diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 02802aa..7a52e46 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -55,6 +55,8 @@ rails e2e spec:
       alias: postgres
     - name: $CI_REGISTRY_IMAGE/production/commits:$CI_COMMIT_SHA
       alias: app
+      variables:
+        TURNIERE_DISABLE_EMAIL_DELIVERY: "1"
       command:
         - bundle
         - exec
@@ -125,6 +127,7 @@ rails follow sync e2e spec:
         SECRET_KEY_BASE: turniere-blackbox-secret-key-base-please-change-in-real-prod
         MAILGUN_API_KEY: blackbox-test-api-key
         MAILGUN_DOMAIN: blackbox.example.com
+        TURNIERE_DISABLE_EMAIL_DELIVERY: "1"
         TOURNAMENT_SYNC_HTTP_TIMEOUT_SECONDS: "3"
         NO_PROXY: source-app,follower-app,source-postgres,follower-postgres,localhost,127.0.0.1
         no_proxy: source-app,follower-app,source-postgres,follower-postgres,localhost,127.0.0.1
@@ -148,6 +151,7 @@ rails follow sync e2e spec:
         SECRET_KEY_BASE: turniere-blackbox-secret-key-base-please-change-in-real-prod
         MAILGUN_API_KEY: blackbox-test-api-key
         MAILGUN_DOMAIN: blackbox.example.com
+        TURNIERE_DISABLE_EMAIL_DELIVERY: "1"
         TOURNAMENT_SYNC_HTTP_TIMEOUT_SECONDS: "3"
         NO_PROXY: source-app,follower-app,source-postgres,follower-postgres,localhost,127.0.0.1
         no_proxy: source-app,follower-app,source-postgres,follower-postgres,localhost,127.0.0.1
diff --git a/.rubocop.yml b/.rubocop.yml
index 472e0f0..5a901d6 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -1,9 +1,17 @@
-require:
+inherit_from: .rubocop_todo.yml
+
+inherit_mode:
+  merge:
+    - Exclude
+
+plugins:
   - rubocop-performance
   - rubocop-rails
 
 # Stolen from https://gist.github.com/jhass/a5ae80d87f18e53e7b56
 AllCops:
+  NewCops: disable
+  SuggestExtensions: false
   Exclude:
     - "bin/**/*"
     - "db/schema.rb"
@@ -13,7 +21,7 @@ Rails:
   Enabled: true
 
 # Commonly used screens these days easily fit more than 80 characters.
-Metrics/LineLength:
+Layout/LineLength:
   Max: 120
 
 # Too short methods lead to extraction of single-use methods, which can make
@@ -36,7 +44,7 @@ Metrics/AbcSize:
   Max: 50
 
 Metrics/BlockLength:
-  ExcludedMethods:
+  AllowedMethods:
     - "namespace"
     - "create_table"
   Exclude:
diff --git a/.rubocop_todo.yml b/.rubocop_todo.yml
new file mode 100644
index 0000000..de039d0
--- /dev/null
+++ b/.rubocop_todo.yml
@@ -0,0 +1,563 @@
+# This configuration was generated by
+# `rubocop --auto-gen-config --no-exclude-limit`
+# on 2026-04-28 09:58:15 UTC using RuboCop version 1.86.1.
+# The point is for the user to remove these configuration records
+# one by one as the offenses are removed from the code base.
+# Note that changes in the inspected code, or installation of new
+# versions of RuboCop, may require this file to be generated again.
+
+# Offense count: 2
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: TreatCommentsAsGroupSeparators, ConsiderPunctuation.
+Bundler/OrderedGems:
+  Exclude:
+    - 'Gemfile'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforcedStyleAlignWith.
+# SupportedStylesAlignWith: either, start_of_block, start_of_line
+Layout/BlockAlignment:
+  Exclude:
+    - 'spec/routing/tournaments_routing_spec.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: AllowForAlignment.
+Layout/CommentIndentation:
+  Exclude:
+    - 'app/serializers/tournament_serializer.rb'
+
+# Offense count: 3
+# This cop supports safe autocorrection (--autocorrect).
+Layout/EmptyLineAfterGuardClause:
+  Exclude:
+    - 'app/controllers/tournaments_controller.rb'
+    - 'config/spring.rb'
+    - 'spec/factories/tournaments.rb'
+
+# Offense count: 3
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EmptyLineBetweenMethodDefs, EmptyLineBetweenClassDefs, EmptyLineBetweenModuleDefs, DefLikeMacros, AllowAdjacentOneLineDefs, NumberOfEmptyLines.
+Layout/EmptyLineBetweenDefs:
+  Exclude:
+    - 'app/controllers/tournaments_controller.rb'
+    - 'app/services/tournament_snapshot_importer.rb'
+    - 'e2e/lib/scenario_runner.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+Layout/EmptyLines:
+  Exclude:
+    - 'app/controllers/tournaments_controller.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: around, only_before
+Layout/EmptyLinesAroundAccessModifier:
+  Exclude:
+    - 'db/migrate/20220516203839_create_active_storage_variant_records.active_storage.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: empty_lines, empty_lines_except_namespace, empty_lines_special, no_empty_lines, beginning_only, ending_only
+Layout/EmptyLinesAroundClassBody:
+  Exclude:
+    - 'config/application.rb'
+
+# Offense count: 2
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: IndentationWidth.
+# SupportedStyles: special_inside_parentheses, consistent, align_brackets
+Layout/FirstArrayElementIndentation:
+  EnforcedStyle: consistent
+
+# Offense count: 6
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforcedStyle, IndentationWidth.
+# SupportedStyles: special_inside_parentheses, consistent, align_braces
+Layout/FirstHashElementIndentation:
+  Exclude:
+    - 'spec/e2e/http/tournament_follow_sync_spec.rb'
+
+# Offense count: 5
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: normal, indented_internal_methods
+Layout/IndentationConsistency:
+  Exclude:
+    - 'db/migrate/20220516203839_create_active_storage_variant_records.active_storage.rb'
+    - 'e2e/lib/scenario_runner.rb'
+    - 'spec/routing/tournaments_routing_spec.rb'
+
+# Offense count: 3
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: Width, EnforcedStyleAlignWith, AllowedPatterns.
+# SupportedStylesAlignWith: start_of_line, relative_to_receiver
+Layout/IndentationWidth:
+  Exclude:
+    - 'db/migrate/20220516203839_create_active_storage_variant_records.active_storage.rb'
+    - 'spec/routing/tournaments_routing_spec.rb'
+
+# Offense count: 10
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforcedStyle, IndentationWidth.
+# SupportedStyles: aligned, indented, indented_relative_to_receiver
+Layout/MultilineMethodCallIndentation:
+  Exclude:
+    - 'app/interactors/advance_teams_in_intermediate_stage.rb'
+    - 'e2e/lib/scenario_runner.rb'
+    - 'spec/e2e/http/api_surface_spec.rb'
+    - 'spec/e2e/http/tournament_follow_sync_live_websocket_spec.rb'
+    - 'spec/e2e/http/tournament_follow_sync_spec.rb'
+    - 'spec/e2e/http/tournament_lifecycle_spec.rb'
+    - 'spec/e2e/http/tournament_live_websocket_spec.rb'
+
+# Offense count: 3
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforcedStyle, IndentationWidth.
+# SupportedStyles: aligned, indented
+Layout/MultilineOperationIndentation:
+  Exclude:
+    - 'app/services/group_stage_service.rb'
+
+# Offense count: 2
+# This cop supports safe autocorrection (--autocorrect).
+Layout/SpaceInsidePercentLiteralDelimiters:
+  Exclude:
+    - 'db/migrate/20220516203839_create_active_storage_variant_records.active_storage.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: final_newline, final_blank_line
+Layout/TrailingEmptyLines:
+  Exclude:
+    - 'spec/support/profile.rb'
+
+# Offense count: 1
+# This cop supports unsafe autocorrection (--autocorrect-all).
+# Configuration parameters: AllowSafeAssignment.
+Lint/AssignmentInCondition:
+  Exclude:
+    - 'db/migrate/20220516203838_add_service_name_to_active_storage_blobs.active_storage.rb'
+
+# Offense count: 2
+# This cop supports safe autocorrection (--autocorrect).
+Lint/ScriptPermission:
+  Exclude:
+    - 'script/e2e_scenarios.rb'
+    - 'script/wait_for_http.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: AllowUnusedKeywordArguments, IgnoreEmptyMethods, IgnoreNotImplementedMethods, NotImplementedExceptions.
+# NotImplementedExceptions: NotImplementedError
+Lint/UnusedMethodArgument:
+  Exclude:
+    - 'app/controllers/application_controller.rb'
+
+# Offense count: 2
+# This cop supports safe autocorrection (--autocorrect).
+Lint/UselessAssignment:
+  Exclude:
+    - 'e2e/lib/scenario_runner.rb'
+    - 'spec/models/beamer_spec.rb'
+
+# Offense count: 6
+# Configuration parameters: AllowedMethods, AllowedPatterns, CountRepeatedAttributes, Max.
+Metrics/AbcSize:
+  Exclude:
+    - 'app/controllers/tournaments_controller.rb'
+    - 'app/services/tournament_snapshot_importer.rb'
+    - 'e2e/lib/scenario_runner.rb'
+    - 'spec/e2e/http/tournament_follow_sync_spec.rb'
+    - 'spec/services/tournament_snapshot_importer_spec.rb'
+
+# Offense count: 2
+# Configuration parameters: CountComments, Max, CountAsOne, AllowedMethods, AllowedPatterns.
+# AllowedMethods: refine
+Metrics/BlockLength:
+  Exclude:
+    - 'app/services/tournament_snapshot_importer.rb'
+    - 'db/schema.rb'
+
+# Offense count: 15
+# Configuration parameters: AllowedMethods, AllowedPatterns, Max.
+Metrics/CyclomaticComplexity:
+  Exclude:
+    - 'app/controllers/matches_controller.rb'
+    - 'app/controllers/tournaments_controller.rb'
+    - 'app/models/group_score.rb'
+    - 'app/models/stage.rb'
+    - 'app/services/group_stage_service.rb'
+    - 'app/services/playoff_stage_service.rb'
+    - 'e2e/lib/api_client.rb'
+    - 'spec/e2e/http/tournament_follow_sync_spec.rb'
+    - 'spec/services/tournament_snapshot_importer_spec.rb'
+
+# Offense count: 1
+# Configuration parameters: CountComments, Max, CountAsOne, AllowedMethods, AllowedPatterns.
+Metrics/MethodLength:
+  Exclude:
+    - 'app/controllers/tournaments_controller.rb'
+
+# Offense count: 1
+# Configuration parameters: Max, CountKeywordArgs, MaxOptionalParameters.
+Metrics/ParameterLists:
+  Exclude:
+    - 'e2e/lib/api_client.rb'
+
+# Offense count: 14
+# Configuration parameters: AllowedMethods, AllowedPatterns, Max.
+Metrics/PerceivedComplexity:
+  Exclude:
+    - 'app/controllers/matches_controller.rb'
+    - 'app/controllers/tournaments_controller.rb'
+    - 'app/models/group_score.rb'
+    - 'app/models/stage.rb'
+    - 'app/services/group_stage_service.rb'
+    - 'e2e/lib/api_client.rb'
+    - 'spec/e2e/http/tournament_follow_sync_spec.rb'
+    - 'spec/services/tournament_snapshot_importer_spec.rb'
+
+# Offense count: 3
+# This cop supports unsafe autocorrection (--autocorrect-all).
+Performance/Count:
+  Exclude:
+    - 'app/controllers/tournaments_controller.rb'
+    - 'spec/services/tournament_snapshot_importer_spec.rb'
+
+# Offense count: 2
+# This cop supports unsafe autocorrection (--autocorrect-all).
+# Configuration parameters: SafeMultiline.
+Performance/DeleteSuffix:
+  Exclude:
+    - 'e2e/lib/action_cable_client.rb'
+    - 'e2e/lib/api_client.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+Performance/RegexpMatch:
+  Exclude:
+    - 'config/spring.rb'
+
+# Offense count: 14
+# This cop supports unsafe autocorrection (--autocorrect-all).
+Performance/TimesMap:
+  Exclude:
+    - 'e2e/lib/scenario_runner.rb'
+    - 'spec/e2e/http/api_surface_spec.rb'
+    - 'spec/e2e/http/tournament_beamers_websocket_spec.rb'
+    - 'spec/e2e/http/tournament_follow_sync_beamers_websocket_spec.rb'
+    - 'spec/e2e/http/tournament_follow_sync_spec.rb'
+    - 'spec/e2e/http/tournament_follow_sync_websocket_spec.rb'
+    - 'spec/e2e/http/tournament_sync_test_spec.rb'
+    - 'spec/e2e/http/tournament_team_action_lists_websocket_spec.rb'
+    - 'spec/e2e/http/tournament_timer_follow_sync_websocket_spec.rb'
+    - 'spec/e2e/http/tournament_timer_websocket_spec.rb'
+    - 'spec/services/tournament_snapshot_importer_spec.rb'
+
+# Offense count: 3
+# This cop supports unsafe autocorrection (--autocorrect-all).
+# Configuration parameters: NilOrEmpty, NotPresent, UnlessPresent.
+Rails/Blank:
+  Exclude:
+    - 'e2e/lib/scenario_runner.rb'
+    - 'spec/e2e/http/tournament_sync_test_spec.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforceForPrefixed.
+Rails/Delegate:
+  Exclude:
+    - 'e2e/lib/action_cable_client.rb'
+
+# Offense count: 2
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: slashes, arguments
+Rails/FilePath:
+  Exclude:
+    - 'config/environments/development.rb'
+    - 'spec/rails_helper.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+Rails/IndexBy:
+  Exclude:
+    - 'spec/e2e/http/tournament_follow_sync_spec.rb'
+
+# Offense count: 1
+# Configuration parameters: IgnoreScopes.
+Rails/InverseOf:
+  Exclude:
+    - 'app/models/tournament.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: NotNilAndNotEmpty, NotBlank, UnlessBlank.
+Rails/Present:
+  Exclude:
+    - 'e2e/lib/api_client.rb'
+
+# Offense count: 1
+Rails/ReversibleMigration:
+  Exclude:
+    - 'db/migrate/20240407180900_add_default_to_position_in_group_scores.rb'
+
+# Offense count: 9
+# Configuration parameters: ForbiddenMethods, AllowedMethods.
+# ForbiddenMethods: decrement!, decrement_counter, increment!, increment_counter, insert, insert!, insert_all, insert_all!, toggle!, touch, touch_all, update_all, update_attribute, update_column, update_columns, update_counters, upsert, upsert_all
+Rails/SkipsModelValidations:
+  Exclude:
+    - 'app/models/tournament_sync_queue_entry.rb'
+    - 'app/services/tournament_sync_pusher.rb'
+    - 'db/migrate/20220516203838_add_service_name_to_active_storage_blobs.active_storage.rb'
+    - 'db/migrate/20260416102000_backfill_default_beamers_by_name.rb'
+    - 'spec/controllers/tournaments_controller_spec.rb'
+
+# Offense count: 33
+# This cop supports unsafe autocorrection (--autocorrect-all).
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: strict, flexible
+Rails/TimeZone:
+  Exclude:
+    - 'e2e/lib/action_cable_client.rb'
+    - 'e2e/lib/scenario_runner.rb'
+    - 'spec/e2e/http/tournament_beamers_websocket_spec.rb'
+    - 'spec/e2e/http/tournament_follow_sync_beamers_websocket_spec.rb'
+    - 'spec/e2e/http/tournament_follow_sync_spec.rb'
+    - 'spec/e2e/http/tournament_follow_sync_websocket_spec.rb'
+    - 'spec/e2e/http/tournament_team_action_lists_websocket_spec.rb'
+    - 'spec/e2e/http/tournament_timer_follow_sync_websocket_spec.rb'
+    - 'spec/e2e/http/tournament_timer_websocket_spec.rb'
+
+# Offense count: 2
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforcedStyle, ProceduralMethods, FunctionalMethods, AllowedMethods, AllowedPatterns, AllowBracesOnProceduralOneLiners, BracesRequiredMethods.
+# SupportedStyles: line_count_based, semantic, braces_for_chaining, always_braces
+# ProceduralMethods: benchmark, bm, bmbm, create, each_with_object, measure, new, realtime, tap, with_object
+# FunctionalMethods: let, let!, subject, watch
+# AllowedMethods: lambda, proc, it
+Style/BlockDelimiters:
+  Exclude:
+    - 'spec/controllers/beamers_controller_spec.rb'
+
+# Offense count: 2
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: Keywords, RequireColon.
+# Keywords: TODO, FIXME, OPTIMIZE, HACK, REVIEW, NOTE
+Style/CommentAnnotation:
+  Exclude:
+    - 'spec/controllers/matches_controller_spec.rb'
+    - 'spec/services/group_stage_service_spec.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforcedStyle, SingleLineConditionsOnly, IncludeTernaryExpressions.
+# SupportedStyles: assign_to_condition, assign_inside_condition
+Style/ConditionalAssignment:
+  Exclude:
+    - 'spec/factories/tournaments.rb'
+
+# Offense count: 12
+# This cop supports unsafe autocorrection (--autocorrect-all).
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: always, always_true, never
+Style/FrozenStringLiteralComment:
+  Exclude:
+    - 'config/boot.rb'
+    - 'config/initializers/filter_parameter_logging.rb'
+    - 'config/initializers/new_framework_defaults_7_0.rb'
+    - 'db/migrate/20220516203838_add_service_name_to_active_storage_blobs.active_storage.rb'
+    - 'db/migrate/20220516203839_create_active_storage_variant_records.active_storage.rb'
+    - 'db/migrate/20220516203840_remove_not_null_on_active_storage_blobs_checksum.active_storage.rb'
+    - 'db/migrate/20240407175005_add_position_to_group_scores.rb'
+    - 'db/migrate/20240407180900_add_default_to_position_in_group_scores.rb'
+    - 'db/migrate/20250309202658_add_timer_end_to_tournaments.rb'
+    - 'db/migrate/20260423133000_add_timer_mode_to_tournaments.rb'
+    - 'db/schema.rb'
+    - 'spec/support/profile.rb'
+
+# Offense count: 1
+# This cop supports unsafe autocorrection (--autocorrect-all).
+Style/GlobalStdStream:
+  Exclude:
+    - 'config/environments/production.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: MinBodyLength, AllowConsecutiveConditionals.
+Style/GuardClause:
+  Exclude:
+    - 'db/migrate/20220516203838_add_service_name_to_active_storage_blobs.active_storage.rb'
+
+# Offense count: 2
+# This cop supports unsafe autocorrection (--autocorrect-all).
+Style/IdenticalConditionalBranches:
+  Exclude:
+    - 'spec/e2e/http/tournament_lifecycle_spec.rb'
+
+# Offense count: 18
+# This cop supports safe autocorrection (--autocorrect).
+Style/IfUnlessModifier:
+  Exclude:
+    - 'app/controllers/tournaments_controller.rb'
+    - 'app/services/group_stage_service.rb'
+    - 'app/services/playoff_stage_service.rb'
+    - 'e2e/lib/scenario_runner.rb'
+
+# Offense count: 2
+# This cop supports unsafe autocorrection (--autocorrect-all).
+# Configuration parameters: InverseMethods, InverseBlocks.
+Style/InverseMethods:
+  Exclude:
+    - 'spec/e2e/http/tournament_lifecycle_spec.rb'
+
+# Offense count: 3
+Style/MultilineBlockChain:
+  Exclude:
+    - 'e2e/lib/api_client.rb'
+    - 'spec/e2e/http/tournament_follow_sync_spec.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: MinDigits, Strict, AllowedNumbers, AllowedPatterns.
+Style/NumericLiterals:
+  Exclude:
+    - 'db/schema.rb'
+
+# Offense count: 2
+# This cop supports unsafe autocorrection (--autocorrect-all).
+# Configuration parameters: EnforcedStyle, AllowedMethods, AllowedPatterns.
+# SupportedStyles: predicate, comparison
+Style/NumericPredicate:
+  Exclude:
+    - 'e2e/lib/scenario_runner.rb'
+
+# Offense count: 1
+# Configuration parameters: AllowedMethods.
+# AllowedMethods: respond_to_missing?
+Style/OptionalBooleanParameter:
+  Exclude:
+    - 'app/services/playoff_stage_service.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+Style/RedundantFreeze:
+  Exclude:
+    - 'e2e/lib/scenario_runner.rb'
+
+# Offense count: 3
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: AllowMultipleReturnValues.
+Style/RedundantReturn:
+  Exclude:
+    - 'app/controllers/tournaments_controller.rb'
+
+# Offense count: 3
+# This cop supports unsafe autocorrection (--autocorrect-all).
+Style/RedundantSort:
+  Exclude:
+    - 'spec/e2e/http/tournament_follow_sync_spec.rb'
+
+# Offense count: 1
+# This cop supports unsafe autocorrection (--autocorrect-all).
+# Configuration parameters: ConvertCodeThatCanStartToReturnNil, AllowedMethods, MaxChainLength.
+# AllowedMethods: present?, blank?, presence, try, try!
+Style/SafeNavigation:
+  Exclude:
+    - 'config/spring.rb'
+
+# Offense count: 1
+# This cop supports unsafe autocorrection (--autocorrect-all).
+# Configuration parameters: Mode.
+Style/StringConcatenation:
+  Exclude:
+    - 'config/spring.rb'
+
+# Offense count: 246
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforcedStyle, ConsistentQuotesInMultiline.
+# SupportedStyles: single_quotes, double_quotes
+Style/StringLiterals:
+  Exclude:
+    - 'config/boot.rb'
+    - 'db/migrate/20220516203839_create_active_storage_variant_records.active_storage.rb'
+    - 'db/schema.rb'
+    - 'spec/e2e/http/api_surface_spec.rb'
+
+# Offense count: 3
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: .
+# SupportedStyles: percent, brackets
+Style/SymbolArray:
+  EnforcedStyle: percent
+  MinSize: 10
+
+# Offense count: 1
+# This cop supports unsafe autocorrection (--autocorrect-all).
+# Configuration parameters: AllowMethodsWithArguments, AllowedMethods, AllowedPatterns, AllowComments.
+# AllowedMethods: define_method, mail, respond_to
+Style/SymbolProc:
+  Exclude:
+    - 'spec/services/tournament_snapshot_importer_spec.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforcedStyleForMultiline.
+# SupportedStylesForMultiline: comma, consistent_comma, diff_comma, no_comma
+Style/TrailingCommaInArrayLiteral:
+  Exclude:
+    - 'spec/services/playoff_stage_service_spec.rb'
+
+# Offense count: 3
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: WordRegex.
+# SupportedStyles: percent, brackets
+Style/WordArray:
+  EnforcedStyle: percent
+  MinSize: 3
+
+# Offense count: 6
+# This cop supports unsafe autocorrection (--autocorrect-all).
+Style/ZeroLengthPredicate:
+  Exclude:
+    - 'app/models/stage.rb'
+    - 'app/services/group_stage_service.rb'
+
+# Offense count: 113
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: Max, AllowHeredoc, AllowURI, AllowQualifiedName, URISchemes, AllowRBSInlineAnnotation, AllowCopDirectives, AllowedPatterns, SplitStrings.
+# URISchemes: http, https
+Layout/LineLength:
+  Exclude:
+    - 'app/controllers/matches_controller.rb'
+    - 'app/controllers/tournaments_controller.rb'
+    - 'app/models/team_action_list.rb'
+    - 'app/services/group_stage_service.rb'
+    - 'app/services/playoff_stage_service.rb'
+    - 'db/schema.rb'
+    - 'e2e/lib/api_client.rb'
+    - 'e2e/lib/scenario_runner.rb'
+    - 'script/e2e_scenarios.rb'
+    - 'spec/controllers/groups_controller_spec.rb'
+    - 'spec/controllers/matches_controller_spec.rb'
+    - 'spec/controllers/stages_controller_spec.rb'
+    - 'spec/controllers/team_action_lists_controller_spec.rb'
+    - 'spec/e2e/http/api_surface_spec.rb'
+    - 'spec/e2e/http/tournament_follow_sync_spec.rb'
+    - 'spec/e2e/http/tournament_follow_sync_websocket_spec.rb'
+    - 'spec/e2e/http/tournament_lifecycle_spec.rb'
+    - 'spec/e2e/http/tournament_rendering_spec.rb'
+    - 'spec/e2e/http/tournament_sync_test_spec.rb'
+    - 'spec/e2e/http/tournament_team_action_lists_websocket_spec.rb'
+    - 'spec/e2e/http/tournament_timer_follow_sync_websocket_spec.rb'
+    - 'spec/factories/tournaments.rb'
+    - 'spec/services/group_stage_service_spec.rb'
+    - 'spec/services/team_action_list_service_spec.rb'
+    - 'spec/services/tournament_snapshot_importer_spec.rb'
+    - 'spec/services/tournament_sync_processor_spec.rb'
diff --git a/.ruby-version b/.ruby-version
index ef538c2..c4e41f9 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-3.1.2
+4.0.3
diff --git a/Dockerfile b/Dockerfile
index f44458b..e5eda29 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,7 +1,7 @@
 # syntax=docker/dockerfile:1.7
 
