fix: retain snapshots for removed workspaces

backend/src/routes/sessions.ts

@@ -72,6 +72,15 @@ export function sessionRoutes(
     return typeof runner.withPrincipal === "function" ? runner.withPrincipal(principal) : runner;
   };
 
+  /** Include retained historical descriptors so removed workspaces remain resumable. */
+  const sessionRevisions = async () => {
+    const registry = d.workspaceRegistry as Partial<WorkspaceRegistry>;
+    if (typeof registry.listRetainedSnapshots === "function") {
+      return await registry.listRetainedSnapshots();
+    }
+    return await d.workspaceRegistry.list();
+  };
+
   const isNotFound = (error: unknown) =>
     /not found|non trovata|inesistente|404/i.test(error instanceof Error ? error.message : String(error));
 
@@ -107,7 +116,7 @@ export function sessionRoutes(
     };
     let revisions: Awaited<ReturnType<typeof d.workspaceRegistry.list>>;
     try {
-      revisions = await d.workspaceRegistry.list();
+      revisions = await sessionRevisions();
     } catch (registryError) {
       // Sessions created before revision pinning still live under the installation's legacy
       // default config. Keep that compatibility path available when a fresh installation has
@@ -394,11 +403,15 @@ export function sessionRoutes(
       // Admin RLS is deliberately disabled for a normal 'mine' listing.
       const scopedPrincipal = scope === "mine" ? { ...principal, isAdmin: false } : principal;
       const runner = runnerFor(scopedPrincipal);
-      const revisions = await d.workspaceRegistry.list();
+      const revisions = await sessionRevisions();
       const lists = await Promise.all(revisions
         .filter((revision) => revision.state === "operational")
         .map((revision) => runner.sessionList(revision.snapshotPath) as Promise<SessionRow[]>));
-      const list = lists.flat();
+      const sessions = new Map<string, SessionRow>();
+      for (const row of lists.flat()) {
+        if (!sessions.has(row.id)) sessions.set(row.id, row);
+      }
+      const list = [...sessions.values()];
       // Only an administrator-visible complete list (or the single local principal) is safe
       // input for retention. A remote per-user view can never discard another principal's pin.
       const reconcileSnapshotRetention = (d.workspaceRegistry as Partial<WorkspaceRegistry>).reconcileSnapshotRetention;