diff --git a/.gitignore b/.gitignore
index fb27d6a..c4110e6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,6 +5,9 @@
 /tmp/
 /test/tmp/
 /test/dummy/log/*.log
+# Rotated logs too: `test.log.0` doesn't match `*.log`, and a 100MB one is how
+# it gets noticed — at the push.
+/test/dummy/log/*.log.*
 /test/dummy/storage/
 /test/dummy/tmp/
 
diff --git a/CHANGELOG.md b/CHANGELOG.md
index f268e04..075e93c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,12 @@ behaviour, and every new surface is off until you switch it on.
 
 ### Added
 
+- `ApprovalEngine::OutboxEvent.purge!` — the outbox is a queue, not a ledger,
+  and nothing swept it: one row per activation, decision and outcome, kept
+  forever. Purges relayed events past a window (30 days by default), keeps dead
+  letters whatever their age, and never touches the audit trail.
+
+
 - `ApprovalEngine.define_flow(name, tenant:, model:)` — a declarative DSL for a
   whole flow (the template, its ordered steps, and the rules that route to it)
   in one block, instead of three `create!` calls whose relationship you have to
@@ -86,6 +92,14 @@ behaviour, and every new surface is off until you switch it on.
   `define_flow` may route to. `nil`, the default, means no vocabulary is declared
   and nothing is checked; set it and a `group:` typo stops the seed instead of
   resolving zero actors at build time.
+- `ApprovalEngine::TestHelpers` — test support for host applications, so an
+  adopter is not hand-rolling fixtures to test their own flow.
+  `approve_approval!` walks a flow to a decision, `reject_approval!` stops at
+  whatever is waiting, `pending_approval_steps` is the inbox for one record, and
+  `drain_approval_outbox!` relays the side-effects — without which
+  `after_approved` has genuinely not run yet, and a test asserting on it fails
+  for the right reason while looking like the wrong one. Actions and queries
+  rather than assertions, so they read the same under Minitest and RSpec.
 
 ### Changed
 
@@ -101,22 +115,20 @@ behaviour, and every new surface is off until you switch it on.
   `Alternatives` section naming the neighbours. `test/docs_test.rb` now fails the
   build if the README documents a config key, an `ApprovalEngine` method, a
   generator, or an image that does not exist.
-
-### Changed
-
+- **Minimum Ruby is now 3.2** and **PostgreSQL 13+ is stated explicitly.** 3.1
+  was claimed but never tested and is past end of life; the tables key on
+  `gen_random_uuid()`, which is core Postgres only from 13.
+- `shiny_json_logic` is pinned to `~> 0.3.6` rather than `~> 0.3`. It is pre-1.0
+  and evaluates every routing rule, so a floating minor could change matching
+  behaviour under an adopter on a routine `bundle update`.
+- The admin renders validation failures with `422` rather than
+  `:unprocessable_entity`, which Rack has deprecated and will remove — the
+  replacement symbol does not exist on Rails 7.1, so the number is the portable
+  spelling.
 - **Minimum Rails is now 7.1**, up from 7.0.8. The outbox relay's retry backoff
   uses `:polynomially_longer`, which 7.0 does not know, and 7.0 is past security
   support. CI now runs the whole supported range rather than one version of it.
 
-### Added
-
-- `ApprovalEngine::TestHelpers` — test support for host applications.
-  `approve_approval!` walks a flow to a decision, `reject_approval!` stops at
-  whatever is waiting, `pending_approval_steps` is the inbox for one record, and
-  `drain_approval_outbox!` relays the side-effects, without which `after_approved`
-  has genuinely not run yet. Actions and queries rather than assertions, so they
-  read the same under Minitest and RSpec.
-
 ### Fixed
 
 - Step notifications ignored delegations. A delegate can act on a step, so
diff --git a/README.md b/README.md
index da9a5c3..c7f8bd0 100644
--- a/README.md
+++ b/README.md
@@ -3,7 +3,7 @@
 [![Gem Version](https://img.shields.io/gem/v/approval_engine?logo=rubygems&color=E9573F)](https://rubygems.org/gems/approval_engine)
 [![Downloads](https://img.shields.io/gem/dt/approval_engine?logo=rubygems&color=blue)](https://rubygems.org/gems/approval_engine)
 [![CI](https://github.com/Harry-kp/approval_engine/actions/workflows/ci.yml/badge.svg)](https://github.com/Harry-kp/approval_engine/actions/workflows/ci.yml)
-![Ruby](https://img.shields.io/badge/ruby-%3E%3D%203.1-CC342D)
+![Ruby](https://img.shields.io/badge/ruby-%3E%3D%203.2-CC342D)
 ![Rails](https://img.shields.io/badge/rails-%3E%3D%207.1-D30001)
 ![License: MIT](https://img.shields.io/badge/license-MIT-blue)
 
@@ -35,7 +35,8 @@ approved, who approves, and what happens next.
 
