fix(host_agent): disks behind a RAID controller each keep their own name (#5806)

smartctl reports every disk behind a PERC/MegaRAID controller as /dev/bus/0
with type megaraid,N; the helper named a drive by its path alone, so all of
VDNT-Docker02's and Docker03's disks read as one drive "0", each overwriting
the last. The slot is now part of the name (bus0-megaraid3), and Steward gives
a repeated name an ordinal so two drives never share a series. Agent 1.20.1.

fix(ansible): Steward stopping mid-run logs no traceback (#5749)

The run's done-callback called exception() on a cancelled task, which raises;
it now logs a run cut short by shutdown at INFO. A finished run's in-memory
state is dropped by a timer rather than a sleeping task, which shutdown found
still pending.

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

docs/plugins/host-agent-design.md

@@ -266,7 +266,7 @@ The figures are recorded at most once every 30 s, whichever manager sent them, s
 
 A maintenance job on a swarm node opens a second window over `docker` / `swarm` beside its host's (`maintenance._swarm_window`). An alert the drain or reboot causes then waits for the job, and one still firing when the window ends is sent then.
 
-### Drive health (1.20.0, #5789)
+### Drive health (1.20.0, #5789; 1.20.1, #5806)
 
 Reading SMART needs root, so the root helper does it, as the one action on its fixed list that only reads: `drives`. Hourly, and at start, the agent leaves a `drives` request. The helper runs `smartctl --scan-open` to find the drives itself (the request names none), reads each with `smartctl --json -a -d <type> <dev>`, and writes a summary to `/var/lib/steward-maint/drives.json` (0644). It writes no job result, because a drive read is not a maintenance job. The agent's newest copy rides every sample, as updates do.
 
@@ -277,7 +277,7 @@ smartctl ≥ 7.0 answers in JSON, the same on every distribution and for SATA, S
 - reallocated / pending / offline-uncorrectable sectors for ATA, and life used where the drive reports it;
 - grown defects for SCSI.
 
-A drive with no SMART (a virtual disk, a bridge that hides it) reads `available: false`, and one smartctl couldn't open carries `error`.
+A drive with no SMART (a virtual disk, a bridge that hides it) reads `available: false`, and one smartctl couldn't open carries `error`. Disks behind a RAID controller share one path (`/dev/bus/0`) and differ by the slot in their type (`megaraid,3`), so the slot is part of the name: `bus0-megaraid3` (1.20.1, #5806). Steward also gives a repeated name an ordinal (`0#2`), so two drives never share a series.
 
 Steward judges the figures in `drives.py`, so the judgment can change without an agent update: