Bug or incorrect usage w/ sub-workflows from a graft with a `cascade_capture`

I have a reproduction below that I asked Claude to extract from our implementation, and seems to suffer the same issue.

The background is we have a workflow that loads data from our DB (populated from a previous job), and then for each item (for us it’s insurance plans) we need to fetch n child items (policies for the plan) from an API. There are ~200 plans and per plan there’s 300-2000 policies. Due to the API’s pagination, and the variability of the number of policies, we use a sub-workflow per plan.

What I’m seeing is that the sub-workflows never run, or insert into the database.

From the documentation, it seems like I should not be using Oban.insert_all in the sub-workflow defining function, as that would result in orphaned sub-workflows.

Am I misusing apply_graft?

defmodule NestedWorkflowRepro do
  @moduledoc """
  Minimal reproduction of multi-level nested workflow pattern using Oban.Pro.Workflow.

  This emulates the structure in PolicyBotPolicySync:
  - Level 1: Main workflow fetches items
  - Level 2: Graft per-item workflows
  - Level 3: Graft per-chunk workflows within each item workflow

  Each step returns simple concatenated strings for easy debugging.
  """

  use Oban.Pro.Worker, queue: :default, max_attempts: 1

  alias Oban.Pro.Workflow

  require Logger

  # Level 1: Main workflow functions

  @doc """
  Fetches the initial list of items to process.
  Returns %{items: ["A", "B", "C"]}
  """
  def fetch_items(_context) do
    items = ["A", "B", "C"]
    Logger.info("fetch_items: #{inspect(items)}")
    %{items: items, result: "fetched_items"}
  end

  @doc """
  Grafts a sub-workflow for each item.
  This is Level 2 grafting - creates per-item workflows.
  """
  def graft_per_item(%{fetch_items: %{items: items}}) do
    Logger.info("graft_per_item: creating workflows for #{length(items)} items")

    {items, &process_item_workflow/2}
    |> Workflow.apply_graft(context: %{batch_size: 2})
    |> Oban.insert_all()
  end

  # Level 2: Per-item workflow functions

  @doc """
  Creates a workflow to process a single item.
  This workflow will:
  1. Process initial batch
  2. Determine if more batches are needed
  3. If needed, graft sub-workflows for remaining batches (Level 3)
  """
  def process_item_workflow(item, %{batch_size: batch_size}) do
    workflow_name = "nested_workflow_repro_item_#{item}"

    Workflow.new(workflow_name: workflow_name)
    |> Workflow.put_context(%{
      item: item,
      batch_size: batch_size
    })
    |> Workflow.add_cascade(:process_initial_batch, &process_initial_batch/1)
    |> Workflow.add_cascade(:determine_remaining, &determine_remaining/1, deps: :process_initial_batch)
    |> Workflow.add_graft(:process_remaining_batches, &graft_remaining_batches/1,
      deps: [:process_initial_batch, :determine_remaining]
    )
  end

  @doc """
  Processes the initial batch for an item.
  Simulates work that determines total work needed.
  """
  def process_initial_batch(%{item: item, batch_size: batch_size}) do
    # Simulate: item "A" has 5 total chunks, "B" has 3, "C" has 1
    total_chunks =
      case item do
        "A" -> 5
        "B" -> 3
        "C" -> 1
      end

    processed = min(batch_size, total_chunks)

    result = "item_#{item}_initial_batch_#{processed}"
    Logger.info("process_initial_batch: #{result}")

    %{
      result: result,
      total_chunks: total_chunks,
      processed: processed,
      needs_more: processed < total_chunks
    }
  end

  @doc """
  Determines what remaining work is needed.
  """
  def determine_remaining(%{
        process_initial_batch: %{total_chunks: total, processed: processed, needs_more: needs_more},
        item: item
      }) do
    result = "item_#{item}_determined_#{total - processed}_remaining"
    Logger.info("determine_remaining: #{result}")

    %{
      result: result,
      remaining_chunks: total - processed,
      needs_more: needs_more
    }
  end

  @doc """
  Grafts sub-workflows for remaining batches if needed.
  This is Level 3 grafting - creates per-chunk workflows.
  """
  def graft_remaining_batches(%{
        process_initial_batch: %{processed: processed, total_chunks: total, needs_more: true},
        item: item,
        batch_size: batch_size
      }) do
    # Calculate chunks needed (similar to calculate_policy_chunks)
    chunks =
      Range.new(processed, total - 1, batch_size)
      |> Enum.map(fn idx -> %{chunk_index: idx, size: batch_size} end)

    Logger.info("graft_remaining_batches: item=#{item}, chunks=#{length(chunks)}")

    # Level 3: Graft per-chunk workflows
    {chunks, &process_chunk/2}
    |> Workflow.apply_graft()
    |> Oban.insert_all()
  end

  # No additional chunks needed
  def graft_remaining_batches(%{process_initial_batch: %{needs_more: false}, item: item}) do
    Logger.info("graft_remaining_batches: item=#{item}, no additional chunks needed")

    # Return empty workflow
    Workflow.new()
    |> Oban.insert_all()
  end

  # Level 3: Per-chunk workflow functions

  @doc """
  Processes a single chunk within an item's workflow.
  """
  def process_chunk(%{chunk_index: idx, size: size}, %{item: item}) do
    result = "item_#{item}_chunk_#{idx}_size_#{size}"
    Logger.info("process_chunk: #{result}")

    %{result: result}
  end

  @doc """
  Builds the main workflow.

  This creates a 3-level nested workflow structure:
  - Level 1: Main workflow (fetch items -> graft per-item)
  - Level 2: Per-item workflows (process initial -> graft per-chunk)
  - Level 3: Per-chunk workflows (process individual chunks)
  """
  def workflow(opts \\ []) do
    batch_size = Keyword.get(opts, :batch_size, 2)

    Workflow.new(workflow_name: "nested_workflow_repro_main")
    |> Workflow.put_context(%{batch_size: batch_size})
    |> Workflow.add_cascade(:fetch_items, &fetch_items/1)
    |> Workflow.add_graft(:process_items, &graft_per_item/1, deps: [:fetch_items])
  end

  @impl Oban.Pro.Worker
  def process(%Oban.Job{args: args}) do
    batch_size = Map.get(args, "batch_size", 2)

    workflow(batch_size: batch_size)
    |> Oban.insert_all()

    :ok
  end
end