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.test.ts

@@ -9,6 +9,7 @@ import {
   getPromptPreview,
   getSessionTitle,
   resolveProvidersToFetch,
+  requiresImportSessionsHostUpgrade,
   type SessionsQueryResult,
   sumFilteredAlreadyImportedCount,
 } from "@/components/import-session-sheet-view-model";
@@ -70,6 +71,35 @@ describe("resolveProvidersToFetch", () => {
   });
 });
 
+describe("requiresImportSessionsHostUpgrade", () => {
+  it("allows home imports on hosts without workspace targeting", () => {
+    expect(
+      requiresImportSessionsHostUpgrade({
+        supportsSnapshot: true,
+        workspaceId: null,
+        supportsWorkspaceTarget: false,
+      }),
+    ).toBe(false);
+  });
+
+  it("requires host support for imports opened from a workspace", () => {
+    expect(
+      requiresImportSessionsHostUpgrade({
+        supportsSnapshot: true,
+        workspaceId: "ws-current",
+        supportsWorkspaceTarget: false,
+      }),
+    ).toBe(true);
+    expect(
+      requiresImportSessionsHostUpgrade({
+        supportsSnapshot: true,
+        workspaceId: "ws-current",
+        supportsWorkspaceTarget: true,
+      }),
+    ).toBe(false);
+  });
+});
+
 describe("buildProviderLabelMap", () => {
   it("returns an empty map when snapshot entries are missing", () => {
     expect(buildProviderLabelMap(undefined).size).toBe(0);