fix(host): resolve Host-005..011 — async startup, HOCON escaping, port-conflict check, dead-config cleanup, migration retry, log-level wiring; Host-002 flagged

tests/ScadaLink.Host.Tests/StartupRetryTests.cs

@@ -0,0 +1,65 @@
+using Microsoft.Extensions.Logging.Abstractions;
+
+namespace ScadaLink.Host.Tests;
+
+/// <summary>
+/// Host-010: startup preconditions (database migration) must tolerate a database
+/// that is briefly unavailable at boot — common when an app container and its DB
+/// container start together — via a bounded retry with backoff.
+/// </summary>
+public class StartupRetryTests
+{
+    [Fact]
+    public async Task ExecuteWithRetry_SucceedsFirstTry_RunsOnce()
+    {
+        var attempts = 0;
+        await StartupRetry.ExecuteWithRetryAsync(
+            "test-op",
+            () => { attempts++; return Task.CompletedTask; },
+            maxAttempts: 5,
+            initialDelay: TimeSpan.FromMilliseconds(1),
+            NullLogger.Instance);
+
+        Assert.Equal(1, attempts);
+    }
+
+    [Fact]
+    public async Task ExecuteWithRetry_TransientFailures_RetriesUntilSuccess()
+    {
+        var attempts = 0;
+        await StartupRetry.ExecuteWithRetryAsync(
+            "test-op",
+            () =>
+            {
+                attempts++;
+                if (attempts < 3)
+                    throw new InvalidOperationException("db not ready");
+                return Task.CompletedTask;
+            },
+            maxAttempts: 5,
+            initialDelay: TimeSpan.FromMilliseconds(1),
+            NullLogger.Instance);
+
+        Assert.Equal(3, attempts);
+    }
+
+    [Fact]
+    public async Task ExecuteWithRetry_ExhaustsAttempts_RethrowsLastException()
+    {
+        var attempts = 0;
+        var ex = await Assert.ThrowsAsync<InvalidOperationException>(() =>
+            StartupRetry.ExecuteWithRetryAsync(
+                "test-op",
+                () =>
+                {
+                    attempts++;
+                    throw new InvalidOperationException($"failure {attempts}");
+                },
+                maxAttempts: 3,
+                initialDelay: TimeSpan.FromMilliseconds(1),
+                NullLogger.Instance));
+
+        Assert.Equal(3, attempts);
+        Assert.Equal("failure 3", ex.Message);
+    }
+}