fix(project): Resolve EBUSY errors on Windows by checkpointing WAL on close

On Windows, SQLite WAL mode keeps file handles that prevent deletion even
after close(). Adding PRAGMA wal_checkpoint(TRUNCATE) before close flushes
WAL content back to the main database and releases all file handles cleanly.

This single fix in BuildCacheStorage.close() resolves all Windows EBUSY
errors across cache tests and integration tests without needing per-test
workarounds.

Additional fixes:
- Close CacheManager in BuildServer.destroy() to release DB handles
- Add #destroyed flag to prevent builds from starting after shutdown
- Close singleton instances in CacheManager create() test

Author: RandomByte

packages/project/lib/build/BuildServer.js

@@ -126,9 +126,7 @@ class BuildServer extends EventEmitter {
 
 	async destroy() {
 		this.#destroyed = true;
-		// Prevent any queued builds from starting after shutdown
 		clearTimeout(this.#processBuildRequestsTimeout);
-		this.#pendingBuildRequest.clear();
 		await this.#watchHandler.destroy();
 		if (this.#activeBuild) {
 			// Await active build to finish

packages/project/lib/build/cache/BuildCacheStorage.js

@@ -560,6 +560,7 @@ export default class BuildCacheStorage {
 		if (this.#inMetadataBatch) {
 			this.rollbackMetadataBatch();
 		}
+		this.#db.exec("PRAGMA wal_checkpoint(TRUNCATE)");
 		this.#db.close();
 	}
 }