Take the review: cache the stopped probe, and never let it cost an answer

Six findings, all real. The one that mattered: `getContainerStaleness` is
called from a `useEffect` that fires whenever the container settles, so
merely opening a stopped project's Overview now committed its whole writable
layer — 44 s on a real project, against ~3 s for the snapshot probe it
replaced. Shipping that would have traded one bad banner for a bad page.

A stopped container's writable layer cannot change, so the probe is exactly
cacheable: `STOPPED_MANIFEST_CACHE` keys on the container's `FinishedAt`,
which moves on every stop. Cold 2967 ms, warm 1 ms, measured. A live test
asserts the restart case as well as the hit, because a cache that failed to
invalidate would plan a migration against a filesystem the project no longer
has — verified by breaking the token and watching that assertion fail.

Skipping the probe for projects that are not stale looked like the cheaper
fix and is unsafe: the deltas would be empty while `probeSettled` stayed
true, and the migrate action in the project menu is not gated on the banner,
so the pre-flight would report nothing to copy while the backend was told to
copy nothing. That is the hazard `canMigrate`'s comment already warns about.
Not done, and written down so it is not tried again.

Also from the review:

- A failed commit no longer costs an answer the snapshot could have given.
  Before this feature a stopped project read its snapshot directly, so
  surfacing this error would have made the banner worse than it was — and
  the failure modes are where the fallback earns its keep: a full disk (the
  commit allocates the whole layer, the snapshot probe allocates nothing)
  and a 409 from a concurrent claim.
- The probe no longer commits while the project is claimed. The collision is
  not symmetric: the probe losing is a retryable `probe_error`, but
  `start_project_container` removes the old container with a hard `?`, so a
  remove that raced a commit would fail the user's Start with an opaque
  error. `stopped_probe_policy` reads `project_lock::held` and probes the
  snapshot instead, or defers with a message that says so.
- The cleanup-failure warning claimed the next probe of the same container
  would reclaim the leftover. Unique names made that false the moment they
  landed; it is `reap_probe_images` that collects it.
- The TS binding still called the command read-only, which is how the
  auto-refresh got added in the first place.
- CLAUDE.md still documented the stable `triple-c-probe-{cid}:latest` name
  this PR removed as unsafe.

548 unit tests, 752 frontend tests, 4 live-Docker tests. Clippy unchanged at
44 warnings.

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

.gitea/workflows/build-app-preview.yml

@@ -299,8 +299,34 @@ jobs:
       - name: Install frontend dependencies
         working-directory: ./app
         run: |
-          rm -rf node_modules package-lock.json
-          npm install
+          # `npm ci` — from the lockfile, never resolving afresh.
+          #
+          # This used to be `rm -rf node_modules package-lock.json && npm
+          # install`, which deleted the lockfile "to ensure correct
+          # platform-specific bindings" (2d4fce9). That made every build
+          # re-resolve the whole tree against the registry, so a dependency
+          # publishing a new version could break CI with no change to this
+          # repo — and one did. Deleting the lockfile then hit a null
+          # dereference in npm 10.9.8's arborist peer-set resolver:
+          #
+          #   npm error Cannot read properties of null (reading 'edgesOut')
+          #     at #loadPeerSet (.../build-ideal-tree.js:1289:38)
+          #
+          # reached through vite → @vitejs/devtools → @vitejs/devtools-vitest
+          # → vitest@* → @vitest/browser-playwright → jsdom@* → canvas.
+          # Reproduced exactly by removing the lockfile locally on the same
+          # Node 22.23.2 the runner installs.
+          #
+          # The binding worry is obsolete: the committed lockfile records 25
+          # rollup platform variants, and `npm ci` on Linux installs precisely
+          # rollup-linux-x64-{gnu,musl} and @esbuild/linux-x64. Verified, along
+          # with a clean tsc, a successful build and 752 passing tests from the
+          # resulting tree.
+          #
+          # Do not "fix" a future dependency error by deleting the lockfile
+          # again. If `npm ci` refuses, package.json and the lockfile have
+          # genuinely diverged, and the fix is to commit an updated lockfile.
+          npm ci
 
       - name: Install Tauri CLI
         working-directory: ./app
@@ -335,7 +361,6 @@ jobs:
         run: |
           mkdir -p artifacts
           cp app/src-tauri/target/release/bundle/appimage/*.AppImage artifacts/ 2>/dev/null || true
-          cp app/src-tauri/target/release/bundle/appimage/*.zsync artifacts/ 2>/dev/null || true
           ls -la artifacts/
 
       # Assets, not workflow artifacts — see the note at the top of this file.
@@ -427,8 +452,10 @@ jobs:
       - name: Install frontend dependencies
         working-directory: ./app
         run: |
-          rm -rf node_modules
-          npm install
+          # `npm ci` here too, so all three platforms install identically and
+          # none of them can re-resolve the tree mid-release. Windows already
+          # did. See the Linux job for what a fresh resolution cost us.
+          npm ci
 
       - name: Install Tauri CLI
         working-directory: ./app

.gitea/workflows/build-app.yml

@@ -172,8 +172,34 @@ jobs:
       - name: Install frontend dependencies
         working-directory: ./app
         run: |
-          rm -rf node_modules package-lock.json
-          npm install
+          # `npm ci` — from the lockfile, never resolving afresh.
+          #
+          # This used to be `rm -rf node_modules package-lock.json && npm
+          # install`, which deleted the lockfile "to ensure correct
+          # platform-specific bindings" (2d4fce9). That made every build
+          # re-resolve the whole tree against the registry, so a dependency
+          # publishing a new version could break CI with no change to this
+          # repo — and one did. Deleting the lockfile then hit a null
+          # dereference in npm 10.9.8's arborist peer-set resolver:
+          #
+          #   npm error Cannot read properties of null (reading 'edgesOut')
+          #     at #loadPeerSet (.../build-ideal-tree.js:1289:38)
+          #
+          # reached through vite → @vitejs/devtools → @vitejs/devtools-vitest
+          # → vitest@* → @vitest/browser-playwright → jsdom@* → canvas.
+          # Reproduced exactly by removing the lockfile locally on the same
+          # Node 22.23.2 the runner installs.
+          #
+          # The binding worry is obsolete: the committed lockfile records 25
+          # rollup platform variants, and `npm ci` on Linux installs precisely
+          # rollup-linux-x64-{gnu,musl} and @esbuild/linux-x64. Verified, along
+          # with a clean tsc, a successful build and 752 passing tests from the
+          # resulting tree.
+          #
+          # Do not "fix" a future dependency error by deleting the lockfile
+          # again. If `npm ci` refuses, package.json and the lockfile have
+          # genuinely diverged, and the fix is to commit an updated lockfile.
+          npm ci
 
       - name: Install Tauri CLI
         working-directory: ./app
@@ -200,10 +226,23 @@ jobs:
       - name: Collect artifacts
         run: |
           mkdir -p artifacts
+          # The versioned AppImage only. The update channel's copy lives in
+          # bundle/appimage/update-channel/ precisely so this glob cannot pick
+          # it up and publish an 80 MB duplicate under a second name.
           cp app/src-tauri/target/release/bundle/appimage/*.AppImage artifacts/ 2>/dev/null || true
-          cp app/src-tauri/target/release/bundle/appimage/*.zsync artifacts/ 2>/dev/null || true
           ls -la artifacts/
 
+          # A green job that published nothing is the worst outcome available:
+          # the release exists, carries no AppImage, and nobody is told. The
+          # `|| true` above is there so a missing bundle does not mask the real
+          # error, which makes this check the thing that catches it.
+          shopt -s nullglob
+          collected=(artifacts/*)
+          if [ ${#collected[@]} -eq 0 ]; then
+            echo "No artifacts collected — the bundler produced nothing." >&2
+            exit 1
+          fi
+
       - name: Upload to Gitea release
         if: gitea.event_name == 'push'
         env:
@@ -286,7 +325,11 @@ jobs:
         if: gitea.event_name == 'push'
         env:
           GH_PAT: ${{ secrets.GH_PAT }}
-        run: bash scripts/publish-update-channel.sh artifacts
+          GITEA_TOKEN: ${{ secrets.REGISTRY_TOKEN }}
+          GITEA_SHA: ${{ gitea.sha }}
+        run: |
+          bash scripts/publish-update-channel.sh \
+            app/src-tauri/target/release/bundle/appimage/update-channel
 
   build-macos:
     runs-on: macos-latest
@@ -343,8 +386,10 @@ jobs:
       - name: Install frontend dependencies
         working-directory: ./app
         run: |
-          rm -rf node_modules
-          npm install
+          # `npm ci` here too, so all three platforms install identically and
+          # none of them can re-resolve the tree mid-release. Windows already
+          # did. See the Linux job for what a fresh resolution cost us.
+          npm ci
 
