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/protocol/src/messages.ts

@@ -1267,6 +1267,7 @@ export const ImportAgentRequestMessageSchema = z.object({
   sessionId: z.string().optional(),
   providerHandleId: z.string().optional(),
   cwd: z.string().optional(),
+  workspaceId: z.string().optional(),
   labels: z.record(z.string(), z.string()).optional(),
   requestId: z.string(),
 });
@@ -2560,6 +2561,8 @@ export const ServerInfoStatusPayloadSchema = z
         commitsList: z.boolean().optional(),
         // COMPAT(providerRemoval): added in v0.1.105, drop the gate when floor >= v0.1.105.
         providerRemoval: z.boolean().optional(),
+        // COMPAT(importSessionWorkspaceTarget): added in v0.1.110, remove gate after 2027-01-16.
+        importSessionWorkspaceTarget: z.boolean().optional(),
       })
       .optional(),
   })