fix: auto-advance branch detail and pin navigation bar

- Auto-advance to next undetailed branch after generation completes,
  using a useEffect that watches the count of detailed branches
- Cap tree preview at max-h-48 with internal scroll so the nav bar
  is never pushed off screen
- Make nav bar sticky bottom-0 with bg-card so it stays visible
  regardless of content height

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/ai-builder/BranchDetailView.tsx

@@ -1,4 +1,4 @@
-import { useState } from 'react'
+import { useState, useEffect, useRef } from 'react'
 import { Check, RefreshCw, SkipForward, ChevronRight, ChevronLeft } from 'lucide-react'
 import { useAIFlowBuilderStore } from '@/store/aiFlowBuilderStore'
 import { GeneratingAnimation } from './GeneratingAnimation'
@@ -21,6 +21,18 @@ export function BranchDetailView() {
   const allBranchesHaveDetail = selectedBranches.every((b) => b.steps)
   const branchesWithDetail = selectedBranches.filter((b) => b.steps).length
 
+  // Auto-advance to next branch without detail after generation completes
+  const prevDetailCount = useRef(branchesWithDetail)
+  useEffect(() => {
+    if (branchesWithDetail > prevDetailCount.current) {
+      prevDetailCount.current = branchesWithDetail
+      const nextIndex = selectedBranches.findIndex((b) => !b.steps)
+      if (nextIndex !== -1) {
+        setViewingIndex(nextIndex)
+      }
+    }
+  }, [branchesWithDetail, selectedBranches])
+
   const handleGenerate = async (branchName: string) => {
     setError(null)
     await generateBranchDetail(branchName)
@@ -35,103 +47,106 @@ export function BranchDetailView() {
   }
 
   return (
-    <div className="space-y-4">
+    <div className="flex flex-col gap-4">
-      {/* Branch tabs */}
+      {/* Content area */}
-      <div className="flex items-center gap-2 overflow-x-auto pb-1">
+      <div className="space-y-4">
-        {selectedBranches.map((branch, i) => (
+        {/* Branch tabs */}
-          <button
+        <div className="flex items-center gap-2 overflow-x-auto pb-1">
-            key={branch.name}
+          {selectedBranches.map((branch, i) => (
-            type="button"
+            <button
-            onClick={() => setViewingIndex(i)}
+              key={branch.name}
-            className={cn(
+              type="button"
-              'flex shrink-0 items-center gap-1.5 rounded-full border px-3 py-1.5 text-xs font-medium transition-colors',
+              onClick={() => setViewingIndex(i)}
-              viewingIndex === i
+              className={cn(
-                ? 'border-primary/30 bg-primary/10 text-foreground'
+                'flex shrink-0 items-center gap-1.5 rounded-full border px-3 py-1.5 text-xs font-medium transition-colors',
-                : 'border-border text-muted-foreground hover:bg-accent',
+                viewingIndex === i
-              branch.steps && 'pr-2'
+                  ? 'border-primary/30 bg-primary/10 text-foreground'
+                  : 'border-border text-muted-foreground hover:bg-accent',
+                branch.steps && 'pr-2'
+              )}
+            >
+              {branch.name}
+              {branch.steps && (
+                <Check className="h-3 w-3 text-green-400" />
+              )}
+            </button>
+          ))}
+        </div>
+
+        {/* Current branch detail */}
+        {currentBranch && (
+          <div className="space-y-3">
+            <div className="flex items-center justify-between">
+              <div>
+                <h3 className="text-sm font-medium text-foreground">{currentBranch.name}</h3>
+                <p className="text-xs text-muted-foreground">{currentBranch.description}</p>
+              </div>
+            </div>
+
+            {currentBranch.steps ? (
+              <div className="space-y-3">
+                {/* Mini tree preview */}
+                <div className="max-h-48 overflow-y-auto rounded-lg border border-border bg-accent/30 p-3">
+                  <NodePreview node={currentBranch.steps} depth={0} />
+                </div>
+
+                <div className="flex items-center gap-2">
+                  <button
+                    type="button"
+                    onClick={() => handleGenerate(currentBranch.name)}
+                    disabled={isLoading}
+                    className="flex items-center gap-1.5 rounded-lg border border-border px-3 py-1.5 text-xs text-muted-foreground hover:bg-accent hover:text-foreground disabled:opacity-50"
+                  >
+                    <RefreshCw className="h-3 w-3" />
+                    Regenerate
+                  </button>
+                </div>
+              </div>
+            ) : (
+              <div className="flex flex-col items-center gap-3 rounded-lg border border-dashed border-border bg-accent/20 py-8">
+                <p className="text-sm text-muted-foreground">
+                  Generate AI detail for this branch
+                </p>
+                <div className="flex gap-2">
+                  <button
+                    type="button"
+                    onClick={() => handleGenerate(currentBranch.name)}
+                    disabled={isLoading}
+                    className={cn(
+                      'rounded-lg bg-gradient-brand px-4 py-2 text-sm font-medium text-white shadow-lg shadow-primary/20',
+                      isLoading ? 'cursor-not-allowed opacity-50' : 'hover:opacity-90'
+                    )}
+                  >
+                    Generate Detail
+                  </button>
+                  <button
+                    type="button"
+                    onClick={() => {
+                      if (viewingIndex < selectedBranches.length - 1) {
+                        setViewingIndex(viewingIndex + 1)
+                      }
+                    }}
+                    className="flex items-center gap-1 rounded-lg border border-border px-3 py-2 text-sm text-muted-foreground hover:bg-accent"
+                  >
+                    <SkipForward className="h-3.5 w-3.5" />
+                    Skip
+                  </button>
+                </div>
+              </div>
             )}
-          >
+          </div>
-            {branch.name}
+        )}
-            {branch.steps && (
+
-              <Check className="h-3 w-3 text-green-400" />
+        {/* Error */}
-            )}
+        {error && (
-          </button>
+          <div className="rounded-lg border border-red-400/20 bg-red-400/5 px-3 py-2 text-sm text-red-400">
-        ))}
+            {error}
+          </div>
+        )}
       </div>
 