 ## 60-second quickstart
 
-Needs PostgreSQL (the routing engine uses `jsonb`), Rails 7.1+, Ruby 3.1+.
+Needs PostgreSQL 13+ (the routing engine uses `jsonb` and `gin`; the tables key
+on `gen_random_uuid()`), Rails 7.1+, Ruby 3.2+.
 
 ```sh
 bundle add approval_engine
@@ -505,6 +506,22 @@ A rule too complex for the simple form — an `or`, a nested group, a substring
 into something it isn't. That fallback is the point: the form is a convenience
 over the storage format, never a lossy replacement for it.
 
+## Housekeeping
+
+The audit trail is the point of the ledger and is never swept. The **outbox is
+not** — it is a queue, one row per activation, decision and outcome, and a
+relayed row has no reader. Sweep it on whatever schedule you already run:
+
+```ruby
+ApprovalEngine::OutboxEvent.purge!                     # relayed, older than 30 days
+ApprovalEngine::OutboxEvent.purge!(older_than: 7.days)
+```
+
+Dead letters are kept whatever their age — an event that exhausted its retries
+is evidence of a callback that needs fixing, not litter. Find them with
+`ApprovalEngine::OutboxEvent.failed`, and clear `failed_at` to let the relay
+pick one up again.
+
 ## Core concepts
 
 | Term | What it is |
@@ -586,7 +603,7 @@ edge cases yet.
 
 ## Development
 
-ApprovalEngine needs Ruby 3.1+ and PostgreSQL.
+ApprovalEngine needs Ruby 3.2+ and PostgreSQL 13+.
 
 ```sh
 bin/setup
diff --git a/app/controllers/approval_engine/admin/template_steps_controller.rb b/app/controllers/approval_engine/admin/template_steps_controller.rb
index a807ab5..a325f08 100644
--- a/app/controllers/approval_engine/admin/template_steps_controller.rb
+++ b/app/controllers/approval_engine/admin/template_steps_controller.rb
@@ -21,7 +21,7 @@ def create
         if @template_step.save
           redirect_to admin_track_template_path(@track_template), notice: "Step added."
         else
-          render :new, status: :unprocessable_entity
+          render :new, status: 422
         end
       end
 
@@ -32,7 +32,7 @@ def update
         if @template_step.update(template_step_params)
           redirect_to admin_track_template_path(@track_template), notice: "Step updated."
         else
-          render :edit, status: :unprocessable_entity
+          render :edit, status: 422
         end
       end
 
diff --git a/app/controllers/approval_engine/admin/track_templates_controller.rb b/app/controllers/approval_engine/admin/track_templates_controller.rb
index f527dee..85fa235 100644
--- a/app/controllers/approval_engine/admin/track_templates_controller.rb
+++ b/app/controllers/approval_engine/admin/track_templates_controller.rb
@@ -36,7 +36,7 @@ def create
         if @track_template.save
           redirect_to admin_track_template_path(@track_template), notice: "Template created."
         else
-          render :new, status: :unprocessable_entity
+          render :new, status: 422
         end
       end
 
@@ -47,7 +47,7 @@ def update
         if @track_template.update(track_template_params)
           redirect_to admin_track_template_path(@track_template), notice: "Template updated."
         else
-          render :edit, status: :unprocessable_entity
+          render :edit, status: 422
         end
       end
 
diff --git a/app/controllers/approval_engine/admin/trigger_rules_controller.rb b/app/controllers/approval_engine/admin/trigger_rules_controller.rb
index d818508..27b03d0 100644
--- a/app/controllers/approval_engine/admin/trigger_rules_controller.rb
+++ b/app/controllers/approval_engine/admin/trigger_rules_controller.rb
@@ -34,7 +34,7 @@ def create
         else
           @trigger_rule.errors.add(:condition, @condition_error) if @condition_error
           prepare_condition_editor
-          render :new, status: :unprocessable_entity
+          render :new, status: 422
         end
       end
 
@@ -50,7 +50,7 @@ def update
         else
           @trigger_rule.errors.add(:condition, @condition_error) if @condition_error
           prepare_condition_editor
-          render :edit, status: :unprocessable_entity
+          render :edit, status: 422
         end
       end
 
diff --git a/app/models/approval_engine/outbox_event.rb b/app/models/approval_engine/outbox_event.rb
index a2c4951..0cc5355 100644
--- a/app/models/approval_engine/outbox_event.rb
+++ b/app/models/approval_engine/outbox_event.rb
@@ -13,6 +13,7 @@ class OutboxEvent < ApplicationRecord
     validates :tenant_id, :event_name, presence: true
 
     scope :unprocessed, -> { where(processed: false) }
+    scope :processed, -> { where(processed: true) }
     # Dead letters: delivery retries were exhausted. Excluded from drain! so a
     # permanently-failing callback isn't resurrected forever; surfaced here for
     # ops to inspect and replay (clear failed_at to let drain! pick it up again).
@@ -34,6 +35,23 @@ def self.drain!(older_than: 1.minute, limit: 1000)
       end
     end
 