       - name: Install Tauri CLI
         working-directory: ./app

CLAUDE.md

@@ -436,6 +436,63 @@ security update. Migration is the non-destructive way out; Reset is the destruct
   bump: churn on the old base, and it would consume the "you should migrate" signal without
   migrating. `get_container_staleness` surfaces it; `migrate_project_to_base` acts on it.
 - **A missing lineage label means "unknown, probe instead", never "stale".**
+- **The snapshot image is not a checkpoint — never read its absence as "nothing to inspect".**
+  `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 legitimately
+  have no `triple-c-snapshot-{id}:latest` at all, and one that has is stale by everything installed
+  since. `pick_probe_source` therefore reads a *stopped* container directly — commit its writable
+  layer to a unique `triple-c-probe-*` image, probe that, drop it — and ranks it **above** the snapshot,
+  for the same reason a running container already outranked it. Assuming a snapshot existed is what
+  made a stopped, never-recreated project report "no container or snapshot image yet" with its
+  container sitting right there, and left Update disabled on the projects furthest behind.
+- **`bollard` never gives you the image id back from a commit.** Its `Commit` response model
+  deserialises `"ID"`; the daemon sends `"Id"`, so `commit_container` returns `id: None` every time
+  (verified: bollard 0.18.1, Engine 29.6). Neither long-standing commit site notices because both
+  discard the response — but it means any commit you need a *reference* to has to be **tagged**.
+- **A tagged leftover is the one orphan no sweep can reach, so the probe image has its own reaper.**
+  `sweep_orphaned_snapshots` collects `dangling` + `triple-c.managed=true`; `reap_stale_migration_pins`
+  and `scrub_secrets_from_snapshots` both filter `triple-c-snapshot-*`. A `triple-c-probe-*` image is
+  tagged and so matches none of them, which would make a crashed probe a permanent multi-gigabyte
+  leak with no UI to find it. `reap_probe_images` runs at startup beside `reap_probe_containers` and
+  is **load-bearing, not tidying** — it is also what makes the probe image's unscrubbed writable
+  layer acceptable. Two rules it earned the hard way:
+  - **Age-gate it** (`PROBE_REAP_MIN_AGE_SECS`, same as the container reaper). `reference=` is
+    daemon-wide, so a second copy of the app has live probe images matching the glob.
+  - **Remove by tag, never by image id.** A `force` removal by id untags an image *everywhere*; a
+    fixture that tagged `alpine:latest` into this namespace deleted the user's alpine that way.
+- **Probe image names are unique per call, and must stay that way.** A stable per-container name was
+  tried: container ids do not survive a recreate, so most leftovers were stranded permanently, and
+  two concurrent probes fought over one tag — whichever finished first force-removed the image the
+  other was still reading, reporting a bogus `probe_error` on a healthy project. `get_container_staleness`
+  takes no `project_lock` claim (the migration banner needs it to answer *during* a migration), so
+  uniqueness is what makes overlapping probes safe.
+- **The stopped-container probe is cached per stop, and that is not an optimisation you may drop.**
+  `getContainerStaleness` is called from a `useEffect` that fires whenever the container settles, so
+  merely opening a stopped project's Overview probes it. Uncached that is a `docker commit` of the
+  whole writable layer per visit — measured at 44 s on a real project, against ~3 s for the snapshot
+  probe it replaced. `STOPPED_MANIFEST_CACHE` is keyed on the container's `FinishedAt`, which is
+  exact rather than merely plausible: nothing can write to a stopped container's writable layer, and
+  `FinishedAt` moves on every stop. A live test asserts the restart case, because a cache that
+  failed to invalidate would plan a migration against a filesystem the project no longer has.
+- **Do not "skip the probe when the project is not stale" to save that cost.** It was tried. The
+  deltas would be empty while `probeSettled` (`!probing && staleness && !probe_error`) stayed *true*,
+  which leaves the migrate action in the project menu enabled — that action is not gated on the
+  banner — so the pre-flight would report nothing to copy while the backend was told to copy
+  nothing. That is the exact hazard `ProjectHome.tsx`'s `canMigrate` comment already warns about.
+- **A failed stopped-container probe falls back to the snapshot whenever one exists.** Before this
+  feature a stopped project read its snapshot directly, so surfacing a commit failure where the
+  snapshot could have answered would make the banner *worse* than it was — and the failure modes are
+  exactly the ones where the fallback earns its keep: a full disk (the commit allocates the whole
+  writable layer; the snapshot probe allocates nothing) and a 409 from a concurrent claim.
+- **`get_container_staleness` never commits while the project is claimed.** It takes no
+  `project_lock` claim itself, deliberately — the banner has to answer *during* a migration — so it
+  reads `project_lock::held` instead and probes the snapshot rather than the container. The
+  collision is not symmetric: the probe losing is a retryable `probe_error`, but
+  `start_project_container` removes the old container with a hard `?`, so a remove that raced a
+  commit would fail the user's Start with an opaque error.
+- **An image's `Created` is the image's own, not its tag's.** Tagging an existing image gives you
+  that image's age; BuildKit stamps `docker build` output with a fixed epoch. Only `docker commit`
+  stamps *now* — which is what real probe images do, and what any fixture for them must do.
 - **`:latest` keeps pointing at the old lineage until the final commit.** That is what makes every
   crash before that point self-heal — `start_project_container` just recreates from the old
   snapshot. After the container swap, the new container's `triple-c.migration-state=in-progress`

app/src-tauri/src/commands/migration_commands.rs

@@ -92,8 +92,111 @@ fn pick_recorded_lineage(
         .or_else(|| from_snapshot.filter(|v| !v.is_empty()))
 }
 
-/// Read-only. Runs two filesystem probes (~3 s each) and is therefore meant to
-/// be called on demand, not polled.
+/// Reported as `probe_error` when there is genuinely nothing to read: no
+/// container, stopped or otherwise, and no snapshot image.
+///
+/// It used to be reported for a *stopped* container too, which was simply
+/// untrue — the container was sitting right there — and it disabled Update on
+/// exactly the long-lived projects that had never been recreated and so had no
+/// snapshot to fall back on.
+const NOTHING_TO_PROBE: &str = "This project has no container or snapshot image yet, so there is nothing to compare against the base image.";
+
+/// Where [`get_container_staleness`] reads the project's *current* filesystem
+/// from, in descending order of how current the answer is.
+#[derive(Debug, PartialEq, Eq)]
+enum ProbeSource {
+    /// `docker exec` into the live container. The only source that includes
+    /// everything installed since the last commit *in this session*.
+    RunningContainer,
+    /// Commit the stopped container's writable layer to a throwaway image and
+    /// probe that. Exactly as current as the container, which is what makes it
+    /// preferable to the snapshot — see below.
+    StoppedContainer,
+    /// A throwaway container from `triple-c-snapshot-<id>:latest`.
+    Snapshot,
+    /// Nothing to read: no container, no snapshot.
+    Nothing,
+}
+
+/// Pick the probe source. `container_running` is `None` when the project has no
+/// container at all, `Some(false)` when it has a stopped one.
+///
+/// **A stopped container outranks the snapshot.** The snapshot image is not a
+/// checkpoint — `commit_container_snapshot` runs only before a removal (a
+/// config-change recreate) or inside a migration, so a project that has never
+/// hit either has *no snapshot at all*, however long it has been in use, and
+/// one that has is stale by everything installed since. The container's
+/// writable layer is the truth in both cases. This is the same argument
+/// [`mig::manifest_from_container`] already makes for the running case; it does
+/// not stop applying when the container is stopped.
+///
+/// Getting this wrong is what made a stopped, never-recreated project report
+/// "no container or snapshot image yet" — with its container sitting right
+/// there — and left Update disabled on the projects that most needed it.
+fn pick_probe_source(container_running: Option<bool>, snapshot_exists: bool) -> ProbeSource {
+    match (container_running, snapshot_exists) {
+        (Some(true), _) => ProbeSource::RunningContainer,
+        (Some(false), _) => ProbeSource::StoppedContainer,
+        (None, true) => ProbeSource::Snapshot,
+        (None, false) => ProbeSource::Nothing,
+    }
+}
+
+/// Reported as `probe_error` when another operation owns the project and there
+/// is no snapshot image to read instead. Deliberately not a claim about the
+/// container: nothing is wrong with it, the answer is simply not safe to take
+/// right now. See [`stopped_probe_policy`].
+const PROJECT_BUSY: &str = "Another operation is running on this project, so its contents could not be inspected. Try again once it finishes.";
+
+/// What to do about a stopped container, whose probe is the expensive one: it
+/// commits the writable layer before it can read anything.
+#[derive(Debug, PartialEq, Eq)]
+enum StoppedProbe {
+    /// Commit and probe. The current answer, and the default.
+    Commit,
+    /// Probe the snapshot image instead. Less current — it lags the container by
+    /// everything installed since the last commit — but it allocates nothing and
+    /// touches nothing, which is what makes it the right answer while another
+    /// operation owns the container.
+    SnapshotInstead,
+    /// Report rather than guess.
+    Defer,
+}
+
+/// Pick what to do about a stopped container.
+///
+/// **Never commits while the project is claimed.** `get_container_staleness`
+/// takes no [`crate::project_lock`] claim of its own, by design, so a commit
+/// here can overlap a Recreate or Reset — and the collision is not symmetric.
+/// The probe losing is harmless: a surfaced `probe_error` the user retries. The
+/// *recreate* losing is not, because `start_project_container` removes the old
+/// container with a hard `?`, so a non-404 from a remove that raced this commit
+/// fails the whole Start with an opaque "Failed to remove container". Reading
+/// the claim costs nothing and takes that failure off the table.
+fn stopped_probe_policy(project_is_busy: bool, snapshot_exists: bool) -> StoppedProbe {
+    match (project_is_busy, snapshot_exists) {
+        (false, _) => StoppedProbe::Commit,
+        (true, true) => StoppedProbe::SnapshotInstead,
+        (true, false) => StoppedProbe::Defer,
+    }
+}
+
+/// Runs two filesystem probes (~3 s each) and is therefore meant to be called
+/// on demand, not polled.
+///
+/// **Not read-only, despite only reporting.** The stopped-container path commits
+/// a throwaway image and force-removes it, which makes this a writer of a
+/// `triple-c-probe-*` image and puts it in the class of thing
+/// [`crate::project_lock`] exists for — and it takes no claim. That is
+/// deliberate: this is what the migration banner calls to decide whether to
+/// offer an update, including while a migration is in flight, so refusing it
+/// under a claim would blank the banner exactly when it has the most to say.
+/// The exposure is bounded to a surfaced error — a concurrent Recreate, Reset or
+/// migration can remove the container out from under the commit, and the result
+/// is a `probe_error` the user can retry, never a damaged container or a
+/// mislabelled image. Two overlapping probes cannot collide either, because
+/// probe image names are unique per call; see
+/// [`crate::docker::container::get_probe_image_name`].
 #[tauri::command]
 pub async fn get_container_staleness(
     project_id: String,
@@ -145,16 +248,62 @@ pub async fn get_container_staleness(
     };
 