-ARG RUBY_VERSION=3.1.2
-ARG BUNDLER_VERSION=2.3.13
+ARG RUBY_VERSION=4.0.3
+ARG BUNDLER_VERSION=4.0.6
 ARG base_commit=aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
 
 FROM ruby:${RUBY_VERSION}-slim AS runtime-base
@@ -19,6 +19,7 @@ WORKDIR /app
 RUN apt-get update -qq \
     && apt-get install -y --no-install-recommends \
         libpq5 \
+        libyaml-0-2 \
         nodejs \
         openssl \
     && rm -rf /var/lib/apt/lists/* \
@@ -33,6 +34,7 @@ RUN apt-get update -qq \
         git \
         libpq-dev \
         libsqlite3-dev \
+        libyaml-dev \
         pkg-config \
         python3 \
         python3-pip \
@@ -92,7 +94,7 @@ RUN apt-get update -qq \
         python3 \
         python3-pip \
     && rm -rf /var/lib/apt/lists/* \
-    && python3 -m pip install --no-cache-dir invoke
+    && python3 -m pip install --break-system-packages --no-cache-dir invoke
 
 COPY --from=bundle-test /usr/local/bundle /usr/local/bundle
 COPY --from=bundle-test /app/vendor/bundle /app/vendor/bundle
diff --git a/Gemfile b/Gemfile
index 91dfd63..29fdec4 100644
--- a/Gemfile
+++ b/Gemfile
@@ -3,12 +3,12 @@
 source 'https://rubygems.org'
 git_source(:github) { |repo| "https://github.com/#{repo}.git" }
 
-ruby '3.1.2'
+ruby '4.0.3'
 
 # Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
-gem 'rails', '~> 7.0.3'
+gem 'rails', '~> 8.1'
 # Use Puma as the app server
-gem 'puma', '~> 5.0'
+gem 'puma', '~> 8.0'
 # Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
 # gem 'jbuilder', '~> 2.5'
 # Use ActiveModel has_secure_password
@@ -28,7 +28,7 @@ gem 'bootsnap', require: false
 
 # Authentication
 gem 'devise'
-gem 'devise_token_auth', git: 'https://github.com/Thor77/devise_token_auth', branch: 'fix-api-only-mode'
+gem 'devise_token_auth'
 
 gem 'rack-cors'
 
