fix(retirement): allow null target_amount for retirement plans

for_owner bootstraps a Goal::Retirement before any target exists, but
goals.target_amount was NOT NULL at the DB level — the target_amount_required?
hook only dropped the AR validation. Creating a plan for a user with no
existing record (the demo user, caught in a live browser smoke) raised
PG::NotNullViolation. Tests missed it because for_owner(family_admin)
finds the retirement_bob fixture and never inserts.

Relaxes the column to nullable and re-asserts the guarantee for savings
goals via a type-aware check (type <> 'Goal' OR target_amount IS NOT NULL),
so base Goal rows still require a target at the DB level. Adds tests that
exercise the create path (a user with no fixture plan).

db/migrate/20260529120150_allow_null_target_amount_for_retirement_goals.rb

@@ -0,0 +1,17 @@
+class AllowNullTargetAmountForRetirementGoals < ActiveRecord::Migration[7.2]
+  # Retirement plans derive their target from the forecast (PR3), so they
+  # are created before any target exists. Relax the column NOT NULL but
+  # keep the guarantee for savings goals via a type-aware check, so base
+  # Goal rows still require a target at the DB level.
+  def up
+    change_column_null :goals, :target_amount, true
+    add_check_constraint :goals,
+      "type <> 'Goal' OR target_amount IS NOT NULL",
+      name: "chk_goals_savings_requires_target"
+  end
+
+  def down
+    remove_check_constraint :goals, name: "chk_goals_savings_requires_target"
+    change_column_null :goals, :target_amount, false
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.2].define(version: 2026_05_29_120140) do
+ActiveRecord::Schema[7.2].define(version: 2026_05_29_120150) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pgcrypto"
   enable_extension "plpgsql"
@@ -822,7 +822,7 @@ ActiveRecord::Schema[7.2].define(version: 2026_05_29_120140) do
   create_table "goals", id: :uuid, default: -> { "gen_random_uuid()" }, force: :cascade do |t|
     t.uuid "family_id", null: false
     t.string "name", null: false
-    t.decimal "target_amount", precision: 19, scale: 4, null: false
+    t.decimal "target_amount", precision: 19, scale: 4
     t.string "currency", null: false
     t.date "target_date"
     t.string "color"
@@ -841,6 +841,7 @@ ActiveRecord::Schema[7.2].define(version: 2026_05_29_120140) do
     t.check_constraint "char_length(name::text) <= 255", name: "chk_savings_goals_name_length"
     t.check_constraint "state::text = ANY (ARRAY['active'::character varying::text, 'paused'::character varying::text, 'completed'::character varying::text, 'archived'::character varying::text])", name: "chk_savings_goals_state_enum"
     t.check_constraint "target_amount > 0::numeric", name: "chk_savings_goals_target_amount_positive"
+    t.check_constraint "type::text <> 'Goal'::text OR target_amount IS NOT NULL", name: "chk_goals_savings_requires_target"
     t.check_constraint "type::text <> 'Goal::Retirement'::text OR user_id IS NOT NULL", name: "chk_goals_retirement_requires_owner"
   end
 

test/models/goal/retirement_test.rb

@@ -74,6 +74,26 @@ class Goal::RetirementTest < ActiveSupport::TestCase
     assert retirement.valid?, retirement.errors.full_messages.to_sentence
   end
 
+  test "for_owner bootstraps a valid plan without a target_amount" do
+    # family_member has no retirement fixture, so this exercises the
+    # create path (family_admin would just find retirement_bob).
+    member = users(:family_member)
+
+    plan = Goal::Retirement.for_owner(member)
+
+    assert plan.persisted?
+    assert_nil plan.target_amount
+    assert_equal member.id, plan.user_id
+    assert_equal member.family_id, plan.family_id
+  end
+
+  test "for_owner is idempotent (one plan per user)" do
+    member = users(:family_member)
+    first = Goal::Retirement.for_owner(member)
+    second = Goal::Retirement.for_owner(member)
+    assert_equal first.id, second.id
+  end
+
   test "has pension sources, statements, adjustments, and bucket accounts" do
     plan = goals(:retirement_bob)
     assert_includes plan.pension_sources, pension_sources(:de_grv_bob)