Fallback for existing sandbox and name collision

README.md

@@ -67,12 +67,34 @@ two things, both idempotent — safe to re-run:
 
    ```sh
    #!/bin/sh
-   exec sbx run -t localhost/opencode-v2:local "$@" opencode
+   # sbx run accepts -t/--template only at sandbox creation time; re-running
+   # against an existing sandbox with a template fails. So pass the template
+   # only when the named sandbox doesn't exist yet.
+   TEMPLATE=localhost/opencode-v2:local
+
+   # Extract --name VALUE / --name=VALUE from the arguments, if given.
+   name=
+   prev=
+   for arg in "$@"; do
+     [ "$prev" = --name ] && name=$arg
+     case "$arg" in
+       --name=*) name=${arg#--name=} ;;
+     esac
+     prev=$arg
+   done
+
+   if [ -n "$name" ] && sbx ls -q 2>/dev/null | grep -Fxq -- "$name"; then
+     exec sbx run "$@" opencode
+   fi
+
+   exec sbx run -t "$TEMPLATE" "$@" opencode
    ```
 
    `-t localhost/opencode-v2:local` points at the template `make build`
-   registers (see below); `opencode` is the agent name; `"$@"` forwards any
-   extra args (e.g. `opencode-sandbox --model claude-sonnet-5`). Being a real
+   registers (see below), passed only when `--name` names a sandbox that
+   doesn't exist yet (sbx rejects a template when re-attaching); `opencode`
+   is the agent name; `"$@"` forwards any extra args
+   (e.g. `opencode-sandbox --model claude-sonnet-5`). Being a real
    executable on `PATH` rather than a shell function means it works
    identically under bash, zsh, fish, or anything else.
 

install.sh

@@ -22,7 +22,27 @@ mkdir -p "$BIN_DIR"
 
 cat > "$SHIM" <<'EOF'
 #!/bin/sh
-exec sbx run -t localhost/opencode-v2:local "$@" opencode
+# sbx run accepts -t/--template only at sandbox creation time; re-running
+# against an existing sandbox with a template fails. So pass the template
+# only when the named sandbox doesn't exist yet.
+TEMPLATE=localhost/opencode-v2:local
+
+# Extract --name VALUE / --name=VALUE from the arguments, if given.
+name=
+prev=
+for arg in "$@"; do
+  [ "$prev" = --name ] && name=$arg
+  case "$arg" in
+    --name=*) name=${arg#--name=} ;;
+  esac
+  prev=$arg
+done
+
+if [ -n "$name" ] && sbx ls -q 2>/dev/null | grep -Fxq -- "$name"; then
+  exec sbx run "$@" opencode
+fi
+
+exec sbx run -t "$TEMPLATE" "$@" opencode
 EOF
 chmod +x "$SHIM"
 echo "==> Installed shim: $SHIM"