fix: preinstall native multisite PHPUnit state

[chubes4]

Summary

Managed wordpress.phpunit multisite preinstall now supports MySQL and mdi-native canonical state.

References Automattic/markdown-database-integration#377.

Root Cause

Native preinstall created canonical state, but the follow-up boot omitted the wp-phpunit installation context. The MDI drop-in then terminated with Error establishing a database connection. The follow-up boot now defines WP_INSTALLING and DISABLE_WP_CRON and loads wp-phpunit functions. Persisted PREINSTALL progress markers bound future installer failures.

Final Exact-Head Verification

• Fresh detached Git checkout HEAD: a735ed3.
• Fresh npm ci and npm run build:release passed.
• Build provenance: 0.26.8 / a735ed3 / a5f1700bcea72eab619dcb183ba42370caa00b0a770bb1a2a55fc7546d76c6af.
• npx tsx tests/phpunit-project-autoload.test.ts passed.
• Native bundled-MDI integration passed from the fresh CLI: single site total 3, passed 2, failed 0, skipped 1; multisite total 3, passed 3, failed 0, skipped 0. The native runtime uses custom-drop-in with no external service.
• Bundled MDI revision: 11652defdfa88576ee91699b3545ecf0d486f055; archive SHA-256: 335bb694f7e6b4185f6d514e61c14ec220ab163fa9d959159d6c26411680cf6c.
• MDI PR395 source was independently pinned at 04c85bf78c1d1c41043cb18e9fd0a62d421b2bac. This retained checkout has tests/probe-native-multisite-wordpress.php but not VenueProfileMutationsTest.php, so no fabricated DME venue result is claimed.
• MySQL E2E command npx tsx tests/disposable-mysql-mysqli.integration.test.ts skipped because Docker is unavailable in this Lab. The focused semantics test covers managed SQLite/MySQL/native backend selection and multisite preinstall branching; a runtime MySQL comparison requires a Docker-capable Lab.

CI Status

At final inspection: workflow-lint, fast contracts, and package check passed; browser and integration were pending.

AI assistance

OpenAI GPT-6 Astra (openai/gpt-6-astra) via OpenCode implemented the original backend-neutral preinstall gate. OpenAI GPT-5.6 Terra (openai/gpt-5.6-terra) via OpenCode reproduced and diagnosed the native Playground failure, implemented the boot-context repair, and ran fresh exact-head verification.

DME Pair Evidence (homeboy-lab)

• Remote Docker verified: /usr/bin/docker, daemon 29.1.3.
• Codebox source/build: a735ed3; MDI source: 04c85bf78c1d1c41043cb18e9fd0a62d421b2bac. Consumer root: /home/chubes/labs/mdi-a735ed3d-04c85bf-consumer.
• Native full VenueProfileMutationsTest run artifact: artifacts/venue-native-a735ed3d-04c85bf. PHPUnit ran 24 tests and exited 2: three direct mysqli root@localhost errors, one failure, two skips. This is not a passing suite.
• Native foreign attachment identity artifact: artifacts/venue-foreign-native-a735ed3d-04c85bf. One test, three assertions, one failure: test_foreign_site_attachment_is_rejected returned an array instead of the expected WP_Error.
• Disposable MySQL identity artifact: artifacts/venue-foreign-mysql-a735ed3d-04c85bf. The identical filtered selector passed.
• This is a native-only DME contract regression exposed by the bootstrap change; full disposable-MySQL Venue comparison remains required before landing.