Let a queued message be taken back into the composer

api/openapi.yaml

@@ -762,6 +762,20 @@ paths:
         "404": { $ref: "#/components/responses/Error" }
         "409": { $ref: "#/components/responses/Error" }
 
+  /api/tasks/{taskId}/queue/{inputId}:
+    parameters:
+      - { name: taskId, in: path, required: true, schema: { type: string } }
+      - { name: inputId, in: path, required: true, schema: { type: integer, format: int64 } }
+    delete:
+      operationId: withdrawMessage
+      description: >
+        Takes back a queued message (the id from its user.queued event) before the agent gets it, and records a
+        user.unqueued event. Refused once the message has been handed over.
+      responses:
+        "204": { description: The message was withdrawn. }
+        "404": { $ref: "#/components/responses/Error" }
+        "409": { $ref: "#/components/responses/Error" }
+
   /api/sessions/{sessionId}:
     parameters:
       - { name: sessionId, in: path, required: true, schema: { type: string } }