feat(host_agent): a disk out of inodes reads as full (#5745)

VDNT-Util01's / ran out of inodes (956 free of 60.8M) with 274G of space
left; every file create failed and Steward's page read healthy at 66%.

- Agent 1.13.0 reports each mount's inodes (statvfs; a filesystem reporting
  none, like btrfs, is left without).
- Ingest records inodes_used_pct per mount, and disk_used_pct_worst is the
  fullest mount by space or inodes, so existing disk-full rules and the
  overview see it.
- The host's health strip, the Hosts widget and the host glance grade / by
  whichever is fuller and name inodes when they are ("Disk / 66% · inodes
  100%", "Inodes on / ... past its critical threshold").

Hosts pick up the inode figures once their agent is updated to 1.13.0.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/plugins/host_agent/test_agent_collectors.py

@@ -78,10 +78,19 @@ def test_collect_storage():
         r.free = free
         return r
 
-    with patch.object(a.shutil, "disk_usage", side_effect=_fake_usage):
+    # Inodes (#5745): "/" has 100 with 1 free; /mnt/data (btrfs-like) reports none.
+    inodes = {"/": (100, 1), "/mnt/data": (0, 0)}
+
+    def _fake_statvfs(path):
+        files, ffree = inodes[path]
+        return type("S", (), {"f_files": files, "f_ffree": ffree})()
+
+    with patch.object(a.shutil, "disk_usage", side_effect=_fake_usage), \
+            patch.object(a.os, "statvfs", side_effect=_fake_statvfs):
         out = a.collect_storage(["/", "/mnt/data"])
     assert out == [
-        {"mount": "/",         "total_bytes": 1000, "used_bytes": 400},
+        {"mount": "/",         "total_bytes": 1000, "used_bytes": 400,
+         "inodes_total": 100, "inodes_used": 99},
         {"mount": "/mnt/data", "total_bytes": 2000, "used_bytes": 500},
     ]
 

tests/plugins/host_agent/test_routes_expand_metrics.py

@@ -96,3 +96,18 @@ def test_expand_empty_storage_emits_no_disk_worst():
     names = {r.metric_name for r in rows}
     assert "disk_used_pct_worst" not in names
     assert "cpu_pct" in names
+
+
+def test_a_mount_out_of_inodes_is_the_fullest_disk():
+    """#5745: VDNT-Util01's / was 66% full by space and 100% by inodes, every
+    file create failed, and Steward read it healthy. Inode use is recorded per
+    mount, and the fullest disk is the fullest by either."""
+    sample = _sample()
+    sample["storage"][0].update(inodes_total=60_850_176, inodes_used=60_849_220)
+    rows = _expand_sample_to_metrics(sample, "testhost", NOW)
+    (inodes,) = _by_metric(rows, "inodes_used_pct")
+    assert inodes.resource_name == "testhost:/" and inodes.value > 99.99
+    (worst,) = _by_metric(rows, "disk_used_pct_worst")
+    assert worst.value == inodes.value
+    # A filesystem reporting no inodes (btrfs) records none.
+    assert len(_by_metric(_expand_sample_to_metrics(_sample(), "testhost", NOW), "inodes_used_pct")) == 0