     // ── Probes ───────────────────────────────────────────────────────────
-    let running = match &container_id {
-        Some(id) => docker::is_container_running(id).await.unwrap_or(false),
-        None => false,
+    let container_running = match &container_id {
+        Some(id) => Some(docker::is_container_running(id).await.unwrap_or(false)),
+        None => None,
     };
-    let from_manifest = if running {
-        mig::manifest_from_container(container_id.as_ref().unwrap()).await
-    } else if docker::image_exists(&snapshot_image).await.unwrap_or(false) {
-        mig::manifest_from_image(&snapshot_image).await
-    } else {
-        Err("This project has no container or snapshot image yet, so there is nothing to compare against the base image.".to_string())
+    let snapshot_exists = docker::image_exists(&snapshot_image).await.unwrap_or(false);
+    let from_manifest = match (
+        pick_probe_source(container_running, snapshot_exists),
+        &container_id,
+    ) {
+        (ProbeSource::RunningContainer, Some(id)) => mig::manifest_from_container(id).await,
+        (ProbeSource::StoppedContainer, Some(id)) => {
+            let busy = crate::project_lock::held(&project_id).is_some();
+            match stopped_probe_policy(busy, snapshot_exists) {
+                StoppedProbe::Commit => {
+                    match mig::manifest_from_stopped_container_cached(id).await {
+                        Ok(m) => Ok(m),
+                        // **Never let a failed commit cost an answer the
+                        // snapshot could have given.** Before stopped
+                        // containers were readable at all, a stopped project
+                        // fell straight through to its snapshot, so surfacing
+                        // this error where the snapshot exists would make the
+                        // banner *worse* than it was — and the ways this fails
+                        // are the ones where the fallback matters most: a full
+                        // disk (the commit has to allocate the whole writable
+                        // layer; the snapshot probe allocates nothing) and a
+                        // 409 from an operation that claimed the project after
+                        // the check above.
+                        Err(e) if snapshot_exists => {
+                            log::warn!(
+                                "Probing the stopped container for project {} failed ({}) — \
+                                 falling back to its snapshot image, which may lag it",
+                                project_id,
+                                e
+                            );
+                            mig::manifest_from_image(&snapshot_image).await
+                        }
+                        Err(e) => Err(e),
+                    }
+                }
+                StoppedProbe::SnapshotInstead => {
+                    log::info!(
+                        "Project {} is claimed by another operation — probing its snapshot image \
+                         rather than committing the container",
+                        project_id
+                    );
+                    mig::manifest_from_image(&snapshot_image).await
+                }
+                StoppedProbe::Defer => Err(PROJECT_BUSY.to_string()),
+            }
+        }
+        (ProbeSource::Snapshot, _) => mig::manifest_from_image(&snapshot_image).await,
+        // `container_running` is `Some` exactly when `container_id` is, so the
+        // two arms above are the only ones those variants can reach. This arm
+        // is `ProbeSource::Nothing` — and now *only* that: it used to also
+        // swallow every stopped container, which is the bug.
+        (_, _) => Err(NOTHING_TO_PROBE.to_string()),
     };
 
     let (from_manifest, base_manifest) = match from_manifest {
@@ -1964,6 +2113,59 @@ mod tests {
         assert_eq!(pick_recorded_lineage(some(""), None), None);
     }
 
+    #[test]
+    fn a_stopped_container_is_probed_rather_than_reported_missing() {
+        // The regression: a container that exists but is stopped, with no
+        // snapshot ever taken, read as "nothing to compare against".
+        assert_eq!(
+            pick_probe_source(Some(false), false),
+            ProbeSource::StoppedContainer
+        );
+    }
+
+    #[test]
+    fn the_container_outranks_the_snapshot_whether_or_not_it_is_running() {
+        // The snapshot lags the container by everything installed since the
+        // last commit, in both states.
+        assert_eq!(
+            pick_probe_source(Some(true), true),
+            ProbeSource::RunningContainer
+        );
+        assert_eq!(
+            pick_probe_source(Some(false), true),
+            ProbeSource::StoppedContainer
+        );
+    }
+
+    #[test]
+    fn the_snapshot_is_the_fallback_only_once_the_container_is_gone() {
+        assert_eq!(pick_probe_source(None, true), ProbeSource::Snapshot);
+    }
+
+    #[test]
+    fn nothing_to_probe_is_reserved_for_no_container_and_no_snapshot() {
+        // The one case the "no container or snapshot image yet" message may
+        // still describe.
+        assert_eq!(pick_probe_source(None, false), ProbeSource::Nothing);
+    }
+
+    #[test]
+    fn a_stopped_container_is_committed_only_when_nothing_else_owns_the_project() {
+        assert_eq!(stopped_probe_policy(false, false), StoppedProbe::Commit);
+        assert_eq!(stopped_probe_policy(false, true), StoppedProbe::Commit);
+    }
+
+    #[test]
+    fn a_busy_project_falls_back_rather_than_racing_a_recreate() {
+        // The snapshot lags, but a stale answer beats failing someone's Start.
+        assert_eq!(
+            stopped_probe_policy(true, true),
+            StoppedProbe::SnapshotInstead
+        );
+        // Nothing to fall back to: say so instead of committing anyway.
+        assert_eq!(stopped_probe_policy(true, false), StoppedProbe::Defer);
+    }
+
     #[test]
     fn byte_sizes_read_the_way_a_disk_warning_should() {
         assert_eq!(human_bytes(512), "512 B");

app/src-tauri/src/docker/container.rs

@@ -3052,6 +3052,118 @@ fn blanked_secret_env() -> Vec<String> {
         .collect()
 }
 
+/// Image-name prefix for the throwaway commit a staleness probe of a stopped
+/// container makes. The reaper's only handle on a leftover — see
+/// [`crate::docker::migration::reap_probe_images`] — so nothing else may use it.
+pub const PROBE_IMAGE_PREFIX: &str = "triple-c-probe-";
+
+/// The throwaway image a staleness probe of a **stopped** container commits to.
+///
+/// **Unique per call**, and both halves of the name earn their place: the
+/// container id prefix makes a leftover traceable in `docker images`, and the
+/// counter makes two overlapping probes independent.
+///
+/// An earlier version of this was deliberately *stable* per container, on the
+/// theory that the next probe would move the tag off an abandoned image and
+/// leave it dangling for [`sweep_orphaned_snapshots`]. That was wrong twice
+/// over. A container id does not survive a recreate, so for most leftovers
+/// there is no "next probe of the same container" and the image was stranded
+/// permanently; and a stable name made two concurrent probes fight over one
+/// tag, where whichever finished first force-removed the image the other was
+/// still reading and turned a healthy project into a bogus `probe_error`.
+/// Uniqueness fixes both, and [`crate::docker::migration::reap_probe_images`]
+/// is what collects the leftovers instead.
+pub fn get_probe_image_name(container_id: &str) -> String {
+    use std::sync::atomic::{AtomicU64, Ordering};
+    static SEQ: AtomicU64 = AtomicU64::new(0);
+
+    let short: String = container_id.chars().take(12).collect();
+    let nanos = std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .map(|d| d.as_nanos())
+        .unwrap_or(0);
+    format!(
+        "{}{}-{}-{}:latest",
+        PROBE_IMAGE_PREFIX,
+        short,
+        nanos,
+        SEQ.fetch_add(1, Ordering::Relaxed)
+    )
+}
+
+/// Commit a **stopped** container's filesystem to a throwaway image, returning
+/// its name. The caller owns the image and must remove it.
+///
+/// This exists so a stopped project can be read at all. `docker exec` needs a
+/// running container and the snapshot image is not a checkpoint — see
+/// [`crate::commands::migration_commands`]'s probe-source pick — so without
+/// this there is no way to see inside a project that is merely stopped.
+///
+/// ## Why it is tagged at all
+///
+/// An untagged commit would be tidier: untagged plus the `triple-c.managed=true`
+/// that `docker commit` copies off the container is exactly the pair
+/// [`sweep_orphaned_snapshots`] already collects, so a leftover would self-heal
+/// with no new machinery. **It is not available.** `bollard`'s `Commit` response
+/// model deserialises `"ID"` while the daemon sends `"Id"`, so
+/// `commit_container` hands back `id: None` every time and there is no
+/// reference left to probe. Neither existing commit site notices, because both
+/// discard the response. Verified against Engine 29.6, bollard 0.18.1.
+///
+/// So the image needs a name, a tagged image is not dangling, and the sweep
+/// therefore cannot be the safety net. [`crate::docker::migration::reap_probe_images`]
+/// is, and [`get_probe_image_name`] carries the rest of that argument.
+///
+/// ## What is in the image, and what is not
+///
+/// `pause: false` because nothing is running — pausing a stopped container is
+/// an error, the same reason [`recommit_without_secrets`]'s scratch commit
+/// passes `false`.
+///
+/// Secrets are blanked from the env for the same reason
+/// [`commit_container_snapshot`] blanks them: the commit bakes the container's
+/// full ENV into the image, and "it only lives a few seconds" is not a property
+/// this function can promise after a crash.
+///
+/// **The writable layer is committed unscrubbed, and that is unavoidable here.**
+/// [`commit_container_snapshot`] runs [`scrub_writable_layer`] first precisely
+/// because a commit stacks a layer and never rewrites one — but that scrub is a
+/// `docker exec`, which is exactly what a stopped container cannot serve, and
+/// scrubbing is not wanted anyway: the probe's whole job is to report the
+/// filesystem as it actually is. What makes it acceptable is that this copies
+/// bytes that are *already on this disk* in the container's own writable layer,
+/// into an image that is never pushed, never created from, and reaped — so it
+/// duplicates data inside one trust domain rather than widening it. That
+/// argument depends on the reaping actually happening; treat
+/// [`crate::docker::migration::reap_probe_images`] as load-bearing, not tidying.
+pub async fn commit_container_for_probe(container_id: &str) -> Result<String, String> {
+    let docker = get_docker()?;
+    let image_name = get_probe_image_name(container_id);
+    let (repo, tag) = image_name
+        .rsplit_once(':')
+        .map(|(r, t)| (r.to_string(), t.to_string()))
+        .expect("get_probe_image_name always emits a tag");
+
+    docker
+        .commit_container(
+            CommitContainerOptions {
+                container: container_id.to_string(),
+                repo,
+                tag,
+                pause: false,
+                ..Default::default()
+            },
+            Config::<String> {
+                env: Some(blanked_secret_env()),
+                ..Default::default()
+            },
+        )
+        .await
+        .map_err(|e| format!("Failed to commit stopped container {}: {}", container_id, e))?;
+
+    Ok(image_name)
+}
+
 /// Whether `env` (an image's `Config.Env`) holds a non-empty value for any
 /// name in [`SECRET_ENV_KEYS`].
 fn env_holds_a_secret(env: &[String]) -> bool {
@@ -3518,9 +3630,10 @@ pub async fn remove_snapshot_image(project: &Project) -> Result<(), String> {
     remove_image_by_name(&get_snapshot_image_name(project)).await
 }
 
