test(db): make exclusive-connection-lease uniqueness test self-contained (#11341)

Merged via consolidated batch validation. Test-only fix: exclusive-connection-lease uniqueness test implicitly depended on lease state from an earlier test in the same file (shared DB instance, reset only in test.after) — now self-contained. No production change.

tests/unit/exclusive-connection-leases.test.ts

@@ -61,6 +61,19 @@ test("uses the live next-free migration slot without runner compatibility specia
 });
 
 test("enforces global active owner and connection uniqueness", () => {
+  // Establish the OWNER_A/conn-a lease this test reuses, rather than depending
+  // on a lease left behind by an earlier test in the file. The DB instance is
+  // shared across tests (reset only in test.after), so relying on prior state
+  // makes this test order-dependent: run in isolation the re-acquire below
+  // returns ACQUIRED instead of REUSED.
+  leases.acquireExclusiveConnectionLease({
+    leaseOwnerId: OWNER_A,
+    apiKeyId: "key-a",
+    provider: "codex",
+    connectionId: "conn-a",
+    now: at(0),
+  });
+
   const ownerA = leases.acquireExclusiveConnectionLease({
     leaseOwnerId: OWNER_A,
     apiKeyId: "key-a",