Validate text limit implemented in oauth_applications.scopes

What does this MR do and why?

Ref #551214 (closed)

This is a follow-up of !195534 (merged).

The purpose of this MR is to complete the oauth_applications.scopes field migration by validating the text limit constraint, as described in Validate the text limit (next release).

• Validates the 2048 character limit added in previous release
• Completes the two-step constraint addition process
• Will fail if any records exceed the limit (manual cleanup required)
• Finalizes oauth_applications scopes field migration series

Database

Migration - when a row violates constraint

daniele@dbracciani--20250523-VYV2F gitlab % bin/rails db:migrate                                                                  
main: == [advisory_lock_connection] object_id: 138740, pg_backend_pid: 19324
main: == 20250624190925 ValidateTextLimitOauthApplicationsScopes: migrating =========
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0003s
main: -- execute("ALTER TABLE oauth_applications VALIDATE CONSTRAINT check_75750847b8;")
main: -- execute("RESET statement_timeout")
main:    -> 0.0003s
main: == [advisory_lock_connection] object_id: 138740, pg_backend_pid: 19324
bin/rails aborted!
StandardError: An error has occurred, all later migrations canceled:

PG::CheckViolation: ERROR:  check constraint "check_75750847b8" of relation "oauth_applications" is violated by some row
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/constraints_helpers.rb:122:in `block in validate_check_constraint'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/timeout_helpers.rb:31:in `disable_statement_timeout'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/constraints_helpers.rb:119:in `validate_check_constraint'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/constraints_helpers.rb:204:in `validate_text_limit'
/Users/daniele/projects/gdk/gitlab/db/post_migrate/20250624190925_validate_text_limit_oauth_applications_scopes.rb:8:in `up'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migration_helpers/restrict_gitlab_schema.rb:33:in `block in exec_migration'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/query_analyzer.rb:83:in `within'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migration_helpers/restrict_gitlab_schema.rb:30:in `exec_migration'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migration_helpers/automatic_lock_writes_on_tables.rb:21:in `exec_migration'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migration_helpers/require_disable_ddl_transaction_for_multiple_locks.rb:35:in `exec_migration'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/lock_retry_mixin.rb:54:in `ddl_transaction'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/runner_backoff/active_record_mixin.rb:21:in `execute_migration_in_transaction'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/pg_backend_pid.rb:14:in `with_advisory_lock'

Caused by:
ActiveRecord::StatementInvalid: PG::CheckViolation: ERROR:  check constraint "check_75750847b8" of relation "oauth_applications" is violated by some row
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/constraints_helpers.rb:122:in `block in validate_check_constraint'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/timeout_helpers.rb:31:in `disable_statement_timeout'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/constraints_helpers.rb:119:in `validate_check_constraint'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/constraints_helpers.rb:204:in `validate_text_limit'
/Users/daniele/projects/gdk/gitlab/db/post_migrate/20250624190925_validate_text_limit_oauth_applications_scopes.rb:8:in `up'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migration_helpers/restrict_gitlab_schema.rb:33:in `block in exec_migration'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/query_analyzer.rb:83:in `within'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migration_helpers/restrict_gitlab_schema.rb:30:in `exec_migration'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migration_helpers/automatic_lock_writes_on_tables.rb:21:in `exec_migration'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migration_helpers/require_disable_ddl_transaction_for_multiple_locks.rb:35:in `exec_migration'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/lock_retry_mixin.rb:54:in `ddl_transaction'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/runner_backoff/active_record_mixin.rb:21:in `execute_migration_in_transaction'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/pg_backend_pid.rb:14:in `with_advisory_lock'

Caused by:
PG::CheckViolation: ERROR:  check constraint "check_75750847b8" of relation "oauth_applications" is violated by some row
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/constraints_helpers.rb:122:in `block in validate_check_constraint'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/timeout_helpers.rb:31:in `disable_statement_timeout'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/constraints_helpers.rb:119:in `validate_check_constraint'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/constraints_helpers.rb:204:in `validate_text_limit'
/Users/daniele/projects/gdk/gitlab/db/post_migrate/20250624190925_validate_text_limit_oauth_applications_scopes.rb:8:in `up'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migration_helpers/restrict_gitlab_schema.rb:33:in `block in exec_migration'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/query_analyzer.rb:83:in `within'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migration_helpers/restrict_gitlab_schema.rb:30:in `exec_migration'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migration_helpers/automatic_lock_writes_on_tables.rb:21:in `exec_migration'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migration_helpers/require_disable_ddl_transaction_for_multiple_locks.rb:35:in `exec_migration'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/lock_retry_mixin.rb:54:in `ddl_transaction'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/runner_backoff/active_record_mixin.rb:21:in `execute_migration_in_transaction'
/Users/daniele/projects/gdk/gitlab/lib/gitlab/database/migrations/pg_backend_pid.rb:14:in `with_advisory_lock'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)

Migration - happy flow

daniele@dbracciani--20250523-VYV2F gitlab % bin/rails db:migrate 
main: == [advisory_lock_connection] object_id: 138740, pg_backend_pid: 19378
main: == 20250624190925 ValidateTextLimitOauthApplicationsScopes: migrating =========
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0004s
main: -- execute("ALTER TABLE oauth_applications VALIDATE CONSTRAINT check_75750847b8;")
main:    -> 0.0012s
main: -- execute("RESET statement_timeout")
main:    -> 0.0007s
main: == 20250624190925 ValidateTextLimitOauthApplicationsScopes: migrated (0.0230s) 

main: == [advisory_lock_connection] object_id: 138740, pg_backend_pid: 19378
ci: == [advisory_lock_connection] object_id: 138740, pg_backend_pid: 19379
ci: == 20250624190925 ValidateTextLimitOauthApplicationsScopes: migrating =========
ci: -- execute("SET statement_timeout TO 0")
ci:    -> 0.0004s
ci: -- execute("ALTER TABLE oauth_applications VALIDATE CONSTRAINT check_75750847b8;")
ci:    -> 0.0019s
ci: -- execute("RESET statement_timeout")
ci:    -> 0.0003s
ci: == 20250624190925 ValidateTextLimitOauthApplicationsScopes: migrated (0.0234s) 

ci: == [advisory_lock_connection] object_id: 138740, pg_backend_pid: 19379

How to set up and validate locally

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