-/// Remove a Docker image by name/tag, treating "does not exist" as success.
-/// Shared by [`remove_snapshot_image`] and the pending-cleanup retry, which
-/// only has the image name (the project record is already gone by then).
+/// Remove a Docker image by name, tag or **id**, treating "does not exist" as
+/// success. Shared by [`remove_snapshot_image`], the pending-cleanup retry
+/// (which only has the image name — the project record is already gone by
+/// then), and the staleness probe's throwaway commit, which has only an id.
 pub async fn remove_image_by_name(image_name: &str) -> Result<(), String> {
     let docker = get_docker()?;
 
@@ -3536,7 +3649,7 @@ pub async fn remove_image_by_name(image_name: &str) -> Result<(), String> {
         .await
     {
         Ok(_) => {
-            log::info!("Removed snapshot image {}", image_name);
+            log::info!("Removed image {}", image_name);
             Ok(())
         }
         Err(bollard::errors::Error::DockerResponseServerError {
@@ -4464,6 +4577,29 @@ mod tests {
         assert!(env_holds_a_secret(&env));
     }
 
+    /// The probe image's name must be **unique per call**. A stable name was
+    /// tried and is wrong twice over: a container id does not survive a
+    /// recreate, so a crashed probe's leftover would never be reclaimed by "the
+    /// next probe of the same container"; and two concurrent probes sharing one
+    /// tag means whichever finishes first force-removes the image the other is
+    /// still reading. See `commit_container_for_probe` and `reap_probe_images`.
+    #[test]
+    fn probe_image_names_are_unique_per_call_and_reapable_by_prefix() {
+        let id = "75993e6d5e1ab473b029a408c5ff0339";
+        let a = get_probe_image_name(id);
+        let b = get_probe_image_name(id);
+        assert_ne!(a, b, "two probes of one container must not share a tag");
+
+        // The prefix is the reaper's only handle on a leftover, so every name
+        // has to carry it — and it must not be the snapshot namespace, which is
+        // what a project is rebuilt from.
+        assert!(a.starts_with(PROBE_IMAGE_PREFIX), "{}", a);
+        assert!(!a.starts_with("triple-c-snapshot-"), "{}", a);
+        // Traceable back to its container, which is the point of the prefix.
+        assert!(a.contains("75993e6d5e1a"), "{}", a);
+        assert!(a.ends_with(":latest"), "{}", a);
+    }
+
     #[test]
     fn the_scrub_report_only_claims_success_when_nothing_is_left() {
         let clean = SnapshotScrubReport {

app/src-tauri/src/docker/migration.rs

@@ -886,6 +886,100 @@ pub async fn reap_probe_containers() {
     }
 }
 
+/// Remove throwaway images left behind by a staleness probe of a stopped
+/// container — [`super::container::commit_container_for_probe`]'s commits.
+///
+/// **Load-bearing, not tidying.** A probe image is *tagged*, because bollard
+/// gives no image id back from a commit and there has to be something to probe.
+/// Tagged means not dangling, so [`super::container::sweep_orphaned_snapshots`]
+/// — which collects every other kind of orphan this app can leave — will never
+/// see one. Without this, a probe that dies between its commit and its own
+/// cleanup (SIGKILL, a crash, a 409 from a concurrent remove) strands a
+/// multi-gigabyte image that **no code path can ever reclaim**, and there is no
+/// UI to find it either. That is the one leak in this app with no floor on it,
+/// so this runs at startup beside [`reap_probe_containers`].
+///
+/// Age-gated for exactly the reason that one is: `reference=` is a daemon-wide
+/// filter, so a second copy of the app probing a project on the same daemon has
+/// images matching this glob, and removing one mid-capture fails that probe with
+/// "No such image" — the bogus `probe_error` the staleness work exists to get
+/// rid of. In-process state cannot see the other instance, so age is the only
+/// brake, and [`PROBE_REAP_MIN_AGE_SECS`] is already the right one: a probe is a
+/// `find` over a root filesystem, not a multi-minute job.
+///
+/// Never fails the caller. Housekeeping, like every other sweep here.
+pub async fn reap_probe_images() {
+    use bollard::image::{ListImagesOptions, RemoveImageOptions};
+
+    let docker = match get_docker() {
+        Ok(d) => d,
+        Err(e) => {
+            log::warn!("Could not reap leftover probe images: {}", e);
+            return;
+        }
+    };
+
+    let filters = HashMap::from([(
+        "reference".to_string(),
+        vec![format!("{}*", super::container::PROBE_IMAGE_PREFIX)],
+    )]);
+    let images = match docker
+        .list_images(Some(ListImagesOptions {
+            all: false,
+            filters,
+            ..Default::default()
+        }))
+        .await
+    {
+        Ok(images) => images,
+        Err(e) => {
+            log::warn!("Could not list leftover probe images: {}", e);
+            return;
+        }
+    };
+
+    let now = chrono::Utc::now().timestamp();
+    for image in images {
+        // Unlike a container summary, an image summary always carries a
+        // `Created`, so there is no unknown-age case to defend against here.
+        if now - image.created < PROBE_REAP_MIN_AGE_SECS {
+            log::info!(
+                "Leaving probe image {:?} alone — it is younger than {} minutes, so it may belong \
+                 to another Triple-C instance's live probe",
+                image.repo_tags,
+                PROBE_REAP_MIN_AGE_SECS / 60
+            );
+            continue;
+        }
+        // By **tag**, never by image id. A `force` removal by id untags an
+        // image everywhere, so an id that happens to carry another name loses
+        // that name too — which is how a test fixture that tagged
+        // `alpine:latest` into this namespace deleted the user's alpine. A real
+        // leftover has exactly the one probe tag, so removing the tag removes
+        // the image; anything else keeps whatever other names it has.
+        for tag in image
+            .repo_tags
+            .iter()
+            .filter(|t| t.starts_with(super::container::PROBE_IMAGE_PREFIX))
+        {
+            log::info!("Removing leftover probe image {}", tag);
+            if let Err(e) = docker
+                .remove_image(
+                    tag,
+                    Some(RemoveImageOptions {
+                        force: true,
+                        noprune: false,
+                    }),
+                    None,
+                )
+                .await
+            {
+                log::warn!("Could not remove leftover probe image {}: {}", tag, e);
+            }
+        }
+    }
+}
+
 /// How old a `triple-c.probe=migration` container must be before
 /// [`reap_probe_containers`] will force-remove it, in seconds.
 ///
@@ -993,6 +1087,119 @@ pub async fn manifest_from_container(container_id: &str) -> Result<Manifest, Str
     Ok(parse_manifest(&out))
 }
 
