Read a stopped container instead of claiming there is nothing to read

A project that was merely stopped reported "This project has no container
or snapshot image yet, so there is nothing to compare against the base
image" — with its container sitting right there — and Update stayed
disabled. Start it and the checks passed, which is the tell: the staleness
probe had only two sources, a *running* container via `docker exec` or the
project's snapshot image.

The snapshot is not a checkpoint. `commit_container_snapshot` runs only
before a container is destroyed (a config-change recreate) or inside a
migration, never on stop, so a project in daily use for a year can have no
snapshot at all — and five of the six projects on the box that reported
this had none. Absence of a snapshot was being read as absence of anything
to inspect.

So probe the stopped container directly: commit its writable layer to a
throwaway image, probe that, drop it. A stopped container now also outranks
the snapshot, for the same reason a running one already did — the snapshot
lags it by everything installed since the last commit. `pick_probe_source`
is the whole decision and is unit-tested; the message it used to emit now
describes only the case it is true of, no container and no snapshot.

Two things found on the way, both documented in CLAUDE.md:

`bollard` never hands back the image id from a commit — its `Commit` model
deserialises "ID" while the daemon sends "Id" — so the probe image has to be
tagged, and a tagged image is dangling-proof and therefore invisible to
`sweep_orphaned_snapshots`, `reap_stale_migration_pins` and
`scrub_secrets_from_snapshots` alike. Without a reaper of its own a crashed
probe would leak a multi-gigabyte image that nothing could ever reclaim, so
`reap_probe_images` runs at startup beside `reap_probe_containers`, age-gated
for the same reason that one is: `reference=` is daemon-wide and a second
instance's live probe matches the glob.

It removes by tag, never by image id: a force removal by id untags an image
everywhere, which is how a first draft of the reaper test deleted an
unrelated `alpine:latest`. Names are unique per call rather than stable per
container, because container ids do not survive a recreate and two
overlapping probes would otherwise fight over one tag.

Verified against the container that reported the bug: 13,365 paths and an
apt delta of cmake, ffmpeg, libobs-dev, qt6-base-dev and nine more — the
migration payload the Update flow could not see. 546 unit tests plus three
live-Docker tests pass; no new clippy warnings.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019RSaoDLovVV2wmH4H8VVxz

app/src-tauri/src/lib.rs

@@ -263,12 +263,20 @@ pub fn run() {
             // logged warning rather than a failed start.
             //
             // Ordering matters. Probes are removed first because a probe holds
-            // an image open and the sweep will not force; pins are untagged
+            // an image open and the sweep will not force — both the probe
+            // containers and the probe images, the latter being the one orphan
+            // the sweep can never reach on its own; pins are untagged
             // second so the images they were holding are dangling by the time
             // the sweep lists them; the sweep runs last and collects both.
             let projects_store_for_cleanup = projects_store_setup.clone();
             tauri::async_runtime::spawn(async move {
                 crate::docker::reap_probe_containers().await;
+                // Probe *images* too, and for a sharper reason: a probe
+                // container merely pins an image the sweep then refuses to
+                // touch, whereas a leftover probe image is tagged and so
+                // nothing else in this app can ever collect it. See
+                // `reap_probe_images`.
+                crate::docker::reap_probe_images().await;
                 let reaped = crate::docker::reap_stale_migration_pins().await;
                 if reaped > 0 {
                     log::info!("Startup housekeeping dropped {} stale rollback pin(s)", reaped);