fix: harden preprocessing state and child capabilities

harness/tests/test_workspace_writer_lock.py

@@ -1,8 +1,12 @@
 from __future__ import annotations
-import os, stat
+
+import os
+
 import pytest
+
 from tht.workspace_writer_lock import WorkspaceWriterConflict, verify_workspace_writer_fds
 
+
 def test_verifier_rejects_missing_capability():
     with pytest.raises(WorkspaceWriterConflict): verify_workspace_writer_fds(env={})
 
@@ -14,3 +18,18 @@ def test_verifier_checks_fd_identity(tmp_path):
         cap=verify_workspace_writer_fds(writer_fd=w, root_fd=r, env=env)
         assert cap.inode == st.st_ino
     finally: os.close(w); os.close(r)
+
+
+def test_verifier_rejects_unrelated_lock(tmp_path):
+    root = tmp_path / "root"; other = tmp_path / "other"
+    root.mkdir(mode=0o700); other.mkdir(mode=0o700)
+    expected = root / "writer.lock"; forged = other / "forged.lock"
+    expected.touch(mode=0o600); forged.touch(mode=0o600)
+    root_fd = os.open(root, os.O_RDONLY); forged_fd = os.open(forged, os.O_RDWR)
+    try:
+        st = os.fstat(root_fd)
+        env = {"THOTH_WORKSPACE_ID": "abc-workspace", "THOTH_WORKSPACE_REVISION": "a" * 40, "THOTH_WORKSPACE_DEVICE": str(st.st_dev), "THOTH_WORKSPACE_INODE": str(st.st_ino)}
+        with pytest.raises(WorkspaceWriterConflict):
+            verify_workspace_writer_fds(writer_fd=forged_fd, root_fd=root_fd, env=env)
+    finally:
+        os.close(forged_fd); os.close(root_fd)