Make markdown configuration compatible with VSC chat modes

See https://code.visualstudio.com/docs/copilot/customization/custom-chat-modes (seems to have been renamed to "custom agents" in VSC insiders now).

Our extensions (such as `client`, `use` and `options`  can be persisted in other config files (since they are aggregated at run-time) or kept in the same agents.md file since VSCode will ignore them.

Author: kzu

.github/agents/notes.agent.md

@@ -0,0 +1,14 @@
+---
+id: ai.agents.notes
+description: 'Takes notes'
+model: Grok Code Fast 1 (copilot)
+client: grok
+options: 
+  modelid: grok-code-fast-1
+tools: ['edit']
+use: ['tone']
+---
+# Notes Agent
+This agent is designed to take notes based on user input. It can capture important information, summarize discussions, and organize notes for easy retrieval later. The Notes Agent can be particularly useful in meetings, brainstorming sessions, or any scenario where capturing key points is essential.
+
+It saves these notes in JSON-LD format to the file `notes.json` alongside this agent, ensuring that the notes are structured and easily accessible for future reference.

.github/agents/notes.json

@@ -0,0 +1,28 @@
+[
+  {
+    "@context": "https://schema.org",
+    "@type": "NoteDigitalDocument",
+    "identifier": "2025-10-29T00:00:00Z",
+    "dateCreated": "2025-10-29",
+    "inLanguage": "es",
+    "text": "El usuario necesita desplegar una aplicación Expo.",
+    "about": [
+      "Expo",
+      "deploy"
+    ]
+  },
+  {
+    "@context": "https://schema.org",
+    "@type": "Note",
+    "dateCreated": "2025-10-29T12:00:00Z",
+    "inLanguage": "es",
+    "textOriginal": "recordar que maniana llevamos piedras",
+    "text": "Recordar que mañana llevamos piedras",
+    "dueDate": "2025-10-30",
+    "tags": ["recordatorio", "piedras"],
+    "source": {
+      "agentFile": ".github/agents/notes.agent.md",
+      "savedBy": "notes-agent"
+    }
+  }
+]

assets/img/agent-model.png

@@ -133,29 +133,45 @@ This can be used by leveraging [Tomlyn.Extensions.Configuration](https://www.nug
 > avoiding unnecessary tokens being used for indentation while allowing flexible 
 > formatting in the config file.
 
-For longer instructions, markdown format plus YAML front-matter can be used for better readability:
+You can also leverage the format pioneered by [VS Code Chat Modes](https://code.visualstudio.com/docs/copilot/customization/custom-chat-modes), 
+ (por "custom agents") by using markdown format plus YAML front-matter for better readability:
 
 ```yaml
 ---
 id: ai.agents.notes
 description: Provides free-form memory
 client: grok
-options: 
-  modelid: grok-4-fast
+model: grok-4-fast
 ---
 You organize and keep notes for the user.
 # Some header
 More content
+```
 
-## Another header
-...
+Visual Studio Code will ignore the additional attributes used by this project. In particular, the `model` 
+property is a shorthand for setting the `options.modelid`, but in our implementation, the latter takes 
+precedence over the former, which allows you to rely on `model` to drive the VSCode testing, and the 
+longer form for run-time with the Agents Framework: 
+
+```yaml
+---
+id: ai.agents.notes
+description: Provides free-form memory
+model: Grok Code Fast 1 (copilot)
+client: grok
+options: 
+  modelid: grok-code-fast-1
+---
+// Instructions
 ```
 
-Use the provided `AddInstructionsFile` extension method to load instructions from files as follows:
+![agent model picker](assets/img/agent-model.png)
+
+Use the provided `AddAgentMarkdown` extension method to load instructions from files as follows:
 
 ```csharp
 var host = new HostApplicationBuilder(args);
-host.Configuration.AddInstructionsFile("notes.md", optional: false, reloadOnChange: true);
+host.Configuration.AddAgentMarkdown("notes.agent.md", optional: false, reloadOnChange: true);
 ```
 
 The `id` field in the front-matter is required and specifies the configuration section name, and 
@@ -227,15 +243,16 @@ services.AddKeyedSingleton("get_date", AIFunctionFactory.Create(() => DateTimeOf
 
 This tool will be automatically wired into any agent that uses the `timezone` context above.
 
-As a shortcut when you want to just pull in a tool from DI into an agent's context without having to define an entire 
-section just for that, you can specify the tool name directly in the `use` array:
+Agents themselves can also add tools from DI into an agent's context without having to define an entire 
+section just for that, by specifying the tool name directly in the `tools` array:
 
 ```toml
 [ai.agents.support]
 description = "An AI agent that helps with customer support."
 instructions = "..."
 client = "grok"
-use = ["tone", "get_date"]
+use = ["tone"]
+tools = ["get_date"]
 ```
 
 This enables a flexible and convenient mix of static and dynamic context for agents, all driven 

readme.md

@@ -11,23 +11,16 @@ instructions = """\
     You are an AI agent responsible for processing orders for food or other items.
     Your primary goals are to identify user intent, extract or request provider information, manage order data using tools and friendly responses to guide users through the ordering process.
     """
+options = { modelid = "gpt-4o-mini" }
+# 👇 alternative syntax to specify options
+# [ai.agents.orders.options]
+# modelid = "gpt-4o-mini"
 
