cmd/sharefs: implement shared filesystem

This is for passing files between applications, similar to android /sdcard.

Signed-off-by: Ophestra <cat@gensokyo.uk>

.gitea/workflows/test.yml

@@ -72,6 +72,23 @@ jobs:
           path: result/*
           retention-days: 1
 
+  sharefs:
+    name: ShareFS
+    runs-on: nix
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Run NixOS test
+        run: nix build --out-link "result" --print-out-paths --print-build-logs .#checks.x86_64-linux.sharefs
+
+      - name: Upload test output
+        uses: actions/upload-artifact@v3
+        with:
+          name: "sharefs-vm-output"
+          path: result/*
+          retention-days: 1
+
   hpkg:
     name: Hpkg
     runs-on: nix
@@ -96,6 +113,7 @@ jobs:
       - race
       - sandbox
       - sandbox-race
+      - sharefs
       - hpkg
     runs-on: nix
     steps: