diff --git a/mobile/src/context/ShareContext.tsx b/mobile/src/context/ShareContext.tsx
index 5c75cefb..caae315c 100644
--- a/mobile/src/context/ShareContext.tsx
+++ b/mobile/src/context/ShareContext.tsx
@@ -9,6 +9,7 @@
  */
 
 import React, { createContext, useCallback, useContext, useState } from "react";
+import { normalizeFileUri } from "../utils/normalizeUri";
 
 export interface SharedFile {
   uri: string;
@@ -28,28 +29,6 @@ const ShareContext = createContext<ShareContextValue>({
   clearPendingFiles: () => {},
 });
 
-/**
- * Aggressively normalise a file URI so that the same physical file is
- * recognised regardless of how the URI was constructed.
- *
- * - Decode percent-encoding (`%20` → ` `)
- * - Collapse consecutive slashes after the scheme (`file:////` → `file:///`)
- * - Strip trailing slashes
- */
-function normalizeFileUri(uri: string): string {
-  let norm: string;
-  try {
-    norm = decodeURIComponent(uri);
-  } catch {
-    norm = uri;
-  }
-  // Collapse multiple slashes after the scheme (e.g. file://// → file:///)
-  norm = norm.replace(/^(file:\/\/)\/{2,}/, "$1/");
-  // Strip trailing slash
-  norm = norm.replace(/\/+$/, "");
-  return norm;
-}
-
 export function ShareProvider({ children }: { children: React.ReactNode }) {
   const [pendingFiles, setPendingFiles] = useState<SharedFile[]>([]);
 
diff --git a/mobile/src/screens/UploadScreen.tsx b/mobile/src/screens/UploadScreen.tsx
index d7feac79..07a1b97e 100644
--- a/mobile/src/screens/UploadScreen.tsx
+++ b/mobile/src/screens/UploadScreen.tsx
@@ -28,30 +28,12 @@ import {
 } from "react-native";
 import { useAuth } from "../context/AuthContext";
 import { useShare } from "../context/ShareContext";
+import { normalizeFileUri } from "../utils/normalizeUri";
 import api from "../services/api";
 
 /** Statuses that indicate processing has finished (no further polling needed). */
 const TERMINAL_STATUSES = new Set(["completed", "failed", "duplicate"]);
 
-/**
- * Normalise a file URI for deduplication.
- *
- * - Decode percent-encoding (`%20` → ` `)
- * - Collapse consecutive slashes after the scheme (`file:////` → `file:///`)
- * - Strip trailing slashes
- */
-function normalizeUri(uri: string): string {
-  let norm: string;
-  try {
-    norm = decodeURIComponent(uri);
-  } catch {
-    norm = uri;
-  }
-  norm = norm.replace(/^(file:\/\/)\/{2,}/, "$1/");
-  norm = norm.replace(/\/+$/, "");
-  return norm;
-}
-
 interface UploadItem {
   id: string;
   filename: string;
@@ -130,7 +112,7 @@ export default function UploadScreen() {
     // Deduplicate: skip if this exact URI was already uploaded in this session.
     // This guards against duplicate share-sheet deliveries from iOS where the
     // Linking handler and +not-found.tsx fire for the same file.
-    const normUri = normalizeUri(uri);
+    const normUri = normalizeFileUri(uri);
     if (uploadedUrisRef.current.has(normUri)) {
       console.debug("[uploadFile] skipping duplicate URI:", uri);
       return;
diff --git a/mobile/src/utils/normalizeUri.ts b/mobile/src/utils/normalizeUri.ts
new file mode 100644
index 00000000..d32e7d7f
--- /dev/null
+++ b/mobile/src/utils/normalizeUri.ts
@@ -0,0 +1,20 @@
+/**
+ * Normalise a file URI for deduplication.
+ *
+ * - Decode percent-encoding (`%20` → ` `)
+ * - Collapse consecutive slashes after the scheme (`file:////` → `file:///`)
+ * - Strip trailing slashes
+ */
+export function normalizeFileUri(uri: string): string {
+  let norm: string;
+  try {
+    norm = decodeURIComponent(uri);
+  } catch {
+    norm = uri;
+  }
+  // Collapse multiple slashes after the scheme (e.g. file://// → file:///)
+  norm = norm.replace(/^(file:\/\/)\/{2,}/, "$1/");
+  // Strip trailing slash
+  norm = norm.replace(/\/+$/, "");
+  return norm;
+}
diff --git a/tests/test_duplicates.py b/tests/test_duplicates.py
index 19ba731b..987b1599 100644
--- a/tests/test_duplicates.py
+++ b/tests/test_duplicates.py
@@ -3,11 +3,12 @@
 Covers:
 - ``GET /api/duplicates``            — list all exact-duplicate groups
 - ``GET /api/files/{id}/duplicates`` — per-file exact + near-duplicate info
-- ``POST /api/ui-upload``            — exact-duplicate warning in upload response
+- ``POST /api/ui-upload``            — exact-duplicate rejection at upload time
 - ``GET /duplicates``                — duplicate management UI page
 """
 
 import json
+import os
 from unittest.mock import patch
 
 import pytest
@@ -395,7 +396,6 @@ class TestUploadDuplicateRejection:
         # The stored_filename is returned so we can verify cleanup
         stored = data.get("stored_filename")
         assert stored is not None
-        import os
 
         from app.config import settings