fix(qwp): reject reconnect_max_duration_millis = 0 -- a zero budget can never work

The builder accepted >= 0, but 0 is a value with no working semantics:

- SYNC initial connect: connectWithRetry's deadline (startNanos + 0)
  expires before the first attempt, so build() throws "failed after
  0ms / 0 attempts" without ever dialing -- even against a healthy
  server. Worse, explicitly setting any reconnect_* knob implicitly
  promotes the initial-connect mode to SYNC, so writing =0 made the
  instant failure the guaranteed outcome, not an edge case.
- Background drainer: capabilityGapBudgetNanos = 0 makes the durable-ack
  settle budget exhaust on the first gap sweep (0 >= 0), quarantining
  the slot instantly instead of after the documented 16-sweep budget.

No consumer treats 0 as a disabled/infinite sentinel (the background
reconnect loop ignores this knob entirely under Invariant B), so nothing
loses expressible behavior. Validation sits in the builder setter -- the
single choke point for the builder, config-string, and view paths --
matching the > 0 contract of the sibling backoff knobs.

Tests cover zero and negative through both the config string and the
builder.

Author: bluestreak01

core/src/main/java/io/questdb/client/Sender.java

@@ -2469,14 +2469,18 @@ public LineSenderBuilder reconnectMaxBackoffMillis(long millis) {
          * auth/upgrade error or {@code close()}.
          * <p>
          * Default {@code 300_000} (5 minutes). Lower for fail-fast startup;
-         * higher for tolerating a slow server boot. WebSocket only.
+         * higher for tolerating a slow server boot. Must be positive: a zero
+         * budget would make the SYNC initial connect throw without a single
+         * attempt (even against a healthy server) and would collapse the
+         * background drainer's durable-ack settle budget to its first sweep.
+         * WebSocket only.
          */
         public LineSenderBuilder reconnectMaxDurationMillis(long millis) {
             if (protocol != PARAMETER_NOT_SET_EXPLICITLY && protocol != PROTOCOL_WEBSOCKET) {
                 throw new LineSenderException("reconnect_max_duration_millis is only supported for WebSocket transport");
             }
-            if (millis < 0) {
-                throw new LineSenderException("reconnect_max_duration_millis must be >= 0: ").put(millis);
+            if (millis <= 0) {
+                throw new LineSenderException("reconnect_max_duration_millis must be > 0: ").put(millis);
             }
             this.reconnectMaxDurationMillis = millis;
             return this;

core/src/test/java/io/questdb/client/test/cutlass/qwp/client/LineSenderBuilderWebSocketTest.java

@@ -924,6 +924,40 @@ public void testWsConfigString_withRetryTimeout_fails() {
                 "unknown configuration key: retry_timeout (use reconnect_max_duration_millis on ws/wss)");
     }
 
+    @Test
+    public void testWsConfigString_reconnectMaxDurationZero_fails() {
+        // A zero budget must be rejected up front: connectWithRetry's deadline
+        // (startNanos + 0) makes the SYNC initial connect throw "after 0ms /
+        // 0 attempts" without ever dialing a healthy server, and the drainer's
+        // capabilityGapBudgetNanos=0 exhausts the durable-ack settle budget
+        // (0 >= 0) on the first gap sweep, quarantining the slot instantly
+        // instead of after the documented 16-sweep budget.
+        assertBadConfig("ws::addr=localhost:9000;reconnect_max_duration_millis=0;",
+                "reconnect_max_duration_millis must be > 0");
+    }
+
+    @Test
+    public void testWsConfigString_reconnectMaxDurationNegative_fails() {
+        assertBadConfig("ws::addr=localhost:9000;reconnect_max_duration_millis=-1;",
+                "reconnect_max_duration_millis must be > 0");
+    }
+
+    @Test
+    public void testReconnectMaxDurationBuilder_zeroRejected() {
+        assertThrows("reconnect_max_duration_millis must be > 0",
+                () -> Sender.builder(Sender.Transport.WEBSOCKET)
+                        .address(LOCALHOST)
+                        .reconnectMaxDurationMillis(0));
+    }
+
+    @Test
+    public void testReconnectMaxDurationBuilder_negativeRejected() {
+        assertThrows("reconnect_max_duration_millis must be > 0",
+                () -> Sender.builder(Sender.Transport.WEBSOCKET)
+                        .address(LOCALHOST)
+                        .reconnectMaxDurationMillis(-1));
+    }
+
     @Test
     public void testWsConfigString_usernameWithoutPassword_fails() {
         // The ingress ws path rejects a username with no password up front in