feat(health): flag NVMe PCIe links below capability (lane-sharing) — 0.38.0

check_pcie_links() warns when an NVMe drive negotiates fewer lanes than it
supports — almost always motherboard lane-sharing (a GPU/second card or another
M.2 stealing lanes), the case the user asked about — and reports speed-only
reductions as info (slower slot / idle ASPM). GPU is excluded: NVIDIA drops its
PCIe gen+width at idle, so a snapshot would false-alarm. Reuses inventory
read_link/nvme_controllers (refactored to public). Wired into run_health_checks;
+tests. Folded into the 0.38.0 PCIe work.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_health.py

@@ -1,8 +1,18 @@
 """Tests for the M4 health report's log scanner (synthetic input)."""
 
 import unittest
+from pathlib import Path
+from unittest import mock
 
-from rigdoctor.core.health import CRITICAL, WARNING, run_health_checks, scan_journal_text
+from rigdoctor.core import health
+from rigdoctor.core.health import (
+    CRITICAL,
+    INFO,
+    WARNING,
+    check_pcie_links,
+    run_health_checks,
+    scan_journal_text,
+)
 
 
 class HealthScanTests(unittest.TestCase):
@@ -42,5 +52,34 @@ class HealthScanTests(unittest.TestCase):
         self.assertEqual(ranks, sorted(ranks))
 
 
+class PcieLinkCheckTests(unittest.TestCase):
+    def _with_link(self, cur_g, cur_w, max_g, max_w):
+        # one fake NVMe controller returning the given link tuple
+        return (mock.patch("rigdoctor.core.inventory.nvme_controllers",
+                           return_value=[("nvme0", Path("/x"))]),
+                mock.patch("rigdoctor.core.inventory.read_link",
+                           return_value=(cur_g, cur_w, max_g, max_w)))
+
+    def test_reduced_width_is_a_warning_about_lane_sharing(self):
+        ctrls, link = self._with_link(4, "2", 4, "4")  # Gen4 x2 but supports x4
+        with ctrls, link:
+            findings = check_pcie_links()
+        self.assertEqual(len(findings), 1)
+        self.assertEqual(findings[0].severity, WARNING)
+        self.assertIn("lane-sharing", findings[0].detail)
+
+    def test_reduced_speed_only_is_info(self):
+        ctrls, link = self._with_link(3, "4", 4, "4")  # Gen3 x4 but supports Gen4
+        with ctrls, link:
+            findings = check_pcie_links()
+        self.assertEqual(len(findings), 1)
+        self.assertEqual(findings[0].severity, INFO)
+
+    def test_full_speed_no_finding(self):
+        ctrls, link = self._with_link(4, "4", 4, "4")
+        with ctrls, link:
+            self.assertEqual(check_pcie_links(), [])
+
+
 if __name__ == "__main__":
     unittest.main()