Phase 2: first real DO write step — CreateDropletSnapshot

DigitalOcean.Client write methods:
- create_droplet_snapshot/3 — POST a snapshot action (async)
- get_droplet_action/3      — poll action status
- list_droplet_snapshots/2  — snapshots for a droplet
- delete_snapshot/2         — DELETE (used by compensation)
All use the "provisioning" token purpose.

Steps.CreateDropletSnapshot — the first saga step that touches real
infra:
- execute: deterministic snapshot name (arcadia-snap-<droplet>-<saga8>);
  checks context for a prior snapshot_id, then checks DO for a snapshot
  already carrying that name (crash-between-post-and-save recovery),
  then posts the action, polls to completion, finds the resulting
  snapshot, records snapshot_id + snapshot_name in context.
- compensate: deletes the snapshot; treats HTTP 404 as success.

Provisioning.snapshot_droplet/2 — convenience saga starter.

Two DO eventual-consistency gotchas surfaced + handled:
- After a snapshot action reports "completed", the snapshot lags a few
  seconds before appearing in /droplets/:id/snapshots. The step now
  retries the lookup (find_snapshot_with_retry, 12x5s) instead of
  failing with :snapshot_not_found_after_completion.
- Deletion has the same lag the other way — a deleted snapshot lingers
  in the listing briefly. compensate just trusts the DELETE 2xx/404;
  no post-delete verification needed.

Live smoke verified end-to-end against holyspiritbraypark.com:
[CreateDropletSnapshot, Fail] saga — the step created real snapshot
229305609, the Fail step triggered compensation, compensation deleted
the snapshot. Final: saga rolled_back, ledger
[create_droplet_snapshot: compensated, fail: failed], zero leftover on DO.

Test-harness note: smoke tests create sagas via Provisioning.create_saga
(no Oban enqueue) so a single manual Runner.perform/1 owns execution —
start_saga/1 enqueues an Oban job, and running both racing the same saga
corrupts the step ledger. Production only ever runs via Oban.

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

lib/arcadia_cloud/digital_ocean/client.ex

@@ -28,6 +28,40 @@ defmodule ArcadiaCloud.DigitalOcean.Client do
     list_paginated("/droplets/#{droplet_id}/backups", "backups", opts)
   end
 
+  def list_droplet_snapshots(droplet_id, opts \\ []) do
+    list_paginated("/droplets/#{droplet_id}/snapshots", "snapshots", opts)
+  end
+
+  # ---- write actions --------------------------------------------------------
+
+  @doc """
+  Request a snapshot of a droplet. Returns {:ok, action} — the snapshot
+  is created asynchronously; poll `get_droplet_action/3` until the action
+  status is "completed".
+  """
+  def create_droplet_snapshot(droplet_id, snapshot_name, opts \\ []) do
+    case request(:post, "/droplets/#{droplet_id}/actions",
+           body: %{type: "snapshot", name: snapshot_name},
+           purpose: opts[:purpose] || "provisioning"
+         ) do
+      {:ok, %{"action" => action}} -> {:ok, action}
+      other -> other
+    end
+  end
+
+  def get_droplet_action(droplet_id, action_id, opts \\ []) do
+    case request(:get, "/droplets/#{droplet_id}/actions/#{action_id}",
+           purpose: opts[:purpose] || "provisioning"
+         ) do
+      {:ok, %{"action" => action}} -> {:ok, action}
+      other -> other
+    end
+  end
+
+  def delete_snapshot(snapshot_id, opts \\ []) do
+    request(:delete, "/snapshots/#{snapshot_id}", purpose: opts[:purpose] || "provisioning")
+  end
+
   # ---- billing --------------------------------------------------------------
 
   def get_balance(opts \\ []) do