diff --git a/tests/unit/test_live_server_asset_diff.py b/tests/unit/test_live_server_asset_diff.py
new file mode 100644
index 0000000..d7c6807
--- /dev/null
+++ b/tests/unit/test_live_server_asset_diff.py
@@ -0,0 +1,240 @@
+"""Acceptance tests for the live-server ``asset_diff`` op (intentumdiff-vscode#25).
+
+The Rust core owns this behaviour and pins it with its own ``#[cfg(test)]`` tests; these
+prove the guarantee survives the binding — that an editor sending a repo-relative path and a
+ref really does get the engine's artifact manifest back over the protocol, rather than a
+plausible-looking summary assembled on this side of the boundary.
+"""
+from __future__ import annotations
+
+import shutil
+import struct
+import subprocess
+import zlib
+from pathlib import Path
+from unittest.mock import MagicMock
+
+import pytest
+
+# Reason string matches the skip ratchet's existing "platform" class (skip_reasons_baseline.json)
+# rather than minting a new one — a new phrasing for an already-classified condition is exactly
+# what that gate exists to stop.
+pytestmark = pytest.mark.skipif(shutil.which("git") is None, reason="git not installed")
+
+# Every layer the perceptual viewer can render. The panel reported "perceptual diff pending"
+# for as long as nothing asked the engine for these, so the test asserts all of them.
+_ARTIFACT_LAYERS = ("before", "after", "diff", "heatmap", "mask", "overlay", "contact_sheet")
+
+
+def _png_bytes(pixels: list[tuple[int, int, int]], width: int, height: int) -> bytes:
+    """A minimal RGB PNG, so the fixture needs no image library on the Python side."""
+    raw = b"".join(
+        b"\x00" + b"".join(struct.pack("BBB", *pixels[y * width + x]) for x in range(width))
+        for y in range(height)
+    )
+
+    def chunk(tag: bytes, data: bytes) -> bytes:
+        crc = zlib.crc32(tag + data) & 0xFFFFFFFF
+        return struct.pack(">I", len(data)) + tag + data + struct.pack(">I", crc)
+
+    return (
+        b"\x89PNG\r\n\x1a\n"
+        + chunk(b"IHDR", struct.pack(">IIBBBBB", width, height, 8, 2, 0, 0, 0))
+        + chunk(b"IDAT", zlib.compress(raw))
+        + chunk(b"IEND", b"")
+    )
+
+
+def _checkerboard(width: int, height: int) -> list[tuple[int, int, int]]:
+    return [
+        (200, 40, 90) if (x // 4 + y // 4) % 2 else (30, 60, 140)
+        for y in range(height)
+        for x in range(width)
+    ]
+
+
+def _git(repo: Path, *args: str) -> None:
+    subprocess.run(
+        ["git", "-C", str(repo), *args],
+        check=True,
+        capture_output=True,
+    )
+
+
+@pytest.fixture()
+def image_repo(tmp_path: Path) -> Path:
+    """A git repo whose committed image differs from its working-tree copy."""
+    repo = tmp_path / "repo"
+    (repo / "assets").mkdir(parents=True)
+    card = repo / "assets" / "card.png"
+    width, height = 32, 32
+    card.write_bytes(_png_bytes(_checkerboard(width, height), width, height))
+    _git(repo, "init")
+    _git(repo, "config", "user.email", "intentumdiff@example.test")
+    _git(repo, "config", "user.name", "IntentumDiff Test")
+    _git(repo, "add", ".")
+    _git(repo, "commit", "-m", "base")
+
+    changed = _checkerboard(width, height)
+    for y in range(8, 22):
+        for x in range(6, 20):
+            changed[y * width + x] = (250, 250, 40)
+    card.write_bytes(_png_bytes(changed, width, height))
+    return repo
+
+
+def _server(repo: Path, ref: str = "HEAD"):
+    from intentumdiff.live_server import LiveServer
+
+    differ = MagicMock()
+    differ._config = MagicMock()
+    differ._registry = MagicMock()
+    return LiveServer(differ, repo_path=str(repo), ref=ref)
+
+
+def _asset_diff(repo: Path, request: dict, ref: str = "HEAD") -> dict:
+    sent: list[dict] = []
+    _server(repo, ref)._process_request({"op": "asset_diff", "seq": 7, **request}, sent.append)
+    assert len(sent) == 1, sent
+    return sent[0]
+
+
+class TestAssetDiffOp:
+    def test_tracked_image_returns_the_engines_artifact_manifest(self, image_repo: Path) -> None:
+        response = _asset_diff(image_repo, {"path": "assets/card.png"})
+
+        assert response["ok"] is True
+        assert response["op"] == "asset_diff"
+        assert response["seq"] == 7
+        result = response["result"]
+        assert result["status"] == "compared"
+        assert result["file_path"] == "assets/card.png"
+
+        for layer in _ARTIFACT_LAYERS:
+            artifact = result["artifacts"].get(layer)
+            assert artifact, f"engine did not report the {layer} artifact"
+            assert Path(artifact).is_file(), f"{layer} announced at {artifact} but not written"
+
+        # The overlay geometry the viewer draws is only meaningful with these three together.
