Phalcon 4 to 5 upgrade alongside PHP 7.4 to 8.x: which compatibility breaks should I expect first?

I'm planning a migration of an application currently on Phalcon 4.x with PHP 7.4 to Phalcon 5.x with PHP 8.1. Since Phalcon is a C extension rather than a Composer-installed library, I know the upgrade isn't just a dependency bump: the ext-phalcon build must match the PHP version, and Composer metapackages only verify the extension is loaded rather than install it.

My uncertainty is about the order of operations and the real failure surface. The documented upgrade notes mention renamed or restructured namespaces and dropped deprecated components in 5.x, but it's unclear which of those typically break first in a standard MVC app using the DI container, dispatcher, Volt, and the ORM with PHQL. I'm also unsure whether prebuilt PECL binaries for PHP 8.1 reliably track the latest Phalcon 5 minor releases, or whether compiling from source is the safer path to get a matching version.

Which namespace or component changes between 4.x and 5.x most commonly require code changes in an otherwise conventional MVC application? Does the PECL channel lag source releases enough to matter when targeting a specific PHP minor version? And is verifying via php -m plus a staging bootstrap sufficient to catch extension-level mismatches before production?