diff --git a/CHANGELOG.md b/CHANGELOG.md
index adcda26..b190092 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -48,6 +48,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- **Characterization tests immune to local fixture pollution** (GH #135
+  residual). `test_graphbuffer_baseline` copies the fixture including any
+  on-disk `README_AI.md` left by a repo-root `scan-all` (gitignored by
+  #136, so only invisible locally); the structural rewrite's
+  enrichment-preserve logic (GH #38) then kept the stale
+  `<!-- enrichment: ok -->` marker and drifted the goldens — CI green,
+  local red, forever. The fixture copy now ignores `README_AI.md`.
 - **CLAUDE.md outdated-hint: one version source + stderr** (GH #161).
   `check_outdated` compared the injected version against
   `importlib.metadata` (stale under editable installs — dist-info is baked
diff --git a/tests/characterization/test_graphbuffer_baseline.py b/tests/characterization/test_graphbuffer_baseline.py
index b9ed72d..bb9ee32 100644
--- a/tests/characterization/test_graphbuffer_baseline.py
+++ b/tests/characterization/test_graphbuffer_baseline.py
@@ -72,7 +72,10 @@ def _copy_fixture(tmp_path: Path) -> Path:
     # into the root dir's enrich prompt as "Parent: ...") is deterministic —
     # pytest's tmp_path basename (test-name + counter) is not stable across runs.
     proj = tmp_path / "wsroot" / "project"
-    shutil.copytree(FIXTURE, proj)
+    # Ignore on-disk README_AI.md pollution from repo-root scan-all (#135):
+    # a stale `<!-- enrichment: ok -->` marker would be preserved by the
+    # structural rewrite (GH #38) and drift the goldens on local runs.
+    shutil.copytree(FIXTURE, proj, ignore=shutil.ignore_patterns("README_AI.md"))
     return proj