+        assert result["comparison_dimensions"] == {"width": 32, "height": 32}
+        assert result["hotspots"], "a 14x14 block change should surface at least one hotspot"
+        assert result["histograms"]["red_delta"]
+        assert result["changed_pixel_percentage"] > 0
+
+    def test_artifacts_land_in_a_cache_that_ignores_itself(self, image_repo: Path) -> None:
+        response = _asset_diff(image_repo, {"path": "assets/card.png"})
+
+        cache = image_repo / ".intentumdiff-cache"
+        artifact = Path(response["result"]["artifacts"]["heatmap"]).resolve()
+        assert cache.resolve() in artifact.parents, "artifacts must not land in the work tree"
+        assert "*" in (cache / ".gitignore").read_text(encoding="utf-8")
+
+    def test_added_image_is_reported_as_skipped_with_a_reason(self, image_repo: Path) -> None:
+        (image_repo / "assets" / "new.png").write_bytes(_png_bytes(_checkerboard(8, 8), 8, 8))
+
+        result = _asset_diff(image_repo, {"path": "assets/new.png"})["result"]
+
+        # An added image has nothing to compare against. Saying so is the point: the state this
+        # replaced claimed a comparison was merely "pending" and never produced one.
+        assert result["status"] == "skipped"
+        assert result["change_type"] == "A"
+        assert "no before" in result["reason"]
+        assert not result.get("artifacts")
+
+    def test_deleted_image_is_reported_as_skipped(self, image_repo: Path) -> None:
+        (image_repo / "assets" / "card.png").unlink()
+
+        result = _asset_diff(image_repo, {"path": "assets/card.png"})["result"]
+
+        assert result["status"] == "skipped"
+        assert result["change_type"] == "D"
+
+    def test_unresolvable_ref_is_an_error_not_an_added_image(self, image_repo: Path) -> None:
+        response = _asset_diff(image_repo, {"path": "assets/card.png", "ref": "no-such-ref"})
+
+        assert response["ok"] is False
+        assert "git rev not found" in response["error"]["message"]
+
+    @pytest.mark.parametrize(
+        "path",
+        ["../outside.png", "..\\outside.png", "assets/../../outside.png"],
+    )
+    def test_path_escaping_the_served_repo_is_refused(self, image_repo: Path, path: str) -> None:
+        response = _asset_diff(image_repo, {"path": path})
+
+        assert response["ok"] is False
+        assert response["error"]["code"] == "invalid_request"
+
+    def test_request_without_a_path_or_pair_is_refused(self, image_repo: Path) -> None:
+        response = _asset_diff(image_repo, {})
+
+        assert response["ok"] is False
+        assert response["error"]["code"] == "invalid_request"
+
+    def test_explicit_before_after_paths_still_work(self, image_repo: Path) -> None:
+        before = image_repo / "assets" / "before.png"
+        after = image_repo / "assets" / "after.png"
+        pixels = _checkerboard(16, 16)
+        before.write_bytes(_png_bytes(pixels, 16, 16))
+        changed = list(pixels)
+        for index in range(20, 60):
+            changed[index] = (255, 255, 255)
+        after.write_bytes(_png_bytes(changed, 16, 16))
+
+        result = _asset_diff(
+            image_repo,
+            {"before_path": "assets/before.png", "after_path": "assets/after.png"},
+        )["result"]
+
+        assert result["status"] == "compared"
+        assert result["artifacts"]["overlay"]
+
+    def test_serving_a_subdirectory_still_resolves_the_base_blob(self, image_repo: Path) -> None:
+        # A monorepo subfolder opened as a workspace addresses files relative to itself; git
+        # addresses blobs from the repository root.
+        result = _asset_diff(image_repo / "assets", {"path": "card.png"})["result"]
+
+        assert result["status"] == "compared"
+        assert result["file_path"] == "card.png"
+
+    def test_a_users_own_cache_gitignore_is_left_alone(self, image_repo: Path) -> None:
+        _asset_diff(image_repo, {"path": "assets/card.png"})
+        marker = image_repo / ".intentumdiff-cache" / ".gitignore"
+        marker.write_text("mine\n", encoding="utf-8")
+
+        _asset_diff(image_repo, {"path": "assets/card.png"})
+
+        assert marker.read_text(encoding="utf-8") == "mine\n"
+
+    def test_a_non_image_path_is_an_error_not_a_comparison(self, image_repo: Path) -> None:
+        (image_repo / "notes.txt").write_text("not an image", encoding="utf-8")
+
+        response = _asset_diff(image_repo, {"path": "notes.txt"})
+
+        assert response["ok"] is False
+        assert "asset diff failed" in response["error"]["message"]
+
+
+class TestAssetDiffContract:
+    """The op is served by BOTH live-servers from one core implementation.