+    # The outbox is a queue, not a ledger: once an event is relayed its row has
+    # no reader, and one is written per step activation, decision and outcome.
+    # Left alone the table grows without bound, so a host is expected to sweep
+    # it — the audit trail lives in AuditLog and is never touched by this.
+    #
+    #   ApprovalEngine::OutboxEvent.purge!                      # processed, 30d+
+    #   ApprovalEngine::OutboxEvent.purge!(older_than: 7.days)
+    #
+    # Returns the number of rows deleted. Dead letters are kept regardless of
+    # age: an event that exhausted its retries is evidence, not litter.
+    def self.purge!(older_than: 30.days, limit: 10_000)
+      ids = processed.where(failed_at: nil)
+                     .where(processed_at: ..older_than.ago)
+                     .order(:processed_at).limit(limit).pluck(:id)
+      where(id: ids).delete_all
+    end
+
     def mark_processed!
       update!(processed: true, processed_at: Time.current, error_payload: nil, delivery_error: nil)
     end
diff --git a/approval_engine.gemspec b/approval_engine.gemspec
index 6c4dbfb..ae4f39e 100644
--- a/approval_engine.gemspec
+++ b/approval_engine.gemspec
@@ -25,7 +25,7 @@ Gem::Specification.new do |spec|
   DESC
   spec.license = "MIT"
 
-  spec.required_ruby_version = ">= 3.1.0"
+  spec.required_ruby_version = ">= 3.2.0"
 
   # `source_code_uri` is pinned to the repository rather than derived from
   # `homepage`: moving the homepage some day must not silently repoint the
@@ -51,5 +51,7 @@ Gem::Specification.new do |spec|
   end
 
   spec.add_dependency "rails", ">= 7.1", "< 9.0"
-  spec.add_dependency "shiny_json_logic", "~> 0.3"
+  # Pinned to the patch series on purpose: pre-1.0 gems may break across a
+  # minor, and this one evaluates every routing rule. Widen deliberately.
+  spec.add_dependency "shiny_json_logic", "~> 0.3.6"
 end
diff --git a/test/models/approval_engine/outbox_retention_test.rb b/test/models/approval_engine/outbox_retention_test.rb
new file mode 100644
index 0000000..c335b4a
--- /dev/null
+++ b/test/models/approval_engine/outbox_retention_test.rb
@@ -0,0 +1,52 @@
+require "test_helper"
+
+module ApprovalEngine
+  # The outbox is a queue: one row per activation, decision and outcome, and
+  # nothing reads a relayed row again. Without a sweep the table grows forever.
+  class OutboxRetentionTest < ApprovalEngine::TestCase
+    setup do
+      invoice   = Invoice.create!(tenant_id: TENANT, amount: 6000)
+      @approval = Approval.create!(tenant_id: TENANT, target: invoice, status: "approved")
+    end
+
+    def event(processed:, processed_at: nil, failed_at: nil)
+      OutboxEvent.create!(tenant_id: TENANT, event_name: "approval.approved", record: @approval).tap do |e|
+        e.update_columns(processed: processed, processed_at: processed_at, failed_at: failed_at)
+      end
+    end
+
+    test "purges relayed events past the window, and keeps recent ones" do
+      old    = event(processed: true, processed_at: 60.days.ago)
+      recent = event(processed: true, processed_at: 1.day.ago)
+
+      assert_equal 1, OutboxEvent.purge!
+
+      assert_not OutboxEvent.exists?(old.id)
+      assert OutboxEvent.exists?(recent.id)
+    end
+
+    test "never purges work that has not been relayed" do
+      pending = event(processed: false, processed_at: nil)
+
+      OutboxEvent.purge!(older_than: 0.seconds)
+
+      assert OutboxEvent.exists?(pending.id), "an unrelayed event is still owed to the host"
+    end
+
+    # An event that exhausted its retries is evidence of a broken callback.
+    test "keeps dead letters however old they are" do
+      dead = event(processed: true, processed_at: 90.days.ago, failed_at: 90.days.ago)
+
+      OutboxEvent.purge!
+
+      assert OutboxEvent.exists?(dead.id)
+    end
+
+    test "honours an explicit window and returns the count deleted" do
+      event(processed: true, processed_at: 10.days.ago)
+      event(processed: true, processed_at: 10.days.ago)
+
+      assert_equal 2, OutboxEvent.purge!(older_than: 7.days)
+    end
+  end
+end