Index lifecycle capacity checks instead of scanning retained jobs

tests/unit/concurrency.test.ts

@@ -43,3 +43,70 @@ it('enforces per-host removal and recovery limits independently of other hosts',
     expect(concurrencyBlocker('b','restart','host')).toContain('recovery');
     expect(concurrencyBlocker('b','restart','other')).toBeNull();
 });
+
+it('retains every capacity owner across failure, cancellation and migration without counting completed history', async () => {
+    const { db } = await import('../../src/lib/server/db/index.js');
+    const { createHost } = await import('../../src/lib/server/hosts/index.js');
+    const { lifecycleHolders, preparingJobs } = await import('../../src/lib/server/provisioning/concurrency.js');
+    const h = db(), host = createHost({name:'Source'});
+    const add = (id: string, state: string, command?: string, migration = false) => {
+        h.prepare("INSERT INTO server_deployments(id,server,action,state,stage,started_at,triggered_by) VALUES(?,?,'rebuild',?,'test','2026-01-01','test')").run(id,id,state);
+        h.prepare("INSERT INTO native_instances(id,server,host_id,library_id,image,port,created_at) VALUES(?,?,?,'lib','img',1,'2026-01-01')").run(id,id,host.id);
+        h.prepare('INSERT INTO native_provisioning(deployment_id,instance_id,generation,operation_id) VALUES(?,?,1,?)').run(id,id,migration ? null : command ? id : null);
+        if (command) h.prepare("INSERT INTO ec_host_operations(id,host_id,kind,state,payload,created_at,updated_at) VALUES(?,?,'instance.rebuild',?,'{}','2026-01-01','2026-01-01')").run(id,host.id,command);
+        if (migration) h.prepare('INSERT INTO ec_host_migrations(deployment_id,source_host_id,instance_id,target_host_id,remove_operation_id) VALUES(?,?,?,?,?)').run(id,host.id,id,'target',command ? id : null);
+    };
+    add('running','running','running');
+    add('health','awaiting-health','completed');
+    add('prepared','queued');
+    add('recovery','failed','failed');
+    add('cancelled-command','cancelled','unknown');
+    add('done-command','done','pending');
+    add('failed-migration','failed','completed',true);
+    add('unknown-migration','legacy-unknown','completed',true);
+    add('cancelled-migration','cancelled','accepted',true);
+    add('waiting-migration','waiting','running',true);
+    add('finished','done','completed');
+    add('cancelled-finished','cancelled','completed',true);
+    add('finished-migration','warning','completed',true);
+    add('queued','queued');
+    h.prepare("INSERT INTO servers(name) VALUES('recovery')").run();
+    h.prepare("INSERT INTO restart_rollout(server,operation_id,requested_at) VALUES('recovery','recovery','2026-01-01')").run();
+    preparingJobs.add('prepared');
+    try {
+        const holders = lifecycleHolders();
+        expect(holders.map(row=>row.id).sort()).toEqual(['running','health','prepared','recovery','cancelled-command','done-command','failed-migration','unknown-migration','cancelled-migration','waiting-migration'].sort());
+        expect(holders.find(row=>row.id==='waiting-migration')).toMatchObject({host_id:host.id,target_host_id:'target',removing:1});
+    } finally { preparingJobs.clear(); }
+});
+
+it('seeks capacity owners through active indexes instead of scanning retained jobs and receipts', async () => {
+    const { db } = await import('../../src/lib/server/db/index.js');
+    const { createHost } = await import('../../src/lib/server/hosts/index.js');
+    const { lifecycleHolders } = await import('../../src/lib/server/provisioning/concurrency.js');
+    const h = db(), host = createHost({name:'History host'});
+    h.transaction(() => {
+        const job = h.prepare("INSERT INTO server_deployments(id,server,action,state,stage,started_at,triggered_by) VALUES(?,'old','restart','done','Done','2026-01-01','test')");
+        const operation = h.prepare("INSERT INTO ec_host_operations(id,host_id,kind,state,payload,created_at,updated_at) VALUES(?,?,'instance.restart','completed','{}','2026-01-01','2026-01-01')");
+        h.prepare("INSERT INTO native_instances(id,server,host_id,library_id,image,port,created_at) VALUES('i','old',?,'lib','img',1,'2026-01-01')").run(host.id);
+        const native = h.prepare("INSERT INTO native_provisioning(deployment_id,instance_id,generation,operation_id) VALUES(?,'i',1,?)");
+        const migration = h.prepare("INSERT INTO ec_host_migrations(deployment_id,source_host_id,instance_id,remove_operation_id,removed_at) VALUES(?,?,'i',?,'2026-01-01')");
+        for (let n=0;n<4000;n++) {
+            const id=String(n); job.run(id); operation.run(id,host.id); native.run(id,id); migration.run(id,host.id,id);
+        }
+    })();
+    const prepare = vi.spyOn(h,'prepare');
+    let sql: string;
+    try {
+        expect(lifecycleHolders()).toEqual([]);
+        sql = prepare.mock.calls.find(([sql])=>sql.startsWith('SELECT d.id,d.action'))![0];
+    } finally { prepare.mockRestore(); }
+    const plan = h.prepare(`EXPLAIN QUERY PLAN ${sql}`).all('[]') as {detail:string}[];
+    const details = plan.map(row=>row.detail).join('\n');
+    for (const index of ['idx_server_deployments_state','idx_server_deployments_unsettled','ec_host_operations_active','native_provisioning_operation','ec_host_migrations_operation']) {
+        expect(details).toContain(index);
+    }
+    expect(details).not.toMatch(/SCAN (?:d|n|m|o)\b/);
+    // Scanning the small partial index of unsettled IDs is intentional.
+    expect(details).not.toMatch(/SCAN server_deployments(?! USING INDEX idx_server_deployments_unsettled)\b/);
+});