fix(host): resolve Host-012..015 — consume DownIfAlone in HOCON, sub-second timing precision, config-driven Serilog sinks, transient-only startup retry

tests/ScadaLink.Host.Tests/StartupRetryTests.cs

@@ -57,9 +57,59 @@ public class StartupRetryTests
                 },
                 maxAttempts: 3,
                 initialDelay: TimeSpan.FromMilliseconds(1),
-                NullLogger.Instance));
+                NullLogger.Instance,
+                isTransient: _ => true));
 
         Assert.Equal(3, attempts);
         Assert.Equal("failure 3", ex.Message);
     }
+
+    [Fact]
+    public async Task ExecuteWithRetry_NonTransientFailure_RethrowsAfterSingleAttempt()
+    {
+        // Host-015: a permanent failure (e.g. a schema-version mismatch) must NOT be
+        // retried — retrying it cannot succeed and only delays the fatal exit by
+        // minutes. The isTransient predicate classifies it as non-retryable, so the
+        // operation runs exactly once before the exception propagates.
+        var attempts = 0;
+        var ex = await Assert.ThrowsAsync<InvalidOperationException>(() =>
+            StartupRetry.ExecuteWithRetryAsync(
+                "test-op",
+                () =>
+                {
+                    attempts++;
+                    throw new InvalidOperationException("permanent schema mismatch");
+                },
+                maxAttempts: 8,
+                initialDelay: TimeSpan.FromMilliseconds(1),
+                NullLogger.Instance,
+                isTransient: _ => false));
+
+        Assert.Equal(1, attempts);
+        Assert.Equal("permanent schema mismatch", ex.Message);
+    }
+
+    [Fact]
+    public async Task ExecuteWithRetry_TransientThenPermanent_StopsAtPermanent()
+    {
+        // A transient fault is retried; a subsequent permanent fault is not.
+        var attempts = 0;
+        await Assert.ThrowsAsync<InvalidOperationException>(() =>
+            StartupRetry.ExecuteWithRetryAsync(
+                "test-op",
+                () =>
+                {
+                    attempts++;
+                    if (attempts == 1)
+                        throw new TimeoutException("transient");
+                    throw new InvalidOperationException("permanent");
+                },
+                maxAttempts: 8,
+                initialDelay: TimeSpan.FromMilliseconds(1),
+                NullLogger.Instance,
+                isTransient: e => e is TimeoutException));
+
+        // 1 transient (retried) + 1 permanent (not retried) = 2.
+        Assert.Equal(2, attempts);
+    }
 }