diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 0000000..653663e
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1,60 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## What this is
+
+A Discourse plugin that adds custom fields to topics so Discourse can be used as a support/ticketing platform. It is currently **backend-only** — the `assets/javascripts` and `test/javascripts` directories are empty placeholders. Almost all logic lives in `plugin.rb`.
+
+## Architecture
+
+### `CUSTOM_FIELDS` registry (`plugin.rb`)
+The `CommunityCustomFields::CUSTOM_FIELDS` hash (name → type) is the single source of truth. Adding a field there automatically: registers its type on `Topic`, preloads it on `TopicList`, exposes it via the `topic_view` serializer, and makes it permittable in the controller's strong params. Add a field in one place only.
+
+### The support-ticket state machine (`plugin.rb` event handlers)
+The non-obvious core is the `topic_created` and `post_created` handlers, which maintain ticket state on topic custom fields. Understand these before editing:
+
+- **`status`** moves through `"new"` → `"open"` → `"snoozed"`/`"closed"` and back. `topic_created` seeds `status = "new"`. Valid values are the `CommunityCustomFields::STATUSES` list.
+- **`waiting_since` / `waiting_id`** track the customer who is waiting on a reply. Set when a non-admin posts; cleared when an admin posts a regular reply.
+- **`post_type`** drives branching: `1` = regular reply, `4` = whisper (staff-only note). Other post types are ignored. The first post (`post_number == 1`) is skipped because `topic_created` already handled it.
+- **Admin regular reply** (type 1): clears `waiting_*`.
+- **Admin whisper** (type 4): does *not* clear `waiting_*`, but can reopen a `snoozed`/`closed` topic.
+- **Customer reply** (non-admin): sets `waiting_*`, reopens `snoozed`, and reopens `closed` — with a **1-month rule**: if the topic was closed more than a month ago (or had no `last_assigned_to_id`), it reopens as `"new"`; otherwise it reopens as `"open"` and is reassigned to the last assignee.
+- `user.id <= 0` (system users) and non-`"regular"` archetypes (e.g. PMs) are skipped.
+
+### Controller (`app/controllers/community_custom_fields/custom_fields_controller.rb`)
+Admin-only `PUT` endpoint to set custom fields on a topic. Mounted at `/admin/plugins/community-custom-fields/:topic_id` (see `config/routes.rb`). Uses `Topic.unscoped.find` so it can update topics that are otherwise filtered out (e.g. deleted/closed). It validates any incoming `status` against `CommunityCustomFields::STATUSES` (rejecting unknown values with `422`) and records a status change (see below).
+
+### Status-change history (`TopicStatusChange`)
+Every status transition is logged to the `community_custom_fields_topic_status_changes` table (model: `app/models/community_custom_fields/topic_status_change.rb`). `TopicStatusChange.record` is the single writer — it no-ops unless the topic's current `status` differs from the passed `from_status`. It's called from two places, and `topic_created` is intentionally *not* recorded (no initial `"new"` row):
+
+- **Controller** (`source: "api_update"`) — passes the acting admin as `user_id`.
+- **`post_created`** (`source: "post_creation"`) — passes the triggering `post_id`.
+
+Row columns:
+- **`from_status` / `to_status`** — the transition; `from_status` is null when the topic had no prior status.
+- **`assignee_id`** — the assignee *before* the change (attributes the change to whoever owned the ticket during the status being left).
+- **`user_id`** (api_update) / **`post_id`** (post_creation) — what triggered the change; only one is set per row.
+- **`duration`** — seconds spent in the status being left. Measured from the prior recorded change; for a topic with no table entry yet, from when the current status was set (its `topic_custom_fields` row); otherwise from `topic.created_at`.
+- **`source`** — `"api_update"` or `"post_creation"`.
+
+## Commands
+
+Tests are **Discourse system specs** and cannot run standalone from this repo — they run inside a Discourse host app with this plugin symlinked into `plugins/`. From the Discourse core root:
+
+```bash
+LOAD_PLUGINS=1 bin/rspec plugins/community-custom-fields/spec/system/core_features_spec.rb
+```
+
+Linting uses Discourse's shared configs (`@discourse/lint-configs`). Install with `pnpm install` (pnpm 9.x, Node ≥ 22 required), then:
+
+```bash
+pnpm eslint .                  # JS
+pnpm ember-template-lint .     # Ember templates
+pnpm stylelint "**/*.scss"     # styles
+pnpm prettier --check .        # formatting
+bundle exec rubocop            # Ruby (rubocop-discourse, stree-compatible)
+bundle exec stree check .      # Ruby formatting (syntax_tree, print-width 100)
+```
+
+CI (`.github/workflows/discourse-plugin.yml`) runs the shared `discourse/.github` plugin workflow on push to `main` and on PRs.
diff --git a/app/controllers/community_custom_fields/custom_fields_controller.rb b/app/controllers/community_custom_fields/custom_fields_controller.rb
index 1f8fea7..6c01476 100644
--- a/app/controllers/community_custom_fields/custom_fields_controller.rb
+++ b/app/controllers/community_custom_fields/custom_fields_controller.rb
@@ -8,12 +8,32 @@ class CommunityCustomFields::CustomFieldsController < ::ApplicationController
 