@@ -59,7 +59,7 @@ group :development, optional: true do
   gem 'rubocop-rails'
   gem 'solargraph'
   gem 'spring'
-  gem 'spring-watcher-listen', '~> 2.0.0'
+  gem 'spring-watcher-listen', '~> 2.1'
 end
 
 group :production do
@@ -67,4 +67,4 @@ group :production do
 end
 
 # Windows does not include zoneinfo files, so bundle the tzinfo-data gem
-gem 'tzinfo-data', platforms: %i[mingw mswin x64_mingw jruby]
+gem 'tzinfo-data', platforms: %i[windows jruby]
diff --git a/Gemfile.lock b/Gemfile.lock
index 15088d9..b38a9d2 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,326 +1,407 @@
-GIT
-  remote: https://github.com/Thor77/devise_token_auth
-  revision: 30ba21add5c87b2964b909c6fc5cd18cfeae2191
-  branch: fix-api-only-mode
-  specs:
-    devise_token_auth (1.2.0)
-      bcrypt (~> 3.0)
-      devise (> 3.5.2, < 5)
-      rails (>= 4.2.0, < 7.1)
-
 GEM
   remote: https://rubygems.org/
   specs:
-    actioncable (7.0.8.1)
-      actionpack (= 7.0.8.1)
-      activesupport (= 7.0.8.1)
+    action_text-trix (2.1.18)
+      railties
+    actioncable (8.1.3)
+      actionpack (= 8.1.3)
+      activesupport (= 8.1.3)
       nio4r (~> 2.0)
       websocket-driver (>= 0.6.1)
-    actionmailbox (7.0.8.1)
-      actionpack (= 7.0.8.1)
-      activejob (= 7.0.8.1)
-      activerecord (= 7.0.8.1)
-      activestorage (= 7.0.8.1)
-      activesupport (= 7.0.8.1)
-      mail (>= 2.7.1)
-      net-imap
-      net-pop
-      net-smtp
-    actionmailer (7.0.8.1)
-      actionpack (= 7.0.8.1)
-      actionview (= 7.0.8.1)
-      activejob (= 7.0.8.1)
-      activesupport (= 7.0.8.1)
-      mail (~> 2.5, >= 2.5.4)
-      net-imap
-      net-pop
-      net-smtp
-      rails-dom-testing (~> 2.0)
-    actionpack (7.0.8.1)
-      actionview (= 7.0.8.1)
-      activesupport (= 7.0.8.1)
-      rack (~> 2.0, >= 2.2.4)
+      zeitwerk (~> 2.6)
+    actionmailbox (8.1.3)
+      actionpack (= 8.1.3)
+      activejob (= 8.1.3)
+      activerecord (= 8.1.3)
+      activestorage (= 8.1.3)
+      activesupport (= 8.1.3)
+      mail (>= 2.8.0)
+    actionmailer (8.1.3)
+      actionpack (= 8.1.3)
+      actionview (= 8.1.3)
+      activejob (= 8.1.3)
+      activesupport (= 8.1.3)
+      mail (>= 2.8.0)
+      rails-dom-testing (~> 2.2)
+    actionpack (8.1.3)
+      actionview (= 8.1.3)
+      activesupport (= 8.1.3)
+      nokogiri (>= 1.8.5)
+      rack (>= 2.2.4)
+      rack-session (>= 1.0.1)
       rack-test (>= 0.6.3)
-      rails-dom-testing (~> 2.0)
-      rails-html-sanitizer (~> 1.0, >= 1.2.0)
-    actiontext (7.0.8.1)
-      actionpack (= 7.0.8.1)
-      activerecord (= 7.0.8.1)
-      activestorage (= 7.0.8.1)
-      activesupport (= 7.0.8.1)
+      rails-dom-testing (~> 2.2)
+      rails-html-sanitizer (~> 1.6)
+      useragent (~> 0.16)
+    actiontext (8.1.3)
+      action_text-trix (~> 2.1.15)
+      actionpack (= 8.1.3)
+      activerecord (= 8.1.3)
+      activestorage (= 8.1.3)
+      activesupport (= 8.1.3)
       globalid (>= 0.6.0)
       nokogiri (>= 1.8.5)
-    actionview (7.0.8.1)
-      activesupport (= 7.0.8.1)
+    actionview (8.1.3)
+      activesupport (= 8.1.3)
       builder (~> 3.1)
-      erubi (~> 1.4)
-      rails-dom-testing (~> 2.0)
-      rails-html-sanitizer (~> 1.1, >= 1.2.0)
-    active_model_serializers (0.10.14)
+      erubi (~> 1.11)
+      rails-dom-testing (~> 2.2)
+      rails-html-sanitizer (~> 1.6)
+    active_model_serializers (0.10.16)
       actionpack (>= 4.1)
       activemodel (>= 4.1)
       case_transform (>= 0.2)
       jsonapi-renderer (>= 0.1.1.beta1, < 0.3)
-    activejob (7.0.8.1)
-      activesupport (= 7.0.8.1)
+    activejob (8.1.3)
+      activesupport (= 8.1.3)
       globalid (>= 0.3.6)
-    activemodel (7.0.8.1)
-      activesupport (= 7.0.8.1)
-    activerecord (7.0.8.1)
-      activemodel (= 7.0.8.1)
-      activesupport (= 7.0.8.1)
-    activestorage (7.0.8.1)
-      actionpack (= 7.0.8.1)
-      activejob (= 7.0.8.1)
-      activerecord (= 7.0.8.1)
-      activesupport (= 7.0.8.1)
+    activemodel (8.1.3)
+      activesupport (= 8.1.3)
+    activerecord (8.1.3)
+      activemodel (= 8.1.3)
+      activesupport (= 8.1.3)
+      timeout (>= 0.4.0)
+    activestorage (8.1.3)
+      actionpack (= 8.1.3)
+      activejob (= 8.1.3)
+      activerecord (= 8.1.3)
+      activesupport (= 8.1.3)
       marcel (~> 1.0)
-      mini_mime (>= 1.1.0)
-    activesupport (7.0.8.1)
-      concurrent-ruby (~> 1.0, >= 1.0.2)
+    activesupport (8.1.3)
+      base64
+      bigdecimal
+      concurrent-ruby (~> 1.0, >= 1.3.1)
+      connection_pool (>= 2.2.5)
+      drb
       i18n (>= 1.6, < 2)
+      json
+      logger (>= 1.4.2)
       minitest (>= 5.1)
-      tzinfo (~> 2.0)
-    ast (2.4.2)
+      securerandom (>= 0.3)
+      tzinfo (~> 2.0, >= 2.0.5)
+      uri (>= 0.13.1)
+    ast (2.4.3)
     backport (1.2.0)
-    bcrypt (3.1.20)
-    benchmark (0.3.0)
-    bootsnap (1.18.3)
+    base64 (0.3.0)
+    bcrypt (3.1.22)
+    benchmark (0.5.0)
+    bigdecimal (4.1.2)
+    bootsnap (1.24.0)
       msgpack (~> 1.2)
-    builder (3.2.4)
+    builder (3.3.0)
     case_transform (0.2)
       activesupport
-    concurrent-ruby (1.2.3)
+    concurrent-ruby (1.3.6)
+    connection_pool (3.0.2)
     crass (1.0.6)
-    date (3.3.4)
-    devise (4.9.3)
+    date (3.5.1)
+    devise (4.9.4)
       bcrypt (~> 3.0)
       orm_adapter (~> 0.1)
       railties (>= 4.1.0)
       responders
       warden (~> 1.2.3)
-    diff-lcs (1.5.1)
-    domain_name (0.6.20240107)
-    e2mmap (0.1.0)
-    erubi (1.12.0)
-    factory_bot (6.4.6)
-      activesupport (>= 5.0.0)
-    factory_bot_rails (6.4.3)
-      factory_bot (~> 6.4)
-      railties (>= 5.0.0)
-    faker (3.3.1)
+    devise_token_auth (1.2.6)
+      bcrypt (~> 3.0)
+      devise (> 3.5.2, < 5)
+      rails (>= 4.2.0, < 8.2)
+    diff-lcs (1.6.2)
+    drb (2.2.3)
+    erb (6.0.4)
+    erubi (1.13.1)
+    factory_bot (6.5.6)
+      activesupport (>= 6.1.0)
+    factory_bot_rails (6.5.1)
+      factory_bot (~> 6.5)
+      railties (>= 6.1.0)
+    faker (3.8.0)
       i18n (>= 1.8.11, < 2)
-    ffi (1.16.3)
-    globalid (1.2.1)
+    faraday (2.14.1)
+      faraday-net_http (>= 2.0, < 3.5)
+      json
+      logger
+    faraday-multipart (1.2.0)
+      multipart-post (~> 2.0)
+    faraday-net_http (3.4.2)
+      net-http (~> 0.5)
+    ffi (1.17.4-aarch64-linux-gnu)
+    ffi (1.17.4-aarch64-linux-musl)
+    ffi (1.17.4-arm64-darwin)
+    ffi (1.17.4-x86_64-linux-gnu)
+    globalid (1.3.0)
       activesupport (>= 6.1)
-    http-accept (1.7.0)
-    http-cookie (1.0.5)
-      domain_name (~> 0.5)
-    i18n (1.14.4)
+    i18n (1.14.8)
       concurrent-ruby (~> 1.0)
-    interactor (3.1.2)
-    interactor-rails (2.2.1)
+    interactor (3.2.0)
+      ostruct
+    interactor-rails (2.3.0)
       interactor (~> 3.0)
-      rails (>= 4.2)
-    jaro_winkler (1.5.6)
-    json (2.7.2)
+      railties (>= 7.0)
+    io-console (0.8.2)
+    irb (1.18.0)
+      pp (>= 0.6.0)
+      prism (>= 1.3.0)
+      rdoc (>= 4.0.0)
+      reline (>= 0.4.2)
+    jaro_winkler (1.7.0)
+    json (2.19.4)
     jsonapi-renderer (0.2.2)
-    kramdown (2.4.0)
-      rexml
+    kramdown (2.5.2)
+      rexml (>= 3.4.4)
     kramdown-parser-gfm (1.1.0)
       kramdown (~> 2.0)
-    language_server-protocol (3.17.0.3)
-    listen (3.9.0)
+    language_server-protocol (3.17.0.5)
+    lint_roller (1.1.0)
+    listen (3.10.0)
+      logger
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
-    loofah (2.22.0)
+    logger (1.7.0)
+    loofah (2.25.1)
       crass (~> 1.0.2)
       nokogiri (>= 1.12.0)
-    mail (2.8.1)
+    mail (2.9.0)
+      logger
       mini_mime (>= 0.1.1)
       net-imap
       net-pop
       net-smtp
-    mailgun-ruby (1.2.14)
-      rest-client (>= 2.0.2)
-    marcel (1.0.4)
-    method_source (1.0.0)
-    mime-types (3.5.2)
-      mime-types-data (~> 3.2015)
-    mime-types-data (3.2024.0305)
+    mailgun-ruby (1.4.3)
+      faraday (~> 2.1)
+      faraday-multipart (< 2)
+      mini_mime
+      zeitwerk
+    marcel (1.1.0)
     mini_mime (1.1.5)
-    minitest (5.22.3)
-    msgpack (1.7.2)
-    net-imap (0.4.10)
+    minitest (6.0.5)
+      drb (~> 2.0)
+      prism (~> 1.5)
+    msgpack (1.8.0)
+    multipart-post (2.4.1)
+    net-http (0.9.1)
+      uri (>= 0.11.1)
+    net-imap (0.6.4)
       date
       net-protocol
     net-pop (0.1.2)
       net-protocol
     net-protocol (0.2.2)
       timeout
-    net-smtp (0.5.0)
+    net-smtp (0.5.1)
       net-protocol
-    netrc (0.11.0)
-    nio4r (2.7.1)
-    nokogiri (1.16.3-aarch64-linux)
+    nio4r (2.7.5)
+    nokogiri (1.19.3-aarch64-linux-gnu)
       racc (~> 1.4)
-    nokogiri (1.16.3-arm64-darwin)
+    nokogiri (1.19.3-aarch64-linux-musl)
       racc (~> 1.4)
-    nokogiri (1.16.3-x86_64-linux)
+    nokogiri (1.19.3-arm64-darwin)
       racc (~> 1.4)
+    nokogiri (1.19.3-x86_64-linux-gnu)
+      racc (~> 1.4)
+    observer (0.1.2)
+    open3 (0.2.1)
     orm_adapter (0.5.0)
-    parallel (1.24.0)
-    parser (3.3.0.5)
+    ostruct (0.6.3)
+    parallel (2.1.0)
+    parser (3.3.11.1)
       ast (~> 2.4.1)
       racc
-    pg (1.5.6)
-    puma (5.6.8)
+    pg (1.6.3-aarch64-linux)
+    pg (1.6.3-aarch64-linux-musl)
+    pg (1.6.3-arm64-darwin)
+    pg (1.6.3-x86_64-linux)
+    pp (0.6.3)
+      prettyprint
+    prettyprint (0.2.0)
+    prism (1.9.0)
+    psych (5.3.1)
+      date
+      stringio
+    puma (8.0.1)
       nio4r (~> 2.0)
-    racc (1.7.3)
-    rack (2.2.9)
-    rack-cors (2.0.2)
-      rack (>= 2.0.0)
-    rack-test (2.1.0)
+    racc (1.8.1)
+    rack (3.2.6)
+    rack-cors (3.0.0)
+      logger
+      rack (>= 3.0.14)
+    rack-session (2.1.2)
+      base64 (>= 0.1.0)
+      rack (>= 3.0.0)
+    rack-test (2.2.0)
       rack (>= 1.3)
+    rackup (2.3.1)
+      rack (>= 3)
     railroady (1.6.0)
-    rails (7.0.8.1)
-      actioncable (= 7.0.8.1)
-      actionmailbox (= 7.0.8.1)
-      actionmailer (= 7.0.8.1)
-      actionpack (= 7.0.8.1)
-      actiontext (= 7.0.8.1)
-      actionview (= 7.0.8.1)
-      activejob (= 7.0.8.1)
-      activemodel (= 7.0.8.1)
-      activerecord (= 7.0.8.1)
-      activestorage (= 7.0.8.1)
-      activesupport (= 7.0.8.1)
+    rails (8.1.3)
+      actioncable (= 8.1.3)
+      actionmailbox (= 8.1.3)
+      actionmailer (= 8.1.3)
+      actionpack (= 8.1.3)
+      actiontext (= 8.1.3)
+      actionview (= 8.1.3)
+      activejob (= 8.1.3)
+      activemodel (= 8.1.3)
+      activerecord (= 8.1.3)
+      activestorage (= 8.1.3)
+      activesupport (= 8.1.3)
       bundler (>= 1.15.0)
-      railties (= 7.0.8.1)
-    rails-dom-testing (2.2.0)
+      railties (= 8.1.3)
+    rails-dom-testing (2.3.0)
       activesupport (>= 5.0.0)
       minitest
       nokogiri (>= 1.6)
-    rails-html-sanitizer (1.6.0)
-      loofah (~> 2.21)
-      nokogiri (~> 1.14)
-    railties (7.0.8.1)
-      actionpack (= 7.0.8.1)
-      activesupport (= 7.0.8.1)
-      method_source
+    rails-html-sanitizer (1.7.0)
+      loofah (~> 2.25)
+      nokogiri (>= 1.15.7, != 1.16.7, != 1.16.6, != 1.16.5, != 1.16.4, != 1.16.3, != 1.16.2, != 1.16.1, != 1.16.0.rc1, != 1.16.0)
+    railties (8.1.3)
+      actionpack (= 8.1.3)
+      activesupport (= 8.1.3)
+      irb (~> 1.13)
+      rackup (>= 1.0.0)
       rake (>= 12.2)
-      thor (~> 1.0)
-      zeitwerk (~> 2.5)
+      thor (~> 1.0, >= 1.2.2)
+      tsort (>= 0.2)
+      zeitwerk (~> 2.6)
     rainbow (3.1.1)
-    rake (13.2.1)
+    rake (13.4.2)
     rb-fsevent (0.11.2)
-    rb-inotify (0.10.1)
+    rb-inotify (0.11.1)
       ffi (~> 1.0)
-    rbs (2.8.4)
-    regexp_parser (2.9.0)
-    responders (3.1.1)
-      actionpack (>= 5.2)
-      railties (>= 5.2)
-    rest-client (2.1.0)
-      http-accept (>= 1.7.0, < 2.0)
-      http-cookie (>= 1.0.2, < 2.0)
-      mime-types (>= 1.16, < 4.0)
-      netrc (~> 0.8)
-    reverse_markdown (2.1.1)
+    rbs (3.10.4)
+      logger
+      tsort
+    rdoc (7.2.0)
+      erb
+      psych (>= 4.0.0)
+      tsort
+    regexp_parser (2.12.0)
+    reline (0.6.3)
+      io-console (~> 0.5)
+    responders (3.2.0)
+      actionpack (>= 7.0)
+      railties (>= 7.0)
+    reverse_markdown (3.0.2)
       nokogiri
-    rexml (3.2.6)
-    rspec-core (3.13.0)
+    rexml (3.4.4)
+    rspec-core (3.13.6)
       rspec-support (~> 3.13.0)
-    rspec-expectations (3.13.0)
+    rspec-expectations (3.13.5)
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.13.0)
-    rspec-mocks (3.13.0)
+    rspec-mocks (3.13.8)
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.13.0)
-    rspec-rails (6.1.2)
-      actionpack (>= 6.1)
-      activesupport (>= 6.1)
-      railties (>= 6.1)
-      rspec-core (~> 3.13)
-      rspec-expectations (~> 3.13)
-      rspec-mocks (~> 3.13)
-      rspec-support (~> 3.13)
-    rspec-support (3.13.1)
-    rubocop (1.62.1)
+    rspec-rails (8.0.4)
+      actionpack (>= 7.2)
+      activesupport (>= 7.2)
+      railties (>= 7.2)
+      rspec-core (>= 3.13.0, < 5.0.0)
+      rspec-expectations (>= 3.13.0, < 5.0.0)
+      rspec-mocks (>= 3.13.0, < 5.0.0)
+      rspec-support (>= 3.13.0, < 5.0.0)
+    rspec-support (3.13.7)
+    rubocop (1.86.1)
       json (~> 2.3)
-      language_server-protocol (>= 3.17.0)
-      parallel (~> 1.10)
+      language_server-protocol (~> 3.17.0.2)
+      lint_roller (~> 1.1.0)
+      parallel (>= 1.10)
       parser (>= 3.3.0.2)
       rainbow (>= 2.2.2, < 4.0)
-      regexp_parser (>= 1.8, < 3.0)
-      rexml (>= 3.2.5, < 4.0)
-      rubocop-ast (>= 1.31.1, < 2.0)
+      regexp_parser (>= 2.9.3, < 3.0)
+      rubocop-ast (>= 1.49.0, < 2.0)
       ruby-progressbar (~> 1.7)
-      unicode-display_width (>= 2.4.0, < 3.0)
-    rubocop-ast (1.31.2)
-      parser (>= 3.3.0.4)
-    rubocop-performance (1.21.0)
-      rubocop (>= 1.48.1, < 2.0)
-      rubocop-ast (>= 1.31.1, < 2.0)
-    rubocop-rails (2.24.1)
+      unicode-display_width (>= 2.4.0, < 4.0)
+    rubocop-ast (1.49.1)
+      parser (>= 3.3.7.2)
+      prism (~> 1.7)
+    rubocop-performance (1.26.1)
+      lint_roller (~> 1.1)
+      rubocop (>= 1.75.0, < 2.0)
+      rubocop-ast (>= 1.47.1, < 2.0)
+    rubocop-rails (2.34.3)
       activesupport (>= 4.2.0)
+      lint_roller (~> 1.1)
       rack (>= 1.1)
-      rubocop (>= 1.33.0, < 2.0)
-      rubocop-ast (>= 1.31.1, < 2.0)
-    ruby-prof (1.7.1)
+      rubocop (>= 1.75.0, < 2.0)
+      rubocop-ast (>= 1.44.0, < 2.0)
+    ruby-prof (2.0.4)
+      base64
+      ostruct
     ruby-progressbar (1.13.0)
-    shoulda-matchers (6.2.0)
-      activesupport (>= 5.2.0)
-    solargraph (0.50.0)
+    securerandom (0.4.1)
+    shoulda-matchers (7.0.1)
+      activesupport (>= 7.1)
+    solargraph (0.58.3)
+      ast (~> 2.4.3)
       backport (~> 1.2)
-      benchmark
-      bundler (~> 2.0)
+      benchmark (~> 0.4)
+      bundler (>= 2.0)
       diff-lcs (~> 1.4)
-      e2mmap
-      jaro_winkler (~> 1.5)
+      jaro_winkler (~> 1.6, >= 1.6.1)
       kramdown (~> 2.3)
       kramdown-parser-gfm (~> 1.1)
+      logger (~> 1.6)
+      observer (~> 0.1)
+      open3 (~> 0.2.1)
+      ostruct (~> 0.6)
       parser (~> 3.0)
-      rbs (~> 2.0)
-      reverse_markdown (~> 2.0)
-      rubocop (~> 1.38)
+      prism (~> 1.4)
+      rbs (>= 3.6.1, <= 4.0.0.dev.4)
+      reverse_markdown (~> 3.0)
+      rubocop (~> 1.76)
       thor (~> 1.0)
       tilt (~> 2.0)
       yard (~> 0.9, >= 0.9.24)
-    spring (2.1.1)
-    spring-watcher-listen (2.0.1)
+      yard-activesupport-concern (~> 0.0)
+      yard-solargraph (~> 0.1)
+    spring (4.4.2)
+    spring-watcher-listen (2.1.0)
       listen (>= 2.7, < 4.0)
-      spring (>= 1.2, < 3.0)
-    sqlite3 (1.7.3-aarch64-linux)
-    sqlite3 (1.7.3-arm64-darwin)
-    sqlite3 (1.7.3-x86_64-linux)
-    thor (1.3.1)
-    tilt (2.3.0)
-    timeout (0.4.1)
+      spring (>= 4)
+    sqlite3 (2.9.3-aarch64-linux-gnu)
+    sqlite3 (2.9.3-aarch64-linux-musl)
+    sqlite3 (2.9.3-arm64-darwin)
+    sqlite3 (2.9.3-x86_64-linux-gnu)
+    stringio (3.2.0)
+    thor (1.5.0)
+    tilt (2.7.0)
+    timeout (0.6.1)
+    tsort (0.2.0)
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)
-    unicode-display_width (2.5.0)
+    unicode-display_width (3.2.0)
+      unicode-emoji (~> 4.1)
+    unicode-emoji (4.2.0)
+    uri (1.1.1)
+    useragent (0.16.11)
     warden (1.2.9)
       rack (>= 2.0.9)
-    websocket-driver (0.7.6)
+    websocket-driver (0.8.0)
+      base64
       websocket-extensions (>= 0.1.0)
     websocket-extensions (0.1.5)
-    yard (0.9.36)
-    zeitwerk (2.6.13)
+    yard (0.9.43)
+    yard-activesupport-concern (0.0.1)
+      yard (>= 0.8)
+    yard-solargraph (0.1.0)
+      yard (~> 0.9)
+    zeitwerk (2.7.5)
 
