Add a searchable combobox control for enum variables

select/radio don't scale to enums with dozens of choices. Reuses the
same cmdk Command/Popover primitives multi-select already uses, just
single-valued instead of an array.

docs/CONFIG_REFERENCE.md

@@ -101,7 +101,7 @@ Type-specific fields:
 | `string`      | `text` (or `password` if `secret: true`) | `textarea` (needs `multiline: true`), `password` |
 | `number`      | `number`                                 | `slider` (requires both `min` and `max`)         |
 | `boolean`     | `checkbox`                               | `switch`                                         |
-| `enum`        | `select`                                 | `radio`                                          |
+| `enum`        | `select`                                 | `radio`, `combobox` (searchable, single-select)  |
 | `multiselect` | `multiselect` (combobox)                 | `checkboxGroup`                                  |
 
 ### `passAs` semantics

src/components/forms/controls/combobox.tsx

@@ -0,0 +1,78 @@
+"use client";
+
+import { useState } from "react";
+import { Check, ChevronsUpDown } from "lucide-react";
+import { buttonVariants } from "@/components/ui/button";
+import {
+  Command,
+  CommandEmpty,
+  CommandGroup,
+  CommandInput,
+  CommandItem,
+  CommandList,
+} from "@/components/ui/command";
+import {
+  Popover,
+  PopoverContent,
+  PopoverTrigger,
+} from "@/components/ui/popover";
+import { cn } from "@/lib/utils";
+
+interface ComboboxProps {
+  choices: string[];
+  value: string;
+  onChange: (value: string) => void;
+  placeholder?: string;
+}
+
+export function Combobox({
+  choices,
+  value,
+  onChange,
+  placeholder = "Select...",
+}: ComboboxProps) {
+  const [open, setOpen] = useState(false);
+
+  return (
+    <Popover open={open} onOpenChange={setOpen}>
+      <PopoverTrigger
+        className={cn(
+          buttonVariants({ variant: "outline" }),
+          "h-auto min-h-8 w-full justify-between font-normal",
+        )}
+      >
+        <span className={cn("flex-1 text-left", !value && "text-muted-foreground")}>
+          {value || placeholder}
+        </span>
+        <ChevronsUpDown className="text-muted-foreground size-4 shrink-0" />
+      </PopoverTrigger>
+      <PopoverContent className="w-80 p-0">
+        <Command>
+          <CommandInput placeholder="Search..." />
+          <CommandList>
+            <CommandEmpty>No matches.</CommandEmpty>
+            <CommandGroup>
+              {choices.map((choice) => (
+                <CommandItem
+                  key={choice}
+                  onSelect={() => {
+                    onChange(choice);
+                    setOpen(false);
+                  }}
+                >
+                  <Check
+                    className={cn(
+                      "mr-2 size-4",
+                      value === choice ? "opacity-100" : "opacity-0",
+                    )}
+                  />
+                  {choice}
+                </CommandItem>
+              ))}
+            </CommandGroup>
+          </CommandList>
+        </Command>
+      </PopoverContent>
+    </Popover>
+  );
+}

src/components/forms/field-renderer.tsx

@@ -24,6 +24,7 @@ import {
 import { Slider } from "@/components/ui/slider";
 import { Label } from "@/components/ui/label";
 import { MultiSelect } from "./controls/multi-select";
+import { Combobox } from "./controls/combobox";
 import type { ClientVariable } from "@/lib/config/serialize";
 
 export function FieldRenderer({ variable }: { variable: ClientVariable }) {
@@ -211,6 +212,31 @@ export function FieldRenderer({ variable }: { variable: ClientVariable }) {
               </FormItem>
             );
 
+          case "combobox":
+            return (
+              <FormItem>
+                <FormLabel>
+                  {label}
+                  {variable.required && (
+                    <span className="text-destructive"> *</span>
+                  )}
+                </FormLabel>
+                <FormControl>
+                  <Combobox
+                    choices={
+                      variable.type === "enum" ? variable.choices : []
+                    }
+                    value={field.value ?? ""}
+                    onChange={(value) => field.onChange(value)}
+                  />
+                </FormControl>
+                {variable.description && (
+                  <FormDescription>{variable.description}</FormDescription>
+                )}
+                <FormMessage />
+              </FormItem>
+            );
+
           case "radio":
             return (
               <FormItem>

src/lib/config/schema.ts

@@ -18,6 +18,7 @@ const controlSchema = z.enum([
   "switch",
   "select",
   "radio",
+  "combobox",
   "multiselect",
   "checkboxGroup",
 ]);
@@ -115,6 +116,13 @@ const variableWithChecks = variableSchema.superRefine((variable, ctx) => {
       path: ["control"],
     });
   }
+  if (variable.control === "combobox" && variable.type !== "enum") {
+    ctx.addIssue({
+      code: "custom",
+      message: "control 'combobox' requires type 'enum'",
+      path: ["control"],
+    });
+  }
   if (
     variable.control === "slider" &&
     variable.type === "number" &&