feat(web): make produced-file overflow discoverable

packages/host/apiproxy/src/api/host.schema.ts

@@ -17,6 +17,7 @@ export const hostDescribeValueSchema = z.object({
   provider: z.string().optional(),
   model: z.string().optional(),
   attachedSessions: z.number().int().nonnegative(),
+  canOpenPath: z.boolean(),
 }) satisfies z.ZodType<Wire<ResponseValue<'host.describe'>>>
 
 /** host.pickDirectory request payload (empty object literal). */

packages/host/apiproxy/src/api/host.ts

@@ -41,6 +41,7 @@ export interface HostApi {
    * applied when a new agent doesn't specify them explicitly, absent when the host configures
    * no explicit default (the adapter falls back internally);
    * attachedSessions = count of currently attached sessions (those with a live agent);
+   * canOpenPath = whether this deployment can hand a path to a user-visible native desktop.
    */
   describe(request: RpcRequest<{}>): Promise<RpcResponse<{
     version: string
@@ -48,6 +49,7 @@ export interface HostApi {
     provider?: string
     model?: string
     attachedSessions: number
+    canOpenPath: boolean
   }>>
 
   /**