Hold a task's merge while another task in the project is merging

web/src/task.ts

@@ -134,10 +134,16 @@ function taskHead(rerender: () => void): Head {
       }
       const target = state.projects.find((p) => p.id === task.project_id)?.default_branch ?? "the default branch";
       const busy = sess?.state === "running" || sess?.state === "queued";
+      const held = task.merge_queued_at !== undefined;
       const merge = h(
         "button",
-        { disabled: busy || unmerged?.taskId !== task.id || !unmerged.has, title: `The agent merges ${target} in, then byre squashes into one commit on ${target} and pushes it to origin` },
-        "Merge",
+        {
+          disabled: busy || held || unmerged?.taskId !== task.id || !unmerged.has,
+          title: held
+            ? "Waiting for the merge in progress in this project to finish"
+            : `The agent merges ${target} in, then byre squashes into one commit on ${target} and pushes it to origin; held while another task in the project is merging`,
+        },
+        held ? "Merge held" : "Merge",
       );
       merge.onclick = async () => {
         let coAuthors;
@@ -1008,6 +1014,9 @@ function renderEvent(ev: ByreEvent, ctx: Ctx): HTMLElement | null {
     case "task.merge_title":
       return h("div", { class: "note" }, `${ev.actor} set the merge commit title to "${String(p["merge_title"])}" `, when);
 
+    case "task.merge_queued":
+      return h("div", { class: "note" }, `${ev.actor} asked to merge; held until the merge in progress in this project is done `, when);
+
     case "setup.started": {
       const base = Number(p["port_base"]);
       return h("div", { class: "note" }, `running ${String(p["script"])} with ports ${base}–${base + 9} `, when);