Phase 2: drift detection

Compares cloud_provisioned.spec (what we asked DO for) against the live
cloud_resources row (what DO actually has). Any divergence becomes an
operator-resolvable drift record.

cloud_drift table: one row per drifted field. status open/accepted/
reverted/stale. Partial unique index keeps at most one OPEN drift per
(resource, field); resolved rows are retained as history.

ArcadiaCloud.Drift context:
- detect_all/0 — sweeps every provisioned resource. Per field in spec,
  resolves the actual value (top-level schema field first, then attrs),
  compares with loose equality (stringified scalars; lists as sets so
  JSON round-trips don't false-positive). Mismatches upsert a cloud_drift
  row + emit a drift_detected event in the resource event log.
- close_stale_drift — an open drift whose field no longer mismatches
  (fixed elsewhere) closes as "stale" on the next sweep.
- accept_drift/2 — the live value becomes the new desired-state: parent
  cloud_provisioned.spec is updated, spec_version bumped, drift closed
  "accepted". Revert (mutating live infra back to spec) is intentionally
  NOT here — it needs a saga and lands with the droplet-resize work.

DriftDetectionWorker — Oban cron at :20 past the hour, offset past the
:15 resource syncs so it compares against fresh inventory.

Provisioning.record_provisioned/3 — populates cloud_provisioned desired-
state (upsert on resource_id, bumps spec_version). Future provisioning
sagas call this; for now it's how drift gets something to detect.

API (platform_admin only):
- GET  /api/v1/drift            — open drift inbox
- POST /api/v1/drift/:id/accept — adopt live value as desired-state

Smoke verified: recorded a droplet's desired spec with a deliberately
wrong size_slug + a correct region; detect_all flagged only size_slug,
wrote the drift_detected event; accept updated the spec to the live
value and closed the drift; re-detect found zero drift.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/arcadia_cloud/provisioning/cloud_drift.ex

@@ -0,0 +1,34 @@
+defmodule ArcadiaCloud.Provisioning.CloudDrift do
+  use Ecto.Schema
+  import Ecto.Changeset
+
+  @primary_key {:id, :binary_id, autogenerate: true}
+  @foreign_key_type :binary_id
+
+  @statuses ~w(open accepted reverted stale)
+
+  schema "cloud_drift" do
+    field :field, :string
+    field :expected, :map
+    field :actual, :map
+    field :status, :string, default: "open"
+    field :detected_at, :utc_datetime
+    field :resolved_at, :utc_datetime
+    field :resolved_by, :string
+
+    belongs_to :resource, ArcadiaCloud.Cloud.CloudResource
+    belongs_to :provisioned, ArcadiaCloud.Provisioning.CloudProvisioned
+
+    timestamps(type: :utc_datetime)
+  end
+
+  @required ~w(resource_id provisioned_id field detected_at)a
+  @optional ~w(expected actual status resolved_at resolved_by)a
+
+  def changeset(drift, attrs) do
+    drift
+    |> cast(attrs, @required ++ @optional)
+    |> validate_required(@required)
+    |> validate_inclusion(:status, @statuses)
+  end
+end