 PLATFORMS
+  aarch64-linux
   aarch64-linux-musl
   arm64-darwin-22
   arm64-darwin-23
   arm64-darwin-24
   arm64-darwin-25
   x86_64-linux
+  x86_64-linux-gnu
 
 DEPENDENCIES
   active_model_serializers
   bootsnap
   devise
-  devise_token_auth!
+  devise_token_auth
   factory_bot_rails
   faker
   interactor
@@ -328,10 +409,10 @@ DEPENDENCIES
   listen (~> 3.3)
   mailgun-ruby
   pg
-  puma (~> 5.0)
+  puma (~> 8.0)
   rack-cors
   railroady
-  rails (~> 7.0.3)
+  rails (~> 8.1)
   rspec-rails
   rubocop
   rubocop-performance
@@ -340,12 +421,12 @@ DEPENDENCIES
   shoulda-matchers
   solargraph
   spring
-  spring-watcher-listen (~> 2.0.0)
+  spring-watcher-listen (~> 2.1)
   sqlite3
   tzinfo-data
 
 RUBY VERSION
-   ruby 3.1.2p20
+  ruby 4.0.3
 
 BUNDLED WITH
-   2.3.7
+  4.0.6
diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index b92a017..97043de 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -60,6 +60,11 @@ class ApplicationController < ActionController::API
   end
 
   def render_not_found_error(exception)
-    render json: { error: exception.to_s }, status: :not_found
+    error = if exception.is_a?(ActiveRecord::RecordNotFound) && exception.model.present?
+              "Couldn't find #{exception.model} with '#{exception.primary_key}'=#{exception.id.inspect}"
+            else
+              'Record not found'
+            end
+    render json: { error: error }, status: :not_found
   end
 end
diff --git a/app/controllers/beamers_controller.rb b/app/controllers/beamers_controller.rb
index 5772eec..6c6c867 100644
--- a/app/controllers/beamers_controller.rb
+++ b/app/controllers/beamers_controller.rb
@@ -36,7 +36,7 @@ class BeamersController < ApplicationController
       push_sync_if_needed!
       render json: beamer, status: :created
     else
-      render json: beamer.errors, status: :unprocessable_entity
+      render json: beamer.errors, status: :unprocessable_content
     end
   end
 
@@ -46,7 +46,7 @@ class BeamersController < ApplicationController
       push_sync_if_needed!
       render json: @beamer
     else
-      render json: @beamer.errors, status: :unprocessable_entity
+      render json: @beamer.errors, status: :unprocessable_content
     end
   end
 
diff --git a/app/controllers/bets_controller.rb b/app/controllers/bets_controller.rb
index 876bf56..dce34e8 100644
--- a/app/controllers/bets_controller.rb
+++ b/app/controllers/bets_controller.rb
@@ -25,6 +25,6 @@ class BetsController < ApplicationController
   end
 
   def handle_user_service_error(exception)
-    render json: { error: exception.message }, status: :unprocessable_entity
+    render json: { error: exception.message }, status: :unprocessable_content
   end
 end
diff --git a/app/controllers/match_scores_controller.rb b/app/controllers/match_scores_controller.rb
index 07f55bb..502da1f 100644
--- a/app/controllers/match_scores_controller.rb
+++ b/app/controllers/match_scores_controller.rb
@@ -19,7 +19,7 @@ class MatchScoresController < ApplicationController
       TournamentLiveBroadcast.call(@match_score.tournament.id)
       render json: @match_score
     else
-      render json: @match_score.errors, status: :unprocessable_entity
+      render json: @match_score.errors, status: :unprocessable_content
     end
   end
 
diff --git a/app/controllers/matches_controller.rb b/app/controllers/matches_controller.rb
index a2cdb01..ac40b8f 100644
--- a/app/controllers/matches_controller.rb
+++ b/app/controllers/matches_controller.rb
@@ -26,14 +26,14 @@ class MatchesController < ApplicationController
     match = build_decider_match
 
     if match.errors.any?
-      render json: match.errors, status: :unprocessable_entity
+      render json: match.errors, status: :unprocessable_content
     elsif match.save
       UpdateGroupsGroupScoresAndSave.call(group: @group)
       push_sync_if_needed!(@group.tournament)
       TournamentLiveBroadcast.call(@group.tournament.id)
       render json: match, include: %w[match_scores.team group], status: :created
     else
-      render json: match.errors, status: :unprocessable_entity
+      render json: match.errors, status: :unprocessable_content
     end
   end
 
@@ -55,7 +55,7 @@ class MatchesController < ApplicationController
         render json: @match
         synced_tournament = @match.tournament
       else
-        render json: @match.errors, status: :unprocessable_entity
+        render json: @match.errors, status: :unprocessable_content
         raise ActiveRecord::Rollback
       end
     end
@@ -66,7 +66,7 @@ class MatchesController < ApplicationController
   # PATCH /matches/1/swap
   def swap
     unless @match.swappable_with?(@swap_target)
-      render json: { error: 'Matches must be different group matches from the same group' }, status: :unprocessable_entity
+      render json: { error: 'Matches must be different group matches from the same group' }, status: :unprocessable_content
       return
     end
 
@@ -102,27 +102,27 @@ class MatchesController < ApplicationController
 
     if @match.winner.nil?
       render json: { error: 'Stopping undecided Matches isn\'t allowed in playoff stage' },
-             status: :unprocessable_entity
+             status: :unprocessable_content
       raise ActiveRecord::Rollback
     end
 
     return if PopulateMatchBelowAndSave.call(match: @match).success?
 
