SEP-2663: Allow ttlSeconds to change during a task

Author: LucaButBoring

docs/seps/2663-tasks-extension.mdx

@@ -140,7 +140,8 @@ interface Task {
 
   /**
    * Time-to-live duration from creation in integer seconds, null for unlimited.
-   * The server may discard the task after the TTL elapses.
+   * The server may discard the task after the TTL elapses. This value MAY change
+   * over the lifetime of a task.
    * Aligns with HTTP cache-control conventions per SEP-2549.
    */
   ttlSeconds: number | null;
@@ -413,7 +414,7 @@ type GetTaskResult = Result & DetailedTask;
 
 The response carries the appropriate response variant for the task's current status (see [Task Status](#task-status)). The `resultType` field **MUST** be set to `"complete"` on this object as it is the standard result shape for the `tasks/get` request.
 
-If the task has a non-null `ttlSeconds`, clients **MAY** treat the TTL as a backstop: if the task's observable status has not reflected the update after `createdAt` plus `ttlSeconds` has elapsed, the client **MAY** consider the task to no longer be usable. Conversely, servers **MAY** mark a task as `failed` at any point after the TTL elapses, and subsequently delete it at any time.
+If the task has a non-null `ttlSeconds`, clients **MAY** treat the TTL as a backstop: if the task's observable status has not reflected the update after `createdAt` plus `ttlSeconds` has elapsed, the client **MAY** consider the task to no longer be usable. Conversely, servers **MAY** mark a task as `failed` at any point after the TTL elapses, and subsequently delete it at any time. The value of `ttlSeconds` **MAY** change over the lifetime of a task.
 
 ### Task Input Requests