Fix cycle end calculation for misaligned cycle_start dates

Make cycle generation idempotent by skipping existing cycles

lib/mv/membership_fees/cycle_generator.ex

@@ -386,18 +386,44 @@ defmodule Mv.MembershipFees.CycleGenerator do
           {:ok, cycle} ->
             {:ok, cycle, []}
 
+          {:error, %Ash.Error.Invalid{errors: [%Ash.Error.Changes.InvalidAttribute{private_vars: %{constraint: constraint, constraint_type: :unique}}]}} = error ->
+            # Cycle already exists (unique constraint violation) - skip it silently
+            # This makes the function idempotent and prevents errors on server restart
+            if constraint == "membership_fee_cycles_unique_cycle_per_member_index" do
+              {:skip, cycle_start}
+            else
+              {:error, {cycle_start, error}}
+            end
+
           {:error, reason} ->
             {:error, {cycle_start, reason}}
         end
       end)
 
-    {successes, errors} = Enum.split_with(results, &match?({:ok, _, _}, &1))
+    {successes, skips, errors} =
+      Enum.reduce(results, {[], [], []}, fn
+        {:ok, cycle, notifications}, {successes, skips, errors} ->
+          {[{:ok, cycle, notifications} | successes], skips, errors}
+
+        {:skip, cycle_start}, {successes, skips, errors} ->
+          {successes, [cycle_start | skips], errors}
+
+        {:error, error}, {successes, skips, errors} ->
+          {successes, skips, [error | errors]}
+      end)
 
     all_notifications =
       Enum.flat_map(successes, fn {:ok, _cycle, notifications} -> notifications end)
 
     if Enum.empty?(errors) do
       successful_cycles = Enum.map(successes, fn {:ok, cycle, _notifications} -> cycle end)
+
+      if Enum.any?(skips) do
+        Logger.debug(
+          "Skipped #{length(skips)} cycles that already exist for member #{member_id}"
+        )
+      end
+
       {:ok, successful_cycles, all_notifications}
     else
       Logger.warning("Some cycles failed to create: #{inspect(errors)}")