feat: ephvm improvements

hosts/ephvm/configuration.nix

@@ -58,8 +58,11 @@
     neovim.dotfiles = inputs.nvim;
   };
 
+  # ensure .config exists with correct ownership before automount
+  systemd.tmpfiles.rules = [ "d /home/matej/.config 0755 matej users -" ];
+
   # writable claude config via 9p
-  fileSystems."/home/matej/.claude" = {
+  fileSystems."/home/matej/.config/claude" = {
     device = "claude";
     fsType = "9p";
     options = [
@@ -70,23 +73,7 @@
     ];
   };
 
-  # .claude.json passed via qemu fw_cfg
-  boot.kernelModules = [ "qemu_fw_cfg" ];
-  systemd.services.claude-json = {
-    after = [ "systemd-modules-load.service" ];
-    wants = [ "systemd-modules-load.service" ];
-    wantedBy = [ "multi-user.target" ];
-    serviceConfig = {
-      Type = "oneshot";
-      RemainAfterExit = true;
-      ExecStart = pkgs.writeShellScript "claude-json" ''
-        src="/sys/firmware/qemu_fw_cfg/by_name/opt/claude.json/raw"
-        [ -f "$src" ] || exit 0
-        cp "$src" /home/matej/.claude.json
-        chown matej:users /home/matej/.claude.json
-      '';
-    };
-  };
+  environment.sessionVariables.CLAUDE_CONFIG_DIR = "/home/matej/.config/claude";
 
   system.stateVersion = "25.11";
 }

justfile

@@ -33,13 +33,9 @@ build:
 iso:
     nixos-rebuild build-image --image-variant iso-installer --flake .#iso
 
-# build ephemeral VM image
-ephvm-build:
-    nixos-rebuild build-image --image-variant qemu --flake .#ephvm
-
 # run ephemeral VM
-ephvm-run *ARGS:
-    bash scripts/ephvm-run.sh $(find -L result -name '*.qcow2' | head -1) {{ARGS}}
+ephvm *ARGS:
+    bash scripts/ephvm-run.sh {{ARGS}}
 
 # ssh into running ephemeral VM
 ephvm-ssh port="2222":

modules/nixos/vm-9p-automount.nix

@@ -20,7 +20,7 @@ in
 
       prefix = lib.mkOption {
         type = lib.types.str;
-        default = "mount_";
+        default = "m_";
         description = "9p mount tag prefix to match";
       };
 

scripts/ephvm-run.sh

@@ -5,18 +5,15 @@ SSH_PORT=2222
 MEMORY=8G
 CPUS=4
 MOUNTS=()
-CLAUDE_DIR=""
-CLAUDE_JSON=""
-IMAGE=""
+CLAUDE=false
 
 usage() {
   cat <<EOF
-Usage: ephvm-run.sh <image.qcow2> [options]
+Usage: ephvm-run.sh [options]
 
 Options:
   --mount <path>       Mount host directory into VM (repeatable)
-  --claude <path>      Mount claude config dir writable into VM
-  --claude-json <path> Copy claude.json into mounted claude dir
+  --claude             Mount claude config dir (requires CLAUDE_CONFIG_DIR)
   --memory <size>      VM memory (default: 8G)
   --cpus <n>           VM CPUs (default: 4)
   --ssh-port <port>    SSH port forward (default: 2222)
@@ -24,25 +21,24 @@ EOF
   exit 1
 }
 
-[ "${1:-}" ] || usage
-
-IMAGE="$1"
-shift
-
 while [ $# -gt 0 ]; do
   case "$1" in
     --mount)      MOUNTS+=("$2"); shift 2 ;;
-    --claude)     CLAUDE_DIR="$2"; shift 2 ;;
-    --claude-json) CLAUDE_JSON="$2"; shift 2 ;;
+    --claude)     CLAUDE=true; shift ;;
     --memory)     MEMORY="$2"; shift 2 ;;
     --cpus)       CPUS="$2"; shift 2 ;;
     --ssh-port)   SSH_PORT="$2"; shift 2 ;;
+    -h|--help)    usage ;;
     *)            echo "unknown option: $1"; usage ;;
   esac
 done
 
-if [ ! -f "$IMAGE" ]; then
-  echo "error: image not found: $IMAGE"
+echo "building ephvm image..."
+IMAGE_DIR=$(nix build --no-link --print-out-paths .#nixosConfigurations.ephvm.config.system.build.images.qemu)
+IMAGE=$(find "$IMAGE_DIR" -name '*.qcow2' -print -quit)
+
+if [ -z "$IMAGE" ]; then
+  echo "error: no qcow2 image found in $IMAGE_DIR"
   exit 1
 fi
 
@@ -67,21 +63,25 @@ FS_ID=0
 for mount_path in "${MOUNTS[@]}"; do
   mount_path=$(realpath "$mount_path")
   name=$(basename "$mount_path")
+  tag="m_${name:0:29}"
   QEMU_ARGS+=(
-    -virtfs "local,path=$mount_path,mount_tag=mount_$name,security_model=none,id=fs${FS_ID}"
+    -virtfs "local,path=$mount_path,mount_tag=$tag,security_model=none,id=fs${FS_ID}"
   )
   FS_ID=$((FS_ID + 1))
 done
 
-if [ -n "$CLAUDE_DIR" ]; then
-  CLAUDE_DIR=$(realpath "$CLAUDE_DIR")
-  QEMU_ARGS+=(
-    -virtfs "local,path=$CLAUDE_DIR,mount_tag=claude,security_model=none,id=fs${FS_ID}"
-  )
-fi
+if [ "$CLAUDE" = true ]; then
+  if [ -z "${CLAUDE_CONFIG_DIR:-}" ]; then
+    echo "error: --claude requires CLAUDE_CONFIG_DIR to be set"
+    exit 1
+  fi
+  mkdir -p "$CLAUDE_CONFIG_DIR"
+  claude_dir=$(realpath "$CLAUDE_CONFIG_DIR")
 
-if [ -n "$CLAUDE_JSON" ]; then
-  QEMU_ARGS+=(-fw_cfg "name=opt/claude.json,file=$CLAUDE_JSON")
+  QEMU_ARGS+=(
+    -virtfs "local,path=$claude_dir,mount_tag=claude,security_model=none,id=fs${FS_ID}"
+  )
+  FS_ID=$((FS_ID + 1))
 fi
 
 exec "${QEMU_ARGS[@]}"