refactor: cleanup Main bootstrap class

[justlevine]

What?

Closes

This PR cleans up some of root-file tech debt. More specifically it:

1. Colocates all constants into the root ai.php file
2. Cleans out inc/bootstrap.php for a WordPress/AI/Main class
3. Moves the requirement checks out of the Main bootstrapper into a WordPress/AI/Requirements class.

And then some cleanup resulting from that.

• Moving the new settings meta functions from the global namespace into the settings class where they are used.
• Add an admin notice for missing build/build.php
• Remove the unused Loader::is_initialized() method, and a public init() method.

Why?

Pre-7.0 cleanup. The Requirements class will likely also become the registry for per-specific features.

How?

See diff.

Use of AI Tools

Opencode + GLM 5.1 to do a first pass of backfilling unit tests, followed by manual deslopping and backfilling cases it didn't get correctly.

Testing Instructions

npm run test:php

Testing Instructions for Keyboard

Screenshots or screencast

Before	After

[github-actions]

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Co-authored-by: justlevine <justlevine@git.wordpress.org>
Co-authored-by: dkotter <dkotter@git.wordpress.org>

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[Copilot]

Pull request overview

Refactors the plugin bootstrap by replacing the procedural includes/bootstrap.php flow with a Main singleton and a dedicated Requirements checker, while moving settings metadata helpers into Settings_Page and updating integration tests accordingly.

Changes:

• Introduces includes/Main.php as the new bootstrap entry (hooking into plugins_loaded/init) and removes includes/bootstrap.php.
• Adds includes/Requirements.php and routes requirement failures through admin notices (incl. missing build/build.php).
• Moves settings feature metadata generation into includes/Settings/Settings_Page.php and updates tests to use the new APIs/loader lifecycle.

Reviewed changes

Copilot reviewed 23 out of 23 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
ai.php	Defines plugin constants, loads autoloader, boots the new Main class.
includes/Main.php	New class-based bootstrap replacing procedural bootstrap logic.
includes/Requirements.php	Centralized runtime requirements checks + admin notice handling.
includes/Settings/Settings_Page.php	Colocates settings feature-group/metadata helpers into Settings_Page.
includes/Features/Loader.php	Adds init() and makes registration/initialization internals private; removes is_initialized().
includes/bootstrap.php	Removed legacy bootstrap implementation.
tests/bootstrap.php	(Context) Activates plugin via ai.php, now gated by Requirements.
tests/Integration/Includes/MainTest.php	Adds integration coverage for new Main behaviors.
tests/Integration/Includes/RequirementsTest.php	Adds integration coverage for new Requirements behavior.
tests/Integration/Includes/Settings/Settings_PageTest.php	Renames/re-namespaces and updates tests for settings metadata now on Settings_Page.
tests/Integration/Includes/Experiment_RegistryTest.php	Updates to Loader::init() and reflection-based initialized assertions.
tests/Integration/Includes/Experiment_LoaderTest.php	Updates tests for new Loader API and private methods.
tests/Integration/Includes/Experiments/*/*Test.php	Updates experiment integration tests to use Loader::init() (or manual registration where needed).
phpunit.xml.dist	Removes ai.php from coverage include list.
docs/ARCHITECTURE_OVERVIEW.md	Updates architecture docs to reflect Main/Requirements and removal of bootstrap.php.
docs/RELEASE_INSTRUCTIONS.md	Updates version-bump instructions to reference ai.php as the constant source.

Comments suppressed due to low confidence (1)

tests/Integration/Includes/Settings/Settings_PageTest.php:247

• This helper uses reflection to invoke a private method, but it never calls $method->setAccessible( true ). Invoking a private method without setting it accessible will throw a ReflectionException/fatal and fail the test run. Add setAccessible(true) before invoke() (or refactor the production code to expose this behavior via a public API that can be tested without reflection).

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[justlevine]

I'm not sure why these tests are failing. They're passing locally. In the meantime, feedback appreciated on the architecture 🙇

edit: was the now-enforced dependency checks looking for the build.php. Added a test const to skip it.

[codecov]

Codecov Report

❌ Patch coverage is 88.93805% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.15%. Comparing base (bee0e30) to head (fa21ba6).
⚠️ Report is 9 commits behind head on develop.

Files with missing lines	Patch %	Lines
includes/Main.php	74.62%	17 Missing ⚠️
includes/Requirements.php	93.75%	5 Missing ⚠️
includes/Settings/Settings_Page.php	95.94%	3 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop     #404      +/-   ##
=============================================
+ Coverage      65.75%   68.15%   +2.40%     
- Complexity       763      808      +45     
=============================================
  Files             53       53              
  Lines           3863     3925      +62     
=============================================
+ Hits            2540     2675     +135     
+ Misses          1323     1250      -73     

Flag	Coverage Δ
unit	68.15% <88.93%> (+2.40%)	⬆️

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[dkotter]

Looks good to me and tests well!