Add fleet and per-host concurrency controls

src/lib/server/provisioning/host-drain.ts

@@ -1,3 +1,4 @@
+import { concurrencyBlocker } from './concurrency.js';
 import { db } from '../db/index.js';
 import { provisioningCancelled } from './cancellation.js';
 import { nativeInstance, nativeRequest, type NativeInstance } from '../backends/native.js';
@@ -143,6 +144,8 @@ export async function processMigrationRemoval(job: Job, instance: NativeInstance
         const removing = db().prepare("SELECT COUNT(*) AS n FROM ec_host_operations WHERE kind='instance.remove' AND state IN ('pending','accepted','running','unknown')").get() as { n: number };
         if (removing.n >= fleetSettings().destroyConcurrency) { hold('Waiting for destruction capacity.'); return; }
         const { host, port } = choosePlacement(options);
+        const capacityBlocker = concurrencyBlocker(job.id, 'rebuild', instance.host_id, true) ?? concurrencyBlocker(job.id, 'rebuild', host.id);
+        if (capacityBlocker) { hold(capacityBlocker); return; }
         reserveHostPort(host.id, instance.id, { port, bindAddress: host.bindAddress, protocol: 'udp' });
         reserveHostPort(host.id, instance.id, { port, bindAddress: host.bindAddress, protocol: 'tcp' });
         const attempt = (db().prepare(`SELECT COUNT(*) AS n FROM ec_host_operations