Prober: no claims under PROBE_MIN_FREE_GB free on the NVMe

At ~200 articles/s what the prober stores (inspections, par2 file lists,
the WAL) took ~0.8-1.1 GB an hour of homelab's root, and nothing stopped it
at the 10 GB floor. Below 12 GB free it claims nothing (resumed 1 GB above):
the lanes go dry and its share shrinks to its minimum.

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

app/services/disk_space.ts

@@ -0,0 +1,40 @@
+import { statfs } from 'node:fs/promises'
+import logger from '@adonisjs/core/services/logger'
+
+/** How often free space is measured. */
+const CHECK_MS = 60_000
+/** Resumed only this much above the floor: not paused and resumed at every flush. */
+const MARGIN_GB = 1
+
+/**
+ * Free space on the filesystem holding `path`, against a floor: low below it, again fine MARGIN_GB above it. In a
+ * container `/` is an overlay on the host's Docker root, which on homelab is the NVMe the catalog and the WAL are on.
+ * The prober filled it ~0.8–1.1 GB an hour at ~200 articles/s, and nothing stopped it at the 10 GB floor (LOG.md
+ * 2026-10-18 (77)). Off when the floor is 0.
+ */
+export class DiskSpace {
+  private checkedAt = 0
+  private low = false
+
+  constructor(
+    private what: string,
+    private path: string,
+    private floorGb: number,
+    private free: (path: string) => Promise<number> = async (p) => {
+      const s = await statfs(p)
+      return s.bavail * s.bsize
+    },
+    private checkMs = CHECK_MS
+  ) {}
+
+  async short(): Promise<boolean> {
+    if (!this.floorGb) return false
+    if (Date.now() - this.checkedAt < this.checkMs) return this.low
+    this.checkedAt = Date.now()
+    const gb = (await this.free(this.path)) / 1e9
+    const was = this.low
+    this.low = gb < this.floorGb + (was ? MARGIN_GB : 0)
+    if (this.low !== was) logger.info(`${gb.toFixed(1)} GB free (floor ${this.floorGb} GB): ${this.what} ${this.low ? 'paused' : 'resumed'}.`)
+    return this.low
+  }
+}