Userscript foundation
ScriptCat is the first implementation substrate and compatibility foundation.
Existing baseline
ScriptCat already supplies userscript management, background scripts, CAT agent APIs, OPFS, provider/model/task/MCP facilities, and a service-worker/offscreen architecture.
Torsionfield additions
Router Core, provider adapter host, transactional script mutation and installation, agent-tab lifecycle, target selection, daemon bridge, identity/capability handling, and effect evidence.
Boundary
Privileged browser behavior belongs in the extension and is exposed through typed granted APIs; a background userscript does not directly own unrestricted browser internals.