fix(scheduler): update existing worker in place on re-push (bug-1494)

When a worker is re-pushed (e.g. it rejoined with fresh resvals after the
controller/worker had been down), sched_update_workers built a new worker and
sched_add_worker's key_add returned EEXIST — the fresh worker was dropped and
the scheduler kept the stale state (slots=0 from the dead/absent period).
PEND jobs never dispatched even after the worker returned with full capacity
(bug-1494, controller-restart self-heal).

sched_update_workers now updates an already-known worker in place: swap the
fresh resvals/resInUse/status into the existing worker (the stale arrays are
freed when the discarded object is torn down) and adopt its host_eval_ctx.
Also NULL-guard make_sched_worker (it can return NULL).

Verified on the t1 cluster: scheduler started while the worker was dead
(slots=0), worker rejoined (slots=8), previously-PEND jobs dispatched and
completed, no ASAN.

Co-Authored-By: Claude <noreply@anthropic.com>

src/scheduler/src/scheduler.c

@@ -740,8 +740,48 @@ static int sched_update_workers(xce_scheduler_t* sched, int nworkers,
 
     for (i = 0; i < nworkers; i++) {
         xce_sched_worker_t* w = make_sched_worker(sched, workers[i]);
+        if (w == NULL) {
+            continue;
+        }
 
         plugin_worker_update(sched, w);
+
+        /* bug-1494 (controller-restart self-heal): a re-push of an already
+         * known worker (e.g. after it rejoined with fresh resvals) must
+         * UPDATE it in place. key_add() would EEXIST-drop the fresh worker
+         * and leave the stale resvals in place — the scheduler keeps the
+         * dead/absent state (slots=0) and PEND jobs never dispatch even after
+         * the worker comes back with full capacity. Swap the fresh
+         * resvals/status into the existing worker, then discard the new
+         * object (which now holds the stale arrays). */
+        xce_sched_worker_t* existing = sched_get_worker(sched, w->name);
+        if (existing != NULL) {
+            zarray_t tmp;
+
+            tmp               = existing->resvals;
+            existing->resvals = w->resvals;
+            w->resvals        = tmp;
+
+            tmp                 = existing->resInUse;
+            existing->resInUse  = w->resInUse;
+            w->resInUse         = tmp;
+
+            existing->status = w->status;
+
+            if (existing->host_eval_ctx != NULL) {
+                sched_worker_release_host_ctx(existing);
+            }
+            existing->host_eval_ctx = w->host_eval_ctx;
+            w->host_eval_ctx        = NULL;
+
+            zarray_fini(&(w->resvals));
+            zarray_fini(&(w->resInUse));
+            /* w->name is an interned string (makeString) owned by the
+             * xstring table — never free() it (bad-free). */
+            free(w);
+            continue;
+        }
+
         sched_add_worker(sched, w);
     }