   def update
     topic = Topic.unscoped.find(params[:topic_id])
-    topic.custom_fields.merge!(custom_fields_params)
+    fields = custom_fields_params
+
+    if fields.key?("status") && !CommunityCustomFields::STATUSES.include?(fields["status"])
+      return render json: { error: "Invalid status: #{fields["status"].inspect}" }, status: 422
+    end
+
+    previous_status = topic.custom_fields["status"]
+    previous_assignee_id = topic.custom_fields["assignee_id"]
+    previous_status_at =
+      TopicCustomField.where(topic_id: topic.id, name: "status").pick(:created_at)
+    topic.custom_fields.merge!(fields)
     if topic.save_custom_fields
+      CommunityCustomFields::TopicStatusChange.record(
+        topic: topic,
+        from_status: previous_status,
+        source: "api_update",
+        assignee_id: previous_assignee_id,
+        user_id: current_user.id,
+        previous_status_at: previous_status_at,
+      )
       topic.touch
       render json: success_json
     else
-      Rails.logger.error("Failed to save custom fields for topic #{topic.id}: #{topic.errors.full_messages}")
+      Rails.logger.error(
+        "Failed to save custom fields for topic #{topic.id}: #{topic.errors.full_messages}",
+      )
       render json: { error: topic.errors.full_messages }, status: 422
     end
   end
@@ -23,4 +43,4 @@ def update
   def custom_fields_params
     params.require(:custom_field).permit(*CommunityCustomFields::CUSTOM_FIELDS.keys)
   end
-end
\ No newline at end of file
+end
diff --git a/app/models/community_custom_fields/topic_status_change.rb b/app/models/community_custom_fields/topic_status_change.rb
new file mode 100644
index 0000000..959d5a8
--- /dev/null
+++ b/app/models/community_custom_fields/topic_status_change.rb
@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+module CommunityCustomFields
+  class TopicStatusChange < ActiveRecord::Base
+    self.table_name = "community_custom_fields_topic_status_changes"
+
+    belongs_to :topic, class_name: "::Topic"
+    belongs_to :assignee, class_name: "::User", optional: true
+    belongs_to :user, class_name: "::User", optional: true
+    belongs_to :post, class_name: "::Post", optional: true
+
+    def self.record(
+      topic:,
+      from_status:,
+      source:,
+      assignee_id:,
+      user_id: nil,
+      post_id: nil,
+      previous_status_at: nil
+    )
+      to_status = topic.custom_fields["status"]
+      return if to_status.blank? || to_status == from_status
+
+      last_change = where(topic_id: topic.id).order(:id).last
+      started_at = last_change&.created_at || previous_status_at || topic.created_at
+      duration = (Time.current - started_at).to_i
+
+      create!(
+        topic_id: topic.id,
+        from_status: from_status,
+        to_status: to_status,
+        source: source,
+        assignee_id: assignee_id,
+        user_id: user_id,
+        post_id: post_id,
+        duration: duration,
+      )
+    end
+  end
+end
+
+# == Schema Information
+#
+# Table name: community_custom_fields_topic_status_changes
+#
+#  id          :bigint           not null, primary key
+#  duration    :bigint           not null
+#  from_status :string
+#  source      :string           not null
+#  to_status   :string           not null
+#  created_at  :datetime         not null
+#  assignee_id :integer
+#  post_id     :integer
+#  topic_id    :integer          not null
+#  user_id     :integer
+#
+# Indexes
+#
+#  idx_on_assignee_id_bc22060231                                   (assignee_id)
+#  index_community_custom_fields_topic_status_changes_on_topic_id  (topic_id)
+#
diff --git a/config/routes.rb b/config/routes.rb
index 9f1ba92..5f7a4bc 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -1,9 +1,7 @@
 # frozen_string_literal: true
 
