diff --git a/graphify/extract.py b/graphify/extract.py
index 39ebfd62e..a6c4fda25 100644
--- a/graphify/extract.py
+++ b/graphify/extract.py
@@ -44,6 +44,8 @@ from graphify.extractors.base import (  # noqa: F401
     _read_source_bytes,
     _read_source_text,
     _read_text,
+    active_scan_root,
+    set_active_scan_root,
 )
 from graphify.extractors.apex import extract_apex  # noqa: F401
 from graphify.extractors.bash import extract_bash  # noqa: F401
@@ -8134,9 +8136,10 @@ def _xaml_project_root(path: Path) -> Path:
                 break
         except OSError:
             continue
-    if _XAML_ACTIVE_EXTRACT_ROOT is None:
+    active_root = active_scan_root()
+    if active_root is None:
         return root
-    boundary = _XAML_ACTIVE_EXTRACT_ROOT.resolve()
+    boundary = active_root.resolve()
     try:
         root.resolve().relative_to(boundary)
         return root
@@ -8147,7 +8150,7 @@ def _xaml_project_root(path: Path) -> Path:
 def _xaml_csharp_class_nodes(path: Path) -> dict[str, list[dict]]:
     from graphify.detect import _is_ignored, _is_noise_dir, _load_graphifyignore
     root = _xaml_project_root(path)
-    cache_key = str(root.resolve()) if _XAML_ACTIVE_EXTRACT_ROOT is not None else None
+    cache_key = str(root.resolve()) if active_scan_root() is not None else None
     if cache_key and cache_key in _XAML_CSHARP_CLASS_CACHE:
         return _XAML_CSHARP_CLASS_CACHE[cache_key]
     classes: dict[str, list[dict]] = {}
@@ -8205,7 +8208,6 @@ def _xaml_pascal_name(name: str) -> str | None:
 
 _XAML_TOOLKIT_FIELD_RE = re.compile(r"\b(?P<name>_?m?_?[A-Za-z_]\w*)\s*(?:=.*)?;")
 _XAML_TOOLKIT_METHOD_RE = re.compile(r"\b(?P<name>[A-Za-z_]\w*)\s*\(")
-_XAML_ACTIVE_EXTRACT_ROOT: Path | None = None
 _XAML_CSHARP_CLASS_CACHE: dict[str, dict[str, list[dict]]] = {}
 
 
@@ -8839,13 +8841,15 @@ def _get_extractor(path: Path) -> Any | None:
 
 
 def _safe_extract_with_xaml_root(extractor, path: Path, root: Path) -> dict:
-    global _XAML_ACTIVE_EXTRACT_ROOT
-    previous_root = _XAML_ACTIVE_EXTRACT_ROOT
-    _XAML_ACTIVE_EXTRACT_ROOT = root.resolve()
+    # Publish the in-flight scan root on extractors.base (the correct import
+    # direction) so root-dependent extractors — Markdown link resolution, the
+    # XAML C# project clamp — can read it without reaching back into this module
+    # (#3666). Despite the XAML-era name this wraps every extractor.
+    previous_root = set_active_scan_root(root.resolve())
     try:
         return _safe_extract(extractor, path, scan_root=root)
     finally:
-        _XAML_ACTIVE_EXTRACT_ROOT = previous_root
+        set_active_scan_root(previous_root)
 
 
 def _worker_init(language_overrides: dict[str, str]) -> None:
diff --git a/graphify/extractors/base.py b/graphify/extractors/base.py
index 8c5f1d523..17d4ce600 100644
--- a/graphify/extractors/base.py
+++ b/graphify/extractors/base.py
@@ -6,6 +6,34 @@ from pathlib import Path
 
 from graphify.ids import make_id
 
+# Ambient scan root of the extraction in flight. extract.py's
+# _safe_extract_with_xaml_root sets it around every per-file extraction; the
+# extractors that need the corpus boundary read it (Markdown link resolution and
+# the XAML C# project-root clamp). It lives here rather than in graphify.extract
+# so those extractors read it in the correct import direction (extract.py ->
+# extractors/, never back), per MIGRATION.md invariant #4 — the old
+# function-local `import graphify.extract` + getattr(..., None) was a package ->
+# parent dependency that also failed silently if the module global were renamed
+# (#3666). None outside extract().
+_ACTIVE_SCAN_ROOT: "Path | None" = None
+
+
+def set_active_scan_root(root: "Path | None") -> "Path | None":
+    """Set the in-flight scan root, returning the previous value so the caller
+    can restore it — extraction nests (a XAML shard re-enters extract())."""
+    global _ACTIVE_SCAN_ROOT
+    previous = _ACTIVE_SCAN_ROOT
+    _ACTIVE_SCAN_ROOT = root
+    return previous
+
+
+def active_scan_root() -> "Path | None":
+    """The scan root of the extraction in flight, or None outside extract().
+
+    A direct ``extract_markdown()`` / ``extract_xaml()`` call (no surrounding
+    ``extract()``) sees None and the root-dependent behavior stays off."""
+    return _ACTIVE_SCAN_ROOT
+
 # Language built-in globals that AST may classify as call targets when used as
 # constructors or coercion functions (e.g. String(x), Number(x), Boolean(x)).
 # Without this filter they become god-nodes accumulating spurious edges from
diff --git a/graphify/extractors/markdown.py b/graphify/extractors/markdown.py
index 6c52f9d94..2a389be9f 100644
--- a/graphify/extractors/markdown.py
+++ b/graphify/extractors/markdown.py
@@ -139,15 +139,11 @@ def _parse_frontmatter_fallback(fm_lines: list[str]) -> dict:
 _MD_LINK_INDEX_CACHE: "dict[str, dict[str, list[tuple[int, str, Path]]]]" = {}
 