-      {/* Current branch detail */}
+      {/* Navigation — sticky so it's always visible */}
-      {currentBranch && (
+      <div className="sticky bottom-0 flex items-center justify-between border-t border-border bg-card pt-3 pb-1">
-        <div className="space-y-3">
-          <div className="flex items-center justify-between">
-            <div>
-              <h3 className="text-sm font-medium text-foreground">{currentBranch.name}</h3>
-              <p className="text-xs text-muted-foreground">{currentBranch.description}</p>
-            </div>
-          </div>
-
-          {currentBranch.steps ? (
-            <div className="space-y-3">
-              {/* Mini tree preview */}
-              <div className="rounded-lg border border-border bg-accent/30 p-3">
-                <NodePreview node={currentBranch.steps} depth={0} />
-              </div>
-
-              <div className="flex items-center gap-2">
-                <button
-                  type="button"
-                  onClick={() => handleGenerate(currentBranch.name)}
-                  disabled={isLoading}
-                  className="flex items-center gap-1.5 rounded-lg border border-border px-3 py-1.5 text-xs text-muted-foreground hover:bg-accent hover:text-foreground disabled:opacity-50"
-                >
-                  <RefreshCw className="h-3 w-3" />
-                  Regenerate
-                </button>
-              </div>
-            </div>
-          ) : (
-            <div className="flex flex-col items-center gap-3 rounded-lg border border-dashed border-border bg-accent/20 py-8">
-              <p className="text-sm text-muted-foreground">
-                Generate AI detail for this branch
-              </p>
-              <div className="flex gap-2">
-                <button
-                  type="button"
-                  onClick={() => handleGenerate(currentBranch.name)}
-                  disabled={isLoading}
-                  className={cn(
-                    'rounded-lg bg-gradient-brand px-4 py-2 text-sm font-medium text-white shadow-lg shadow-primary/20',
-                    isLoading ? 'cursor-not-allowed opacity-50' : 'hover:opacity-90'
-                  )}
-                >
-                  Generate Detail
-                </button>
-                <button
-                  type="button"
-                  onClick={() => {
-                    if (viewingIndex < selectedBranches.length - 1) {
-                      setViewingIndex(viewingIndex + 1)
-                    }
-                  }}
-                  className="flex items-center gap-1 rounded-lg border border-border px-3 py-2 text-sm text-muted-foreground hover:bg-accent"
-                >
-                  <SkipForward className="h-3.5 w-3.5" />
-                  Skip
-                </button>
-              </div>
-            </div>
-          )}
-        </div>
-      )}
-
-      {/* Error */}
-      {error && (
-        <div className="rounded-lg border border-red-400/20 bg-red-400/5 px-3 py-2 text-sm text-red-400">
-          {error}
-        </div>
-      )}
-
-      {/* Navigation */}
-      <div className="flex items-center justify-between border-t border-border pt-3">
         <div className="flex items-center gap-2">
           <button
             type="button"