diff --git a/web/src/pages/agent/form/components/prompt-editor/index.tsx b/web/src/pages/agent/form/components/prompt-editor/index.tsx
index d9e2a688ba..5ec8cb4c9b 100644
--- a/web/src/pages/agent/form/components/prompt-editor/index.tsx
+++ b/web/src/pages/agent/form/components/prompt-editor/index.tsx
@@ -153,7 +153,7 @@ function PromptContent({
           <div className="absolute inset-y-0 right-2 z-10 flex items-center">
             <Tooltip>
               <TooltipTrigger asChild>
-                <label className="flex cursor-pointer items-center rounded-sm border border-border bg-bg-base/95 px-1 py-0.5 shadow-sm backdrop-blur-sm">
+                <label className="flex cursor-pointer items-center rounded-sm px-1 py-0.5 shadow-sm backdrop-blur-sm">
                   <span className="sr-only">{t('flow.mergePath')}</span>
                   <div className="origin-right scale-75">
                     <Switch
diff --git a/web/src/pages/agent/form/components/prompt-editor/variable-path-transform.ts b/web/src/pages/agent/form/components/prompt-editor/variable-path-transform.ts
index d095afe780..6ba21bf10b 100644
--- a/web/src/pages/agent/form/components/prompt-editor/variable-path-transform.ts
+++ b/web/src/pages/agent/form/components/prompt-editor/variable-path-transform.ts
@@ -1,4 +1,4 @@
-import { TextNode } from 'lexical';
+import { $getSelection, $isRangeSelection, TextNode } from 'lexical';
 import {
   appendPromptVariablePath,
   extractLeadingPromptVariablePath,
@@ -19,6 +19,30 @@ export function mergeLeadingVariablePathTextNode(textNode: TextNode): boolean {
     return false;
   }
 
+  // Don't merge while the user may still be typing the path.
+  //
+  // Case 1: The path suffix reaches the end of the text (no remaining text).
+  //         The user may type more identifier characters to extend the path.
+  //
+  // Case 2: The cursor sits right after the matched path suffix even though
+  //         there is trailing text (e.g. a space left over from a previous
+  //         merge). This means the user is actively typing the path before
+  //         that pre-existing text, and the path may still grow. Merging now
+  //         would lock the path to its current length.
+  if (leadingPath.remainingText === '') {
+    return false;
+  }
+
+  const selection = $getSelection();
+  if (
+    $isRangeSelection(selection) &&
+    selection.isCollapsed() &&
+    selection.anchor.key === textNode.getKey() &&
+    selection.anchor.offset === leadingPath.pathSuffix.length
+  ) {
+    return false;
+  }
+
   const nextVariable = appendPromptVariablePath(
     {
       value: previousSibling.__value,