diff --git a/mdedit/js/file-system.js b/mdedit/js/file-system.js
index 810cb2c..f805e0f 100644
--- a/mdedit/js/file-system.js
+++ b/mdedit/js/file-system.js
@@ -683,9 +683,38 @@ async function readServerDirectory(dirUrl, parentNode, depth) {
 async function loadServerDirectory() {
     if (!(location.protocol === 'http:' || location.protocol === 'https:')) return;
 
+    // Compute the directory URL the file tree should be rooted at.
+    //
+    //   <project>/working/         → root = <project>/working/
+    //   <project>/working/x/y/     → root = <project>/working/x/y/
+    //   <project>/working          → root = <project>/working/    (no-slash
+    //                                 canonical-folder URL — the dispatcher
+    //                                 routes mdedit here directly without
+    //                                 a redirect, so we infer "directory"
+    //                                 from the absence of a `.` in the
+    //                                 last segment rather than stripping
+    //                                 back to the parent.)
+    //   <project>/x/y/mdedit.html  → root = <project>/x/y/        (the leaf
+    //                                 segment IS a file; strip to parent.)
+    //
+    // The rule: if the last path segment contains a "." it's a file,
+    // strip it; otherwise treat the whole path as the directory.
     let href = window.location.href.split('?')[0].split('#')[0];
-    const lastSlash = href.lastIndexOf('/');
-    const baseUrl = (lastSlash >= 0) ? href.substring(0, lastSlash + 1) : href + '/';
+    let baseUrl;
+    if (href.endsWith('/')) {
+        baseUrl = href;
+    } else {
+        const lastSlash = href.lastIndexOf('/');
+        const lastSeg = lastSlash >= 0 ? href.substring(lastSlash + 1) : href;
+        if (lastSeg.indexOf('.') !== -1) {
+            // Looks like a file (has an extension) — strip to parent.
+            baseUrl = lastSlash >= 0 ? href.substring(0, lastSlash + 1) : href + '/';
+        } else {
+            // Looks like a directory — append the trailing slash so all
+            // subsequent listing URLs are computed correctly.
+            baseUrl = href + '/';
+        }
+    }
 
     // Only enter server-source mode if the host actually serves JSON directory
     // listings (zddc-server / Caddy). On a plain static host the probe fails