+/// Cached stopped-container manifests, keyed by container id, each paired with
+/// the container's `FinishedAt` at the time it was captured.
+///
+/// **Sound because a stopped container's writable layer cannot change.** Nothing
+/// can write to it while it is not running, so a manifest captured after it
+/// stopped stays true until it is started again — and `FinishedAt` moves on
+/// every stop, which is what makes the key exact rather than merely plausible.
+///
+/// This exists because `get_container_staleness` is called from a `useEffect`
+/// that fires whenever the container settles, so simply opening a stopped
+/// project's Overview probes it. Uncached that meant a `docker commit` of the
+/// whole writable layer per visit — measured at 44 s on a real project — where
+/// before this feature the same visit cost one throwaway container or nothing at
+/// all. A regression like that is not worth the answer it buys.
+///
+/// Capped, because a `Manifest` of a real container is a few MB: this only has
+/// to serve "the project whose page is open", so a handful of entries is the
+/// whole working set and the oldest is dropped past that.
+static STOPPED_MANIFEST_CACHE: std::sync::Mutex<
+    Option<Vec<(String, String, Manifest)>>,
+> = std::sync::Mutex::new(None);
+
+/// How many stopped-container manifests [`STOPPED_MANIFEST_CACHE`] keeps.
+const STOPPED_MANIFEST_CACHE_MAX: usize = 4;
+
+/// `FinishedAt` for a container, the cache's validity token. `None` when it
+/// cannot be read, which is never treated as a hit.
+async fn container_finished_at(container_id: &str) -> Option<String> {
+    let docker = get_docker().ok()?;
+    docker
+        .inspect_container(container_id, None)
+        .await
+        .ok()?
+        .state?
+        .finished_at
+        .filter(|s| !s.is_empty())
+}
+
+/// Capture a [`Manifest`] from a **stopped** container, reusing a cached one
+/// when the container has not been started since it was taken.
+///
+/// See [`STOPPED_MANIFEST_CACHE`] for why this is exact and why it is needed.
+pub async fn manifest_from_stopped_container_cached(
+    container_id: &str,
+) -> Result<Manifest, String> {
+    let finished_at = container_finished_at(container_id).await;
+
+    if let Some(token) = &finished_at {
+        let guard = STOPPED_MANIFEST_CACHE.lock();
+        if let Ok(cache) = guard {
+            if let Some(entries) = cache.as_ref() {
+                if let Some((_, _, manifest)) = entries
+                    .iter()
+                    .find(|(id, tok, _)| id == container_id && tok == token)
+                {
+                    log::debug!(
+                        "Reusing the cached manifest for stopped container {}",
+                        container_id
+                    );
+                    return Ok(manifest.clone());
+                }
+            }
+        }
+    }
+
+    let manifest = manifest_from_stopped_container(container_id).await?;
+
+    // Only cacheable if the container's state could be read at all; an unknown
+    // `FinishedAt` means there is no token that could later be compared.
+    if let Some(token) = finished_at {
+        if let Ok(mut cache) = STOPPED_MANIFEST_CACHE.lock() {
+            let entries = cache.get_or_insert_with(Vec::new);
+            entries.retain(|(id, _, _)| id != container_id);
+            entries.push((container_id.to_string(), token, manifest.clone()));
+            while entries.len() > STOPPED_MANIFEST_CACHE_MAX {
+                entries.remove(0);
+            }
+        }
+    }
+
+    Ok(manifest)
+}
+
+/// Capture a [`Manifest`] from a **stopped** container.
+///
+/// Commits the container's writable layer to a throwaway image, probes that,
+/// and removes it. This is as current as [`manifest_from_container`] — it reads
+/// the same filesystem — and it is why a stopped project no longer has to fall
+/// back to its snapshot image, which may not exist at all and lags the
+/// container by everything installed since the last commit when it does.
+///
+/// The image is removed on every path, including a failed probe. See
+/// [`super::container::commit_container_for_probe`] for what a crash in the
+/// window between the two costs, and why it is bounded.
+pub async fn manifest_from_stopped_container(container_id: &str) -> Result<Manifest, String> {
+    let image = super::container::commit_container_for_probe(container_id).await?;
+
+    let manifest = manifest_from_image(&image)
+        .await
+        .map_err(|e| format!("Probe of the stopped container did not complete: {}", e));
+
+    if let Err(e) = super::container::remove_image_by_name(&image).await {
+        log::warn!(
+            "Could not remove the staleness probe's throwaway image {}: {} — `reap_probe_images` \
+             collects it at the next app start; the orphan sweep never will, because it is tagged",
+            image,
+            e
+        );
+    }
+
+    manifest
+}
+
 /// The image ID (`sha256:…`) of a local image, or `None` if it is not present.
 ///
 /// Deliberately the **ID**, not a repo digest: locally built images and custom
@@ -2146,4 +2353,258 @@ mod tests {
         assert!(!pin_is_reapable("pre-migration-handmade", false, ancient, &now));
         assert!(!pin_is_reapable("latest", false, ancient, &now));
     }
+
+    // ── Live Docker ─────────────────────────────────────────────────────────
+
+    /// The cache serves a second read of an unchanged stopped container, and —
+    /// the half that matters — stops serving it the moment the container is
+    /// started and stopped again. If invalidation were wrong this would report a
+    /// filesystem the project no longer has, and a migration would be planned
+    /// against it.
+    ///
+    /// ```text
+    /// cargo test -- --ignored --nocapture stopped_manifest_cache
+    /// ```
+    #[cfg(unix)]
+    #[tokio::test]
+    #[ignore = "needs a Docker daemon; creates, commits and removes a throwaway container"]
+    async fn the_stopped_manifest_cache_survives_a_reread_but_not_a_restart() {
+        fn docker_cli(args: &[&str]) -> String {
+            let out = std::process::Command::new("docker")
+                .args(args)
+                .output()
+                .expect("docker CLI");
+            assert!(
+                out.status.success(),
+                "docker {:?} failed: {}",
+                args,
+                String::from_utf8_lossy(&out.stderr)
+            );
+            String::from_utf8_lossy(&out.stdout).trim().to_string()
+        }
+
+        let image = std::env::var("TRIPLE_C_TEST_IMAGE")
+            .unwrap_or_else(|_| "ghcr.io/shadowdao/triple-c-sandbox:latest".to_string());
+        let first = format!("/opt/cache-marker-a-{}", std::process::id());
+        let second = format!("/opt/cache-marker-b-{}", std::process::id());
+
+        let id = docker_cli(&[
+            "run", "-d", "--label", "triple-c.managed=true",
+            "--entrypoint", "/bin/sh",
+            &image, "-c", "sleep 600",
+        ]);
+        let cleanup = || {
+            let _ = std::process::Command::new("docker")
+                .args(["rm", "-f", &id])
+                .output();
+        };
+
+        docker_cli(&["exec", &id, "mkdir", "-p", &first]);
+        docker_cli(&["stop", "-t", "1", &id]);
+
+        let t0 = std::time::Instant::now();
+        let cold = manifest_from_stopped_container_cached(&id).await;
+        let cold_ms = t0.elapsed().as_millis();
+
+        let t1 = std::time::Instant::now();
+        let warm = manifest_from_stopped_container_cached(&id).await;
+        let warm_ms = t1.elapsed().as_millis();
+
+        // Restart, change the filesystem, stop again — `FinishedAt` moves.
+        docker_cli(&["start", &id]);
+        docker_cli(&["exec", &id, "mkdir", "-p", &second]);
+        docker_cli(&["stop", "-t", "1", &id]);
+        let after_restart = manifest_from_stopped_container_cached(&id).await;
+
+        cleanup();
+
+        let has = |m: &Manifest, p: &str| m.paths.iter().any(|e| e.path == p && e.is_dir());
+
+        let cold = cold.expect("cold read");
+        let warm = warm.expect("warm read");
+        let after_restart = after_restart.expect("read after restart");
+
+        assert!(has(&cold, &first), "cold read missed {}", first);
+        assert!(has(&warm, &first), "warm read missed {}", first);
+        println!("cold {} ms, warm {} ms", cold_ms, warm_ms);
+        assert!(
+            warm_ms * 5 < cold_ms.max(5),
+            "the second read cost {} ms against a cold {} ms — it re-committed \
+             instead of using the cache",
+            warm_ms,
+            cold_ms
+        );
+
+        // The restart must have invalidated it: the new directory has to show up.
+        assert!(
+            has(&after_restart, &second),
+            "a restart did not invalidate the cache — {} is missing, so this is \
+             a stale manifest of a filesystem the container no longer has",
+            second
+        );
+        assert!(has(&after_restart, &first), "the restart lost {}", first);
+    }
+
+    /// The reaper finds a leftover probe image by prefix and — crucially —
+    /// refuses to remove a young one, because that image may be another
+    /// Triple-C instance's live probe. Only a real daemon can say whether the
+    /// `reference=` glob matches the names `get_probe_image_name` produces.
+    ///
+    /// The fixture is **committed**, not tagged and not built. An image's
+    /// `Created` is its own, not its tag's, so tagging something already on disk
+    /// into this namespace yields a fixture the reaper is right to call ancient
+    /// — and BuildKit stamps a fixed epoch on `docker build` output, so a built
+    /// one looks ancient too. A commit stamps *now*, verified against Engine
+    /// 29.6, which is also how real probe images get their age.
+    ///
+    /// Both of those mistakes were made here first, and one of them deleted an
+    /// unrelated `alpine:latest` — which is why `reap_probe_images` removes by
+    /// tag rather than by image id.
+    ///
+    /// ```text
+    /// cargo test -- --ignored --nocapture reaper_spares
+    /// ```
+    #[cfg(unix)]
+    #[tokio::test]
+    #[ignore = "needs a Docker daemon; builds and removes a throwaway image"]
+    async fn the_reaper_spares_a_probe_image_young_enough_to_be_someone_elses() {
+        use std::process::Command;
+
+        fn docker_out(args: &[&str]) -> std::process::Output {
+            Command::new("docker").args(args).output().expect("docker CLI")
+        }
+
+        let base = std::env::var("TRIPLE_C_TEST_IMAGE")
+            .unwrap_or_else(|_| "alpine:latest".to_string());
+        let name = crate::docker::container::get_probe_image_name("reapertest01234");
+
+        // A never-started container is enough to commit from, and leaves the
+        // daemon's run state alone entirely.
+        let created = docker_out(&["create", &base, "true"]);
+        assert!(
+            created.status.success(),
+            "could not create the fixture container from {}: {}",
+            base,
+            String::from_utf8_lossy(&created.stderr)
+        );
+        let cid = String::from_utf8_lossy(&created.stdout).trim().to_string();
+
+        let committed = docker_out(&["commit", "--pause=false", &cid, &name]);
+        let _ = docker_out(&["rm", "-f", &cid]);
+        assert!(
+            committed.status.success(),
+            "could not commit the fixture image: {}",
+            String::from_utf8_lossy(&committed.stderr)
+        );
+
+        reap_probe_images().await;
+
+        let still_there = Command::new("docker")
+            .args(["image", "inspect", &name])
+            .output()
+            .expect("docker image inspect")
+            .status
+            .success();
+
+        let _ = Command::new("docker").args(["rmi", &name]).output();
+
+        assert!(
+            still_there,
+            "a probe image committed seconds ago was reaped — that is another \
+             instance's live probe being broken, see PROBE_REAP_MIN_AGE_SECS"
+        );
+    }
+
+    /// A *stopped* container is readable, and what comes back is its writable
+    /// layer rather than the image it was created from. This is the whole point
+    /// of the function: the base image cannot answer it, and the project may
+    /// well have no snapshot image at all.
+    ///
+    /// Also asserts the throwaway commit leaves nothing behind, which no unit
+    /// test can. It has to assert on the `triple-c-probe-*` tags specifically:
+    /// the probe image is *tagged*, so a leak never shows up as a dangling
+    /// image and a dangling-set assertion here would pass either way.
+    ///
+    /// Ignored because it needs Docker and commits a container; run it with
+    ///
+    /// ```text
+    /// cargo test -- --ignored --nocapture stopped_container
+    /// ```
+    #[cfg(unix)]
+    #[tokio::test]
+    #[ignore = "needs a Docker daemon; creates, commits and removes a throwaway container"]
+    async fn a_stopped_container_is_read_from_its_writable_layer() {
+        fn docker_cli(args: &[&str]) -> String {
+            let out = std::process::Command::new("docker")
+                .args(args)
+                .output()
+                .expect("docker CLI");
+            assert!(
+                out.status.success(),
+                "docker {:?} failed: {}",
+                args,
+                String::from_utf8_lossy(&out.stderr)
+            );
+            String::from_utf8_lossy(&out.stdout).trim().to_string()
+        }
+        fn probe_images() -> Vec<String> {
+            let mut ids: Vec<String> = docker_cli(&[
+                "images", "-q",
+                "--filter",
+                &format!("reference={}*", crate::docker::container::PROBE_IMAGE_PREFIX),
+            ])
+            .lines()
+            .map(|l| l.trim().to_string())
+            .filter(|l| !l.is_empty())
+            .collect();
+            ids.sort();
+            ids
+        }
+
+        let image = std::env::var("TRIPLE_C_TEST_IMAGE")
+            .unwrap_or_else(|_| "ghcr.io/shadowdao/triple-c-sandbox:latest".to_string());
+        // A marker only the writable layer can carry, under a MANIFEST_ROOTS root.
+        let marker = format!("/opt/probe-marker-{}", std::process::id());
+
+        // Another instance's live probe images are allowed to exist; what must
+        // hold is that this probe adds none of its own.
+        let before = probe_images();
+
+        let id = docker_cli(&[
+            "run", "-d", "--label", "triple-c.managed=true",
+            "--entrypoint", "/bin/sh",
+            &image, "-c", "sleep 300",
+        ]);
+        let cleanup = |id: &str| {
+            let _ = std::process::Command::new("docker")
+                .args(["rm", "-f", id])
+                .output();
+        };
+
+        docker_cli(&["exec", &id, "mkdir", "-p", &marker]);
+        docker_cli(&["stop", "-t", "1", &id]);
+
+        let result = manifest_from_stopped_container(&id).await;
+
+        cleanup(&id);
+
+        let manifest = result.expect("a stopped container must be probeable");
+        assert!(
+            manifest.paths.iter().any(|e| e.path == marker && e.is_dir()),
+            "the probe read the image, not the container's writable layer: {} missing",
+            marker
+        );
+        // Non-empty package sets prove the probe script really ran, rather than
+        // parsing an empty transcript into an empty-but-Ok manifest.
+        assert!(
+            !manifest.apt_manual.is_empty(),
+            "apt-mark showmanual came back empty, so the probe did not run"
+        );
+
+        assert_eq!(
+            probe_images(),
+            before,
+            "the throwaway probe image was not cleaned up"
+        );
+    }
 }

