Expose DedicatedWorkerGlobalScope identity

[wieslawsoltes]

Problem and change

Code OSS detects a browser worker through self.constructor.name === 'DedicatedWorkerGlobalScope'. Without browser-compatible worker-global identity it selects its Node loader, attempts import('module'), and reports the paired bare-module rejection and Monaco worker fallback.

This layer installs the browser interface chain DedicatedWorkerGlobalScope -> WorkerGlobalScope -> EventTarget in every dedicated worker realm. Both interface constructors are illegal to invoke directly, and the global exposes the expected constructor, instanceof behavior, and [object DedicatedWorkerGlobalScope] string tag while retaining the isolated runtime and bounded messaging implementation.

The module-worker contract uses the Code OSS loader decision and proves that the worker path is selected.

Focused validation on the cumulative stack:

• module-worker clone/global contract: 10/10 assertions;
• cumulative worker/MessagePort hybrid filter, including throughput and queue bounds: passed.

Stack: #172 -> #173 -> #174 -> #175. This is layer 3 of 4, based on #173. Reconstructs the focused behavior from #110 on current main.

Advances #108 and #81. Both issues remain open for rebuilt packaged Monaco and browser-extension acceptance.