Keep local artifacts under the storage directory

Servers have always moved a local artifact store under the storage
directory at startup, whatever `local.root` said. Browser-wizard installs
write `local.root = "<storage>/objects"`, so honoring that root would move
their store and hide every artifact already written, with nothing to
migrate it. Restore the storage-directory override for local roots and
leave honoring custom roots to a change that migrates existing objects.

Installer metadata still goes through the override, so it lands where the
server reads.

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

docs/public/administration/server-configuration.mdx

@@ -247,10 +247,6 @@ prefix = "artifacts"
 root = "/var/lib/fabro/objects"
 ```
 
-A custom local artifact root is preserved at startup and when `--storage-dir`
-changes the server's storage directory. When `local.root` is omitted, the
-default `<storage_root>/objects/artifacts` location follows that override.
-
 The wizard only covers AWS S3 bucket/region plus one of:
 
 - runtime credentials already supplied by the deployment environment

lib/apps/fabro-cli/tests/it/scenario/artifacts.rs

@@ -16,14 +16,14 @@ async fn artifact_worker_captures_large_files_in_the_configured_local_store() {
         return;
     }
     let context = test_context!();
-    let objects = context.temp_dir.join("selected-artifact-root");
-    let settings = format!(
-        "\n[server.artifacts]\nprovider = \"local\"\nprefix = \"selected-prefix\"\n[server.artifacts.local]\nroot = {:?}\n",
-        objects.to_str().unwrap()
-    );
-    // RunningServer also passes --storage-dir. The explicit artifact directory
-    // must still receive the captures, independently of the database root.
-    let server = RunningServer::start_with(&settings, &[]).await;
+    let server = RunningServer::start_with(
+        "\n[server.artifacts]\nprovider = \"local\"\nprefix = \"selected-prefix\"\n",
+        &[],
+    )
+    .await;
+    // RunningServer explicitly selects --storage-dir, which also selects the
+    // local artifact root. Inspect that resolved backend, outside the sandbox.
+    let objects = server.storage_dir.join("objects/artifacts");
     let workspace = artifact_workspace(&context);
     tokio::fs::write(workspace.join("workflow.fabro"), r#"digraph Capture {
         graph [goal="Capture binary files", default_max_retries=0]
@@ -58,13 +58,6 @@ async fn artifact_worker_captures_large_files_in_the_configured_local_store() {
         serde_json::to_value(rebuilt.unwrap().artifacts).unwrap(),
         projection["artifacts"]
     );
-    assert!(
-        !server
-            .storage_dir
-            .join(format!("objects/artifacts/selected-prefix/{run_id}"))
-            .exists(),
-        "captures must not be redirected to the default artifact directory"
-    );
 
     for (path, size) in [
         ("medium.bin", 3 * 1024 * 1024),

lib/apps/fabro-server/src/serve.rs

@@ -1348,16 +1348,18 @@ mod tests {
     }
 
     #[test]
-    fn runtime_server_settings_preserve_custom_artifact_root() {
+    fn runtime_server_settings_keep_local_artifacts_under_storage_dir() {
+        // Servers have always kept local artifacts under the storage
+        // directory, including installs whose settings name a `local.root`.
         let settings = server_settings(
             r#"
 _version = 1
 [server.storage]
 root = "/srv/from-disk"
 [server.artifacts]
-prefix = "selected-prefix"
+prefix = "artifacts"
 [server.artifacts.local]
-root = "/mnt/artifact-files"
+root = "/srv/from-disk/objects"
 "#,
         );
         for storage_root in ["/srv/from-disk", "/srv/from-runtime"] {
@@ -1365,7 +1367,13 @@ root = "/mnt/artifact-files"
                 .clone()
                 .with_storage_override(Path::new(storage_root));
             assert_eq!(resolved.server.storage.root, storage_root);
-            assert_eq!(resolved.server.artifacts, settings.server.artifacts);
+            assert_eq!(resolved.server.artifacts.prefix, "artifacts");
+            assert_eq!(
+                resolved.server.artifacts.store,
+                fabro_types::settings::ObjectStoreSettings::Local {
+                    root: format!("{storage_root}/objects/artifacts"),
+                }
+            );
             // Startup and config reload can apply the same override again.
             assert_eq!(
                 resolved

lib/foundation/fabro-types/src/dense.rs

@@ -16,14 +16,11 @@ pub struct ServerSettings {
 impl ServerSettings {
     #[must_use]
     pub fn with_storage_override(mut self, path: &Path) -> Self {
-        // Only the derived default follows the storage directory. A custom
-        // artifact location is independent of the database and runtime root.
-        let default_artifact_root =
-            ServerArtifactsSettings::default_local_root(Path::new(&self.server.storage.root));
+        // The local artifact store always lives under the storage directory.
+        // A configured `local.root` has never moved it, and existing objects
+        // are only found there.
         if let ObjectStoreSettings::Local { root } = &mut self.server.artifacts.store {
-            if *root == default_artifact_root {
-                *root = ServerArtifactsSettings::default_local_root(path);
-            }
+            *root = ServerArtifactsSettings::default_local_root(path);
         }
         self.server.storage.root = path.display().to_string();
         self