fix(external-system-gateway): resolve ExternalSystemGateway-015..017 — treat MaxRetries=0 as unset, scope HTTP connection cap to gateway clients, no bare trailing '?'

tests/ScadaLink.ExternalSystemGateway.Tests/ExternalSystemClientTests.cs

@@ -396,9 +396,14 @@ public class ExternalSystemClientTests
     }
 
     [Fact]
-    public async Task CachedCall_TransientFailure_ZeroMaxRetriesIsHonouredNotTreatedAsUnset()
+    public async Task CachedCall_TransientFailure_ZeroMaxRetriesIsTreatedAsUnsetNotRetryForever()
     {
-        // MaxRetries == 0 must mean "never retry", not "fall back to the S&F default".
+        // ExternalSystemGateway-015: the Store-and-Forward engine interprets a stored
+        // MaxRetries of 0 as "no limit" (retry forever) — see StoreAndForwardMessage.cs
+        // and the retry-sweep guard `MaxRetries > 0 && ...`. The entity's non-nullable
+        // int default is also 0, so passing 0 verbatim would buffer every cached call
+        // as an unbounded retry loop. The ESG must therefore treat the entity's
+        // MaxRetries == 0 as "unset" and pass null, so the bounded S&F default applies.
         var system = new ExternalSystemDefinition("TestAPI", "https://api.example.com", "none")
         {
             Id = 1,
@@ -432,7 +437,9 @@ public class ExternalSystemClientTests
         await client.CachedCallAsync("TestAPI", "postData");
 
         var (maxRetries, _) = ReadBufferedRetrySettings(connStr);
-        Assert.Equal(0, maxRetries); // honoured — not the default of 99
+        // Must be the bounded S&F default, never 0 — a stored 0 would mean retry-forever.
+        Assert.Equal(99, maxRetries);
+        Assert.NotEqual(0, maxRetries);
     }
 
     // ── ExternalSystemGateway-005: HttpRequestMessage / HttpResponseMessage disposal ──
@@ -615,6 +622,33 @@ public class ExternalSystemClientTests
         Assert.Contains("page=2", uri);
     }
 
+    [Fact]
+    public async Task Call_GetWithAllNullParameters_DoesNotAppendTrailingQuestionMark()
+    {
+        // ExternalSystemGateway-017: a GET method invoked with a non-empty parameter
+        // dictionary whose values are all null has an effectively empty query string.
+        // The URL must be identical to the no-parameters case — no bare trailing '?'.
+        var system = new ExternalSystemDefinition("TestAPI", "https://api.example.com", "none") { Id = 1 };
+        var method = new ExternalSystemMethod("search", "GET", "/search") { Id = 1, ExternalSystemDefinitionId = 1 };
+        StubResolution(system, method);
+
+        var handler = new RequestCapturingHandler(HttpStatusCode.OK, "{}");
+        _httpClientFactory.CreateClient(Arg.Any<string>()).Returns(new HttpClient(handler));
+
+        var client = new ExternalSystemClient(
+            _httpClientFactory, _repository, NullLogger<ExternalSystemClient>.Instance);
+
+        await client.CallAsync("TestAPI", "search", new Dictionary<string, object?>
+        {
+            ["q"] = null,
+            ["page"] = null,
+        });
+
+        var uri = handler.LastUri!.AbsoluteUri;
+        Assert.Equal("https://api.example.com/search", uri);
+        Assert.DoesNotContain("?", uri);
+    }
+
     [Fact]
     public async Task Call_PostWithParameters_SendsJsonBody()
     {