diff --git a/scripts/docker-runtime-smoke.sh b/scripts/docker-runtime-smoke.sh
index ad20b5c..c2c6b85 100644
--- a/scripts/docker-runtime-smoke.sh
+++ b/scripts/docker-runtime-smoke.sh
@@ -18,7 +18,9 @@ cleanup() {
   docker logs "$CONTAINER_NAME" >/dev/null 2>&1 || true
   docker rm -f "$CONTAINER_NAME" >/dev/null 2>&1 || true
   if [[ -z "${VOXVERA_DOCKER_SMOKE_TMPDIR:-}" ]]; then
-    rm -rf "$TMP_DIR"
+    chmod -R u+w "$TMP_DIR" 2>/dev/null || true
+    docker run --rm -v "$TMP_DIR:/cleanup" python:3.11-slim sh -lc 'rm -rf /cleanup/* /cleanup/.[!.]* /cleanup/..?* 2>/dev/null || true' >/dev/null 2>&1 || true
+    rm -rf "$TMP_DIR" 2>/dev/null || true
   fi
 }
 trap cleanup EXIT
diff --git a/tests/test_integrity.py b/tests/test_integrity.py
index 7e786d1..27aeabd 100644
--- a/tests/test_integrity.py
+++ b/tests/test_integrity.py
@@ -97,6 +97,14 @@ def test_docker_runtime_assets_are_present():
     assert "scripts/docker-runtime-smoke.sh" in ci_workflow
     assert "starts an in-container Tor daemon" in docker_doc
 
+
+def test_support_matrix_path_has_runtime_fallbacks():
+    base_platform = (REPO_ROOT / "voxvera" / "platforms" / "base.py").read_text(encoding="utf-8")
+
+    assert "VOXVERA_SUPPORT_MATRIX_PATH" in base_platform
+    assert 'Path.cwd() / "support-matrix.json"' in base_platform
+    assert 'Path("/opt/voxvera/support-matrix.json")' in base_platform
+
 def test_locale_completeness():
     """Verify that all non-English locales have the same keys as English."""
     locales_dir = REPO_ROOT / "voxvera" / "locales"
diff --git a/voxvera/platforms/base.py b/voxvera/platforms/base.py
index c49b389..80772fd 100644
--- a/voxvera/platforms/base.py
+++ b/voxvera/platforms/base.py
@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import json
+import os
 import platform
 import shutil
 import subprocess
@@ -33,6 +34,20 @@ class PlatformAdapter:
 
     @property
     def support_matrix_path(self) -> Path:
+        candidates = []
+        env_path = os.environ.get("VOXVERA_SUPPORT_MATRIX_PATH")
+        if env_path:
+            candidates.append(Path(env_path))
+        candidates.extend(
+            [
+                self.repo_root / "support-matrix.json",
+                Path.cwd() / "support-matrix.json",
+                Path("/opt/voxvera/support-matrix.json"),
+            ]
+        )
+        for candidate in candidates:
+            if candidate.exists():
+                return candidate
         return self.repo_root / "support-matrix.json"
 
     def _run_capture(self, args: list[str]) -> tuple[bool, str]: