Switch over to a reverse connection scheme (bridge to a guest bus)

README.md

@@ -14,9 +14,8 @@ A cross-domain smart D-Bus proxying system that makes (some) [XDG Desktop Portal
 
 - `sidebus-broker` host process:
   - to be launched alongside the VMM
-  - hosts D-Bus servers in-process, based on [busd](https://github.com/dbus2/busd):
-    - a "private" bus for VM-instance-specific daemons such as permission-store and document-portal
-    - a "VM" bus, the one actually exposed to the guest over vsock
+  - hosts a "private" bus for VM-instance-specific daemons such as permission-store and document-portal
+  - listens on vsock (or on a unix socket that muvm would proxy as vsock) and connects to the VM bus as a client when the agent connects
   - orchestrates the lifecycle of the aforementioned daemons + virtiofsd
     - (we are sharing the directory *provided by* the document-portal FUSE filesystem!)
   - provides portal front-end interfaces like `org.freedesktop.portal.FileChooser` on the VM bus
@@ -24,11 +23,10 @@ A cross-domain smart D-Bus proxying system that makes (some) [XDG Desktop Portal
       - (not talking directly to impls: don't want to reimplement per-DE portal selection; also 1:1 mapping is nicer to code)
     - but with extra hooks like exposing files to the guest using our private (per-VM) document-portal!
 - `sidebus-agent` guest process:
-  - listens on a guest unix socket, proxies D-Bus messages to a vsock
-  - spawned on-demand by systemd via socket activation
+  - connects to the broker over vsock and splices the connection into the VM (session) bus
+  - can be spawned spawned on-demand by D-Bus
   - uses systemd credentials for config args like vsock port
     - (very convenient to pass via the VMM, e.g. qemu: `-smbios type=11,value=io.systemd.credential:sidebus.port=1337`)
-  - guest NixOS configuration exposed via the flake
 
 ## Development Notes