diff --git a/graphlink_app/graphlink_plugins/gitlink/agent.py b/graphlink_app/graphlink_plugins/gitlink/agent.py
index 7107635..7d83111 100644
--- a/graphlink_app/graphlink_plugins/gitlink/agent.py
+++ b/graphlink_app/graphlink_plugins/gitlink/agent.py
@@ -86,6 +86,19 @@ def _normalize_repo_path(path_text):
     normalized = PurePosixPath(raw_path)
     if normalized.is_absolute() or ".." in normalized.parts:
         raise RuntimeError("Repository paths must stay inside the selected repository.")
+    # A Windows drive letter ("C:/config/app.txt", "C:app.txt") or an NTFS
+    # Alternate Data Stream ("file.txt:hidden") isn't "absolute" by POSIX's
+    # is_absolute() (no leading '/'), so it slipped past the check above -
+    # not as a real escape (_safe_local_target's resolve()+containment check
+    # still catches a genuine cross-drive path), but as silent aliasing:
+    # Windows pathlib treats a same-drive "C:" path segment as a no-op
+    # drive-relative reference rather than a literal folder, so
+    # "C:/config/app.txt" resolved to the exact same target as the plain
+    # "config/app.txt" - not rejected as "absolute-looking input" the way
+    # this guard's own contract says it should be. Reject any ':' in a path
+    # segment loudly instead of letting it collapse silently.
+    if any(":" in part for part in normalized.parts):
+        raise RuntimeError("Repository paths must stay inside the selected repository.")
     return normalized.as_posix()
 
 
diff --git a/graphlink_app/tests/test_gitlink_path_safety.py b/graphlink_app/tests/test_gitlink_path_safety.py
index e0bd866..7bf7886 100644
--- a/graphlink_app/tests/test_gitlink_path_safety.py
+++ b/graphlink_app/tests/test_gitlink_path_safety.py
@@ -61,6 +61,41 @@ def test_unc_style_path_is_rejected(self):
         with pytest.raises(RuntimeError):
             _normalize_repo_path("//server/share/evil.txt")
 
+    def test_windows_drive_letter_path_is_rejected(self):
+        # Bug-scan finding: a drive-lettered path isn't "absolute" by POSIX's
+        # is_absolute() (no leading '/'), so it slipped past the check above.
+        # Not a real escape - _safe_local_target's containment check still
+        # holds - but silent ALIASING: Windows pathlib treats a same-drive
+        # "C:" path segment as a no-op drive-relative reference rather than a
+        # literal folder, so this used to resolve to the exact same target as
+        # the plain "config/app.txt", contrary to this guard's own contract
+        # of rejecting absolute-looking input.
+        with pytest.raises(RuntimeError):
+            _normalize_repo_path("C:/config/app.txt")
+
+    def test_windows_drive_relative_path_with_no_slash_is_rejected(self):
+        # "C:app.txt" (no slash) is the same drive-relative hazard as above,
+        # via a different textual shape - PurePosixPath keeps it as one part
+        # ("C:app.txt") rather than splitting off "C:", but the substring
+        # check still catches it.
+        with pytest.raises(RuntimeError):
+            _normalize_repo_path("C:app.txt")
+
+    def test_cross_drive_path_is_rejected(self):
+        with pytest.raises(RuntimeError):
+            _normalize_repo_path("D:/config/app.txt")
+
+    def test_alternate_data_stream_style_path_is_rejected(self):
+        # An NTFS Alternate Data Stream marker - same defensive "reject any
+        # colon" guard, though ADS addressing doesn't actually work through
+        # this path-join code path.
+        with pytest.raises(RuntimeError):
+            _normalize_repo_path("file.txt:hidden_stream")
+
+    def test_a_colon_deeper_in_the_path_is_still_rejected(self):
+        with pytest.raises(RuntimeError):
+            _normalize_repo_path("src/weird:name.py")
+
 
 class TestSafeLocalTarget:
     def test_normal_path_resolves_under_root(self, tmp_path):
@@ -71,12 +106,12 @@ def test_parent_traversal_is_rejected(self, tmp_path):
         with pytest.raises(RuntimeError):
             _safe_local_target(tmp_path, "../../outside.py")
 
-    def test_windows_drive_letter_injection_stays_contained(self, tmp_path):
-        # A path that looks like a Windows absolute path (drive letter) must not
-        # be able to escape the repo root once re-joined onto it.
-        target = _safe_local_target(tmp_path, "C:/Windows/System32/evil.txt")
-        resolved_root = tmp_path.resolve()
-        assert target == resolved_root or resolved_root in target.parents
+    def test_windows_drive_letter_path_is_rejected_at_normalization(self, tmp_path):
+        # _safe_local_target normalizes first, and normalization now rejects
+        # a drive-lettered path outright (see TestNormalizeRepoPath) instead
+        # of silently aliasing it onto some path under the repo root.
+        with pytest.raises(RuntimeError):
+            _safe_local_target(tmp_path, "C:/Windows/System32/evil.txt")
 
     def test_unc_style_path_is_rejected_at_normalization(self, tmp_path):
         # _safe_local_target normalizes first, and normalization now rejects