Enforce required on string/multiselect variables without explicit bounds

required:true only worked by accident: a bare z.string() or
z.array(...) accepts "" / [] just fine, so a required field with no
minLength (e.g. secret tokens like webhookToken, apiKey) could be
submitted empty and the run would start anyway. Required now implies
min(1) when no stricter bound is already configured, for both string
and multiselect fields. This is the single schema shared by the client
form resolver and the server run-creation route, so both now reject it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/src/lib/validation/variable-schema.ts

@@ -7,7 +7,12 @@ function fieldSchema(variable: VariableConfig): z.ZodTypeAny {
   switch (variable.type) {
     case "string": {
       let s = z.string();
-      if (variable.minLength !== undefined) s = s.min(variable.minLength);
+      // `required` alone has to reject "" even when the author didn't set an explicit
+      // minLength - otherwise an empty string satisfies a bare z.string() and the run starts
+      // with a "required" field effectively unset.
+      const minLength =
+        variable.minLength ?? (variable.required ? 1 : undefined);
+      if (minLength !== undefined) s = s.min(minLength);
       if (variable.maxLength !== undefined) s = s.max(variable.maxLength);
       if (variable.pattern) s = s.regex(new RegExp(variable.pattern));
       field = s;
@@ -26,10 +31,13 @@ function fieldSchema(variable: VariableConfig): z.ZodTypeAny {
     case "enum":
       field = z.enum(variable.choices as [string, ...string[]]);
       break;
-    case "multiselect":
+    case "multiselect": {
-      field = z.array(z.enum(variable.choices as [string, ...string[]]));
+      let arr = z.array(z.enum(variable.choices as [string, ...string[]]));
+      if (variable.required) arr = arr.min(1);
+      field = arr;
       break;
     }
+  }
 
   if (!variable.required) {
     field = field.optional().or(z.literal(""));