Clean up agent config environment selector

Show the environment override selector only when a meaningful alternative exists, remove the explanatory helper copy, relabel the inherited option, and rename the section header to Environment.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

ui/src/components/AgentConfigForm.tsx

@@ -400,10 +400,12 @@ export function AgentConfigForm(props: AgentConfigFormProps) {
     }),
     [environments, supportedEnvironmentDrivers],
   );
+  // `runnableEnvironments` excludes the always-available Local environment, so a
+  // single entry already means the user has more than one environment configured
+  // (Local + that environment) and the override selector is meaningful.
   const showEnvironmentOverrideControl = environmentsEnabled && (
     forcedKubernetes ||
-    currentDefaultEnvironmentId.length > 0 ||
-    runnableEnvironments.length > 1
+    runnableEnvironments.length >= 1
   );
   const inheritedEnvironmentLabel = instanceDefaultEnvironment
     ? `${instanceDefaultEnvironment.name} (${instanceDefaultEnvironment.driver})`
@@ -883,8 +885,8 @@ export function AgentConfigForm(props: AgentConfigFormProps) {
         // Render the environment read-only instead of the selectable picker.
         <div className={cn(!cards && (isCreate ? "border-t border-border" : "border-b border-border"))}>
           {cards
-            ? <h3 className="text-sm font-medium mb-3">Execution</h3>
-            : <div className="px-4 py-2 text-xs font-medium text-muted-foreground">Execution</div>
+            ? <h3 className="text-sm font-medium mb-3">Environment</h3>
+            : <div className="px-4 py-2 text-xs font-medium text-muted-foreground">Environment</div>
           }
           <div className={cn(cards ? "border border-border rounded-lg p-4 space-y-3" : "px-4 pb-3 space-y-3")}>
             <Field
@@ -908,20 +910,12 @@ export function AgentConfigForm(props: AgentConfigFormProps) {
       ) : showEnvironmentOverrideControl ? (
         <div className={cn(!cards && (isCreate ? "border-t border-border" : "border-b border-border"))}>
           {cards
-            ? <h3 className="text-sm font-medium mb-3">Execution</h3>
-            : <div className="px-4 py-2 text-xs font-medium text-muted-foreground">Execution</div>
+            ? <h3 className="text-sm font-medium mb-3">Environment</h3>
+            : <div className="px-4 py-2 text-xs font-medium text-muted-foreground">Environment</div>
           }
           <div className={cn(cards ? "border border-border rounded-lg p-4 space-y-3" : "px-4 pb-3 space-y-3")}>
-            <Field
-              label="Environment override"
-              hint="Leave this unset to inherit the instance default. Agent-specific overrides only appear when there is a real alternative."
-            >
+            <Field label="Environment override">
               <div className="space-y-2">
-                <div className="text-xs text-muted-foreground">
-                  {currentDefaultEnvironment
-                    ? `Overriding the instance default with ${currentDefaultEnvironment.name}.`
-                    : `Inheriting the instance default: ${inheritedEnvironmentLabel}.`}
-                </div>
                 <select
                   className={inputClass}
                   value={currentDefaultEnvironmentId}
@@ -934,7 +928,7 @@ export function AgentConfigForm(props: AgentConfigFormProps) {
                     mark("identity", "defaultEnvironmentId", nextValue || null);
                   }}
                 >
-                  <option value="">Inherit instance default ({inheritedEnvironmentLabel})</option>
+                  <option value="">Default: {inheritedEnvironmentLabel}</option>
                   {runnableEnvironments.map((environment) => (
                     <option key={environment.id} value={environment.id}>
                       {environment.name} · {environment.driver}