diff --git a/tests/test_package_runtime_assets_contract.sh b/tests/test_package_runtime_assets_contract.sh
index 04446f82c..8ef4a36c8 100644
--- a/tests/test_package_runtime_assets_contract.sh
+++ b/tests/test_package_runtime_assets_contract.sh
@@ -7,7 +7,7 @@ set -euo pipefail
 
 ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
 
-python3 - "$ROOT" <<'PY'
+python3 - "$ROOT" "$BASH" <<'PY'
 from __future__ import annotations
 
 import json
@@ -26,6 +26,7 @@ import zipfile
 
 
 root = pathlib.Path(sys.argv[1])
+bash_executable = pathlib.Path(sys.argv[2])
 failures: list[str] = []
 
 
@@ -382,7 +383,7 @@ def package_fixture(
     archive_name = f"codebase-memory-mcp{'-ui' if variant == 'ui' else ''}-{host_goos}-fixture{archive_suffix}"
     packaged = subprocess.run(
         [
-            "bash",
+            str(bash_executable),
             str(root / "scripts/package-release.sh"),
             host_goos,
             "fixture",
diff --git a/tests/test_release_archive_extractor_contract.sh b/tests/test_release_archive_extractor_contract.sh
index 60ce4ed27..ddb184d7b 100644
--- a/tests/test_release_archive_extractor_contract.sh
+++ b/tests/test_release_archive_extractor_contract.sh
@@ -6,7 +6,7 @@ set -euo pipefail
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd)"
 
-python3 - "$ROOT" <<'PY'
+python3 - "$ROOT" "$BASH" <<'PY'
 from __future__ import annotations
 
 import csv
@@ -25,6 +25,7 @@ from typing import Dict, List, Optional, Tuple
 
 
 root = pathlib.Path(sys.argv[1])
+bash_executable = pathlib.Path(sys.argv[2])
 extractor = root / "scripts/ci/extract-release-archives.sh"
 unix_targets = (
     "linux-amd64",
@@ -307,7 +308,13 @@ def invoke(
     args: Optional[List[str]] = None,
 ) -> subprocess.CompletedProcess:
     return subprocess.run(
-        ["bash", str(extractor), str(archive_dir), str(output_dir), *(args or count_args)],
+        [
+            str(bash_executable),
+            str(extractor),
+            str(archive_dir),
+            str(output_dir),
+            *(args or count_args),
+        ],
         cwd=root,
         text=True,
         stdout=subprocess.PIPE,
diff --git a/tests/test_venue_parity_contract.sh b/tests/test_venue_parity_contract.sh
index 48c4ea2ef..d137c01a5 100755
--- a/tests/test_venue_parity_contract.sh
+++ b/tests/test_venue_parity_contract.sh
@@ -318,6 +318,31 @@ for local, pattern, why in LOCAL_REQUIRED:
     if path.exists() and not re.search(pattern, path.read_text()):
         failures.append(f"{local}: missing required `{pattern}` — {why}")
 
+# Native Windows process lookup searches system locations before PATH. A bare
+# `bash` argv launched by embedded Python can therefore select the WSL alias
+# instead of the MSYS2 Bash that is already running this contract. Every
+# shell-hosted Python block must receive the current `$BASH` as an explicit
+# argument and launch that resolved path. Enforce this textually on every
+# maintained shell surface so the rule is deterministic on non-Windows hosts
+# too, rather than relying on a runner to happen to have the WSL alias.
+BARE_BASH_ARGV = re.compile(r"""[\[(]\s*["']bash["']\s*,""")
+shell_surfaces = list(root.glob("*.sh"))
+for directory in ("tests", "scripts", "test-infrastructure", "pkg"):
+    base = root / directory
+    if not base.exists():
+        continue
+    shell_surfaces.extend(base.rglob("*.sh"))
+for path in sorted(shell_surfaces):
+    text = path.read_text(encoding="utf-8")
+    for match in BARE_BASH_ARGV.finditer(text):
+        number = text.count("\n", 0, match.start()) + 1
+        relative = path.relative_to(root).as_posix()
+        failures.append(
+            f"{relative}:{number}: embedded Python must launch the current "
+            "$BASH by explicit argv path; bare `bash` is WSL-alias-sensitive "
+            "under native Windows process lookup"
+        )
+
 if failures:
     print("VENUE PARITY CONTRACT VIOLATED — one harness, every venue:")
     for failure in failures: