Reimport archived sessions into the current workspace (#2123)

* fix(sessions): reimport archived sessions in their workspace

Archived agent records were treated as active imports, hiding their provider sessions permanently. Workspace-originated imports also discarded their workspace identity and created a duplicate workspace.

* fix(sessions): validate archived session restores

Restore archived imports under their existing Paseo agent identity, reject stale workspace ownership, and gate workspace targeting when the host cannot honor it.

* fix(sessions): roll back failed archived imports

If provider resume or history hydration fails, close any partial runtime, re-archive the provider session, and restore the original stored agent record.

* fix(sessions): validate restored import ownership

* fix(sessions): serialize concurrent restores

* fix(sessions): harden archived import recovery

* fix(sessions): validate archived import placement

* refactor(sessions): centralize provider session imports

Keep workspace placement rollback and stored-agent activation behind their existing owners so Session remains the wire boundary.

packages/app/src/components/import-session-sheet-view-model.ts

@@ -5,6 +5,14 @@ import { i18n } from "@/i18n/i18next";
 export const PER_PROVIDER_LIMIT = 15;
 export const ALL_FILTER_VALUE = "__all__";
 
+export function requiresImportSessionsHostUpgrade(input: {
+  supportsSnapshot: boolean;
+  workspaceId?: string | null;
+  supportsWorkspaceTarget: boolean;
+}): boolean {
+  return !input.supportsSnapshot || (Boolean(input.workspaceId) && !input.supportsWorkspaceTarget);
+}
+
 export interface SessionsQueryResult {
   data:
     | {