Fix race in kill-job! overwriting :killed with :failed

Commit :killed to the registry before destroying the process so the
exit monitor can't race ahead and overwrite it with :failed (exit 143).
Fixes the flaky background-job-lifecycle integration test. (#510)

🤖 Generated with [ECA](https://eca.dev) (nubank-anthropic/opus-4.8 - max)

Co-Authored-By: eca-agent <git@eca.dev>

Author: ericdallo

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- Bugfix: `kill-job!` commits `:killed` before destroying the process, fixing a race where the exit monitor overwrote it with `:failed` (exit 143). (#510)
+
 ## 0.142.1
 
 - Bugfix: `postRequest` hook no longer fires for subagent chats; subagents use `subagentPostRequest` only, preventing duplicate hook notifications. (#505)

src/eca/features/background_tasks.clj

@@ -214,11 +214,13 @@
   (if-let [job (get-job job-id)]
     (if (= :running (:status job))
       (do
-        (kill-job-impl job)
+        ;; Commit :killed before destroying the process so monitor-process-exit!
+        ;; never races ahead and overwrites it with :failed (exit 143/SIGTERM).
         (swap! registry* (fn [reg]
                            (-> reg
                                (assoc-in [:jobs job-id :status] :killed)
                                (assoc-in [:jobs job-id :ended-at] (Instant/now)))))
+        (kill-job-impl job)
         (logger/info logger-tag "Killed background job" {:id job-id})
         true)
       (do