tools-sync: mirror 阶段只链接含 SKILL.md 的目录

Claude Code 会把账号侧下发的 skills 缓存进 ~\.claude\skills\synced\<guid>\，
它不是 skill（顶层没有 SKILL.md），但内层目录各自带 SKILL.md。旧逻辑无条件
镜像主副本下的每个非点开头目录，于是给 Codex 建了 synced 的 junction —— Codex
递归扫到内层那批，会把账号已经提供的 skills 再注册一遍。

改为以顶层 SKILL.md 作为判据（与脚本自己 '\' 检查、以及 Codex 的注册
规则一致），并把被跳过的目录打印出来。

tools-sync/scripts/sync_repos.ps1

@@ -376,8 +376,17 @@ if ($MirrorRegistry) {
 
     # A primary entry that is itself a link belongs to whichever host installed it (its real home
     # is a registry the host already exposes to Codex). Mirroring it would register it twice.
-    $primarySkills = Get-ChildItem $ClaudeSkills -Directory -Force |
+    $primaryDirs = Get-ChildItem $ClaudeSkills -Directory -Force |
         Where-Object { $_.Name -notlike ".*" -and -not (Test-IsLink $_) }
+    # A directory without SKILL.md at its top level is not a skill -- e.g. 'synced/', the
+    # runtime cache of account-side skills Claude Code downloads. Mirroring it is worse than
+    # useless: its NESTED directories do carry SKILL.md, so Codex would register that whole
+    # set a second time alongside the ones it already gets from the account.
+    $primarySkills = $primaryDirs | Where-Object { Test-Path (Join-Path $_.FullName "SKILL.md") }
+    $notSkills     = $primaryDirs | Where-Object { -not (Test-Path (Join-Path $_.FullName "SKILL.md")) }
+    if ($notSkills) {
+        Write-Host "  not skills (no SKILL.md), not mirrored: $(($notSkills | ForEach-Object Name) -join ', ')"
+    }
     foreach ($d in $primarySkills) {
         $link = Join-Path $MirrorRegistry $d.Name
         if (Test-Path $link) { continue }