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);

app/src/lib/tauri-commands.ts

@@ -350,8 +350,8 @@ export const sweepClaudeTokenSnapshots = () =>
 // without deleting its volumes. Reset is the destructive alternative: it wipes
 // ~/.claude, the OAuth credential, installed skills and every transcript.
 //
-// Flow: getContainerStaleness (read-only, ~6s — two filesystem probes, so call
-// it on demand rather than polling) → migrateProjectToBase → the project sits
+// Flow: getContainerStaleness (~6s — two filesystem probes, so call it on demand
+// rather than polling) → migrateProjectToBase → the project sits
 // in "awaiting-confirmation" while the user tries it → confirmMigration or
 // rollbackMigration.
 //
@@ -361,7 +361,19 @@ export const sweepClaudeTokenSnapshots = () =>
 //
 // Progress arrives on the existing `container-progress` event.
 
-/** Read-only. Runs two container/image filesystem probes; not for polling. */
+/**
+ * Runs two container/image filesystem probes; not for polling.
+ *
+ * **Not read-only, despite only reporting.** When the container is *stopped*
+ * the backend has to commit its writable layer to a throwaway image before it
+ * can read anything — `docker exec` needs a running container — so this writes
+ * (and then removes) an image. The result is cached per stop, so repeat calls
+ * while the container stays stopped are cheap, but the first one after each stop
+ * pays for a commit of the whole layer: seconds on a small project, tens of
+ * seconds on a large one. Do not add a caller that fires more often than "the
+ * container settled into a new state" without re-reading
+ * `get_container_staleness`'s doc comment first.
+ */
 export const getContainerStaleness = (projectId: string) =>
   invoke<ContainerStaleness>("get_container_staleness", { projectId });
 

scripts/finalize-appimage.sh

@@ -91,6 +91,11 @@ HOOK="apprun-hooks/triple-c-wayland-fallback.sh"
 APPIMAGE_TOOL_URL="https://github.com/AppImage/appimagetool/releases/download/continuous/appimagetool-x86_64.AppImage"
 
 APP_ID="com.triple-c.desktop"
+# The channel pair lives in its own directory. Left beside the versioned image
+# they are picked up by the release job's `*.AppImage` glob, and every release
+# then carries an eighty-megabyte byte-identical duplicate under a second name
+# — which is exactly as confusing on a downloads page as it sounds.
+CHANNEL_DIR="update-channel"
 STABLE_NAME="Triple-C_x86_64.AppImage"
 UPDATE_TAG="linux-latest"
 UPDATE_INFO="zsync|https://github.com/shadowdao/triple-c/releases/download/${UPDATE_TAG}/${STABLE_NAME}.zsync"
@@ -98,8 +103,13 @@ CATEGORIES="Development;Utility;"
 
 repo_root="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
 appdata_src="$repo_root/packaging/appimage/$APP_ID.appdata.xml"
+# appimagetool looks for `<desktop basename>.appdata.xml` and warns the
+# metadata is missing under any other name — while the script cheerfully
+# reported it present. The AppStream id inside the file is unchanged and is
+# what actually identifies the component; only the filename follows the tool.
+appdata_installed_as="Triple-C.appdata.xml"
 
-dir="${1:?usage: unbundle-wayland-client.sh <bundle/appimage directory>}"
+dir="${1:?usage: finalize-appimage.sh <bundle/appimage directory>}"
 cd "$dir"
 
 shopt -s nullglob
@@ -109,6 +119,14 @@ if [ ${#images[@]} -eq 0 ]; then
   echo "No .AppImage in $dir — nothing to do." >&2
   exit 0
 fi
+# Refused here rather than after the repack: with two present the old position
+# let the script download appimagetool, repack, overwrite the versioned
+# artifact and write the channel pair, *then* fail — and it silently picked
+# images[0], which is glob order, i.e. the older version.
+if [ ${#images[@]} -ne 1 ]; then
+  echo "Expected 1 AppImage in $dir, found ${#images[@]}: ${images[*]}" >&2
+  exit 1
+fi
 appimage="${images[0]}"
 here="$PWD"
 
@@ -120,15 +138,15 @@ echo "Inspecting $appimage"
 ( cd "$work" && "$here/$appimage" --appimage-extract >/dev/null )
 root="$work/squashfs-root"
 
-if [ ! -e "$root/usr/lib/$LIB" ]; then
-  # Not a failure: linuxdeploy may have stopped bundling it, which is the
-  # outcome this script exists to produce.
-  echo "$LIB is not bundled — leaving $appimage alone."
-  exit 0
-fi
+# The demotion and the metadata are independent jobs, and an absent library
+# must not skip the second. An early exit here also left `update-channel/`
+# uncreated, which killed the publish step on a missing directory and took the
+# tag and mirror jobs down with it — a half-published release.
+demoted=false
+if [ -e "$root/usr/lib/$LIB" ]; then
 
-mkdir -p "$root/$FALLBACK_DIR"
-mv "$root/usr/lib/$LIB" "$root/$FALLBACK_DIR/$LIB"
+  mkdir -p "$root/$FALLBACK_DIR"
+  mv "$root/usr/lib/$LIB" "$root/$FALLBACK_DIR/$LIB"
 
 cat > "$root/$HOOK" <<'HOOK_EOF'
 #! /usr/bin/env bash
@@ -177,6 +195,11 @@ src = src.replace(
 )
 open(path, "w").write(src)
 PATCH_EOF
+  fi
+  demoted=true
+  echo "Demoted $LIB to $FALLBACK_DIR."
+else
+  echo "$LIB is not bundled — nothing to demote."
 fi
 
 # --- metadata -------------------------------------------------------------
@@ -188,22 +211,29 @@ version="$(printf '%s' "$appimage" | sed -n 's/.*_\([0-9][0-9.]*\)_.*/\1/p')"
 if [ -f "$appdata_src" ]; then
   mkdir -p "$root/usr/share/metainfo"
   sed -e "s/@VERSION@/$version/" -e "s/@DATE@/$(date -u +%Y-%m-%d)/" \
-    "$appdata_src" > "$root/usr/share/metainfo/$APP_ID.appdata.xml"
+    "$appdata_src" > "$root/usr/share/metainfo/$appdata_installed_as"
   echo "Added AppStream metadata for $version."
 else
   echo "No AppStream source at $appdata_src — skipping." >&2
 fi
 
 # linuxdeploy emits `Categories=` empty, which files the app nowhere.
-for desktop in "$root"/*.desktop; do
+#
+# The AppDir root entry is a **symlink** into usr/share/applications, so a
+# plain `sed -i` replaces the link with a regular file and leaves the real entry
+# untouched — two divergent copies, of which the empty one is the one that
+# actually ships and the filled one is the only one a root-only guard can see.
+# `--follow-symlinks` writes through. Both locations are globbed because the
+# layout is linuxdeploy's, not ours, and it is free to stop symlinking.
+for desktop in "$root"/*.desktop "$root"/usr/share/applications/*.desktop; do
   [ -e "$desktop" ] || continue
   if grep -q "^Categories=$" "$desktop"; then
-    sed -i "s/^Categories=$/Categories=$CATEGORIES/" "$desktop"
-    echo "Filled in Categories for $(basename "$desktop")."
+    sed -i --follow-symlinks "s/^Categories=$/Categories=$CATEGORIES/" "$desktop"
+    echo "Filled in Categories for ${desktop#"$root"/}."
   fi
 done
 