-CommunityCustomFields::Engine.routes.draw do
-  put '/:topic_id' => 'custom_fields#update'
-end
+CommunityCustomFields::Engine.routes.draw { put "/:topic_id" => "custom_fields#update" }
 
 Discourse::Application.routes.draw do
-  mount ::CommunityCustomFields::Engine, at: '/admin/plugins/community-custom-fields'
-end
\ No newline at end of file
+  mount ::CommunityCustomFields::Engine, at: "/admin/plugins/community-custom-fields"
+end
diff --git a/db/migrate/20260616011522_create_topic_status_changes.rb b/db/migrate/20260616011522_create_topic_status_changes.rb
new file mode 100644
index 0000000..70b0f5d
--- /dev/null
+++ b/db/migrate/20260616011522_create_topic_status_changes.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+class CreateTopicStatusChanges < ActiveRecord::Migration[7.2]
+  def change
+    create_table :community_custom_fields_topic_status_changes do |t|
+      t.integer :topic_id, null: false
+      t.integer :assignee_id
+      t.string :from_status
+      t.string :to_status, null: false
+      t.string :source, null: false
+      t.datetime :created_at, null: false
+    end
+
+    add_index :community_custom_fields_topic_status_changes, :topic_id
+    add_index :community_custom_fields_topic_status_changes, :assignee_id
+  end
+end
diff --git a/db/migrate/20260724172111_add_trigger_and_duration_to_topic_status_changes.rb b/db/migrate/20260724172111_add_trigger_and_duration_to_topic_status_changes.rb
new file mode 100644
index 0000000..70a93fd
--- /dev/null
+++ b/db/migrate/20260724172111_add_trigger_and_duration_to_topic_status_changes.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+class AddTriggerAndDurationToTopicStatusChanges < ActiveRecord::Migration[7.2]
+  def up
+    add_column :community_custom_fields_topic_status_changes, :user_id, :integer
+    add_column :community_custom_fields_topic_status_changes, :post_id, :integer
+    add_column :community_custom_fields_topic_status_changes, :duration, :bigint
+
+    # Backfill existing rows: seconds spent in the status being left, measured
+    # from the prior change for the topic (or the topic's creation).
+    execute <<~SQL
+      UPDATE community_custom_fields_topic_status_changes sc
+      SET duration = GREATEST(
+        TRUNC(
+          EXTRACT(EPOCH FROM (sc.created_at - COALESCE(prev.prev_created_at, t.created_at, sc.created_at)))
+        )::bigint,
+        0
+      )
+      FROM (
+        SELECT id, topic_id,
+               LAG(created_at) OVER (PARTITION BY topic_id ORDER BY id) AS prev_created_at
+        FROM community_custom_fields_topic_status_changes
+      ) prev
+      LEFT JOIN topics t ON t.id = prev.topic_id
+      WHERE sc.id = prev.id;
+    SQL
+
+    change_column_null :community_custom_fields_topic_status_changes, :duration, false
+  end
+
+  def down
+    remove_column :community_custom_fields_topic_status_changes, :duration
+    remove_column :community_custom_fields_topic_status_changes, :post_id
+    remove_column :community_custom_fields_topic_status_changes, :user_id
+  end
+end
diff --git a/lib/community_custom_fields/engine.rb b/lib/community_custom_fields/engine.rb
index 685ff68..b71c97b 100644
--- a/lib/community_custom_fields/engine.rb
+++ b/lib/community_custom_fields/engine.rb
@@ -10,4 +10,4 @@ class Engine < ::Rails::Engine
       Rails.autoloaders.main.eager_load_dir(scheduled_job_dir) if Dir.exist?(scheduled_job_dir)
     end
   end
-end
\ No newline at end of file
+end
diff --git a/plugin.rb b/plugin.rb
index 9c36a63..1e92381 100644
--- a/plugin.rb
+++ b/plugin.rb
@@ -13,7 +13,7 @@ module ::CommunityCustomFields
   CUSTOM_FIELDS = {
     assignee_id: :integer,
     first_assigned_to_id: :integer,
-    first_assigned_at: :datetime, 
+    first_assigned_at: :datetime,
     last_assigned_to_id: :integer,
     last_assigned_at: :datetime,
     account_name: :string,
@@ -26,11 +26,13 @@ module ::CommunityCustomFields
     closed_at: :datetime,
     snoozed_until: :datetime,
     waiting_since: :datetime,
-    waiting_id: :integer
+    waiting_id: :integer,
   }
+
+  STATUSES = %w[new open snoozed closed]
 end
 
