--- a/reuse_surface/cli.py
+++ b/reuse_surface/cli.py
@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import argparse
+from collections import Counter
 import json
 import sys
 from pathlib import Path
@@ -87,6 +88,7 @@
     parse_vector,
     registry_paths,
     resolve_repo_root,
+    vectors_match,
 )
 
 
@@ -120,6 +122,31 @@
         warnings.append(f"index drift: entry file not indexed: {path}")
     for path in sorted(indexed_paths - file_paths):
         warnings.append(f"index drift: index references missing file: {path}")
+    rows = index.get("capabilities", [])
+    for field in ("id", "path"):
+        for value, count in sorted(Counter(row[field] for row in rows).items()):
+            if count > 1:
+                warnings.append(f"index drift: duplicate {field}: {value} ({count} rows)")
+    for row in rows:
+        path = repo_root / row["path"]
+        if not path.is_file():
+            continue
+        try:
+            entry = parse_front_matter(path)
+        except (ValueError, yaml.YAMLError):
+            continue  # The entry validation pass reports malformed source.
+        # The index projects the owner entry; index-only changes cannot replace it.
+        for field in ("id", "name", "summary", "domain", "status", "owner", "tags"):
+            if row.get(field) != entry.get(field):
+                warnings.append(f"index drift: {row['path']}: {field} differs from entry")
+        modes = entry.get("availability", {}).get("consumption_modes")
+        if row.get("consumption_modes") != modes:
+            warnings.append(f"index drift: {row['path']}: consumption_modes differs from entry")
+        try:
+            if not vectors_match(row["vector"], entry):
+                warnings.append(f"index drift: {row['path']}: vector differs from entry")
+        except (KeyError, TypeError, AttributeError):
+            warnings.append(f"index drift: {row['path']}: vector cannot be compared to entry")
     return warnings
 
 
--- /dev/null
+++ b/tests/test_index_parity.py
@@ -0,0 +1,69 @@
+"""Exercise the same strict native validator used by the existing Forgejo job."""
+from __future__ import annotations
+
+import copy
+import subprocess
+import sys
+from pathlib import Path
+
+import pytest
+import yaml
+
+ROOT = Path(__file__).resolve().parent.parent
+
+
+def fixture_registry(tmp_path):
+    index = yaml.safe_load((ROOT / "registry/indexes/capabilities.yaml").read_text())
+    row = copy.deepcopy(index["capabilities"][0])
+    source = ROOT / row["path"]
+    target = tmp_path / row["path"]
+    target.parent.mkdir(parents=True)
+    target.write_bytes(source.read_bytes())
+    index["capabilities"] = [row]
+    index_path = tmp_path / "registry/indexes/capabilities.yaml"
+    index_path.parent.mkdir(parents=True)
+    return index_path, index
+
+
+def validate(root):
+    return subprocess.run(
+        [sys.executable, "-m", "reuse_surface.cli", "validate", "--root", str(root),
+         "--fail-on-warnings"], cwd=ROOT, capture_output=True, text=True,
+    )
+
+
+@pytest.mark.parametrize("field,value", [
+    ("id", "capability.synthetic.stale"), ("name", "stale name"),
+    ("summary", "stale summary"), ("domain", "stale-domain"),
+    ("status", "retired"), ("owner", "wrong-owner"),
+    ("tags", ["stale"]), ("consumption_modes", ["stale"]),
+    ("vector", "D0 / A0 / C0 / R0"),
+])
+def test_existing_strict_validator_refuses_stale_projection(tmp_path, field, value):
+    path, index = fixture_registry(tmp_path)
+    path.write_text(yaml.safe_dump(index))
+    assert validate(tmp_path).returncode == 0
+    original_entry = (tmp_path / index["capabilities"][0]["path"]).read_bytes()
+    index["capabilities"][0][field] = value
+    path.write_text(yaml.safe_dump(index))
+    result = validate(tmp_path)
+    assert result.returncode == 1, result.stdout + result.stderr
+    assert f"{field} differs from entry" in result.stderr
+    assert (tmp_path / index["capabilities"][0]["path"]).read_bytes() == original_entry
+
+
+def test_duplicate_id_and_path_cannot_satisfy_exactly_once(tmp_path):
+    path, index = fixture_registry(tmp_path)
+    index["capabilities"].append(copy.deepcopy(index["capabilities"][0]))
+    path.write_text(yaml.safe_dump(index))
+    result = validate(tmp_path)
+    assert result.returncode == 1
+    assert "duplicate id:" in result.stderr
+    assert "duplicate path:" in result.stderr
+
+
+def test_equivalent_vector_whitespace_is_allowed(tmp_path):
+    path, index = fixture_registry(tmp_path)
+    index["capabilities"][0]["vector"] = index["capabilities"][0]["vector"].replace(" ", "")
+    path.write_text(yaml.safe_dump(index))
+    assert validate(tmp_path).returncode == 0