fix: honor project bootstrap before plugin test discovery

[chubes4]

Problem

wordpress.phpunit in project mode discovers plugin test files before executing the bootstrap declared by the mounted project's phpunit.xml. A repository whose tests depend on bootstrap-owned fixtures crashes before any selected tests execute.

This regresses the project-bootstrap contract completed in #644 and the harness-before-discovery fix completed in #1771.

Reproduction

From Extra-Chill/extrachill-artist-platform PR #171 at commit ac7ea32:

homeboy review test extrachill-artist-platform \
  --path /var/lib/datamachine/workspace/extrachill-artist-platform@refactor-170-owner-neutral-operations \
  --changed-since origin/main \
  --placement local \
  -- --filter LinkPageOperationsTest

Homeboy correctly scopes the request to:

• tests/AbilityAuthorizationTest.php
• tests/LinkPageOperationsTest.php
• tests/LinkPageOwnerReferenceTest.php

The Codebox runtime still discovers tests/ArtistDirectSubscriberTest.php and crashes before running any tests:

wordpress.phpunit crashed before producing a structured response
Error: Class \"EcTestWpdb\" not found at
/wordpress/wp-content/plugins/extrachill-artist-platform/tests/ArtistDirectSubscriberTest.php:5
[test-results] Total: 0, Passed: 0, Failed: 0, Skipped: 0

The class exists in tests/bootstrap.php, and the repository's local PHPUnit command honors that bootstrap: 246 tests / 1,330 assertions pass. Earlier aggregate runs also reported missing AgentsAPI\\AI\\WP_Agent_Execution_Principal, get_site(), and switch_to_blog(), all defined by the same project bootstrap.

Persisted Homeboy runs:

• aggregate changed-file run: defad187-aa51-498a-95fe-bc0387df14cd
• explicit filtered run: 3694ac54-17ab-4e3b-b4c4-fb71f19aa072

Expected

1. Read the mounted project's PHPUnit configuration before test discovery.
2. Execute its declared bootstrap before loading any test class.
3. Restrict discovery to the selected files/filter when a focused workload is requested.
4. Return structured zero/failure evidence only after the project bootstrap and selected test workload actually run.

Acceptance criteria

• A fixture class defined only in tests/bootstrap.php is available to every discovered test.
• --filter LinkPageOperationsTest does not discover unrelated plugin test classes first.
• The Extra Chill Artist Platform reproduction executes its selected tests instead of reporting zero tests.

AI assistance

• AI assistance: Yes
• Tool: OpenCode
• Used for: Reproducing the failure, inspecting persisted Codebox artifacts, and drafting this report.