PropertyMap tests went through SetPermissions, which looks up the `dokku` user/group; the fresh `golang:1.26.2` container used by `go-test-plugin-in-docker` has neither, so the chown failed with `unknown group dokku`. Override `DOKKU_SYSTEM_USER` and `DOKKU_SYSTEM_GROUP` to `root` in the property and chart-migration test setups so the chown targets an identity that exists everywhere. The config tests also called `plugn trigger post-config-update` without `PLUGIN_CORE_AVAILABLE_PATH` set, so the hook tried to source `/common/functions` and logged a noisy warning on every test; point the env var at the canonical `/var/lib/dokku/core-plugins/available` location.
Chart property names containing `/` failed because per-key flat-file storage interpreted the slash as a filesystem path separator, and any move to line-based storage would silently truncate multi-line values. A new `PropertyMap*` helper family in `common` persists each map as a single JSON file so both `/` in keys and `\n` in values round-trip losslessly. Chart overrides move to `chart-overrides.<chart>` and an idempotent `TriggerInstall` migration rewrites any legacy `chart.<chart>.<key>` files into the new layout. The deprecated `scheduler-k3s:set --global chart.*` form is rerouted through the same map storage so it does not silently orphan writes. Closes#8717.
