fix: Decode percent-encoded filenames from URLs (#12906)

getFileNameFromUrl returned the raw URL path segment, so attachments
created from a URL were stored with encoded names (e.g. "My%20File.pdf").
Decode the filename, falling back to the raw value on malformed encoding.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

shared/utils/files.test.ts

@@ -82,4 +82,22 @@ describe("getFileNameFromUrl", () => {
     ).toBe("file.txt");
     expect(getFileNameFromUrl("https://example.com/")).toBe("");
   });
+
+  it("decodes percent-encoded filenames", () => {
+    expect(getFileNameFromUrl("https://example.com/My%20Report.pdf")).toBe(
+      "My Report.pdf"
+    );
+    expect(getFileNameFromUrl("https://example.com/caf%C3%A9%20menu.png")).toBe(
+      "café menu.png"
+    );
+    expect(
+      getFileNameFromUrl("https://example.com/report%20final.pdf?v=2#top")
+    ).toBe("report final.pdf");
+  });
+
+  it("falls back to the raw filename on malformed encoding", () => {
+    expect(getFileNameFromUrl("https://example.com/bad%name.txt")).toBe(
+      "bad%name.txt"
+    );
+  });
 });

shared/utils/files.ts

@@ -157,7 +157,14 @@ export function getFileNameFromUrl(url: string) {
     const urlObj = new URL(url);
     const pathname = urlObj.pathname;
     const filename = pathname.substring(pathname.lastIndexOf("/") + 1);
-    return filename;
+
+    try {
+      // Decode percent-encoding so the name is human readable (e.g. "My%20File.pdf" → "My File.pdf").
+      return decodeURIComponent(filename);
+    } catch (_err) {
+      // Malformed percent-encoding, fall back to the raw filename.
+      return filename;
+    }
   } catch (_err) {
     return null;
   }