-echo "Demoted $LIB to $FALLBACK_DIR; repacking."
+echo "Repacking."
 
 tool="$work/appimagetool"
 curl -fsSL -o "$tool" "$APPIMAGE_TOOL_URL"
@@ -211,13 +241,19 @@ chmod +x "$tool"
 
 # --appimage-extract-and-run: CI runners generally have no FUSE.
 # -u embeds the update string and writes "$STABLE_NAME.zsync" beside the image.
+rm -rf "$CHANNEL_DIR"
+mkdir -p "$CHANNEL_DIR"
 ARCH=x86_64 "$tool" --appimage-extract-and-run \
-  -u "$UPDATE_INFO" "$root" "$STABLE_NAME" >/dev/null
-chmod +x "$STABLE_NAME"
+  -u "$UPDATE_INFO" "$root" "$CHANNEL_DIR/$STABLE_NAME" >/dev/null
+chmod +x "$CHANNEL_DIR/$STABLE_NAME"
 
 # The versioned name is what the per-version release publishes; the stable one
-# and its .zsync go to the rolling tag. Same bytes, two names.
-cp "$STABLE_NAME" "$appimage"
+# and its .zsync go to the rolling tag. Same bytes, two names, two places.
+# zsyncmake writes the .zsync into the working directory, not beside the image
+# it describes, so it has to be collected rather than assumed in place.
+[ -e "$STABLE_NAME.zsync" ] && mv "$STABLE_NAME.zsync" "$CHANNEL_DIR/"
+
+cp "$CHANNEL_DIR/$STABLE_NAME" "$appimage"
 chmod +x "$appimage"
 
 # The guards are the test. Each one is a way the repack could look like it
@@ -227,16 +263,28 @@ out="$check/squashfs-root"
 
 fail() { echo "FAILED: $1" >&2; exit 1; }
 
-[ -e "$out/usr/lib/$LIB" ] && fail "$LIB is still on the loader path."
-[ -e "$out/$FALLBACK_DIR/$LIB" ] || fail "the fallback copy of $LIB is missing."
-[ -e "$out/$HOOK" ] || fail "the fallback hook is missing."
-grep -q "triple-c-wayland-fallback" "$out/AppRun" || fail "AppRun does not source the hook."
+if [ "$demoted" = true ]; then
+  [ -e "$out/usr/lib/$LIB" ] && fail "$LIB is still on the loader path."
+  [ -e "$out/$FALLBACK_DIR/$LIB" ] || fail "the fallback copy of $LIB is missing."
+  [ -e "$out/$HOOK" ] || fail "the fallback hook is missing."
+  grep -q "triple-c-wayland-fallback" "$out/AppRun" || fail "AppRun does not source the hook."
+fi
 [ -x "$out/usr/bin/triple-c" ] || fail "no executable usr/bin/triple-c."
 
 # An empty Categories or missing metadata ships an image a manager cannot file
 # or describe, and both fail silently at runtime rather than at build time.
-grep -q "^Categories=.\+" "$out"/*.desktop || fail "Categories is still empty."
-[ -f "$appdata_src" ] && { [ -e "$out/usr/share/metainfo/$APP_ID.appdata.xml" ] \
+# Asserted positively, over every entry: the earlier form checked only that no
+# *root* file held an empty value, which passed while the real entry under
+# usr/share/applications shipped empty, and also passed on a missing key.
+desktops=0
+for desktop in "$out"/*.desktop "$out"/usr/share/applications/*.desktop; do
+  [ -e "$desktop" ] || continue
+  desktops=$((desktops + 1))
+  grep -q "^Categories=$CATEGORIES$" "$desktop" \
+    || fail "${desktop#"$out"/} does not carry Categories=$CATEGORIES."
+done
+[ "$desktops" -gt 0 ] || fail "the image contains no .desktop entry at all."
+[ -f "$appdata_src" ] && { [ -e "$out/usr/share/metainfo/$appdata_installed_as" ] \
   || fail "AppStream metadata did not make it into the image."; }
 
 # The update string is the difference between adoptable and updatable. It
@@ -245,13 +293,25 @@ grep -q "^Categories=.\+" "$out"/*.desktop || fail "Categories is still empty."
 # the URL it fetched the .zsync from. That is exactly why the output is named
 # for the fixed tag: a versioned name here resolves to the build the client
 # already has.
-[ -e "$STABLE_NAME" ] || fail "the stable-named image is missing."
-[ -e "$STABLE_NAME.zsync" ] || fail "appimagetool wrote no $STABLE_NAME.zsync."
+[ -e "$CHANNEL_DIR/$STABLE_NAME" ] || fail "the stable-named image is missing."
+[ -e "$CHANNEL_DIR/$STABLE_NAME.zsync" ] || fail "appimagetool wrote no .zsync."
 
-readelf -p .upd_info "$STABLE_NAME" 2>/dev/null | grep -q "$UPDATE_TAG" \
-  || fail "the image carries no update information for the $UPDATE_TAG tag."
-grep -aq "^Filename: $STABLE_NAME$" "$STABLE_NAME.zsync" \
+readelf -p .upd_info "$CHANNEL_DIR/$STABLE_NAME" 2>/dev/null | grep -qF "$UPDATE_INFO" \
+  || fail "the image does not carry exactly the expected update information."
+grep -aq "^Filename: $STABLE_NAME$" "$CHANNEL_DIR/$STABLE_NAME.zsync" \
   || fail "the .zsync names something other than $STABLE_NAME."
 
-echo "OK: $appimage prefers the host $LIB (fallback kept), carries AppStream"
-echo "    metadata, and updates from the $UPDATE_TAG tag via $STABLE_NAME.zsync."
+# The versioned release must carry one AppImage, not two. This is the guard
+# for the duplicate that shipped in 0.4.20 and 0.4.21.
+shopt -s nullglob
+beside=(*.AppImage)
+shopt -u nullglob
+[ "${#beside[@]}" -eq 1 ] \
+  || fail "expected 1 AppImage beside the release, found ${#beside[@]}."
+
+if [ "$demoted" = true ]; then
+  echo "OK: $appimage prefers the host $LIB (fallback kept) and carries"
+else
+  echo "OK: $appimage had no bundled $LIB to demote, and carries"
+fi
+echo "    AppStream metadata. Channel pair in $CHANNEL_DIR/, updating from $UPDATE_TAG."

scripts/publish-update-channel.sh

@@ -17,7 +17,22 @@
 # It writes to GitHub rather than Gitea because that mirror is where updates
 # are pulled from. Needs GH_PAT with contents write on the mirror.
 #
-# Usage: GH_PAT=... publish-update-channel.sh <directory holding the artifacts>
+# **The tag has to exist in Gitea, not just on GitHub, and that is the whole
+# reason this script touches Gitea at all.** Gitea push-mirrors this repo to
+# GitHub, and a mirror push deletes remote refs that have no local counterpart.
+# A tag created only by GitHub's release API therefore survives until the next
+# mirror run and then vanishes — which is exactly what happened to 0.4.20 and
+# 0.4.21: the release was created and both URLs verified 200 at 00:38, and the
+# 13:04 mirror deleted the tag, leaving every installed copy checking a 404.
+# Versioned tags never had this problem because `create-tag` creates them in
+# Gitea first. So does this one, now, and before the GitHub release rather than
+# after, so there is no window where the two disagree.
+#
+# Note what this means for verification: publishing correctly is not evidence
+# the channel still works hours later. The Gitea tag is what makes it durable,
+# so its absence is treated as a failure rather than a warning.
+#
+# Usage: GH_PAT=... GITEA_TOKEN=... GITEA_SHA=... publish-update-channel.sh <dir>
 
 set -euo pipefail
 
@@ -26,7 +41,12 @@ TAG="linux-latest"
 API="https://api.github.com/repos/$REPO"
 ASSETS=("Triple-C_x86_64.AppImage" "Triple-C_x86_64.AppImage.zsync")
 
+GITEA_API="${GITEA_API:-https://repo.anhonesthost.net/api/v1}"
+GITEA_REPO="${GITEA_REPO:-CyberCoveLLC/Triple-C}"
+
 : "${GH_PAT:?GH_PAT is required to publish the update channel}"
+: "${GITEA_TOKEN:?GITEA_TOKEN is required to anchor the $TAG tag against the mirror}"
+: "${GITEA_SHA:?GITEA_SHA is required to point the $TAG tag at this build}"
 dir="${1:?usage: publish-update-channel.sh <artifacts directory>}"
 cd "$dir"
 
@@ -35,46 +55,179 @@ for asset in "${ASSETS[@]}"; do
 done
 
 gh() { curl -sf -H "Authorization: Bearer $GH_PAT" -H "Accept: application/vnd.github+json" "$@"; }
+tea() { curl -sf -H "Authorization: token $GITEA_TOKEN" -H "Content-Type: application/json" "$@"; }
+# Status, not a boolean. `curl -sf` fails identically for "404, the tag is
+# genuinely absent" and "503, Gitea is briefly unreachable", and treating the
+# second as the first means POSTing over a tag that already exists, taking a
+# 409, and aborting the last step of build-linux — which `create-tag` and
+# `sync-to-github` both depend on. A transient blip would cost the release, not
+# just the channel update. Same `case`-on-code idiom as `Upload to Gitea
+# release` two steps above in the workflow. A refused connection reports 000
+# and lands in the catch-all.
+tea_code() { curl -s -o /dev/null -w '%{http_code}' -H "Authorization: token $GITEA_TOKEN" "$@"; }
 
