tools-sync: 修复会删掉宿主自装 skill 的 registry 对账缺陷

本次同步实跑触发了数据丢失：orca-cli 的物理副本在 ~\.agents\skills（Orca 就是
这样装的——真目录放 .agents，再把每个工具链过去，本机 8 个工具全指向它），
而主副本里的同名条目本身是指向它的 junction。对账循环从不检查"主副本条目是不是
链接"，于是 fingerprint 比对经链接解析到同一份内容判为"identical"，删掉 registry
副本并建 junction → 主副本与 registry 互指成环，唯一的真副本没了。
orchestration 走 INGEST 分支，则把 Orca 的布局反了过来。

两者均已用 `orca skills install --skill <name>` 恢复为 Orca 自己的布局。

修复三处：
- 对账循环：主副本条目本身是链接时，判定该 skill 归宿主所有，计入 foreign 跳过。
- INGEST：新增 Get-SkillDirLinkers，若 ~\.* 下其他工具的 skills 目录有链接指向
  这个目录，说明它是宿主自装 skill 的物理家，不搬进主副本。
- 镜像阶段：跳过本身是链接的主副本条目，否则 Codex 会把同一 skill 注册两遍
  （.agents 与 .codex 都在扫）。

回归测试新增 hostowned 夹具（真目录在 registry、主副本是链接）：在修复前的脚本上
以"real dir was collapsed into a link"失败，修复后通过。

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01438Zbcx49e4o46uSA71mFF

tools-sync/tests/test_sync_repos_registries.ps1

@@ -27,6 +27,12 @@ try {
     # A link into the other registry rather than the primary: the drift case.
     New-Item -ItemType Junction -Path (Join-Path $codex "shared") -Target (Join-Path $agents "shared") | Out-Null
 
+    # Host-installed shape: the real directory lives in a registry and the PRIMARY is the link
+    # (Orca installs this way). Collapsing the registry copy here would make the link point at
+    # itself and delete the only copy - the reconciler must recognise it and keep its hands off.
+    New-Skill (Join-Path $agents "hostowned") "installed by the host"
+    New-Item -ItemType Junction -Path (Join-Path $primary "hostowned") -Target (Join-Path $agents "hostowned") | Out-Null
+
     # A local bare repo stands in for origin so Phase 1 completes and Phase 2 actually runs.
     $origin = Join-Path $root "origin.git"
     & git init --quiet --bare $origin
@@ -57,6 +63,15 @@ try {
     if ((Get-Content -Raw (Join-Path $primary "forked\SKILL.md")) -notmatch 'primary body') { throw "primary was overwritten by a conflict`n$output" }
 
     if ($output -notmatch 'not a skill dir') { throw "directory without SKILL.md not reported`n$output" }
+
+    # The host-installed skill must survive intact, with the primary still a link at the registry.
+    $hostReal = Get-Item -Force (Join-Path $agents "hostowned")
+    if ($hostReal.LinkType -eq "Junction") { throw "host-installed skill's real dir was collapsed into a link`n$output" }
+    if ((Get-Content -Raw (Join-Path $agents "hostowned\SKILL.md")) -notmatch 'installed by the host') { throw "host-installed skill's content was lost`n$output" }
+    $hostPrimary = Get-Item -Force (Join-Path $primary "hostowned")
+    if (($hostPrimary.Target | Select-Object -First 1) -ne (Join-Path $agents "hostowned")) { throw "primary link to the host-installed skill was repointed`n$output" }
+    # Mirroring it into the registry Codex scans would register the same skill twice.
+    if (Test-Path (Join-Path $codex "hostowned")) { throw "host-installed skill was mirrored, double-registering it`n$output" }
     # Mirror registry must expose every primary skill, including the freshly ingested one.
     foreach ($name in @("shared", "forked", "codexborn")) {
         if (-not (Test-Path (Join-Path $codex "$name\SKILL.md"))) { throw "mirror missing $name`n$output" }