diff --git a/app/controllers/api/v1/accounts_controller.rb b/app/controllers/api/v1/accounts_controller.rb
index e5e4cad3c..07b654112 100644
--- a/app/controllers/api/v1/accounts_controller.rb
+++ b/app/controllers/api/v1/accounts_controller.rb
@@ -28,7 +28,7 @@ class Api::V1::AccountsController < Api::V1::BaseController
 
     render json: {
       error: "internal_server_error",
-      message: "Error: #{e.message}"
+      message: "An unexpected error occurred"
     }, status: :internal_server_error
 end
 
diff --git a/app/controllers/api/v1/auth_controller.rb b/app/controllers/api/v1/auth_controller.rb
index e522fb03f..c92e80334 100644
--- a/app/controllers/api/v1/auth_controller.rb
+++ b/app/controllers/api/v1/auth_controller.rb
@@ -45,23 +45,28 @@ module Api
         user.family = family
         user.role = User.role_for_new_family_creator
 
-        if user.save
-          # Claim invite code if provided
-          InviteCode.claim!(params[:invite_code]) if params[:invite_code].present?
-
-          # Create device and OAuth token
-          begin
+        # Atomic: user creation, invite-code claim, and device/token issuance
+        # either all commit or none do. Without this, a post-commit device
+        # failure (e.g., racing uniqueness) would leave the user/invite/family
+        # committed while the client got a 422 "Failed to register device".
+        token_response = nil
+        begin
+          ActiveRecord::Base.transaction do
+            unless user.save
+              render json: { errors: user.errors.full_messages }, status: :unprocessable_entity
+              raise ActiveRecord::Rollback
+            end
+            InviteCode.claim!(params[:invite_code]) if params[:invite_code].present?
             device = MobileDevice.upsert_device!(user, device_params)
             token_response = device.issue_token!
-          rescue ActiveRecord::RecordInvalid => e
-            render json: { error: "Failed to register device: #{e.message}" }, status: :unprocessable_entity
-            return
           end
-
-          render json: token_response.merge(user: mobile_user_payload(user)), status: :created
-        else
-          render json: { errors: user.errors.full_messages }, status: :unprocessable_entity
+        rescue ActiveRecord::RecordInvalid => e
+          Rails.logger.error("[Auth] Device registration failed: #{e.class} - #{e.message}")
+          render json: { error: "Failed to register device" }, status: :unprocessable_entity
+          return
         end
+
+        render json: token_response.merge(user: mobile_user_payload(user)), status: :created if token_response
       end
 
       def login
@@ -90,7 +95,8 @@ module Api
             device = MobileDevice.upsert_device!(user, device_params)
             token_response = device.issue_token!
           rescue ActiveRecord::RecordInvalid => e
-            render json: { error: "Failed to register device: #{e.message}" }, status: :unprocessable_entity
+            Rails.logger.error("[Auth] Device registration failed: #{e.message}")
+            render json: { error: "Failed to register device" }, status: :unprocessable_entity
             return
           end
 
@@ -312,7 +318,20 @@ module Api
           return false if device.nil?
 
           required_fields = %w[device_id device_name device_type os_version app_version]
-          required_fields.all? { |field| device[field].present? }
+          return false unless required_fields.all? { |field| device[field].present? }
+
+          # Run MobileDevice's attribute-level validations up front (e.g.,
+          # device_type must be ios/android/web) so a misconfigured client
+          # is rejected BEFORE signup commits user/family/invite. Skip
+          # errors we can't evaluate without a user: the :user belongs_to
+          # presence check, and device_id uniqueness scoped to user_id
+          # (upsert_device! treats collisions as updates anyway).
+          preview = MobileDevice.new(device_params)
+          preview.valid?
+          relevant_errors = preview.errors.errors.reject do |err|
+            err.type == :taken || err.attribute == :user
+          end
+          relevant_errors.empty?
         end
 
         def device_params
@@ -373,7 +392,8 @@ module Api
 
           render json: token_response.merge(user: mobile_user_payload(user))
         rescue ActiveRecord::RecordInvalid => e
-          render json: { error: "Failed to register device: #{e.message}" }, status: :unprocessable_entity
+          Rails.logger.error("[Auth] Device registration failed: #{e.message}")
+          render json: { error: "Failed to register device" }, status: :unprocessable_entity
         end
 
         def ensure_write_scope
diff --git a/app/controllers/api/v1/categories_controller.rb b/app/controllers/api/v1/categories_controller.rb
index c810ffa25..fa30d53d4 100644
--- a/app/controllers/api/v1/categories_controller.rb
+++ b/app/controllers/api/v1/categories_controller.rb
@@ -29,7 +29,7 @@ class Api::V1::CategoriesController < Api::V1::BaseController
 
     render json: {
       error: "internal_server_error",
-      message: "Error: #{e.message}"
+      message: "An unexpected error occurred"
     }, status: :internal_server_error
   end
 
