PLAN: Space scans a disk or a pool, from a dropdown

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

PLAN.md

@@ -327,17 +327,19 @@ something long in one, switch away and back, refresh — it's all still there.
   users`, `hamlab user-rm <user>`; `hamlab install` names the first account after the
   service user. Not done: a read-only viewer role.
 - **Space tab** — **shipped 2026-09-22** (`internal/space`, `internal/api/space.go`,
-  `Space.tsx`), asked for as "exactly WizTree": what is using a disk. A **disk** is picked at
-  the top, not a partition: the scan covers every filesystem the disk backs — its partitions'
-  mountpoints, and for a disk in a ZFS pool every mounted dataset of the pool (any of `tank`'s
-  eight disks shows `tank`). The walk runs as a helper process, `hamlab space-walk <roots>`,
+  `Space.tsx`), asked for as "exactly WizTree": what is using a disk. The unit is a whole
+  volume, picked from a dropdown at the top: a **disk on its own** (every filesystem its
+  partitions back) or a **ZFS pool as a whole** (every mounted dataset) — a pool's member
+  disks are listed under it with the layout (raidz2, 8 disks: sda …) and never offered
+  apart, since one disk's share of a pool means nothing (Mitchell's call, same day, after a
+  first cut that listed the disks as chips). The walk runs as a helper process, `hamlab space-walk <roots>`,
   as root through `priv` when the host allows (so `/var/lib/docker` and `/root` count), 32
   workers reading directories depth-first, never crossing a filesystem boundary by itself;
   each root is grafted into one tree at its path. Files under 128 KiB are not kept one by one
   but summed per folder as "N smaller files" — what keeps a scan of millions of files to tens
   of MB in the daemon; the tree crosses back as a varint stream (`codec.go`), and the helper's
   memory goes with it. core's root: 646k files in ~1.2 s. Progress (files, bytes, current
-  folder) every 250 ms; Cancel sends SIGTERM. The page: disk chips → Scan/Rescan → **Folders**
+  folder) every 250 ms; Cancel sends SIGTERM. The page: picker → Scan/Rescan → **Folders**
   (a tree largest-first: size, share of parent as a bar, files, folders, modified; expand in
   place) over a **treemap** of the selected folder — squarified, nested to the file, tiles
   coloured by kind (video, images, audio, archives & disk images, documents, code & config,