fix: call onSpawn after pod enters Running state to prevent UI desync

The k8s adapter never called ctx.onSpawn(), so the Paperclip server
had no processStartedAt timestamp for the run. The stale-run reaper
(reapOrphanedRuns) would then mark live k8s runs as failed/orphaned,
causing the UI to show no active runs and triggering duplicate run
attempts that hit the concurrency guard.

Uses pid=-1 as a sentinel since there is no local process — the
server's isProcessAlive check safely returns false for pid <= 0.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/server/execute.ts

@@ -387,6 +387,19 @@ export async function execute(ctx: AdapterExecutionContext): Promise<AdapterExec
     try {
       podName = await waitForPod(namespace, jobName, scheduleTimeoutMs, onLog, kubeconfigPath);
       await onLog("stdout", `[paperclip] Pod running: ${podName}\n`);
+
+      // Notify the server that execution has started. Without this call,
+      // the server has no processStartedAt timestamp for the run, so the
+      // stale-run reaper (reapOrphanedRuns) cannot distinguish a live K8s
+      // job from an orphaned run and may mark it as failed — causing the
+      // UI to show no active runs and triggering duplicate run attempts.
+      if (ctx.onSpawn) {
+        await ctx.onSpawn({
+          pid: -1,              // no local process; sentinel for K8s Job
+          processGroupId: null,
+          startedAt: new Date().toISOString(),
+        });
+      }
     } catch (err) {
       const msg = err instanceof Error ? err.message : String(err);
       await onLog("stderr", `[paperclip] Pod scheduling failed: ${msg}\n`);