@@ -41,7 +41,7 @@ class Api::V1::CategoriesController < Api::V1::BaseController
 
     render json: {
       error: "internal_server_error",
-      message: "Error: #{e.message}"
+      message: "An unexpected error occurred"
     }, status: :internal_server_error
   end
 
diff --git a/app/controllers/api/v1/holdings_controller.rb b/app/controllers/api/v1/holdings_controller.rb
index 58d094abd..7f08dfe3b 100644
--- a/app/controllers/api/v1/holdings_controller.rb
+++ b/app/controllers/api/v1/holdings_controller.rb
@@ -102,7 +102,7 @@ class Api::V1::HoldingsController < Api::V1::BaseController
       Rails.logger.error exception.backtrace.join("\n")
       render json: {
         error: "internal_server_error",
-        message: "Error: #{exception.message}"
+        message: "An unexpected error occurred"
       }, status: :internal_server_error
     end
 end
diff --git a/app/controllers/api/v1/sync_controller.rb b/app/controllers/api/v1/sync_controller.rb
index b5f89fb60..add56fd44 100644
--- a/app/controllers/api/v1/sync_controller.rb
+++ b/app/controllers/api/v1/sync_controller.rb
@@ -21,7 +21,7 @@ class Api::V1::SyncController < Api::V1::BaseController
 
     render json: {
       error: "internal_server_error",
-      message: "Error: #{e.message}"
+      message: "An unexpected error occurred"
     }, status: :internal_server_error
   end
 
diff --git a/app/controllers/api/v1/trades_controller.rb b/app/controllers/api/v1/trades_controller.rb
index 8f442c81a..0538fe321 100644
--- a/app/controllers/api/v1/trades_controller.rb
+++ b/app/controllers/api/v1/trades_controller.rb
@@ -292,7 +292,7 @@ class Api::V1::TradesController < Api::V1::BaseController
       Rails.logger.error exception.backtrace.join("\n")
       render json: {
         error: "internal_server_error",
-        message: "Error: #{exception.message}"
+        message: "An unexpected error occurred"
       }, status: :internal_server_error
     end
 
diff --git a/app/controllers/api/v1/transactions_controller.rb b/app/controllers/api/v1/transactions_controller.rb
index b5942b7fc..c3538c79e 100644
--- a/app/controllers/api/v1/transactions_controller.rb
+++ b/app/controllers/api/v1/transactions_controller.rb
@@ -47,7 +47,7 @@ class Api::V1::TransactionsController < Api::V1::BaseController
 
     render json: {
       error: "internal_server_error",
-      message: "Error: #{e.message}"
+      message: "An unexpected error occurred"
     }, status: :internal_server_error
   end
 
@@ -61,7 +61,7 @@ class Api::V1::TransactionsController < Api::V1::BaseController
 
     render json: {
       error: "internal_server_error",
-      message: "Error: #{e.message}"
+      message: "An unexpected error occurred"
     }, status: :internal_server_error
   end
 
@@ -102,7 +102,7 @@ class Api::V1::TransactionsController < Api::V1::BaseController
 
     render json: {
       error: "internal_server_error",
-      message: "Error: #{e.message}"
+      message: "An unexpected error occurred"
     }, status: :internal_server_error
 end
 
@@ -148,7 +148,7 @@ end
 
     render json: {
       error: "internal_server_error",
-      message: "Error: #{e.message}"
+      message: "An unexpected error occurred"
     }, status: :internal_server_error
   end
 
@@ -171,7 +171,7 @@ end
 
     render json: {
       error: "internal_server_error",
-      message: "Error: #{e.message}"
+      message: "An unexpected error occurred"
     }, status: :internal_server_error
   end
 
diff --git a/app/controllers/api/v1/valuations_controller.rb b/app/controllers/api/v1/valuations_controller.rb
index 633a90461..495259bf5 100644
--- a/app/controllers/api/v1/valuations_controller.rb
+++ b/app/controllers/api/v1/valuations_controller.rb
@@ -13,7 +13,7 @@ class Api::V1::ValuationsController < Api::V1::BaseController
 
     render json: {
       error: "internal_server_error",
-      message: "Error: #{e.message}"
+      message: "An unexpected error occurred"
     }, status: :internal_server_error
   end
 
@@ -100,7 +100,7 @@ class Api::V1::ValuationsController < Api::V1::BaseController
 
     render json: {
       error: "internal_server_error",
-      message: "Error: #{e.message}"
+      message: "An unexpected error occurred"
     }, status: :internal_server_error
   end
 
