Fix SSE crash + React layout error boundaries

- documents_loader: skip missing files (print warning + continue) instead
  of raising HTTPException inside SSE generator — prevents "response
  already started" runtime error when temp files are wiped on restart
- V1ContentRender: wrap non-edit mode render in SlideErrorBoundary so
  broken custom layout components show a red placeholder instead of
  crashing the page (React error #62)
- CustomTemplateCard: wrap LayoutPreview in SlideErrorBoundary for the
  same reason — bad compiled TSX from master deck parsing no longer
  crashes the outline template picker

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

backend/services/documents_loader.py

@@ -1,5 +1,4 @@
 import mimetypes
-from fastapi import HTTPException
 import os, asyncio
 from typing import List, Optional, Tuple
 import pdfplumber
@@ -44,9 +43,8 @@ class DocumentsLoader:
 
         for file_path in self._file_paths:
             if not os.path.exists(file_path):
-                raise HTTPException(
-                    status_code=404, detail=f"File {file_path} not found"
-                )
+                print(f"[DocumentsLoader] Warning: file not found, skipping: {file_path}")
+                continue
 
             document = ""
             imgs = []

frontend/app/(presentation-generator)/components/V1ContentRender.tsx

@@ -129,11 +129,13 @@ export const V1ContentRender = ({ slide, isEditMode, theme }: { slide: any, isEd
         );
     }
     return (
-        <LayoutComp data={{
-            ...slide.content,
-            _logo_url__: theme ? theme.logo_url : null,
-            __companyName__: (theme && theme.company_name) ? theme.company_name : null,
-        }} />
+        <SlideErrorBoundary label={`Slide ${slide.index + 1}`}>
+            <LayoutComp data={{
+                ...slide.content,
+                _logo_url__: theme ? theme.logo_url : null,
+                __companyName__: (theme && theme.company_name) ? theme.company_name : null,
+            }} />
+        </SlideErrorBoundary>
     )
 };
 

frontend/app/(presentation-generator)/outline/components/CustomTemplateCard.tsx

@@ -4,6 +4,7 @@ import { Card } from "@/components/ui/card";
 import { CustomTemplates, useCustomTemplatePreview } from "@/app/hooks/useCustomTemplates";
 import { Loader2 } from "lucide-react";
 import { CompiledLayout } from "@/app/hooks/compileLayout";
+import { SlideErrorBoundary } from "../../components/SlideErrorBoundary";
 
 // Memoized preview component to prevent re-renders during scroll
 export const LayoutPreview = memo(({ layout, templateId, index }: { layout: CompiledLayout, templateId: string, index: number }) => {
@@ -19,7 +20,9 @@ export const LayoutPreview = memo(({ layout, templateId, index }: { layout: Comp
                 className="transform scale-[0.2] flex justify-center items-center origin-top-left w-[500%] h-[500%]"
                 style={{ transform: 'scale(0.2) translateZ(0)', backfaceVisibility: 'hidden' }}
             >
-                <LayoutComponent data={layout.sampleData} />
+                <SlideErrorBoundary label={layout.layoutName}>
+                    <LayoutComponent data={layout.sampleData} />
+                </SlideErrorBoundary>
             </div>
         </div>
     );