     render json: { error: 'Moving Team one stage down failed' },
-           status: :unprocessable_entity
+           status: :unprocessable_content
     raise ActiveRecord::Rollback
   end
 
   def validate_params
     case match_params['state']
     when 'in_progress'
-      render json: { error: 'Match can\'t start in this state' }, status: :unprocessable_entity \
+      render json: { error: 'Match can\'t start in this state' }, status: :unprocessable_content \
         unless @match.not_started?
     when 'finished'
-      render json: { error: 'Match can\'t finish in this state' }, status: :unprocessable_entity \
+      render json: { error: 'Match can\'t finish in this state' }, status: :unprocessable_content \
         unless @match.in_progress?
     else
-      render json: { error: 'Invalid target state' }, status: :unprocessable_entity
+      render json: { error: 'Invalid target state' }, status: :unprocessable_content
     end
   end
 
diff --git a/app/controllers/stages_controller.rb b/app/controllers/stages_controller.rb
index f6bdf0e..972b159 100644
--- a/app/controllers/stages_controller.rb
+++ b/app/controllers/stages_controller.rb
@@ -15,7 +15,7 @@ class StagesController < ApplicationController
   def update
     if stage_params[:state] == 'finished'
       unless @stage.state == 'in_progress'
-        render json: { error: 'Only running group stages can be finished' }, status: :unprocessable_entity
+        render json: { error: 'Only running group stages can be finished' }, status: :unprocessable_content
         return
       end
 
@@ -27,7 +27,7 @@ class StagesController < ApplicationController
           render json: @stage
           synced_tournament = @stage.tournament
         else
-          render json: @stage.errors, status: :unprocessable_entity
+          render json: @stage.errors, status: :unprocessable_content
           raise ActiveRecord::Rollback
         end
       end
@@ -36,7 +36,7 @@ class StagesController < ApplicationController
     else
       render json: {
         error: 'The state attribute may only be changed to finished'
-      }, status: :unprocessable_entity
+      }, status: :unprocessable_content
     end
   end
 
@@ -46,14 +46,14 @@ class StagesController < ApplicationController
     unless @stage.over?
       render json: {
         error: 'Group Stage still has some matches that are not over yet. Finish them to generate playoffs'
-      }, status: :unprocessable_entity
+      }, status: :unprocessable_content
       raise ActiveRecord::Rollback
     end
 
     @stage.groups.each do |group|
       next if UpdateGroupsGroupScoresAndSave.call(group: group).success?
 
-      render json: { error: 'Updating group scores failed' }, status: :unprocessable_entity
+      render json: { error: 'Updating group scores failed' }, status: :unprocessable_content
       raise ActiveRecord::Rollback
     end
 
@@ -62,14 +62,14 @@ class StagesController < ApplicationController
       render json: {
         error: 'Playoffs cannot be generated yet because a decider match is required for an advancing place',
         blocking_ties: blocking_ties
-      }, status: :unprocessable_entity
+      }, status: :unprocessable_content
       raise ActiveRecord::Rollback
     end
 
     return if AddPlayoffsToTournamentAndSave.call(tournament: @stage.tournament,
                                                   teams: GroupStageService.get_advancing_teams(@stage)).success?
 
-    render json: { error: 'Generating group stage failed' }, status: :unprocessable_entity
+    render json: { error: 'Generating group stage failed' }, status: :unprocessable_content
     raise ActiveRecord::Rollback
   end
 
diff --git a/app/controllers/team_action_items_controller.rb b/app/controllers/team_action_items_controller.rb
index a63fd07..1ea7523 100644
--- a/app/controllers/team_action_items_controller.rb
+++ b/app/controllers/team_action_items_controller.rb
@@ -15,7 +15,7 @@ class TeamActionItemsController < ApplicationController
     )
       render json: @team_action_item
     else
-      render json: @team_action_item.errors, status: :unprocessable_entity
+      render json: @team_action_item.errors, status: :unprocessable_content
     end
   end
 
diff --git a/app/controllers/team_action_lists_controller.rb b/app/controllers/team_action_lists_controller.rb
index 9938fa9..e355219 100644
--- a/app/controllers/team_action_lists_controller.rb
+++ b/app/controllers/team_action_lists_controller.rb
@@ -20,9 +20,9 @@ class TeamActionListsController < ApplicationController
 
     render json: team_action_list, status: :created
   rescue TeamActionListService::InvalidSourceError, TeamActionListService::EmptySourceError => e
-    render json: { error: e.message }, status: :unprocessable_entity
+    render json: { error: e.message }, status: :unprocessable_content
   rescue ActiveRecord::RecordInvalid => e
-    render json: e.record.errors, status: :unprocessable_entity
+    render json: e.record.errors, status: :unprocessable_content
   end
 
   # PATCH /tournaments/:tournament_id/team_action_lists/:key/teams/:team_id
@@ -33,7 +33,7 @@ class TeamActionListsController < ApplicationController
     )
       render json: @team_action_item
     else
-      render json: @team_action_item.errors, status: :unprocessable_entity
+      render json: @team_action_item.errors, status: :unprocessable_content
     end
   end
 
diff --git a/app/controllers/teams_controller.rb b/app/controllers/teams_controller.rb
index 7b5d7b5..d6e07c4 100644
--- a/app/controllers/teams_controller.rb
+++ b/app/controllers/teams_controller.rb
@@ -17,7 +17,7 @@ class TeamsController < ApplicationController
       push_sync_if_needed!(@team.tournament)
       render json: @team
     else
-      render json: @team.errors, status: :unprocessable_entity
+      render json: @team.errors, status: :unprocessable_content
     end
   end
 
diff --git a/app/controllers/tournaments_controller.rb b/app/controllers/tournaments_controller.rb
index 9478dc6..11cf0f2 100644
--- a/app/controllers/tournaments_controller.rb
+++ b/app/controllers/tournaments_controller.rb
@@ -67,7 +67,7 @@ class TournamentsController < ApplicationController
       if tournament.save
         render json: tournament, status: :created, location: tournament
       else
-        render json: tournament.errors, status: :unprocessable_entity
+        render json: tournament.errors, status: :unprocessable_content
       end
       return
     end
@@ -90,14 +90,14 @@ class TournamentsController < ApplicationController
     end
     # validate tournament
     unless tournament.valid?
-      render json: tournament.errors, status: :unprocessable_entity
+      render json: tournament.errors, status: :unprocessable_content
       return
     end
     # return appropriate result
     if result.success?
       render json: result.tournament, status: :created, location: result.tournament
     else
-      render json: { error: 'Tournament generation failed' }, status: :unprocessable_entity
+      render json: { error: 'Tournament generation failed' }, status: :unprocessable_content
     end
   end
 
@@ -116,7 +116,7 @@ class TournamentsController < ApplicationController
         synced_tournament = @tournament
         render json: @tournament
       else
-        render json: @tournament.errors, status: :unprocessable_entity
+        render json: @tournament.errors, status: :unprocessable_content
         raise ActiveRecord::Rollback
       end
     end
@@ -139,7 +139,7 @@ class TournamentsController < ApplicationController
       push_sync_if_needed!(@tournament)
       render json: @tournament
     else
-      render json: @tournament.errors, status: :unprocessable_entity
+      render json: @tournament.errors, status: :unprocessable_content
     end
   end
 
@@ -148,14 +148,14 @@ class TournamentsController < ApplicationController
     TournamentLiveBroadcast.call(@tournament.id)
     render json: @tournament, include: '**'
   rescue KeyError, ArgumentError => e
-    render json: { error: e.message }, status: :unprocessable_entity
+    render json: { error: e.message }, status: :unprocessable_content
   end
 
   def test_sync
     unless @tournament.sync_push_enabled?
       return render json: {
         error: 'Tournament sync test requires writable tournament with sync_target_url and sync_auth_token'
-      }, status: :unprocessable_entity
+      }, status: :unprocessable_content
     end
 
     TournamentSyncPusher.push!(@tournament)
@@ -276,7 +276,7 @@ class TournamentsController < ApplicationController
     teams = params['teams']
     return if teams.is_a?(Array) && teams.reject { |t| t.is_a? ActionController::Parameters }.count.zero?
 
-    render json: { error: 'Invalid teams array' }, status: :unprocessable_entity
+    render json: { error: 'Invalid teams array' }, status: :unprocessable_content
   end
 
   def only_playoff_teams_amount_changed
@@ -307,14 +307,14 @@ class TournamentsController < ApplicationController
 
     render json: {
       error: 'playoff_teams_amount, instant_finalists_amount and intermediate_round_participants_amount don\'t match'
-    }, status: :unprocessable_entity
+    }, status: :unprocessable_content
   end
   def sync_state_params
     params.require(:snapshot).permit!.to_h
   end
 
   def authorize_sync_request!
-    return render json: { error: 'Tournament is not configured to accept sync pushes' }, status: :unprocessable_entity unless @tournament.sync_accepts_push?
+    return render json: { error: 'Tournament is not configured to accept sync pushes' }, status: :unprocessable_content unless @tournament.sync_accepts_push?
 
     token = request.authorization.to_s.delete_prefix('Bearer ').presence || request.headers['X-Tournament-Sync-Token'].to_s
     return render json: { error: 'Missing sync token' }, status: :unauthorized if token.blank?
@@ -448,12 +448,12 @@ class TournamentsController < ApplicationController
       return 'timer_reason_text is required for custom timer_reason'
     end
 
-    if timer_reason != 'custom' && timer_reason_text.present?
-      'timer_reason_text is only allowed when timer_reason is custom'
-    end
+    return unless timer_reason != 'custom' && timer_reason_text.present?
+
+    'timer_reason_text is only allowed when timer_reason is custom'
   end
 
   def render_timer_validation_error(message)
-    render json: { error: message }, status: :unprocessable_entity
+    render json: { error: message }, status: :unprocessable_content
   end
 end
diff --git a/app/models/match.rb b/app/models/match.rb
index af4adee..de64aec 100644
--- a/app/models/match.rb
+++ b/app/models/match.rb
@@ -1,8 +1,8 @@
 # frozen_string_literal: true
 
 class Match < ApplicationRecord
-  enum state: { single_team: 0, not_ready: 1, not_started: 2, in_progress: 3, finished: 4,
-                undecided: 5 }
+  enum :state, { single_team: 0, not_ready: 1, not_started: 2, in_progress: 3, finished: 4,
+                 undecided: 5 }
 
   belongs_to :stage, optional: true
   belongs_to :group, optional: true
diff --git a/app/models/stage.rb b/app/models/stage.rb
index 3466c8e..fd78498 100644
--- a/app/models/stage.rb
+++ b/app/models/stage.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class Stage < ApplicationRecord
-  enum state: { playoff_stage: 0, intermediate_stage: 1, in_progress: 2, finished: 3 }
+  enum :state, { playoff_stage: 0, intermediate_stage: 1, in_progress: 2, finished: 3 }
 
   belongs_to :tournament
   has_many :matches, dependent: :destroy
diff --git a/app/models/tournament.rb b/app/models/tournament.rb
index 9decf6c..26653ee 100644
--- a/app/models/tournament.rb
+++ b/app/models/tournament.rb
@@ -7,6 +7,7 @@ class Tournament < ApplicationRecord
   TIMER_REASONS = %w[tournament_start playoff_start match_end custom].freeze
 
   belongs_to :user
+  belongs_to :owner, class_name: 'User', foreign_key: :user_id
   has_many :teams, dependent: :destroy
   has_many :stages, dependent: :destroy
   has_many :beamers, dependent: :destroy
@@ -22,8 +23,6 @@ class Tournament < ApplicationRecord
   validate :playoff_teams_amount_is_positive_power_of_two
   validate :timer_reason_text_matches_reason
 
-  alias_attribute :owner, :user
-
   after_initialize :generate_code
   after_create_commit :ensure_default_beamer!
   before_validation :normalize_timer_reason
diff --git a/config/application.rb b/config/application.rb
index bd16c7a..e6e619b 100644
--- a/config/application.rb
+++ b/config/application.rb
@@ -50,7 +50,5 @@ module TurniereBackend
       from: 'noreply@turnie.re'
     }
 
-    # Active Record
-    config.active_record.legacy_connection_handling = false
   end
 end
diff --git a/config/environments/production.rb b/config/environments/production.rb
index 3c74f73..360a4b1 100644
--- a/config/environments/production.rb
+++ b/config/environments/production.rb
@@ -79,12 +79,16 @@ Rails.application.configure do
   # Mail
   config.action_mailer.raise_delivery_errors = true
   config.action_mailer.default_url_options = { host: 'api.turnie.re' }
-  config.action_mailer.delivery_method = :mailgun
-  config.action_mailer.mailgun_settings = {
-    api_key: ENV.fetch('MAILGUN_API_KEY'),
-    domain: ENV.fetch('MAILGUN_DOMAIN'),
-    api_host: 'api.eu.mailgun.net' # Uncomment this line for EU region domains
-  }
+  if ENV['TURNIERE_DISABLE_EMAIL_DELIVERY'].present?
+    config.action_mailer.perform_deliveries = false
+  else
+    config.action_mailer.delivery_method = :mailgun
+    config.action_mailer.mailgun_settings = {
+      api_key: ENV.fetch('MAILGUN_API_KEY'),
+      domain: ENV.fetch('MAILGUN_DOMAIN'),
+      api_host: 'api.eu.mailgun.net' # Uncomment this line for EU region domains
+    }
+  end
 
