Add tests/test_genericarchive_contract.py: drift probes for GenericArchive

4 probes covering the capabilities that test the heavyweight/skipped
unit-tier tests would otherwise exercise:
- LPP cache server still serves text via any_loc_open
- LPP data server still serves binary via any_loc_open
- MMS FPI burst products still resolve via the CDA mirror (smaller
  time range than the dropped unit-tier test to keep daily cron cheap)
- Vbias HTML resource still returns a parseable HTML document

Author: jeandet

tests/test_genericarchive_contract.py

@@ -0,0 +1,65 @@
+"""Daily real-server probes for GenericArchive upstream-drift detection.
+
+These tests run on the contract tier (daily cron) and hit the live
+LPP and CDA mirror endpoints. Failures here mean an upstream changed
+something we depend on — the relevant cassettes in
+tests/cassettes/test_direct_archive_downloader/ or test_file_access/
+need re-recording, or a code-side adjustment.
+
+Keep small (4-5 probes); the bulk of GenericArchive coverage runs on
+the unit tier via cassettes.
+"""
+
+from __future__ import annotations
+
+import unittest
+from datetime import datetime
+
+import pytest
+
+import speasy as spz
+from speasy.core.any_files import any_loc_open
+from speasy.products import SpeasyVariable
+
+pytestmark = pytest.mark.contract
+
+
+class GenericArchiveContractProbes(unittest.TestCase):
+
+    def test_can_open_remote_http_text_resource(self) -> None:
+        """LPP cache server still serves HTML at /cache/."""
+        f = any_loc_open(
+            "http://sciqlop.lpp.polytechnique.fr/cache/", mode="r"
+        )
+        content = f.read()
+        self.assertIn("<", content)
+
+    def test_can_open_remote_http_binary_resource(self) -> None:
+        """LPP data server still serves binary files at /data/."""
+        f = any_loc_open(
+            "https://hephaistos.lpp.polytechnique.fr/data/LFR/SW/LFR-FSW/3.0.0.0/fsw",
+            mode="rb",
+        )
+        content = f.read(4)
+        self.assertGreater(len(content), 0)
+
+    def test_mms_fpi_burst_returns_data(self) -> None:
+        """MMS FPI burst products still resolve via the CDA mirror.
+        Skipped from the unit tier because cassettes are ~370-650 MB."""
+        result = spz.get_data(
+            "archive/cda/MMS/MMS1/FPI/BURST/MOMS/mms1_fpi_brst_l2_des_moms/mms1_des_energyspectr_mz_brst",
+            "2018-01-30T10",
+            "2018-01-30T11",  # 1 hour to limit transfer
+            disable_cache=True,
+        )
+        self.assertIsInstance(result, SpeasyVariable)
+
+    def test_remote_text_resource_assertion_still_holds(self) -> None:
+        """The Vbias HTML resource still returns a parseable HTML document.
+        Skipped from the unit tier because the response body is ~137 MB."""
+        f = any_loc_open(
+            "https://hephaistos.lpp.polytechnique.fr/data/jeandet/Vbias.html",
+            mode="r",
+        )
+        head = f.read(1024)
+        self.assertIn("<!DOCTYPE", head.upper())