diff --git a/services/web/app/src/Features/Compile/CompileController.mjs b/services/web/app/src/Features/Compile/CompileController.mjs
index 8f5be3f659..cae9e0712b 100644
--- a/services/web/app/src/Features/Compile/CompileController.mjs
+++ b/services/web/app/src/Features/Compile/CompileController.mjs
@@ -187,6 +187,24 @@ const _CompileController = {
       options.pdfCachingMinChunkSize = pdfCachingMinChunkSize
     }
 
+    if (!options.rootResourcePath) {
+      const agent = (req.headers['user-agent'] || '').toLowerCase()
+      const isKnownOtherFrontend = agent.includes('node-fetch')
+      logger.warn(
+        { isKnownOtherFrontend, req, projectId, userId, options },
+        'rootResourcePath is missing in request body'
+      )
+      if (isKnownOtherFrontend) {
+        // Reject malformed compile request from "known" other frontend.
+        res.status(400).json({
+          error: 'rootResourcePath is missing in request body',
+        })
+        return
+      }
+      // All others: Log for now and fall back to old compile mode.
+      options.compileFromHistory = false
+    }
+
     const {
       status,
       outputFiles,
diff --git a/services/web/frontend/js/features/pdf-preview/util/compiler.ts b/services/web/frontend/js/features/pdf-preview/util/compiler.ts
index 404ee2336b..dfbf3c4641 100644
--- a/services/web/frontend/js/features/pdf-preview/util/compiler.ts
+++ b/services/web/frontend/js/features/pdf-preview/util/compiler.ts
@@ -136,18 +136,12 @@ export default class DocumentCompiler {
 
       const t0 = performance.now()
 
-      let rootDocIdOverride = this.getRootDocOverrideId()
-      let rootResourcePath
-      try {
-        // Only required for compile-from-history
-        rootDocIdOverride = rootDocIdOverride || this.projectRootDocId
-        rootResourcePath = rootDocIdOverride
-          ? this.pathInFolder(rootDocIdOverride)
-          : 'main.tex'
-      } catch {}
+      const rootDocId = this.getRootDocOverrideId() || this.projectRootDocId
+      const rootResourcePath =
+        (rootDocId && this.pathInFolder(rootDocId)) || 'main.tex'
 
       const body = {
-        rootDoc_id: rootDocIdOverride,
+        rootDoc_id: rootDocId,
         rootResourcePath,
         draft: options.draft,
         check: 'silent', // NOTE: 'error' and 'validate' are possible, but unused
@@ -176,7 +170,7 @@ export default class DocumentCompiler {
       this.setError(undefined)
 
       data.options = options
-      data.rootDocId = rootDocIdOverride
+      data.rootDocId = rootDocId
       if (data.clsiServerId) {
         this.clsiServerId = data.clsiServerId
       }