@@ -181,7 +181,7 @@ class Api::V1::ValuationsController < Api::V1::BaseController
 
     render json: {
       error: "internal_server_error",
-      message: "Error: #{e.message}"
+      message: "An unexpected error occurred"
     }, status: :internal_server_error
   end
 
diff --git a/app/controllers/settings/providers_controller.rb b/app/controllers/settings/providers_controller.rb
index ed32b8893..f95e94a2b 100644
--- a/app/controllers/settings/providers_controller.rb
+++ b/app/controllers/settings/providers_controller.rb
@@ -71,8 +71,8 @@ class Settings::ProvidersController < ApplicationController
       redirect_to settings_providers_path, notice: "No changes were made"
     end
   rescue => error
-    Rails.logger.error("Failed to update provider settings: #{error.message}")
-    flash.now[:alert] = "Failed to update provider settings: #{error.message}"
+    Rails.logger.error("Failed to update provider settings: #{error.class} - #{error.message}")
+    flash.now[:alert] = "Failed to update provider settings. Please try again."
     prepare_show_context
     render :show, status: :unprocessable_entity
   end
diff --git a/app/controllers/webhooks_controller.rb b/app/controllers/webhooks_controller.rb
index 54cf8331f..e50325dcd 100644
--- a/app/controllers/webhooks_controller.rb
+++ b/app/controllers/webhooks_controller.rb
@@ -15,7 +15,8 @@ class WebhooksController < ApplicationController
     render json: { received: true }, status: :ok
   rescue => error
     Sentry.capture_exception(error)
-    render json: { error: "Invalid webhook: #{error.message}" }, status: :bad_request
+    Rails.logger.error("Webhook error: #{error.class} - #{error.message}")
+    render json: { error: "Invalid webhook" }, status: :bad_request
   end
 
   def plaid_eu
@@ -31,7 +32,8 @@ class WebhooksController < ApplicationController
     render json: { received: true }, status: :ok
   rescue => error
     Sentry.capture_exception(error)
-    render json: { error: "Invalid webhook: #{error.message}" }, status: :bad_request
+    Rails.logger.error("Webhook error: #{error.class} - #{error.message}")
+    render json: { error: "Invalid webhook" }, status: :bad_request
   end
 
   def stripe
diff --git a/test/controllers/api/v1/auth_controller_test.rb b/test/controllers/api/v1/auth_controller_test.rb
index 52207df3a..9760c22dc 100644
--- a/test/controllers/api/v1/auth_controller_test.rb
+++ b/test/controllers/api/v1/auth_controller_test.rb
@@ -94,6 +94,25 @@ class Api::V1::AuthControllerTest < ActionDispatch::IntegrationTest
     assert_equal "Device information is required", response_data["error"]
   end
 
+  test "should reject signup with invalid device_type before committing any state" do
+    # Pre-validation catches bad device_type and returns 400 without creating
+    # user/family/device/token. Guards against a partial-commit state where the
+    # account exists but the mobile session handoff fails.
+    assert_no_difference([ "User.count", "MobileDevice.count", "Doorkeeper::AccessToken.count" ]) do
+      post "/api/v1/auth/signup", params: {
+        user: {
+          email: "newuser@example.com",
+          password: "SecurePass123!",
+          first_name: "New",
+          last_name: "User"
+        },
+        device: @device_info.merge(device_type: "windows") # not in allowlist
+      }
+    end
+
+    assert_response :bad_request
+  end
+
   test "should not signup with invalid password" do
     assert_no_difference("User.count") do
       post "/api/v1/auth/signup", params: {
diff --git a/test/controllers/settings/providers_controller_test.rb b/test/controllers/settings/providers_controller_test.rb
index 63ac52888..a7358e06e 100644
--- a/test/controllers/settings/providers_controller_test.rb
+++ b/test/controllers/settings/providers_controller_test.rb
@@ -270,16 +270,17 @@ class Settings::ProvidersControllerTest < ActionDispatch::IntegrationTest
       # We'll force an error by making the []= method raise
       Setting.expects(:[]=).with("plaid_client_id", "test").raises(StandardError.new("Database error")).once
 
-      # Mock logger to verify error is logged
-      Rails.logger.expects(:error).with(regexp_matches(/Failed to update provider settings.*Database error/)).once
+      # Mock logger to verify error is logged (pin both the exception class
+      # name and the message so a regression that drops one still fails).
+      Rails.logger.expects(:error).with(regexp_matches(/Failed to update provider settings: StandardError - Database error/)).once
 
       patch settings_providers_url, params: {
         setting: { plaid_client_id: "test" }
       }
 
-      # Controller should handle the error gracefully
+      # Controller should handle the error gracefully with generic message (no internal details)
       assert_response :unprocessable_entity
-      assert_equal "Failed to update provider settings: Database error", flash[:alert]
+      assert_equal "Failed to update provider settings. Please try again.", flash[:alert]
     end
   end