Accept index links to the knowledge root

A link such as [Knowledge](../..) from repos/<repo>/_index.md resolves
to the knowledge root, which check_index_links looked up among head's
directories and never found (top-level files have dirname "", the
link resolves to "."), so it reported index_link_broken for a valid
link. The root is now a directory every tree has; a link above it
still escapes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: tzhouam

doc/architecture/SPEC/knowledge_service/l1.md

@@ -38,7 +38,7 @@
   再只对路径做百分号解码；引用定义、标题、转义、代码段/代码块、
   HTML 块/注释都由解析器按渲染器的方式处理，不手写匹配。URL、纯锚点不算目标。
   对每个新增或改动的 `_index.md`：
-  - 本次新增的链接必须解析到 head 中的文件或目录、不得逃出知识树（`index_link_broken` /
+  - 本次新增的链接必须解析到 head 中的文件或目录（知识树根目录本身，如 `../..`，算已存在的目录）、不得逃出知识树（`index_link_broken` /
     `index_link_escapes`，绝对路径保留各自的 `/…` 身份且一律算逃逸；base 已有的链接不重新判定——
     有些指向 `doc/`）。
   - 保留：base 的链接（按解析后的路径）必须仍在 head 的链接里，否则 `index_link_dropped`——把链接挪进

src/infermatrix_copilot/knowledge_service/l1.py

@@ -483,6 +483,8 @@ def check_index_links(base: Mapping[str, str], head: Mapping[str, str]) -> list[
                 continue
             if resolved == ".." or resolved.startswith(("../", "/")):
                 issues.append(Issue("index_link_escapes", path, written))
+            elif resolved in (".", ""):
+                continue  # the knowledge root itself: a directory every tree has
             elif resolved not in head and not any(d == resolved or d.startswith(resolved + "/")
                                                   for d in head_dirs):
                 issues.append(Issue("index_link_broken", path, written))

test/test_kb_init_l1.py

@@ -306,3 +306,12 @@ def test_only_kb_init_may_pass_bootstrap():
         if path not in allowed and re.search(r"bootstrap\s*=\s*True", path.read_text(encoding="utf-8"))
     ]
     assert offenders == []
+
+
+def test_index_links_accept_the_knowledge_root_and_its_directories():
+    base = _base()
+    head = dict(base)
+    head["repos/old/_index.md"] += "- [Knowledge](../..)\n- [Knowledge](../../)\n- [Repos](..)\n"
+    assert check_index_links(base, head) == []
+    head["repos/old/_index.md"] += "- [Above](../../..)\n"
+    assert [(i.code, i.detail) for i in check_index_links(base, head)] == [("index_link_escapes", "../../..")]