Resume interrupted editor co-op runs

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/campaign_doc.rs

@@ -18,6 +18,12 @@ pub struct CampaignProgress {
     // random maps are rolled once per run of the campaign: this seed is fixed for the run
     #[serde(default)]
     pub run_seed: u32,
+    // co-op runs (kept by the host): the mission the run goes on with and what every master carries
+    // into it; None once the run is over
+    #[serde(default)]
+    pub next: Option<usize>,
+    #[serde(default)]
+    pub carry: Vec<(u8, crate::campaign::Carry)>,
 }
 
 impl CampaignProgress {
@@ -27,6 +33,8 @@ impl CampaignProgress {
             done: vec![false; n],
             completed_choice: vec![None; n],
             run_seed: (macroquad::miniquad::date::now() * 1000.0) as u64 as u32 | 1,
+            next: None,
+            carry: Vec::new(),
         }
     }