"backend", string(backend),
+		"request_id", req.RequestId,
+		"caller", caller,
+	)
+
+	err := callBackendVoid(breaker, fn)
+
+	outcome := dropOutcome(err)
+	dropTotal.WithLabelValues(resType, string(backend), outcome).Inc()
+
+	if err != nil {
+		slog.Warn("provisioner.drop.failed",
+			"event", "provisioner.drop.failed",
+			"token", req.Token,
+			"provider_resource_id", req.ProviderResourceId,
+			"resource_type", resType,
+			"backend", string(backend),
+			"request_id", req.RequestId,
+			"caller", caller,
+			"outcome", outcome,
+			"error", err,
+		)
+	}
+	return err
+}
+
+// dropOutcome maps a backend deprovision error to the metric outcome label.
+func dropOutcome(err error) string {
+	switch {
+	case err == nil:
+		return "ok"
+	case err == circuit.ErrOpen:
+		return "breaker_open"
+	default:
+		return "error"
+	}
+}

internal/server/drop_chokepoint_test.go

@@ -0,0 +1,136 @@
+package server
+
+// drop_chokepoint_test.go — unit tests for the sanctioned customer-data drop
+// chokepoint (guardedDrop). These assert the truehomie-incident invariant: every
+// drop the provisioner performs is recorded (metric + audit log) and attributed,
+// and the metric outcome label is correct for ok / error / breaker-open.
+
+import (
+	"context"
+	"errors"
+	"net"
+	"testing"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus/testutil"
+	"google.golang.org/grpc/peer"
+
+	commonv1 "instant.dev/proto/common/v1"
+	provisionerv1 "instant.dev/proto/provisioner/v1"
+
+	"instant.dev/provisioner/internal/circuit"
+)
+
+// freshBreaker returns a closed breaker with a high threshold so a single
+// failure in a test never trips it (we drive the open state explicitly).
+func freshBreaker() *circuit.Breaker {
+	return circuit.NewBreaker("test", 1000, time.Minute)
+}
+
+func dropReq(token string) *provisionerv1.DeprovisionRequest {
+	return &provisionerv1.DeprovisionRequest{
+		Token:              token,
+		ProviderResourceId: "local:0",
+		ResourceType:       commonv1.ResourceType_RESOURCE_TYPE_POSTGRES,
+		RequestId:          "req-test",
+	}
+}
+
+func TestGuardedDrop_Success_IncrementsOkOutcome(t *testing.T) {
+	s := &Server{breakers: circuit.NewBreakers()}
+	before := testutil.ToFloat64(dropTotal.WithLabelValues("RESOURCE_TYPE_POSTGRES", "shared", "ok"))
+
+	called := false
+	err := s.guardedDrop(context.Background(), dropReq("tok-ok"), dropBackendShared, freshBreaker(), func() error {
+		called = true
+		return nil
+	})
+	if err != nil {
+		t.Fatalf("guardedDrop returned error: %v", err)
+	}
+	if !called {
+		t.Fatal("backend fn was not invoked")
+	}
+	after := testutil.ToFloat64(dropTotal.WithLabelValues("RESOURCE_TYPE_POSTGRES", "shared", "ok"))
+	if after != before+1 {
+		t.Fatalf("ok counter: got %v want %v", after, before+1)
+	}
+}
+
+func TestGuardedDrop_BackendError_IncrementsErrorOutcome_AndPropagates(t *testing.T) {
+	s := &Server{breakers: circuit.NewBreakers()}
+	before := testutil.ToFloat64(dropTotal.WithLabelValues("RESOURCE_TYPE_POSTGRES", "shared", "error"))
+
+	sentinel := errors.New("boom")
+	err := s.guardedDrop(context.Background(), dropReq("tok-err"), dropBackendShared, freshBreaker(), func() error {
+		return sentinel
+	})
+	if !errors.Is(err, sentinel) {
+		t.Fatalf("expected sentinel error to propagate, got %v", err)
+	}
+	after := testutil.ToFloat64(dropTotal.WithLabelValues("RESOURCE_TYPE_POSTGRES", "shared", "error"))
+	if after != before+1 {
+		t.Fatalf("error counter: got %v want %v", after, before+1)
+	}
+}
+
+func TestGuardedDrop_BreakerOpen_DoesNotInvokeBackend_AndRecordsBreakerOpen(t *testing.T) {
+	s := &Server{breakers: circuit.NewBreakers()}
+	before := testutil.ToFloat64(dropTotal.WithLabelValues("RESOURCE_TYPE_POSTGRES", "shared", "breaker_open"))
+
+	// Trip a fresh breaker: threshold 1, so one recorded failure opens it.
+	br := circuit.NewBreaker("test-open", 1, time.Minute)
+	br.Record(errors.New("trip"))
+	if br.Allow() {
+		t.Fatal("breaker should be open after exceeding threshold")
+	}
+
+	called := false
+	err := s.guardedDrop(context.Background(), dropReq("tok-open"), dropBackendShared, br, func() error {
+		called = true
+		return nil
+	})
+	if !errors.Is(err, circuit.ErrOpen) {
+		t.Fatalf("expected circuit.ErrOpen, got %v", err)
+	}
+	if called {
+		t.Fatal("backend fn must NOT be invoked when breaker is open — a drop must never reach the backend through an open breaker")
+	}
+	after := testutil.ToFloat64(dropTotal.WithLabelValues("RESOURCE_TYPE_POSTGRES", "shared", "breaker_open"))
+	if after != before+1 {
+		t.Fatalf("breaker_open counter: got %v want %v", after, before+1)
+	}
+}
+
+func TestCallerFromContext_WithPeer_ReturnsAddr(t *testing.T) {
+	ctx := peer.NewContext(context.Background(), &peer.Peer{
+		Addr: &net.TCPAddr{IP: net.IPv4(10, 109, 3, 201), Port: 54422},
+	})
+	got := callerFromContext(ctx)
+	if got != "10.109.3.201:54422" {
+		t.Fatalf("callerFromContext: got %q want %q", got, "10.109.3.201:54422")
+	}
+}
+
+func TestCallerFromContext_NoPeer_ReturnsUnknown(t *testing.T) {
+	if got := callerFromContext(context.Background()); got != "unknown" {
+		t.Fatalf("callerFromContext: got %q want %q", got, "unknown")
+	}
+}
+
+func TestDropOutcome_Mapping(t *testing.T) {
+	cases := []struct {
+		name string
+		err  error
+		want string
+	}{
+		{"nil", nil, "ok"},
+		{"breaker", circuit.ErrOpen, "breaker_open"},
+		{"other", errors.New("x"), "error"},
+	}
+	for _, c := range cases {
+		if got := dropOutcome(c.err); got != c.want {
+			t.Errorf("%s: dropOutcome=%q want %q", c.name, got, c.want)
+		}
+	}
+}