feat(apiserver): populate hosts num_run from the job store

num_run was declared in the host model but never set anywhere — the
controller's worker push carries no running-job count, so hosts always
showed 0 regardless of running jobs. Compute it live in the hosts list
handler by counting RUN jobs per exec host from store.Jobs — the same
source the jobs list uses, so the two stay consistent.

Verified: t1 with 5 RUN jobs shows num_run 5, matching the jobs list.

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

src/frontend/apiserver/controllers/hosts_numrun_test.go

@@ -0,0 +1,61 @@
+package controllers
+
+import (
+	"testing"
+
+	"apiserver/models"
+	"apiserver/store"
+)
+
+func TestCountRunningJobsPerHost(t *testing.T) {
+	store.InitStores()
+
+	// RUN job on t1.
+	store.Jobs.Put(1, models.JobInfo{
+		JobStatus: models.JOBSTAT["RUN"],
+		ExecHosts: models.Jsonb{String: `{"host_slots":[{"host_name":"t1","num_slots":1}],"num_hosts":1}`},
+	})
+	// RUN|USUSP job on t2 — the RUN bit must still count it.
+	store.Jobs.Put(2, models.JobInfo{
+		JobStatus: models.JOBSTAT["RUN"] | models.JOBSTAT["USUSP"],
+		ExecHosts: models.Jsonb{String: `{"host_slots":[{"host_name":"t2","num_slots":1}],"num_hosts":1}`},
+	})
+	// Multi-host RUN job: one job on t1 + t3 counts on both.
+	store.Jobs.Put(3, models.JobInfo{
+		JobStatus: models.JOBSTAT["RUN"],
+		ExecHosts: models.Jsonb{String: `{"host_slots":[{"host_name":"t1","num_slots":1},{"host_name":"t3","num_slots":1}],"num_hosts":2}`},
+	})
+	// PEND and DONE jobs must NOT count.
+	store.Jobs.Put(4, models.JobInfo{
+		JobStatus: models.JOBSTAT["PEND"],
+		ExecHosts: models.Jsonb{String: `{"host_slots":[{"host_name":"t3","num_slots":1}],"num_hosts":1}`},
+	})
+	store.Jobs.Put(5, models.JobInfo{
+		JobStatus: models.JOBSTAT["DONE"],
+		ExecHosts: models.Jsonb{String: `{"host_slots":[{"host_name":"t1","num_slots":1}],"num_hosts":1}`},
+	})
+	// RUN job with empty/bad exec_hosts must not crash or count.
+	store.Jobs.Put(6, models.JobInfo{
+		JobStatus: models.JOBSTAT["RUN"],
+		ExecHosts: models.Jsonb{String: ``},
+	})
+	store.Jobs.Put(7, models.JobInfo{
+		JobStatus: models.JOBSTAT["RUN"],
+		ExecHosts: models.Jsonb{String: `not-json`},
+	})
+
+	counts := countRunningJobsPerHost()
+
+	if counts["t1"] != 2 { // jobs 1 + 3
+		t.Errorf("t1 running = %d, want 2", counts["t1"])
+	}
+	if counts["t2"] != 1 {
+		t.Errorf("t2 running = %d, want 1", counts["t2"])
+	}
+	if counts["t3"] != 1 { // job 3 only (job 4 is PEND)
+		t.Errorf("t3 running = %d, want 1", counts["t3"])
+	}
+	if _, ok := counts["nohost"]; ok {
+		t.Error("unexpected host 'nohost' in counts")
+	}
+}