Complete packaged Playground PHPUnit runtime support

[chubes4]

Summary

• forward PHP version, extension manifests, and backend package options through the PHPUnit recipe builder
• pass extension manifests to packaged Playground CLI backends
• expose PHPUnit arguments before project bootstrap so project-owned bootstrap logic can select a testsuite
• fail closed when structured PHPUnit diagnostics report a bootstrap death despite a zero process exit

Follow-up to #1843 and #1825, discovered while running WPCOM PHPUnit against a locally rebuilt PHP.wasm runtime and Sodium side module.

Backwards compatibility

The builder inputs are additive. Existing PHPUnit recipes retain their current defaults. The diagnostic change only converts previously false-positive successful runs containing STAGE_FAIL or STAGE_DIE into failures.

How to test

1. Run npm ci.
2. Run npm run build.
3. Run npm run test:runtime-services.
4. Run npx tsx tests/playground-cli-runner-bootstrap-ini.test.ts.
5. Run npx tsx tests/phpunit-project-autoload.test.ts.
6. Run npm run test:php-wasm-extension-manifests.

AI assistance

• AI assistance: Yes
• Tool(s): OpenAI GPT-5.6 Sol with OpenCode
• Used for: Diagnosed the downstream runtime integration failures, implemented the generic builder/runtime fixes, and added deterministic coverage.