+
+    The Python server and the native binary (``crates/live-server``) call the same
+    ``live_handle_asset_diff``, so what they advertise and what they answer cannot drift apart —
+    which matters because the extension prefers the native binary whenever one is bundled, and
+    for a while that binary had no arm for this op at all.
+    """
+
+    def test_capabilities_advertise_the_asset_diff_op(self, image_repo: Path) -> None:
+        capabilities = _server(image_repo)._capabilities()
+
+        assert "asset_diff" in capabilities["operations"]
+
+    def test_the_response_comes_from_the_core_not_this_layer(self, image_repo: Path) -> None:
+        from intentumdiff import rust_core
+
+        request = {"op": "asset_diff", "seq": 7, "path": "assets/card.png"}
+        expected = rust_core.live_handle_asset_diff(str(image_repo), "HEAD", request, 7)
+        served = _asset_diff(image_repo, {"path": "assets/card.png"})
+
+        # Same request, same engine, same content-addressed output -> identical answer.
+        assert served == expected
diff --git a/tests/unit/test_rename_does_not_hide_behaviour.py b/tests/unit/test_rename_does_not_hide_behaviour.py
new file mode 100644
index 0000000..075852b
--- /dev/null
+++ b/tests/unit/test_rename_does_not_hide_behaviour.py
@@ -0,0 +1,79 @@
+"""A rename must never hide a behavioural change in the same function.
+
+# Why this exists
+
+Renaming a function while editing its body is one of the commonest shapes in real review —
+extract, rename, adjust. The engine collapsed that into a single `REFACTORING` change and
+discarded the body edits with the DELETION/ADDITION pair it replaced.
+
+`REFACTORING` means "structure changed, behaviour did not". So the tool was not merely missing
+a change; it was *asserting the change was safe* in its own vocabulary, and a reviewer acting
+on that label would skim past it.
+
+The guard that allowed it asked "does the function start on the same line?" and, if so, treated
+the rename as compatible without ever comparing the bodies. Same start line is evidence of
+nothing.
+
+See intentumdiff-core#18. The Rust half lives in `draft_suppressors.rs`; this is the
+acceptance half proving it survives the binding.
+"""
+
+from __future__ import annotations
+
+from intentumdiff import SemanticDiffer
+
+BEFORE = "def total(cart):\n    return sum(i.price for i in cart)\n"
+
+RENAMED_ONLY = "def calculate_total(cart):\n    return sum(i.price for i in cart)\n"
+
+# Totals over 100 now get 10% off. A reviewer MUST see this.
+BODY_CHANGED = (
+    "def total(cart):\n"
+    "    subtotal = sum(i.price for i in cart)\n"
+    "    if subtotal > 100:\n"
+    "        return subtotal * 0.9\n"
+    "    return subtotal\n"
+)
+
+RENAMED_AND_BODY_CHANGED = (
+    "def calculate_total(cart):\n"
+    "    subtotal = sum(i.price for i in cart)\n"
+    "    if subtotal > 100:\n"
+    "        return subtotal * 0.9\n"
+    "    return subtotal\n"
+)
+
+
+def _kinds(old: str, new: str) -> list[str]:
+    diff = SemanticDiffer().diff_strings(old, new, "billing.py")
+    return [str(c.change_type).rsplit(".", 1)[-1] for c in diff.changes]
+
+
+def test_a_rename_with_a_changed_body_is_not_reported_as_refactoring() -> None:
+    """THE regression.
+
+    Not "reports more changes" — the load-bearing assertion is that it does NOT claim
+    REFACTORING, because that label tells a reviewer the behaviour is unchanged.
+    """
+    kinds = _kinds(BEFORE, RENAMED_AND_BODY_CHANGED)
+    assert "REFACTORING" not in kinds, (
+        "A rename that also changed the body was labelled REFACTORING — which asserts "
+        f"behaviour did not change. The discount logic would be skimmed. Got: {kinds}"
+    )
+    assert kinds, "a rename plus a behavioural change must report something"
+
+
+def test_a_pure_rename_is_still_one_refactoring() -> None:
+    """The fix must not be 'disable rename detection'.
+
+    A rename with an untouched body is exactly what REFACTORING is for, and collapsing it to
+    one change is the value the feature adds.
+    """
+    assert _kinds(BEFORE, RENAMED_ONLY) == ["REFACTORING"]
+
+
+def test_a_body_change_without_a_rename_is_unaffected() -> None:
+    """Control: the path that always worked must keep working."""
+    kinds = _kinds(BEFORE, BODY_CHANGED)
+    assert "REFACTORING" not in kinds
+    assert len(kinds) >= 3, f"expected the inserted statements to surface, got {kinds}"