 
-def _active_scan_root() -> "Path | None":
-    """The scan root of the extraction in flight, or None outside extract().
-
-    _safe_extract_with_xaml_root sets this for every extraction despite its
-    XAML-era name; a direct extract_markdown() call has no root and the
-    fallback stays off.
-    """
-    import graphify.extract as _extract
-    return getattr(_extract, "_XAML_ACTIVE_EXTRACT_ROOT", None)
+# The in-flight scan root now lives on extractors.base (correct import
+# direction: extract.py -> extractors/, never back), so a rename can no longer
+# silently disable link resolution the way the old getattr(graphify.extract, …,
+# None) could (#3666).
+from graphify.extractors.base import active_scan_root as _active_scan_root
 
 
 def _nfc(s: str) -> str:
diff --git a/tests/test_extractor_scan_root_context.py b/tests/test_extractor_scan_root_context.py
new file mode 100644
index 000000000..cb509fa16
--- /dev/null
+++ b/tests/test_extractor_scan_root_context.py
@@ -0,0 +1,73 @@
+"""The in-flight scan root is shared through extractors.base, not by reaching
+back into graphify.extract — MIGRATION.md invariant #4 (#3666)."""
+from __future__ import annotations
+
+import ast
+from pathlib import Path
+
+from graphify.extractors import base as base_mod
+from graphify.extractors import markdown as markdown_mod
+
+
+def _imports_graphify_extract(module) -> bool:
+    """True if the module's source imports graphify.extract anywhere — a
+    top-level or a function-local `import graphify.extract` / `from
+    graphify.extract import ...`."""
+    source = Path(module.__file__).read_text(encoding="utf-8")
+    for node in ast.walk(ast.parse(source)):
+        if isinstance(node, ast.Import):
+            if any(a.name == "graphify.extract" or a.name.startswith("graphify.extract.")
+                   for a in node.names):
+                return True
+        elif isinstance(node, ast.ImportFrom):
+            if node.module == "graphify.extract" or (node.module or "").startswith("graphify.extract."):
+                return True
+    return False
+
+
+def test_markdown_extractor_does_not_import_graphify_extract():
+    """The Markdown extractor read the in-flight scan root via a function-local
+    `import graphify.extract` + getattr, a package->parent dependency that
+    violated invariant #4 and degraded silently on a rename (#3666). It must now
+    reach the shared context through extractors.base instead."""
+    assert not _imports_graphify_extract(markdown_mod), (
+        "extractors/markdown.py must not import graphify.extract — read the scan "
+        "root via extractors.base.active_scan_root() (MIGRATION.md invariant #4)"
+    )
+
+
+def test_active_scan_root_defaults_to_none():
+    # A fresh process (no extraction in flight) has no active root.
+    assert base_mod.active_scan_root() is None
+
+
+def test_active_scan_root_set_get_restore_nested():
+    """set_active_scan_root returns the previous value so nested extraction can
+    restore it; active_scan_root reflects the current top of that stack."""
+    assert base_mod.active_scan_root() is None
+    outer = Path("/repo").resolve()
+    inner = Path("/repo/vendored").resolve()
+
+    prev_outer = base_mod.set_active_scan_root(outer)
+    try:
+        assert prev_outer is None
+        assert base_mod.active_scan_root() == outer
+
+        prev_inner = base_mod.set_active_scan_root(inner)
+        try:
+            assert prev_inner == outer
+            assert base_mod.active_scan_root() == inner
+        finally:
+            base_mod.set_active_scan_root(prev_inner)
+
+        assert base_mod.active_scan_root() == outer
+    finally:
+        base_mod.set_active_scan_root(prev_outer)
+
+    assert base_mod.active_scan_root() is None
+
+
+def test_markdown_active_scan_root_alias_is_base_accessor():
+    """The Markdown extractor's _active_scan_root is the base accessor, so the
+    scan root extract() publishes is exactly what link resolution reads."""
+    assert markdown_mod._active_scan_root is base_mod.active_scan_root