Each environment declares what it carries

Two portals can run the same image and carry different content, said once in each environment's own configuration. A feature flag is a named switch a deployment declares for itself — under Features:Flags:{name}, beside the capability toggles that were already there — and it can carry the packages that environment always has:

Features__Flags__plugins__Packages__0=Plugins/*
Features__Flags__games__Enabled=false

An enabled flag installs the packages it names; a declared-but-disabled one excludes them, and the exclusion wins over every other selection. So "all of the plugin repo, without the games" is one shared declaration plus one line in the environment that does not want them — no rebuild, and nothing in the platform knows any package by name.

Crucially this re-asserts on every boot, which the existing InstallByDefault seed deliberately does not: the seed runs once so an admin who later removes a package is not fought by the next restart, which also means it can say nothing at all about a portal that is already populated. The two knobs now sit side by side with their own meanings. Reconciling costs an up-to-date portal one catalog listing and no writes.

Flags are read reactively — a view binds them and re-renders when configuration reloads, rather than sampling a value that goes stale.

Packages can also declare what they need from their environment: a connection string, another service's endpoint, a provisioned value. They resolve from the environment's service graph — the same names Aspire's resource references and the deployment charts already inject — instead of each package inventing its own configuration key. A required parameter the environment does not supply refuses the install loudly, naming the exact variable to set, so nothing is ever installed half-configured and no failure is quietly skipped.

Settings → Administration → Composition (platform admins) shows the whole picture for the portal you are on: every declared flag, whether it installs or excludes, and every parameter the installed packages need — with the variable to provision for any that is missing.