Edit the drafted merge message before confirming

api/openapi.yaml

@@ -276,13 +276,24 @@ paths:
     post:
       operationId: mergeTask
       description: >
-        Starts the same agent turn as merge-in. When that turn ends normally, byre squashes the task's worktree
+        Sets the task's merge_title to the confirmed title, then starts the same agent turn as merge-in, without
+        its invitation to revise the title. When that turn ends normally, byre squashes the task's worktree
         into one commit titled with the task's merge_title on the project's default branch, authored by the caller with
         a Co-authored-by trailer for each of the task's co-authors, pushes it to origin, fast-forwards the project's
         checkout to it, then removes the worktree and branch and marks the task merged. While another task in the
         project is merging, the merge is held instead (merge_queued_at is set) and starts when no merge is in progress
-        in the project and the task's session is idle, oldest first. Refused while a turn is running, or the
-        merge is already held.
+        in the project and the task's session is idle, oldest first. The title is fixed from here until the task
+        closes. Refused while a turn is running, or the merge is already held.
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              type: object
+              additionalProperties: false
+              required: [merge_title]
+              properties:
+                merge_title: { type: string, description: "The squash commit's title: one line, at most 72 characters." }
       responses:
         "202":
           description: The merge was started or held.