-echo "==> Looking for the $TAG release"
-release="$(gh "$API/releases/tags/$TAG" 2>/dev/null || true)"
-release_id="$(printf '%s' "$release" | python3 -c 'import sys,json;print(json.load(sys.stdin).get("id",""))' 2>/dev/null || true)"
+# Anchor the tag in Gitea — see the header. **Created if absent, never moved.**
+#
+# An earlier version deleted and recreated it so the tag would name the current
+# build. That was worse than useless: nothing about the channel depends on
+# which commit the tag points at — the update string resolves the tag by *name*
+# and the assets hang off the release object — while a DELETE followed by a
+# failed POST destroys a working anchor and leaves a window in which a mirror
+# run prunes GitHub's copy. A transient Gitea error would have converted a
+# healthy channel into a dead one, which is strictly worse than this step not
+# existing. Gitea's POST /tags has no force semantics, so the DELETE was only
+# ever there to get around a 409; asking first removes the need.
+echo "==> Anchoring the $TAG tag in Gitea"
+anchor_probe="$(tea_code "$GITEA_API/repos/$GITEA_REPO/tags/$TAG")"
+case "$anchor_probe" in
+  200)
+    echo "    already anchored — left alone"
+    ;;
+  404)
+    echo "    creating it at ${GITEA_SHA:0:9}"
+    tea -X POST "$GITEA_API/repos/$GITEA_REPO/tags" \
+      -d "{\"tag_name\": \"$TAG\", \"target\": \"$GITEA_SHA\", \"message\": \"Rolling Linux update channel\"}" \
+      >/dev/null
+    ;;
+  *)
+    echo "FAILED: Gitea answered $anchor_probe asking whether the $TAG tag exists." >&2
+    echo "        Refusing to guess — creating it blindly would 409 over an" >&2
+    echo "        existing tag and abort the release." >&2
+    exit 1
+    ;;
+esac
+
+# Not best-effort. Without this tag the mirror removes GitHub's and the
+# channel dies silently somewhere between now and four hours from now. Reported
+# by code, so "Gitea was unreachable" cannot masquerade as "the tag is gone".
+anchor_code="$(tea_code "$GITEA_API/repos/$GITEA_REPO/tags/$TAG")"
+[ "$anchor_code" = "200" ] || {
+  echo "FAILED: the $TAG tag is not readable in Gitea (HTTP $anchor_code);" >&2
+  echo "        without it the mirror would delete GitHub's copy." >&2
+  exit 1
+}
+
+# Look through the authenticated list rather than /releases/tags/, which never
+# returns drafts. That matters here specifically: GitHub demotes a published
+# release to a draft when its tag is deleted, which is the state every mirror
+# run left behind, so the by-tag lookup reports "absent" while orphaned drafts
+# sit there holding 86 MB each. Reuse the newest and delete the rest, or they
+# accumulate one per release forever.
+echo "==> Looking for the $TAG release (drafts included)"
+all_releases="$(gh "$API/releases?per_page=100")"
+mapfile -t existing < <(printf '%s' "$all_releases" | python3 -c '
+import sys, json
+tag = sys.argv[1]
+rs = [r for r in json.load(sys.stdin) if r.get("tag_name") == tag]
+rs.sort(key=lambda r: r.get("created_at",""), reverse=True)
+for r in rs:
+    print(r["id"])
+' "$TAG")
+
+release_id="${existing[0]:-}"
+
+for stale in "${existing[@]:1}"; do
+  echo "    deleting orphaned duplicate release $stale"
+  gh -X DELETE "$API/releases/$stale" >/dev/null || true
+done
+
+if [ -n "$release_id" ]; then
+  # A draft has no tag and serves no download URL, so it has to be republished.
+  echo "    reusing release $release_id"
+  # `make_latest` is not optional here even though this release already exists.
+  # Publishing a draft is a publish transition, where the API's documented
+  # default is `true` — so omitting it would quietly promote this channel to
+  # the repository's "Latest release" and bury the versioned release a person
+  # actually wants from the releases page.
+  #
+  # `tag_name` is re-sent deliberately, and must be: the API removes the tag
+  # when a PATCH omits it. Given this whole change exists because a tag
+  # disappeared, that is an expensive line to tidy away.
+  gh -X PATCH "$API/releases/$release_id" \
+    -d "{\"tag_name\": \"$TAG\", \"draft\": false, \"make_latest\": \"false\"}" >/dev/null
+  release="$(gh "$API/releases/$release_id")"
+fi
 
 if [ -z "$release_id" ]; then
   echo "==> Creating it"
   # Not a prerelease, but deliberately not the "latest" release either: this
   # tag is a channel, and it must never displace the versioned release a
   # person lands on from the releases page.
-  release="$(gh -X POST "$API/releases" -d "$(python3 -c '
+  body_json="$(python3 -c '
 import json
 print(json.dumps({
     "tag_name": "'"$TAG"'",
     "name": "Linux update channel",
-    "body": "Rolling AppImage build that Triple-C’s in-app updater reads. "
+    "body": "Rolling AppImage build that Triple-C\u2019s in-app updater reads. "
             "The two files here are replaced on every release; for a specific "
             "version, use the versioned releases instead.",
     "draft": False,
     "prerelease": False,
     "make_latest": "false",
-}))')")"
+}))')"
+
+  # `already_exists` is a benign, recoverable answer, not a reason to abort the
+  # last step of build-linux and lose the release with it. It means a release
+  # for this tag exists but the listing above did not show it — a draft that has
+  # sunk past the first page, since a draft's created_at is frozen while newer
+  # releases push it down. Re-ask by tag and carry on.
+  create_body="$(mktemp)"
+  create_code="$(curl -s -o "$create_body" -w '%{http_code}' \
+    -H "Authorization: Bearer $GH_PAT" -H "Accept: application/vnd.github+json" \
+    -X POST "$API/releases" -d "$body_json")"
+
+  case "$create_code" in
+    201)
+      release="$(cat "$create_body")"
+      ;;
+    422)
+      if grep -q "already_exists" "$create_body"; then
+        echo "    a release for $TAG already exists but was not listed — reusing it"
+        release="$(gh "$API/releases/tags/$TAG")"
+      else
+        echo "FAILED: GitHub rejected the release (422):" >&2
+        cat "$create_body" >&2
+        rm -f "$create_body"
+        exit 1
+      fi
+      ;;
+    *)
+      echo "FAILED: creating the $TAG release returned $create_code:" >&2
+      cat "$create_body" >&2
+      rm -f "$create_body"
+      exit 1
+      ;;
+  esac
+  rm -f "$create_body"
+
   release_id="$(printf '%s' "$release" | python3 -c 'import sys,json;print(json.load(sys.stdin)["id"])')"
 fi
 
-echo "==> Removing superseded assets from release $release_id"
-printf '%s' "$release" | python3 -c '
+# One asset at a time, delete immediately followed by upload. Deleting both up
+# front leaves the channel holding a fresh AppImage and no .zsync if the second
+# upload fails, and a client that cannot fetch the .zsync simply stops updating
+# — no error anyone here would see.
+asset_ids="$(printf '%s' "$release" | python3 -c '
 import sys, json
 keep = set(sys.argv[1:])
+out = {}
 for a in json.load(sys.stdin).get("assets", []):
     if a["name"] in keep:
-        print(a["id"])
-' "${ASSETS[@]}" | while read -r asset_id; do
-  [ -n "$asset_id" ] || continue
-  gh -X DELETE "$API/releases/assets/$asset_id" >/dev/null || true
-done
+        out[a["name"]] = a["id"]
+print(json.dumps(out))
+' "${ASSETS[@]}")"
 
+# --retry/--max-time/--http1.1 for the reason the Gitea upload steps in this
+# repo carry them: real mid-stream failures on large assets (curl 92 and 28).
 for asset in "${ASSETS[@]}"; do
+  stale_id="$(printf '%s' "$asset_ids" | python3 -c 'import sys,json;print(json.load(sys.stdin).get(sys.argv[1],""))' "$asset")"
+  if [ -n "$stale_id" ]; then
+    echo "==> Replacing $asset (dropping superseded asset $stale_id)"
+    gh -X DELETE "$API/releases/assets/$stale_id" >/dev/null || true
+  fi
   echo "==> Uploading $asset ($(du -h "$asset" | cut -f1))"
-  curl -sf -X POST \
+  curl -sf --http1.1 --retry 5 --retry-all-errors --retry-delay 5 --max-time 900 \
+    -X POST \
     -H "Authorization: Bearer $GH_PAT" \
     -H "Content-Type: application/octet-stream" \
     --data-binary "@$asset" \
@@ -84,12 +237,22 @@ done
 # The updater is only as good as this URL, and a silent failure here means
 # every installed copy quietly stops updating. Confirm both are actually
 # fetchable at the address the AppImage was built to check.
+# Size as well as status: a 200 only proves something is served at the
+# address, not that it is this build. GitHub accepting a truncated upload
+# would pass a status-only check and then fail every client's checksum.
 echo "==> Verifying the published URLs"
 for asset in "${ASSETS[@]}"; do
   url="https://github.com/$REPO/releases/download/$TAG/$asset"
-  code="$(curl -s -o /dev/null -w '%{http_code}' -L "$url")"
-  [ "$code" = "200" ] || { echo "FAILED: $url returned $code" >&2; exit 1; }
-  echo "    $code  $url"
+  local_size="$(stat -c %s "$asset")"
+
+  headers="$(curl -sIL "$url" | tr -d '\r')"
+  code="$(printf '%s\n' "$headers" | awk '/^HTTP\//{c=$2} END{print c}')"
+  served="$(printf '%s\n' "$headers" | awk 'tolower($1)=="content-length:"{n=$2} END{print n}')"
+
+  [ "$code" = "200" ] || { echo "FAILED: $url returned ${code:-no status}" >&2; exit 1; }
+  [ "$served" = "$local_size" ] \
+    || { echo "FAILED: $url serves ${served:-unknown} bytes, built $local_size." >&2; exit 1; }
+  echo "    $code  $served bytes  $url"
 done
 
-echo "OK: $TAG updated."
+echo "OK: $TAG updated, and anchored in Gitea so the mirror preserves it."