-require_relative 'lib/community_custom_fields/engine.rb'
+require_relative "lib/community_custom_fields/engine.rb"
 
 after_initialize do
   CommunityCustomFields::CUSTOM_FIELDS.each do |name, type|
@@ -38,7 +40,7 @@ module ::CommunityCustomFields
   end
 
   TopicList.preloaded_custom_fields.merge(CommunityCustomFields::CUSTOM_FIELDS.keys)
-  
+
   add_to_serializer(:topic_view, :custom_fields) do
     object.topic.custom_fields.slice(*CommunityCustomFields::CUSTOM_FIELDS.keys)
   end
@@ -62,9 +64,13 @@ module ::CommunityCustomFields
     next if user.id <= 0
     next unless post.post_type == 1 || post.post_type == 4
     next if post.post_number == 1
-    
+
     topic = post.topic
     topic.custom_fields[:status] ||= "new"
+    previous_status = topic.custom_fields[:status]
+    previous_assignee_id = topic.custom_fields[:assignee_id]
+    previous_status_at =
+      TopicCustomField.where(topic_id: topic.id, name: "status").pick(:created_at)
 
     if user.admin && post.post_type == 1
       topic.custom_fields[:waiting_since] = nil
@@ -86,11 +92,11 @@ module ::CommunityCustomFields
           topic.custom_fields[:assignee_id] = topic.custom_fields[:last_assigned_to_id]
           topic.custom_fields[:last_assigned_at] = Time.current.iso8601
         end
-        
+
         topic.custom_fields[:outcome] = nil
         topic.custom_fields[:closed_at] = nil
       end
-    else 
+    else
       if user.id != topic.custom_fields[:waiting_id].to_i
         topic.custom_fields[:waiting_since] = Time.current.iso8601
         topic.custom_fields[:waiting_id] = user.id
@@ -105,19 +111,29 @@ module ::CommunityCustomFields
         # this handles an edge case where `closed_at` was never set
         topic.custom_fields[:closed_at] ||= Time.current.iso8601
 
-        if topic.custom_fields[:last_assigned_to_id].nil? || Time.iso8601(topic.custom_fields[:closed_at]) < 1.month.ago.iso8601
+        if topic.custom_fields[:last_assigned_to_id].nil? ||
+             Time.iso8601(topic.custom_fields[:closed_at]) < 1.month.ago.iso8601
           topic.custom_fields[:status] = "new"
         else
           topic.custom_fields[:status] = "open"
           topic.custom_fields[:assignee_id] = topic.custom_fields[:last_assigned_to_id]
           topic.custom_fields[:last_assigned_at] = Time.current.iso8601
         end
-        
+
         topic.custom_fields[:outcome] = nil
         topic.custom_fields[:closed_at] = nil
       end
     end
-    
+
     topic.save_custom_fields
+
+    CommunityCustomFields::TopicStatusChange.record(
+      topic: topic,
+      from_status: previous_status,
+      source: "post_creation",
+      assignee_id: previous_assignee_id,
+      post_id: post.id,
+      previous_status_at: previous_status_at,
+    )
   end
 end
diff --git a/spec/system/core_features_spec.rb b/spec/system/core_features_spec.rb
index 72ab0bf..db86db2 100644
--- a/spec/system/core_features_spec.rb
+++ b/spec/system/core_features_spec.rb
@@ -4,4 +4,4 @@
   before { enable_current_plugin }
 
   it_behaves_like "having working core features"
-end
\ No newline at end of file
+end