browser/openspec/changes/add-scum-ue4ss-dll-runtime-extension/proposal.md

Why

The current SCUM plugin declares a separately built companion client, but the new SCUM RCON integration is a prebuilt UE4SS DLL that must load with the SCUM server process. Operators must not compile it, Run must not execute arbitrary binaries or inject a running process, and the platform currently has no declared, version-pinned DLL extension lifecycle.

What Changes

• Add a plugin-declared Windows-only UE4SS DLL extension profile with a fixed HTTPS release URL, SHA-256 checksum, file size, compatible SCUM executable checksum, UE4SS ABI marker, logical deployment target, and loopback RCON health probe.
• Freeze the declared extension plan into the existing fenced process.start job. Run stages the approved DLL, generated configuration, and deterministic mods.txt entry before the normal SCUM process starts; there is no independent sync job or background poller.
• Add Run-side verified DLL synchronization with bounded HTTPS download, scoped file ownership, atomic replacement, rollback, no runtime process injection, and an explicit Linux rejection for the Windows DLL extension.
• Surface declared extension metadata and safe per-server state in plugin and server management views. The UI shows the release/version/checksum/loading mode and that Linux is unsupported, without exposing host paths, RCON passwords, or Run credentials.
• Replace the SCUM example's new-server dependency on the scum-client-manager path with the UE4SS RCON extension declaration. Existing client-manager records remain compatible and are not deleted by this change.
• Provision the extension's loopback-only Source RCON configuration for the existing declared remote-access boundary. This change does not create a second command console, per-command confirmation, or raw-command history.

Capabilities

New Capabilities

• plugin-runtime-dll-extensions: Plugin manifest, Platform validation, safe projections, and server-start ordering for versioned Windows UE4SS DLL extensions.
• run-ue4ss-dll-synchronization: Independent Run download, staging, activation, UE4SS configuration, health preconditions, and rollback behavior for an approved UE4SS DLL extension.

Modified Capabilities

• None.

Impact

• plugins/: manifest schema, validator, SCUM example declaration, and fixtures.
• platform/: domain/DTO/validation/job contracts, server start dispatch, fenced extension-sync input, safe state projection, and API handlers.
• platform_web/: API types and existing plugin/server detail surfaces for declared extension state.
• Independent run/: protocol copies, extension-sync executor, generated local-only RCON configuration, tests, and documentation. It remains an independent Git repository and is not added to this repository.
• No user-side compiler, arbitrary executable launch, runtime remote-process injection, Linux DLL support, raw host-path exposure, raw RCON-password exposure, or unrelated product areas are introduced.

The supplied CDN URL currently has no downloadable DLL. The SCUM example therefore carries an explicit unpublished declaration rather than an invented checksum, and it is not bound to process.start until the publisher supplies the real release pins. Ready declarations remain fully immutable and are the only declarations that can be frozen into a start job.