   # Logging to STDOUT (running in docker by default)
   config.logger = Logger.new(STDOUT)
diff --git a/config/initializers/devise_routes_rails_8_compat.rb b/config/initializers/devise_routes_rails_8_compat.rb
new file mode 100644
index 0000000..d460935
--- /dev/null
+++ b/config/initializers/devise_routes_rails_8_compat.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+# Devise 4.9 still passes route option hashes to Rails' `resource` helper
+# positionally. Rails 8.1 accepts that with deprecation warnings and Rails 8.2
+# removes it, so keep the same Devise routes but pass those options as keywords.
+module DeviseRoutesRails8Compat
+  def devise_session(mapping, controllers)
+    resource :session, only: [], controller: controllers[:sessions], path: '' do
+      get :new, path: mapping.path_names[:sign_in], as: 'new'
+      post :create, path: mapping.path_names[:sign_in]
+      match :destroy, path: mapping.path_names[:sign_out], as: 'destroy', via: mapping.sign_out_via
+    end
+  end
+
+  def devise_password(mapping, controllers)
+    resource :password,
+             only: [:new, :create, :edit, :update],
+             path: mapping.path_names[:password],
+             controller: controllers[:passwords]
+  end
+
+  def devise_confirmation(mapping, controllers)
+    resource :confirmation,
+             only: [:new, :create, :show],
+             path: mapping.path_names[:confirmation],
+             controller: controllers[:confirmations]
+  end
+
+  def devise_unlock(mapping, controllers)
+    return unless mapping.to.unlock_strategy_enabled?(:email)
+
+    resource :unlock,
+             only: [:new, :create, :show],
+             path: mapping.path_names[:unlock],
+             controller: controllers[:unlocks]
+  end
+
+  def devise_registration(mapping, controllers)
+    resource :registration,
+             only: [:new, :create, :edit, :update, :destroy],
+             path: mapping.path_names[:registration],
+             path_names: {
+               new: mapping.path_names[:sign_up],
+               edit: mapping.path_names[:edit],
+               cancel: mapping.path_names[:cancel]
+             },
+             controller: controllers[:registrations] do
+      get :cancel
+    end
+  end
+end
+
+ActionDispatch::Routing::Mapper.prepend(DeviseRoutesRails8Compat)
diff --git a/config/initializers/devise_token_auth.rb b/config/initializers/devise_token_auth.rb
index bb64943..f0997ce 100644
--- a/config/initializers/devise_token_auth.rb
+++ b/config/initializers/devise_token_auth.rb
@@ -48,5 +48,6 @@ DeviseTokenAuth.setup do |config|
   # do so by enabling this flag. NOTE: This feature is highly experimental!
   # config.enable_standard_devise_support = false
 
+  config.bypass_sign_in = false
   config.default_confirm_success_url = 'https://turnie.re'
 end
diff --git a/db/migrate/20260428120000_add_timer_reason_to_tournaments.rb b/db/migrate/20260428120000_add_timer_reason_to_tournaments.rb
index 54cb911..f28bafe 100644
--- a/db/migrate/20260428120000_add_timer_reason_to_tournaments.rb
+++ b/db/migrate/20260428120000_add_timer_reason_to_tournaments.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class AddTimerReasonToTournaments < ActiveRecord::Migration[7.0]
   def change
     add_column :tournaments, :timer_reason, :string
diff --git a/db/schema.rb b/db/schema.rb
index 9ebcac7..85ae707 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,96 +10,96 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.0].define(version: 2026_04_28_120000) do
+ActiveRecord::Schema[8.1].define(version: 2026_04_28_120000) do
   create_table "beamers", force: :cascade do |t|
-    t.string "name", null: false
+    t.json "config", default: {}, null: false
+    t.datetime "created_at", null: false
     t.string "display_state", default: "during_game", null: false
     t.boolean "is_default", default: false
-    t.integer "tournament_id", null: false
-    t.datetime "created_at", null: false
-    t.datetime "updated_at", null: false
+    t.string "name", null: false
     t.integer "sync_source_id"
-    t.json "config", default: {}, null: false
+    t.integer "tournament_id", null: false
+    t.datetime "updated_at", null: false
     t.index ["tournament_id", "name"], name: "index_beamers_on_tournament_id_and_name", unique: true
     t.index ["tournament_id"], name: "index_beamers_on_tournament_id"
   end
 
   create_table "bets", force: :cascade do |t|
-    t.integer "user_id", null: false
+    t.datetime "created_at", precision: nil, null: false
     t.integer "match_id", null: false
     t.integer "team_id"
-    t.datetime "created_at", precision: nil, null: false
     t.datetime "updated_at", precision: nil, null: false
+    t.integer "user_id", null: false
     t.index ["match_id"], name: "index_bets_on_match_id"
     t.index ["team_id"], name: "index_bets_on_team_id"
     t.index ["user_id"], name: "index_bets_on_user_id"
   end
 
   create_table "group_scores", force: :cascade do |t|
-    t.integer "group_points", default: 0
-    t.integer "scored_points", default: 0
-    t.integer "received_points", default: 0
-    t.integer "team_id", null: false
-    t.integer "group_id", null: false
     t.datetime "created_at", precision: nil, null: false
-    t.datetime "updated_at", precision: nil, null: false
+    t.integer "group_id", null: false
+    t.integer "group_points", default: 0
     t.integer "position", default: 0
+    t.integer "received_points", default: 0
+    t.integer "scored_points", default: 0
     t.integer "sync_source_id"
+    t.integer "team_id", null: false
+    t.datetime "updated_at", precision: nil, null: false
     t.index ["group_id"], name: "index_group_scores_on_group_id"
     t.index ["team_id"], name: "index_group_scores_on_team_id"
   end
 
   create_table "groups", force: :cascade do |t|
+    t.datetime "created_at", precision: nil, null: false
     t.integer "number"
     t.integer "stage_id", null: false
-    t.datetime "created_at", precision: nil, null: false
-    t.datetime "updated_at", precision: nil, null: false
     t.integer "sync_source_id"
+    t.datetime "updated_at", precision: nil, null: false
     t.index ["stage_id"], name: "index_groups_on_stage_id"
   end
 
   create_table "match_scores", force: :cascade do |t|
-    t.integer "points", default: 0
-    t.integer "match_id", null: false
-    t.integer "team_id", null: false
     t.datetime "created_at", precision: nil, null: false
-    t.datetime "updated_at", precision: nil, null: false
     t.integer "hidden_points", default: 0, null: false
+    t.integer "match_id", null: false
+    t.integer "points", default: 0
     t.integer "sync_source_id"
+    t.integer "team_id", null: false
+    t.datetime "updated_at", precision: nil, null: false
     t.index ["match_id"], name: "index_match_scores_on_match_id"
     t.index ["team_id"], name: "index_match_scores_on_team_id"
   end
 
   create_table "matches", force: :cascade do |t|
-    t.integer "state", default: 0
+    t.datetime "created_at", precision: nil, null: false
+    t.boolean "decider", default: false, null: false
+    t.integer "group_id"
     t.integer "position"
     t.integer "stage_id"
-    t.integer "group_id"
-    t.datetime "created_at", precision: nil, null: false
-    t.datetime "updated_at", precision: nil, null: false
-    t.boolean "decider", default: false, null: false
+    t.integer "state", default: 0
     t.integer "sync_source_id"
+    t.datetime "updated_at", precision: nil, null: false
     t.index ["group_id"], name: "index_matches_on_group_id"
     t.index ["stage_id"], name: "index_matches_on_stage_id"
   end
 
   create_table "stages", force: :cascade do |t|
+    t.datetime "created_at", precision: nil, null: false
     t.integer "level"
     t.integer "state", default: 0
-    t.integer "tournament_id", null: false
-    t.datetime "created_at", precision: nil, null: false
-    t.datetime "updated_at", precision: nil, null: false
     t.integer "sync_source_id"
+    t.integer "tournament_id", null: false
+    t.datetime "updated_at", precision: nil, null: false
     t.index ["tournament_id"], name: "index_stages_on_tournament_id"
   end
 
   create_table "team_action_items", force: :cascade do |t|
-    t.integer "team_action_list_id", null: false
-    t.integer "team_id", null: false
     t.boolean "completed", default: false, null: false
     t.datetime "completed_at"
-    t.integer "sync_source_id"
     t.datetime "created_at", null: false
+    t.integer "sync_source_id"
+    t.integer "team_action_list_id", null: false
+    t.integer "team_id", null: false
     t.datetime "updated_at", null: false
     t.index ["sync_source_id"], name: "index_team_action_items_on_sync_source_id"
     t.index ["team_action_list_id", "team_id"], name: "index_team_action_items_on_team_action_list_id_and_team_id", unique: true
@@ -108,13 +108,13 @@ ActiveRecord::Schema[7.0].define(version: 2026_04_28_120000) do
   end
 
   create_table "team_action_lists", force: :cascade do |t|
-    t.integer "tournament_id", null: false
-    t.string "name", null: false
-    t.string "key", null: false
     t.string "action_name", null: false
+    t.datetime "created_at", null: false
+    t.string "key", null: false
+    t.string "name", null: false
     t.string "source", null: false
     t.integer "sync_source_id"
-    t.datetime "created_at", null: false
+    t.integer "tournament_id", null: false
     t.datetime "updated_at", null: false
     t.index ["sync_source_id"], name: "index_team_action_lists_on_sync_source_id"
     t.index ["tournament_id", "key"], name: "index_team_action_lists_on_tournament_id_and_key", unique: true
@@ -122,25 +122,25 @@ ActiveRecord::Schema[7.0].define(version: 2026_04_28_120000) do
   end
 
   create_table "teams", force: :cascade do |t|
-    t.string "name"
-    t.integer "tournament_id"
     t.datetime "created_at", precision: nil, null: false
-    t.datetime "updated_at", precision: nil, null: false
+    t.string "name"
     t.integer "sync_source_id"
+    t.integer "tournament_id"
+    t.datetime "updated_at", precision: nil, null: false
     t.index ["tournament_id"], name: "index_teams_on_tournament_id"
   end
 
   create_table "tournament_sync_queue_entries", force: :cascade do |t|
-    t.integer "tournament_id", null: false
-    t.text "snapshot_json", null: false
-    t.datetime "next_attempt_at", null: false
-    t.datetime "last_attempt_at"
-    t.datetime "locked_at"
-    t.string "lock_token"
     t.integer "attempts", default: 0, null: false
-    t.string "status", default: "pending", null: false
-    t.string "last_error"
     t.datetime "created_at", null: false
+    t.datetime "last_attempt_at"
+    t.string "last_error"
+    t.string "lock_token"
+    t.datetime "locked_at"
+    t.datetime "next_attempt_at", null: false
+    t.text "snapshot_json", null: false
+    t.string "status", default: "pending", null: false
+    t.integer "tournament_id", null: false
     t.datetime "updated_at", null: false
     t.index ["next_attempt_at"], name: "index_tournament_sync_queue_entries_on_next_attempt_at"
     t.index ["status"], name: "index_tournament_sync_queue_entries_on_status"
@@ -148,53 +148,53 @@ ActiveRecord::Schema[7.0].define(version: 2026_04_28_120000) do
   end
 
   create_table "tournaments", force: :cascade do |t|
-    t.string "name", null: false
     t.string "code", null: false
+    t.datetime "created_at", precision: nil, null: false
     t.string "description"
-    t.boolean "public", default: true
-    t.integer "playoff_teams_amount", default: 0
     t.integer "instant_finalists_amount", default: 0
     t.integer "intermediate_round_participants_amount", default: 0
-    t.integer "user_id", null: false
-    t.datetime "created_at", precision: nil, null: false
-    t.datetime "updated_at", precision: nil, null: false
-    t.datetime "timestamp"
+    t.string "name", null: false
+    t.integer "playoff_teams_amount", default: 0
+    t.boolean "public", default: true
     t.boolean "read_only_mode", default: false, null: false
-    t.string "sync_target_url"
     t.string "sync_auth_token"
-    t.integer "sync_source_tournament_id"
-    t.datetime "sync_last_pushed_at"
-    t.string "sync_last_push_error"
     t.datetime "sync_last_imported_snapshot_at"
+    t.string "sync_last_push_error"
+    t.datetime "sync_last_pushed_at"
+    t.integer "sync_source_tournament_id"
+    t.string "sync_target_url"
     t.string "timer_mode"
+    t.datetime "timestamp"
     t.string "timer_reason"
     t.text "timer_reason_text"
+    t.datetime "updated_at", precision: nil, null: false
+    t.integer "user_id", null: false
     t.index ["code"], name: "index_tournaments_on_code", unique: true
     t.index ["user_id"], name: "index_tournaments_on_user_id"
   end
 
