Add Disk Usage plugin

.bb/plugins.json

@@ -4,6 +4,7 @@
   "name": "charpeni-plugins",
   "plugins": [
     { "name": "dependabot", "source": "./plugins/dependabot" },
+    { "name": "disk-usage", "source": "./plugins/disk-usage" },
     { "name": "system-monitor", "source": "./plugins/system-monitor" }
   ]
 }

README.md

@@ -29,6 +29,7 @@ bb plugin install system-monitor@charpeni
 | Plugin                                   | Description                                                                        |
 | ---------------------------------------- | ---------------------------------------------------------------------------------- |
 | [Dependabot](plugins/dependabot)         | Review GitHub Dependabot alerts by dependency and send grouped fixes to BB agents. |
+| [Disk Usage](plugins/disk-usage)         | See what's taking up disk space on the bb server host, with drill-down.            |
 | [System Monitor](plugins/system-monitor) | Live CPU, memory, disk, load, and uptime statistics for the bb server host.        |
 
 Each plugin can also be installed directly, without the marketplace:

plugins/disk-usage/.gitignore

@@ -0,0 +1,2 @@
+dist/
+node_modules/

plugins/disk-usage/README.md

@@ -0,0 +1,40 @@
+# Disk Usage
+
+See what's taking up disk space on the bb server host, `ncdu`-style: scan a
+directory, get its immediate children sorted by recursive size, and drill down
+until you find the culprit.
+
+## What it does
+
+- **Disk Usage panel** — a sidebar panel that scans a directory (default: the
+  server home directory) and lists its children largest-first with share bars,
+  breadcrumbs, drill-down by click, and a free-form path input. While a scan
+  runs, a live progress card streams entries visited, bytes so far, and the
+  directory currently being walked.
+- **Per-path cache** — the last result for each path is kept in memory, so
+  drilling back up (or reopening the panel) is instant; the header shows the
+  snapshot's age and **Rescan** forces a fresh walk. Concurrent requests for
+  the same path join a single walk.
+- **`bb disk-usage` CLI** — the same scan for agents and scripts:
+
+  ```sh
+  bb disk-usage                     # scan the server home directory
+  bb disk-usage /var --top 10       # the 10 largest entries under /var
+  bb disk-usage ~/GitHub --json     # machine-readable output
+  bb disk-usage --refresh           # bypass the per-path cache
+  ```
+
+## How sizes are measured
+
+- Sizes are **allocated disk blocks** (`blocks × 512`), not apparent size, so
+  sparse files are reported by what they actually occupy.
+- Symlinks are **never followed** and count as zero bytes.
+- Hardlinked files are counted **once** per scan.
+- Unreadable entries (permissions, races) are skipped and counted, never fatal.
+- Directories are walked concurrently (bounded), and a scan visits at most
+  500,000 entries; past that it stops descending and the result is flagged as
+  truncated, with the budget spread across the tree rather than exhausted
+  depth-first.
+
+The scan runs on the machine hosting the bb server, so paths are server-host
+paths — the same model as the System Monitor plugin.