wip(scheduler): compose storage configuration compatibility

Sprint SPRINT_20260417_002_JobEngine_scheduler_storage_compose_compatibility
(SCHEDULER-COMPAT-001 still DOING — sprint remains active).

Adds scheduler storage configuration adapter layer so the web host
accepts the compose-shaped storage configuration without manual remapping,
plus SchedulerStorageConfigurationTests.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/JobEngine/StellaOps.Scheduler.WebService/Configuration/SchedulerStorageConfiguration.cs

@@ -0,0 +1,32 @@
+using Microsoft.Extensions.Configuration;
+
+namespace StellaOps.Scheduler.WebService.Configuration;
+
+public static class SchedulerStorageConfiguration
+{
+    public const string FlatSectionPath = "Scheduler:Storage";
+    public const string ComposeNestedSectionPath = "Scheduler:Storage:Postgres:Scheduler";
+    public const string LegacySectionPath = "Postgres:Scheduler";
+
+    public static string? ResolveSectionPath(IConfiguration configuration)
+    {
+        foreach (var sectionPath in GetCandidateSectionPaths())
+        {
+            if (!string.IsNullOrWhiteSpace(configuration[$"{sectionPath}:ConnectionString"]))
+            {
+                return sectionPath;
+            }
+        }
+
+        return null;
+    }
+
+    public static string? ResolveConnectionString(IConfiguration configuration)
+    {
+        var sectionPath = ResolveSectionPath(configuration);
+        return sectionPath is null ? null : configuration[$"{sectionPath}:ConnectionString"];
+    }
+
+    private static string[] GetCandidateSectionPaths()
+        => [FlatSectionPath, ComposeNestedSectionPath, LegacySectionPath];
+}

src/JobEngine/StellaOps.Scheduler.__Tests/StellaOps.Scheduler.WebService.Tests/SchedulerStorageConfigurationTests.cs

@@ -0,0 +1,49 @@
+using Microsoft.Extensions.Configuration;
+using StellaOps.Scheduler.WebService.Configuration;
+
+namespace StellaOps.Scheduler.WebService.Tests;
+
+public sealed class SchedulerStorageConfigurationTests
+{
+    [Fact]
+    public void ResolveConnectionString_PrefersFlatSchedulerStorage()
+    {
+        var configuration = BuildConfiguration(
+        [
+            new("Scheduler:Storage:ConnectionString", "Host=flat;Database=scheduler"),
+            new("Scheduler:Storage:Postgres:Scheduler:ConnectionString", "Host=nested;Database=scheduler"),
+        ]);
+
+        Assert.Equal(SchedulerStorageConfiguration.FlatSectionPath, SchedulerStorageConfiguration.ResolveSectionPath(configuration));
+        Assert.Equal("Host=flat;Database=scheduler", SchedulerStorageConfiguration.ResolveConnectionString(configuration));
+    }
+
+    [Fact]
+    public void ResolveConnectionString_AcceptsComposeNestedStorage()
+    {
+        var configuration = BuildConfiguration(
+        [
+            new("Scheduler:Storage:Postgres:Scheduler:ConnectionString", "Host=nested;Database=scheduler"),
+        ]);
+
+        Assert.Equal(SchedulerStorageConfiguration.ComposeNestedSectionPath, SchedulerStorageConfiguration.ResolveSectionPath(configuration));
+        Assert.Equal("Host=nested;Database=scheduler", SchedulerStorageConfiguration.ResolveConnectionString(configuration));
+    }
+
+    [Fact]
+    public void ResolveConnectionString_FallsBackToLegacyPostgresScheduler()
+    {
+        var configuration = BuildConfiguration(
+        [
+            new("Postgres:Scheduler:ConnectionString", "Host=legacy;Database=scheduler"),
+        ]);
+
+        Assert.Equal(SchedulerStorageConfiguration.LegacySectionPath, SchedulerStorageConfiguration.ResolveSectionPath(configuration));
+        Assert.Equal("Host=legacy;Database=scheduler", SchedulerStorageConfiguration.ResolveConnectionString(configuration));
+    }
+
+    private static IConfiguration BuildConfiguration(IEnumerable<KeyValuePair<string, string?>> values)
+        => new ConfigurationBuilder()
+            .AddInMemoryCollection(values)
+            .Build();
+}