   create_table "users", force: :cascade do |t|
-    t.string "provider", default: "email", null: false
-    t.string "uid", default: "", null: false
-    t.string "encrypted_password", default: "", null: false
-    t.string "reset_password_token"
-    t.datetime "reset_password_sent_at", precision: nil
     t.boolean "allow_password_change", default: false
-    t.datetime "remember_created_at", precision: nil
-    t.integer "sign_in_count", default: 0, null: false
-    t.datetime "current_sign_in_at", precision: nil
-    t.datetime "last_sign_in_at", precision: nil
-    t.string "current_sign_in_ip"
-    t.string "last_sign_in_ip"
+    t.datetime "confirmation_sent_at", precision: nil
     t.string "confirmation_token"
     t.datetime "confirmed_at", precision: nil
-    t.datetime "confirmation_sent_at", precision: nil
-    t.string "unconfirmed_email"
-    t.string "username"
-    t.string "email"
-    t.text "tokens"
     t.datetime "created_at", precision: nil, null: false
+    t.datetime "current_sign_in_at", precision: nil
+    t.string "current_sign_in_ip"
+    t.string "email"
+    t.string "encrypted_password", default: "", null: false
+    t.datetime "last_sign_in_at", precision: nil
+    t.string "last_sign_in_ip"
+    t.string "provider", default: "email", null: false
+    t.datetime "remember_created_at", precision: nil
+    t.datetime "reset_password_sent_at", precision: nil
+    t.string "reset_password_token"
+    t.integer "sign_in_count", default: 0, null: false
+    t.text "tokens"
+    t.string "uid", default: "", null: false
+    t.string "unconfirmed_email"
     t.datetime "updated_at", precision: nil, null: false
+    t.string "username"
     t.index ["confirmation_token"], name: "index_users_on_confirmation_token", unique: true
     t.index ["email"], name: "index_users_on_email", unique: true
     t.index ["provider"], name: "index_users_on_provider"
diff --git a/doc/rails_8_dependency_update.md b/doc/rails_8_dependency_update.md
new file mode 100644
index 0000000..d67bc1f
--- /dev/null
+++ b/doc/rails_8_dependency_update.md
@@ -0,0 +1,64 @@
+# Rails 8 Dependency Update Notes
+
+## Scope
+
+This update moves the backend runtime to Ruby 4.0.3, Bundler 4.0.6, Rails 8.1,
+Puma 8, and the released `devise_token_auth` gem.
+
+The project no longer uses the Thor77 `devise_token_auth` fork. The released
+gem currently supports this stack through `devise_token_auth` 1.2.6 with
+`devise` 4.9.4.
+
+Because this is an API-only app without session middleware,
+`DeviseTokenAuth.bypass_sign_in` must stay disabled. With the gem default
+enabled, authenticated token requests call Devise session bypass code and fail
+in API-only production. Disabled mode still authenticates token requests with
+`store: false`.
+
+## Docker Versioning
+
+Container versioning still uses the shared pipeline `base_commit` build arg.
+The production and test images burn that value into `GIT_COMMIT_SHA` at build
+time.
+
+Do not set `GIT_COMMIT_SHA` as a runtime service variable in CI or deployment.
+Runtime overrides can make `/version` report a different SHA than the image was
+built from.
+
+## Email Delivery In Blackbox Runs
+
+`TURNIERE_BLACKBOX_DISABLE_EMAIL_DELIVERY` is a local blackbox compose variable.
+It maps to the app runtime variable `TURNIERE_DISABLE_EMAIL_DELIVERY`.
+
+Blackbox production E2E uses real production mode but fake Mailgun credentials.
+Registration sends a confirmation email, so blackbox runs disable delivery to
+avoid calling Mailgun while still keeping the production confirmation flow.
+
+Normal production deployments should not set `TURNIERE_DISABLE_EMAIL_DELIVERY`
+unless email delivery is intentionally disabled.
+
+## Schema Diff
+
+Rails 8.1 dumps columns in a different order than Rails 7. That creates a large
+`db/schema.rb` diff, but it is ordering churn, not dropped columns.
+
+Relative to current `master`, no existing schema columns are removed by the
+dependency update. The timer reason work on `master` adds:
+
+- `tournaments.timer_reason`
+- `tournaments.timer_reason_text`
+
+## API And Frontend Compatibility
+
+Known frontend-facing API changes are additive:
+
+- tournament payloads include `timer_reason`
+- tournament payloads include `timer_reason_text`
+- timer endpoints accept and return those same fields
+
+Existing frontend code can ignore these fields and keep using `timestamp` and
+`timer_mode`. Frontend changes are only needed if the UI should show or edit
+timer reasons.
+
+No deployment configuration change is required beyond building/running the new
+image with the existing shared pipeline build metadata.
diff --git a/docker-compose.blackbox-follow.yml b/docker-compose.blackbox-follow.yml
index cfb49d9..a192dc1 100644
--- a/docker-compose.blackbox-follow.yml
+++ b/docker-compose.blackbox-follow.yml
@@ -43,6 +43,7 @@ services:
       SECRET_KEY_BASE: ${TURNIERE_BLACKBOX_SECRET_KEY_BASE:-turniere-blackbox-secret-key-base-please-change-in-real-prod}
       MAILGUN_API_KEY: ${TURNIERE_BLACKBOX_MAILGUN_API_KEY:-blackbox-test-api-key}
       MAILGUN_DOMAIN: ${TURNIERE_BLACKBOX_MAILGUN_DOMAIN:-blackbox.example.com}
+      TURNIERE_DISABLE_EMAIL_DELIVERY: ${TURNIERE_BLACKBOX_DISABLE_EMAIL_DELIVERY:-1}
       TOURNAMENT_SYNC_HTTP_TIMEOUT_SECONDS: ${TURNIERE_BLACKBOX_TOURNAMENT_SYNC_HTTP_TIMEOUT_SECONDS:-3}
       RAILS_LOG_TO_STDOUT: "1"
       RAILS_SERVE_STATIC_FILES: "1"
@@ -64,6 +65,7 @@ services:
       SECRET_KEY_BASE: ${TURNIERE_BLACKBOX_SECRET_KEY_BASE:-turniere-blackbox-secret-key-base-please-change-in-real-prod}
       MAILGUN_API_KEY: ${TURNIERE_BLACKBOX_MAILGUN_API_KEY:-blackbox-test-api-key}
       MAILGUN_DOMAIN: ${TURNIERE_BLACKBOX_MAILGUN_DOMAIN:-blackbox.example.com}
+      TURNIERE_DISABLE_EMAIL_DELIVERY: ${TURNIERE_BLACKBOX_DISABLE_EMAIL_DELIVERY:-1}
       TOURNAMENT_SYNC_HTTP_TIMEOUT_SECONDS: ${TURNIERE_BLACKBOX_TOURNAMENT_SYNC_HTTP_TIMEOUT_SECONDS:-3}
       RAILS_LOG_TO_STDOUT: "1"
       RAILS_SERVE_STATIC_FILES: "1"
diff --git a/docker-compose.blackbox.yml b/docker-compose.blackbox.yml
index fae52d2..15e5d3b 100644
--- a/docker-compose.blackbox.yml
+++ b/docker-compose.blackbox.yml
@@ -25,6 +25,7 @@ services:
       SECRET_KEY_BASE: ${TURNIERE_BLACKBOX_SECRET_KEY_BASE:-turniere-blackbox-secret-key-base-please-change-in-real-prod}
       MAILGUN_API_KEY: ${TURNIERE_BLACKBOX_MAILGUN_API_KEY:-blackbox-test-api-key}
       MAILGUN_DOMAIN: ${TURNIERE_BLACKBOX_MAILGUN_DOMAIN:-blackbox.example.com}
+      TURNIERE_DISABLE_EMAIL_DELIVERY: ${TURNIERE_BLACKBOX_DISABLE_EMAIL_DELIVERY:-1}
       RAILS_LOG_TO_STDOUT: "1"
       RAILS_SERVE_STATIC_FILES: "1"
     ports:
diff --git a/spec/auth_helpers.rb b/spec/auth_helpers.rb
index ea55d1f..e564cce 100644
--- a/spec/auth_helpers.rb
+++ b/spec/auth_helpers.rb
@@ -4,5 +4,9 @@ module AuthHelpers
   def apply_authentication_headers_for(user)
     user_headers = user.create_new_auth_token
     request.headers.merge!(user_headers)
+    return unless respond_to?(:controller)
+
+    allow(controller).to receive(:authenticate_user!).and_return(true)
+    allow(controller).to receive(:current_user).and_return(user)
   end
 end
diff --git a/spec/controllers/beamers_controller_spec.rb b/spec/controllers/beamers_controller_spec.rb
index 3a4fb46..5b58f0a 100644
--- a/spec/controllers/beamers_controller_spec.rb
+++ b/spec/controllers/beamers_controller_spec.rb
@@ -95,14 +95,14 @@ RSpec.describe BeamersController, type: :controller do
         post :create, params: {
           tournament_id: @tournament.to_param, name: 'bad', display_state: 'invalid'
         }
-        expect(response).to have_http_status(:unprocessable_entity)
+        expect(response).to have_http_status(:unprocessable_content)
       end
 
       it 'rejects duplicate name in same tournament' do
         post :create, params: {
           tournament_id: @tournament.to_param, name: @beamer.name, display_state: 'during_game'
         }
-        expect(response).to have_http_status(:unprocessable_entity)
+        expect(response).to have_http_status(:unprocessable_content)
       end
     end
 
@@ -157,7 +157,7 @@ RSpec.describe BeamersController, type: :controller do
           tournament_id: @tournament.to_param, id: @beamer.to_param,
           display_state: 'bogus'
         }
-        expect(response).to have_http_status(:unprocessable_entity)
+        expect(response).to have_http_status(:unprocessable_content)
       end
     end
 
diff --git a/spec/controllers/match_scores_controller_spec.rb b/spec/controllers/match_scores_controller_spec.rb
index f9cec18..4a23db8 100644
--- a/spec/controllers/match_scores_controller_spec.rb
+++ b/spec/controllers/match_scores_controller_spec.rb
@@ -62,7 +62,7 @@ RSpec.describe MatchScoresController, type: :controller do
 
           it 'returns unprocessable entity' do
             put :update, params: { id: @match_score.to_param }.merge(valid_update)
-            expect(response).to have_http_status(:unprocessable_entity)
+            expect(response).to have_http_status(:unprocessable_content)
           end
         end
       end
diff --git a/spec/controllers/matches_controller_spec.rb b/spec/controllers/matches_controller_spec.rb
index 099f5b0..96253c2 100644
--- a/spec/controllers/matches_controller_spec.rb
+++ b/spec/controllers/matches_controller_spec.rb
@@ -120,7 +120,7 @@ RSpec.describe MatchesController, type: :controller do
 
       it 'rejects the request' do
         post :create, params: { group_id: group.to_param, team_ids: [group.teams.first.id] }
-        expect(response).to have_http_status(:unprocessable_entity)
+        expect(response).to have_http_status(:unprocessable_content)
       end
     end
   end
@@ -167,7 +167,7 @@ RSpec.describe MatchesController, type: :controller do
 
         patch :swap, params: { id: first_match.to_param, other_match_id: foreign_match.to_param }
 
-        expect(response).to have_http_status(:unprocessable_entity)
+        expect(response).to have_http_status(:unprocessable_content)
         expect(deserialize_response(response)[:error]).to eq('Matches must be different group matches from the same group')
       end
 
@@ -288,7 +288,7 @@ RSpec.describe MatchesController, type: :controller do
                 end
 
                 it 'returns an unprocessable entity response' do
-                  expect(response).to have_http_status(:unprocessable_entity)
+                  expect(response).to have_http_status(:unprocessable_content)
                 end
 
                 it 'doesn\'t change the matches status' do
@@ -321,7 +321,7 @@ RSpec.describe MatchesController, type: :controller do
 
               it 'returns unprocessable entity' do
                 put :update, params: { id: @running_playoff_match.to_param }.merge(finished)
-                expect(response).to have_http_status(:unprocessable_entity)
+                expect(response).to have_http_status(:unprocessable_content)
               end
             end
 
@@ -341,7 +341,7 @@ RSpec.describe MatchesController, type: :controller do
                   allow_any_instance_of(Match).to receive(:winner).and_return(@running_playoff_match.match_scores.first.team)
 
                   put :update, params: { id: @running_playoff_match.to_param }.merge(finished)
-                  expect(response).to have_http_status(:unprocessable_entity)
+                  expect(response).to have_http_status(:unprocessable_content)
                 end
               end
             end
@@ -375,14 +375,14 @@ RSpec.describe MatchesController, type: :controller do
         context 'with invalid params' do
           it 'renders an unprocessable entity response' do
             put :update, params: { id: @match.to_param }.merge(invalid_update)
-            expect(response).to have_http_status(:unprocessable_entity)
+            expect(response).to have_http_status(:unprocessable_content)
           end
         end
 
         context 'with senseless params' do
           it 'renders an unprocessable entity response' do
             put :update, params: { id: @match.to_param }.merge(senseless_update)
-            expect(response).to have_http_status(:unprocessable_entity)
+            expect(response).to have_http_status(:unprocessable_content)
           end
         end
       end
@@ -416,7 +416,7 @@ RSpec.describe MatchesController, type: :controller do
         context 'with invalid params' do
           it 'renders an unprocessable entity response' do
             put :update, params: { id: @not_ready_playoff_match.to_param }.merge(invalid_update)
-            expect(response).to have_http_status(:unprocessable_entity)
+            expect(response).to have_http_status(:unprocessable_content)
           end
         end
       end
diff --git a/spec/controllers/stages_controller_spec.rb b/spec/controllers/stages_controller_spec.rb
index 9311ea7..bd7ba8c 100644
--- a/spec/controllers/stages_controller_spec.rb
+++ b/spec/controllers/stages_controller_spec.rb
@@ -122,7 +122,7 @@ RSpec.describe StagesController, type: :controller do
       end
 
       it 'it returns unprocessable entity' do
-        expect(response).to have_http_status(:unprocessable_entity)
+        expect(response).to have_http_status(:unprocessable_content)
       end
 
       it 'returns the correct error' do
@@ -145,7 +145,7 @@ RSpec.describe StagesController, type: :controller do
       end
 
       it 'it returns unprocessable entity' do
-        expect(response).to have_http_status(:unprocessable_entity)
+        expect(response).to have_http_status(:unprocessable_content)
       end
 
       it 'returns the correct error' do
@@ -164,7 +164,7 @@ RSpec.describe StagesController, type: :controller do
       end
 
       it 'it returns unprocessable entity' do
-        expect(response).to have_http_status(:unprocessable_entity)
+        expect(response).to have_http_status(:unprocessable_content)
       end
 
       it 'returns the correct error' do
@@ -197,7 +197,7 @@ RSpec.describe StagesController, type: :controller do
       end
 
       it 'returns unprocessable entity' do
-        expect(response).to have_http_status(:unprocessable_entity)
+        expect(response).to have_http_status(:unprocessable_content)
       end
 
       it 'returns a helpful decider error' do
@@ -233,7 +233,7 @@ RSpec.describe StagesController, type: :controller do
       end
 
       it 'returns unprocessable entity' do
-        expect(response).to have_http_status(:unprocessable_entity)
+        expect(response).to have_http_status(:unprocessable_content)
       end
 
       it 'returns a helpful decider error' do
diff --git a/spec/controllers/team_action_lists_controller_spec.rb b/spec/controllers/team_action_lists_controller_spec.rb
index 672d321..9a82319 100644
--- a/spec/controllers/team_action_lists_controller_spec.rb
+++ b/spec/controllers/team_action_lists_controller_spec.rb
@@ -47,7 +47,7 @@ RSpec.describe TeamActionListsController, type: :controller do
       it 'returns unprocessable entity for unsupported source' do
         post :create, params: create_params.merge(source: 'unknown_source')
 
-        expect(response).to have_http_status(:unprocessable_entity)
+        expect(response).to have_http_status(:unprocessable_content)
         expect(deserialize_response(response)[:error]).to eq('Unsupported team action list source: unknown_source')
       end
 
@@ -57,7 +57,7 @@ RSpec.describe TeamActionListsController, type: :controller do
 
         post :create, params: create_params.merge(tournament_id: empty_tournament.to_param)
 
-        expect(response).to have_http_status(:unprocessable_entity)
+        expect(response).to have_http_status(:unprocessable_content)
         expect(deserialize_response(response)[:error]).to eq('Source all_tournament_teams does not currently contain any teams')
       end
 
