Extension install fails in VSCodium due to missing Open VSX entry

Goal: Deploy a production VSCodium fleet that installs the exact same extensions used in a developer’s local VS Code workspace without manual intervention.

Constraint: Several required extensions are published only to Microsoft’s Visual Studio Marketplace and carry licenses that prohibit redistribution outside Microsoft‑branded builds, so they are absent from the public Open VSX Registry. Because VSCodium’s product.json replaces the marketplace URL with Open VSX, attempts to install those IDs fail silently or with an error during automated image builds. The exact set of missing IDs varies with extension version and the Open VSX sync frequency, creating uncertainty about whether a self‑hosted Open VSX instance or a private registry can reliably fill the gap, or whether the team must accept reduced extension coverage.

Questions: How can the extensionsGallery entry be safely overridden for a production fleet without violating extension licenses? What verification steps confirm that all required extension IDs are resolvable in the chosen registry before image creation?