fix(workspace): use directory symlinks for missing Windows targets

When a configured workspace path is temporarily missing on Windows,
create the composite link with explicit dir type and rebuild existing
links once the target appears if the current link is not traversable as a
directory. This prevents file-typed symlinks from becoming stuck.

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

src/agents/workspace.ts

@@ -759,11 +759,14 @@ export async function ensureCompositeWorkspace(params: {
   // Create or update symlinks.
   for (const { linkName, target } of linkEntries) {
     const linkPath = path.join(compositeDir, linkName);
+    const targetExists = await fs
+      .access(target)
+      .then(() => true)
+      .catch(() => false);
+    const symlinkType = process.platform === "win32" ? "dir" : undefined;
 
     // Warn on missing targets but still create the symlink.
-    try {
-      await fs.access(target);
-    } catch {
+    if (!targetExists) {
       compositeLog.warn(`Workspace target does not exist: ${target}`);
     }
 
@@ -771,9 +774,23 @@ export async function ensureCompositeWorkspace(params: {
     try {
       const existingTarget = await fs.readlink(linkPath);
       if (path.resolve(existingTarget) === path.resolve(target)) {
-        continue;
+        // On Windows, a missing target created without an explicit "dir" type can leave
+        // behind a file-typed symlink that resolves to the right target string but is not
+        // usable as a directory once the target appears. When the target exists, verify the
+        // resolved link is traversable as a directory before keeping it.
+        if (!(process.platform === "win32" && targetExists)) {
+          continue;
+        }
+        try {
+          const stats = await fs.stat(linkPath);
+          if (stats.isDirectory()) {
+            continue;
+          }
+        } catch {
+          // Recreate the symlink with the explicit directory type below.
+        }
       }
-      // Target changed — remove old symlink.
+      // Target changed or existing Windows link is unusable — remove old symlink.
       await fs.unlink(linkPath);
     } catch {
       // Symlink doesn't exist or isn't a symlink — try to remove whatever is there.
@@ -785,7 +802,7 @@ export async function ensureCompositeWorkspace(params: {
       }
     }
 
-    await fs.symlink(target, linkPath);
+    await fs.symlink(target, linkPath, symlinkType);
     compositeLog.info(`Symlinked ${linkName} -> ${target}`);
   }
 }