fix(plugin): create missing plugin directories instead of failing

src/SquidStd.Plugin/Extensions/SquidStdBootstrapPluginExtensions.cs

@@ -18,7 +18,8 @@ public static class SquidStdBootstrapPluginExtensions
     /// across the whole set, and invokes <see cref="ISquidStdPlugin.Configure" /> for each plugin
     /// in order against the bootstrap container. Must be called before the bootstrap starts, so
     /// plugins can register configuration sections before the configuration is loaded. Relative
-    /// directories are resolved against the bootstrap root directory. Any failure aborts startup:
+    /// directories are resolved against the bootstrap root directory and created when missing
+    /// (an empty directory yields no plugins). Any failure aborts startup:
     /// loader problems raise <see cref="Exceptions.PluginLoadException" /> and plugin exceptions
     /// propagate unchanged. Plugin assemblies load into the default AssemblyLoadContext and are
     /// fully trusted: there is no unloading and no version isolation. Note that plugin load
@@ -56,6 +57,10 @@ Action<PluginCollectionBuilder> configure
                 ? directory
                 : Path.Combine(bootstrap.Options.RootDirectory, directory);
 
+            // Managed like the bootstrap's DirectoriesConfig entries: a missing plugin
+            // directory is created (and simply yields no plugins), not treated as an error.
+            Directory.CreateDirectory(resolved);
+
             plugins.AddRange(PluginAssemblyScanner.Scan(resolved));
         }
 

src/SquidStd.Plugin/PluginCollectionBuilder.cs

@@ -44,7 +44,8 @@ public PluginCollectionBuilder Add(ISquidStdPlugin plugin)
 
     /// <summary>
     /// Adds a directory to scan for external plugin assemblies (*.dll, non-recursive).
-    /// Relative paths are resolved against the bootstrap root directory.
+    /// Relative paths are resolved against the bootstrap root directory; a missing
+    /// directory is created and yields no plugins.
     /// </summary>
     /// <param name="path">Absolute or root-relative directory path.</param>
     /// <returns>The same builder for chaining.</returns>

src/SquidStd.Plugin/README.md

@@ -40,6 +40,8 @@ await bootstrap.RunAsync();
   can depend on an internal one and vice versa.
 - `Configure` runs before the configuration load, so plugins can register their own configuration
   sections and services ahead of time.
+- Plugin directories are managed like the other bootstrap directories: a missing directory is
+  created on the spot and simply yields no plugins.
 - Each plugin receives a `PluginContext` populated with the standard keys: `PluginContextKeys.RootDirectory`
   (the bootstrap root directory) and `PluginContextKeys.AppName` (the bootstrap app name).
 

tests/SquidStd.Tests/Plugin/SquidStdBootstrapPluginExtensionsTests.cs

@@ -93,6 +93,20 @@ public async Task UsePlugins_LoadsExternalPluginsFromRelativeDirectory()
         Assert.Equal("tests.external", bootstrap.Container.Resolve<string>(serviceKey: "plugin-marker"));
     }
 
+    [Fact]
+    public async Task UsePlugins_MissingDirectory_IsCreatedAndYieldsNoPlugins()
+    {
+        using var root = new TempDirectory();
+
+        await using var bootstrap = SquidStdBootstrap.Create(
+            new SquidStdOptions { ConfigName = "plugintest", RootDirectory = root.Path }
+        );
+
+        bootstrap.UsePlugins(plugins => plugins.FromDirectory("plugins"));
+
+        Assert.True(Directory.Exists(root.Combine("plugins")));
+    }
+
     [Fact]
     public async Task UsePlugins_AfterStart_Throws()
     {