Fix global plugin mappings in HEADLESS mode

[bagel786]

This PR

• Fixes a bug

Install global plugins immediately during HEADLESS startup so configured mappings are available when scenes boot. Add regression coverage for scene injection.

Tests:

• npx vitest run tests/plugins/PluginManager.test.js
• npx vitest run tests/plugins

Fixes #7348

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Continues #7357 — the fork repo backing that PR was accidentally deleted from this account, and GitHub blocks reopening a PR whose submitting repository was deleted (a restore request is being filed with GitHub Support). This PR resumes the identical work from the same commit (fe96f3e500842982ce4d056c86e3d04b414da4f4); review discussion continues on the original PR.

[Copilot]

🔵 Needs a closer look

Defer HEADLESS plugin activation until Game initialization is complete.

Pull request overview

Fixes global plugin mappings in HEADLESS mode so configured plugins are available before scenes boot.

Changes:

• Installs configured global plugins during HEADLESS startup.
• Adds regression coverage for mapped plugin injection.

File summaries

File	Summary
tests/plugins/PluginManager.test.js	Adds HEADLESS mapping regression coverage.
src/plugins/PluginManager.js	Adjusts HEADLESS plugin installation timing; activation may occur before Game state is initialized.

Review details

Suppressed comments (1)

src/plugins/PluginManager.js:455

• HEADLESS PluginManager instances are constructed before Game assigns this.plugins (src/core/Game.js:280), and the constructor calls boot() immediately (src/plugins/PluginManager.js:117-120). With this condition, a mapped config plugin is instantiated and its init/start run inside that constructor, so this.game.plugins (and later Game fields such as noReturn) are still unset. This makes HEADLESS plugin startup observably earlier than Canvas/WebGL and can break valid plugins that access public Game state; defer HEADLESS activation until after Game construction, or separate cache registration from activation while still making mappings available before Scene Systems boot.

        if (!this.game.isBooted && this.game.config.renderType !== CONST.HEADLESS)

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite

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