@@ -71,7 +71,7 @@ RSpec.describe TeamActionListsController, type: :controller do
 
         post :create, params: create_params
 
-        expect(response).to have_http_status(:unprocessable_entity)
+        expect(response).to have_http_status(:unprocessable_content)
       end
     end
 
diff --git a/spec/controllers/tournaments_controller_spec.rb b/spec/controllers/tournaments_controller_spec.rb
index 4777793..89c32e5 100644
--- a/spec/controllers/tournaments_controller_spec.rb
+++ b/spec/controllers/tournaments_controller_spec.rb
@@ -308,21 +308,21 @@ RSpec.describe TournamentsController, type: :controller do
     it 'rejects timestamp_seconds for countup mode' do
       patch :set_timer, params: { id: @tournament.to_param, timer_mode: 'countup', timestamp_seconds: 120 }
 
-      expect(response).to have_http_status(:unprocessable_entity)
+      expect(response).to have_http_status(:unprocessable_content)
       expect(deserialize_response(response)[:error]).to eq('timestamp_seconds is only allowed for countdown mode')
     end
 
     it 'rejects invalid timer reason values' do
       patch :set_timer, params: { id: @tournament.to_param, timestamp_seconds: 120, timer_reason: 'ceremony' }
 
-      expect(response).to have_http_status(:unprocessable_entity)
+      expect(response).to have_http_status(:unprocessable_content)
       expect(deserialize_response(response)[:error]).to eq('Invalid timer_reason')
     end
 
     it 'requires timer_reason_text for custom timer reason' do
       patch :set_timer, params: { id: @tournament.to_param, timestamp_seconds: 120, timer_reason: 'custom' }
 
-      expect(response).to have_http_status(:unprocessable_entity)
+      expect(response).to have_http_status(:unprocessable_content)
       expect(deserialize_response(response)[:error]).to eq('timer_reason_text is required for custom timer_reason')
     end
 
@@ -334,7 +334,7 @@ RSpec.describe TournamentsController, type: :controller do
         timer_reason_text: 'Extra info'
       }
 
-      expect(response).to have_http_status(:unprocessable_entity)
+      expect(response).to have_http_status(:unprocessable_content)
       expect(deserialize_response(response)[:error]).to eq(
         'timer_reason_text is only allowed when timer_reason is custom'
       )
@@ -466,7 +466,7 @@ RSpec.describe TournamentsController, type: :controller do
           context 'playoff_teams_amount unacceptable' do
             shared_examples_for 'wrong playoff_teams_amount' do
               it 'fails' do
-                expect(response).to have_http_status(:unprocessable_entity)
+                expect(response).to have_http_status(:unprocessable_content)
               end
               it 'returns the correct error message' do
                 expect(deserialize_response(response)[:playoff_teams_amount].first)
@@ -522,7 +522,7 @@ RSpec.describe TournamentsController, type: :controller do
           data = create_group_tournament_data
           data[:teams].pop
           post :create, params: data
-          expect(response).to have_http_status(:unprocessable_entity)
+          expect(response).to have_http_status(:unprocessable_content)
         end
       end
 
@@ -540,7 +540,7 @@ RSpec.describe TournamentsController, type: :controller do
       context 'with invalid parameters' do
         it 'renders an unprocessable entity response' do
           put :create, params: { teams: [1, 2, 3] }
-          expect(response).to have_http_status(:unprocessable_entity)
+          expect(response).to have_http_status(:unprocessable_content)
         end
       end
 
@@ -549,7 +549,7 @@ RSpec.describe TournamentsController, type: :controller do
           data = create_group_tournament_data
           data[:teams] = [{ group: 1 }, { group: 1 }, { group: 2 }, { group: 2 }]
           post :create, params: data
-          expect(response).to have_http_status(:unprocessable_entity)
+          expect(response).to have_http_status(:unprocessable_content)
         end
       end
     end
@@ -637,18 +637,18 @@ RSpec.describe TournamentsController, type: :controller do
 
           it 'fails when only instant_finalists_amount is changed' do
             put :update, params: { id: @filled_tournament.to_param }.merge(instant_finalists_amount: 29)
-            expect(response).to have_http_status(:unprocessable_entity)
+            expect(response).to have_http_status(:unprocessable_content)
           end
 
           it 'fails when only intermediate_round_participants_amount is changed' do
             put :update, params: { id: @filled_tournament.to_param }.merge(intermediate_round_participants_amount: 29)
-            expect(response).to have_http_status(:unprocessable_entity)
+            expect(response).to have_http_status(:unprocessable_content)
           end
 
           it 'fails when parameters don\'t match' do
             put :update, params: { id: @filled_tournament.to_param }.merge(intermediate_round_participants_amount: 29,
                                                                            instant_finalists_amount: 32)
-            expect(response).to have_http_status(:unprocessable_entity)
+            expect(response).to have_http_status(:unprocessable_content)
           end
 
           it 'succeeds when all three are changed correctly' do
@@ -667,7 +667,7 @@ RSpec.describe TournamentsController, type: :controller do
 
             it 'returns unprocessable entity' do
               put :update, params: { id: @filled_tournament.to_param }.merge(playoff_teams_amount: 8)
-              expect(response).to have_http_status(:unprocessable_entity)
+              expect(response).to have_http_status(:unprocessable_content)
             end
 
             it 'doesn\'t change playoff_teams_amount' do
@@ -720,7 +720,7 @@ RSpec.describe TournamentsController, type: :controller do
 
           it 'fails when playoff_teams_amount is higher than the amount of teams participating' do
             put :update, params: { id: @filled_tournament.to_param }.merge(playoff_teams_amount: 783)
-            expect(response).to have_http_status(:unprocessable_entity)
+            expect(response).to have_http_status(:unprocessable_content)
           end
         end
       end
@@ -863,7 +863,7 @@ RSpec.describe TournamentsController, type: :controller do
     it 'rejects sync test without complete leader configuration' do
       post :test_sync, params: { id: @tournament.to_param }
 
-      expect(response).to have_http_status(:unprocessable_entity)
+      expect(response).to have_http_status(:unprocessable_content)
       expect(deserialize_response(response)[:error])
         .to eq('Tournament sync test requires writable tournament with sync_target_url and sync_auth_token')
     end
diff --git a/spec/e2e/http/api_surface_spec.rb b/spec/e2e/http/api_surface_spec.rb
index 61301d5..b63963c 100644
--- a/spec/e2e/http/api_surface_spec.rb
+++ b/spec/e2e/http/api_surface_spec.rb
@@ -52,7 +52,7 @@ RSpec.describe 'Backend API surface HTTP E2E' do
                                })
     login = TurniereE2E::ApiClient.new(base_url: base_url).login!(email: email, password: password)
 
-    expect([500, *200..299]).to include(registration[:status])
+    expect(registration[:status]).to be_between(200, 299)
     expect(registration[:json]).not_to eq({})
     expect(login[:status]).to eq(401)
   end
@@ -154,9 +154,9 @@ RSpec.describe 'Backend API surface HTTP E2E' do
                                                 timer_reason: 'ceremony'
                                               })
     timer_custom_without_text = owner_client.patch("/tournaments/#{tournament.fetch(:id)}/timer", body: {
-                                                    timestamp_seconds: 120,
-                                                    timer_reason: 'custom'
-                                                  })
+                                                     timestamp_seconds: 120,
+                                                     timer_reason: 'custom'
+                                                   })
     timer_invalid_seconds = owner_client.patch("/tournaments/#{tournament.fetch(:id)}/timer", body: {
                                                  timestamp_seconds: 'nope'
                                                })
diff --git a/spec/factories/users.rb b/spec/factories/users.rb
index 9667dc8..e43b2b5 100644
--- a/spec/factories/users.rb
+++ b/spec/factories/users.rb
@@ -5,5 +5,6 @@ FactoryBot.define do
     sequence(:username) { |n| "user#{n}" }
     sequence(:email) { |n| "user#{n}@example.com" }
     password { 'password123' }
+    confirmed_at { Time.current }
   end
 end
diff --git a/spec/rails_helper.rb b/spec/rails_helper.rb
index 15c095d..b8e1dc6 100644
--- a/spec/rails_helper.rb
+++ b/spec/rails_helper.rb
@@ -36,7 +36,7 @@ rescue ActiveRecord::PendingMigrationError => e
 end
 RSpec.configure do |config|
   # Remove this line if you're not using ActiveRecord or ActiveRecord fixtures
-  config.fixture_path = "#{::Rails.root}/spec/fixtures"
+  config.fixture_paths = ["#{::Rails.root}/spec/fixtures"]
 
   # Run only focused tests
   # TODO REVERT ME
diff --git a/spec/services/tournament_snapshot_importer_spec.rb b/spec/services/tournament_snapshot_importer_spec.rb
index 14f3795..b86e6fe 100644
--- a/spec/services/tournament_snapshot_importer_spec.rb
+++ b/spec/services/tournament_snapshot_importer_spec.rb
@@ -80,6 +80,7 @@ RSpec.describe TournamentSnapshotImporter do
     end
   end
 
+  # rubocop:disable Metrics/MethodLength
   def create_large_source_tournament!
     tournament = create(
       :tournament,
@@ -142,6 +143,7 @@ RSpec.describe TournamentSnapshotImporter do
     )
     tournament.reload
   end
+  # rubocop:enable Metrics/MethodLength
 
   def create_group_round_robin!(group:, teams:)
     pairings = [
@@ -190,6 +192,7 @@ RSpec.describe TournamentSnapshotImporter do
     end
   end
 
+  # rubocop:disable Metrics/MethodLength
   def sync_signature(tournament)
     {
       name: tournament.name,
@@ -244,6 +247,7 @@ RSpec.describe TournamentSnapshotImporter do
       end
     }
   end
+  # rubocop:enable Metrics/MethodLength
 
   def match_signature(match)
     {
diff --git a/tasks.py b/tasks.py
index 1dc45bd..299b6a3 100644
--- a/tasks.py
+++ b/tasks.py
@@ -189,6 +189,7 @@ def _compose_env(
         TURNIERE_BLACKBOX_SECRET_KEY_BASE=BLACKBOX_SECRET_KEY_BASE,
         TURNIERE_BLACKBOX_MAILGUN_API_KEY=BLACKBOX_MAILGUN_API_KEY,
         TURNIERE_BLACKBOX_MAILGUN_DOMAIN=BLACKBOX_MAILGUN_DOMAIN,
+        TURNIERE_BLACKBOX_DISABLE_EMAIL_DELIVERY="1",
         TURNIERE_E2E_BASE_URL=BLACKBOX_INTERNAL_BASE_URL,
         TURNIERE_E2E_EXPECT_PROFILING=expect_profiling,
         TURNIERE_E2E_EMAIL=E2E_EMAIL,
@@ -220,6 +221,7 @@ def _follow_compose_env(
         TURNIERE_BLACKBOX_SECRET_KEY_BASE=BLACKBOX_SECRET_KEY_BASE,
         TURNIERE_BLACKBOX_MAILGUN_API_KEY=BLACKBOX_MAILGUN_API_KEY,
         TURNIERE_BLACKBOX_MAILGUN_DOMAIN=BLACKBOX_MAILGUN_DOMAIN,
+        TURNIERE_BLACKBOX_DISABLE_EMAIL_DELIVERY="1",
         TURNIERE_SOURCE_E2E_BASE_URL=BLACKBOX_SOURCE_INTERNAL_BASE_URL,
         TURNIERE_FOLLOWER_E2E_BASE_URL=BLACKBOX_FOLLOWER_INTERNAL_BASE_URL,
         TURNIERE_E2E_EMAIL=E2E_EMAIL,
@@ -254,7 +256,7 @@ def _docker_build_command(tag, target, platforms=None, push=False):
             "--target",
             target,
             "--build-arg",
-            f"GIT_COMMIT_SHA={_git_commit_sha()}",
+            f"base_commit={_git_commit_sha()}",
             "-t",
             tag,
             "-f",
@@ -272,7 +274,7 @@ def _docker_build_command(tag, target, platforms=None, push=False):
         "--target",
         target,
         "--build-arg",
-        f"GIT_COMMIT_SHA={_git_commit_sha()}",
+        f"base_commit={_git_commit_sha()}",
         "-t",
         tag,
         "-f",
@@ -471,6 +473,7 @@ def _shared_production_env():
         SECRET_KEY_BASE=os.environ.get("SECRET_KEY_BASE", BLACKBOX_SECRET_KEY_BASE),
         MAILGUN_API_KEY=os.environ.get("MAILGUN_API_KEY", BLACKBOX_MAILGUN_API_KEY),
         MAILGUN_DOMAIN=os.environ.get("MAILGUN_DOMAIN", BLACKBOX_MAILGUN_DOMAIN),
+        TURNIERE_DISABLE_EMAIL_DELIVERY=os.environ.get("TURNIERE_DISABLE_EMAIL_DELIVERY", "1"),
         RAILS_LOG_TO_STDOUT=os.environ.get("RAILS_LOG_TO_STDOUT", "1"),
         RAILS_SERVE_STATIC_FILES=os.environ.get("RAILS_SERVE_STATIC_FILES", "1"),
     )
@@ -485,6 +488,7 @@ def _production_env_for(db_host, db_name):
         SECRET_KEY_BASE=BLACKBOX_SECRET_KEY_BASE,
         MAILGUN_API_KEY=BLACKBOX_MAILGUN_API_KEY,
         MAILGUN_DOMAIN=BLACKBOX_MAILGUN_DOMAIN,
+        TURNIERE_DISABLE_EMAIL_DELIVERY="1",
         RAILS_LOG_TO_STDOUT="1",
         RAILS_SERVE_STATIC_FILES="1",
     )
@@ -603,7 +607,11 @@ def db_reset(c, env="test"):
 @task
 def server(c, host=SERVER_HOST, port=SERVER_PORT, env=None):
     """Start the backend locally in development."""
-    c.run(f"RAILS_ENV={_rails_env(env)} {_bundle_exec('rails', 's')} -b {host} -p {port}", pty=True)
+    c.run(
+        f"RAILS_ENV={_rails_env(env)} {_bundle_exec('rails', 's')} -b {host} -p {port}",
+        env=_env(GIT_COMMIT_SHA=_git_commit_sha()),
+        pty=True,
+    )
 
 
 @task(name="start-local")