tests: short IDs for long string parameters (Windows env-var cap)

tests/conftest.py

@@ -0,0 +1,25 @@
+"""Suite-wide pytest hooks.
+
+Long string parameters get short test IDs. pytest puts every test's node ID in the
+PYTEST_CURRENT_TEST environment variable, and Windows caps one environment
+variable at 32,767 characters. A ReDoS test that parametrizes on its own
+pathological payload (e.g. `"COMMAREA " * 5000`) therefore fails on Windows during
+setup with "the environment variable is longer than 32767 characters", before the
+test body runs, while Linux and macOS pass. That surfaced first on the labelled
+full-suite Windows jobs for #3404, from test_commarea_contract.py (#3369).
+
+A string longer than _MAX_ID_CHARS becomes its first characters plus a length and
+a short content hash. The ID stays readable, stays stable across runs, and stays
+distinct for payloads that share a prefix.
+"""
+
+import hashlib
+
+_MAX_ID_CHARS = 64
+
+
+def pytest_make_parametrize_id(val):
+    if isinstance(val, str) and len(val) > _MAX_ID_CHARS:
+        digest = hashlib.sha256(val.encode("utf-8", "surrogatepass")).hexdigest()[:8]
+        return f"{val[:40]!r}...len{len(val)}-{digest}"
+    return None