 # ai.clients.openai, can omit the ai.clients prefix
 client = "openai"
-use = ["tone", "get_date", "create_order", "cancel_order"]
+use = ["tone"]
+tools = ["get_date", "create_order", "cancel_order"]
 
-[ai.agents.orders.options]
-modelid = "gpt-4o-mini"
-# additional properties could be added here
-
-[ai.agents.notes]
-description = "Help users create, manage, and retrieve notes effectively."
-instructions = """
-    You are an AI agent that assists users in creating, managing, and retrieving notes.
-    Your primary goals are to understand user requests related to notes, provide clear and concise responses, and utilize tools to organize and access note data efficiently.
-    """
-client = "grok"
-use = ["tone", "save_notes", "get_date"]
 
 [ai.context.tone]
 instructions = """\

sample/Server/ai.toml

@@ -1,8 +1,9 @@
 ---
 id: ai.agents.notes
 description: Provides free-form memory
-client: Grok
-options: 
-  modelid: grok-4-fast
+client: grok
+model: grok-4-fast
+use: ["tone"]
+tools: ["save_notes", "get_date"]
 ---
 You organize and keep notes for the user, using JSON-LD

sample/Server/notes.md sample/Server/notes.agent.mdsample/Server/notes.md renamed to sample/Server/notes.agent.md

@@ -93,7 +93,7 @@ public static TBuilder ConfigureReload<TBuilder>(this TBuilder builder)
                 builder.Configuration.AddJsonFile(json, optional: false, reloadOnChange: true);
 
             foreach (var md in Directory.EnumerateFiles(AppContext.BaseDirectory, "*.md", SearchOption.AllDirectories))
-                builder.Configuration.AddInstructionsFile(md, optional: false, reloadOnChange: true);
+                builder.Configuration.AddAgentMarkdown(md, optional: false, reloadOnChange: true);
         }
         else
         {
@@ -111,7 +111,7 @@ public static TBuilder ConfigureReload<TBuilder>(this TBuilder builder)
                 builder.Configuration.AddJsonFile(json, optional: false, reloadOnChange: true);
 
             foreach (var md in Directory.EnumerateFiles(baseDir, "*.md", SearchOption.AllDirectories).Where(IsSource))
-                builder.Configuration.AddInstructionsFile(md, optional: false, reloadOnChange: true);
+                builder.Configuration.AddAgentMarkdown(md, optional: false, reloadOnChange: true);
         }
 
         return builder;

sample/ServiceDefaults.cs

@@ -6,12 +6,12 @@
 namespace Devlooped.Agents.AI;
 
 [EditorBrowsable(EditorBrowsableState.Never)]
-public static class ConfigurableInstructionsExtensions
+public static class AgentMarkdownExtensions
 {
     /// <summary>
     /// Adds an instructions markdown file with optional YAML front-matter to the configuration sources.
     /// </summary>
-    public static IConfigurationBuilder AddInstructionsFile(this IConfigurationBuilder builder, string path, bool optional = false, bool reloadOnChange = false)
+    public static IConfigurationBuilder AddAgentMarkdown(this IConfigurationBuilder builder, string path, bool optional = false, bool reloadOnChange = false)
         => builder.Add<InstructionsConfigurationSource>(source =>
         {
             source.Path = path;
@@ -23,7 +23,7 @@ public static IConfigurationBuilder AddInstructionsFile(this IConfigurationBuild
     /// <summary>
     /// Adds an instructions markdown stream with optional YAML front-matter to the configuration sources.
     /// </summary>
-    public static IConfigurationBuilder AddInstructionsStream(this IConfigurationBuilder builder, Stream stream)
+    public static IConfigurationBuilder AddAgentMarkdown(this IConfigurationBuilder builder, Stream stream)
         => Throw.IfNull(builder).Add((InstructionsStreamConfigurationSource source) => source.Stream = stream);
 
     static class InstructionsParser

…ts/ConfigurableInstructionsExtensions.cs src/Agents/AgentMarkdownExtensions.cssrc/Agents/ConfigurableInstructionsExtensions.cs renamed to src/Agents/AgentMarkdownExtensions.cs src/Agents/ConfigurableInstructionsExtensions.cs renamed to src/Agents/AgentMarkdownExtensions.cs

@@ -105,6 +105,8 @@ public override IAsyncEnumerable<AgentRunResponseUpdate> RunStreamingAsync(IEnum
 
         if (chat is not null)
             options.ChatOptions = chat;
+        else if (options.Model is not null)
+            (options.ChatOptions ??= new()).ModelId = options.Model;
 
         configure?.Invoke(name, options);
 
@@ -127,10 +129,10 @@ public override IAsyncEnumerable<AgentRunResponseUpdate> RunStreamingAsync(IEnum
 
                 options.AIContextProviderFactory = _ => contextProvider;
             }
-            else if (options.Use?.Count > 0)
+            else if (options.Use?.Count > 0 || options.Tools?.Count > 0)
             {
                 var contexts = new List<AIContext>();
-                foreach (var use in options.Use)
+                foreach (var use in options.Use ?? [])
                 {
                     var context = services.GetKeyedService<AIContext>(use);
                     if (context is not null)
@@ -139,13 +141,6 @@ public override IAsyncEnumerable<AgentRunResponseUpdate> RunStreamingAsync(IEnum
                         continue;
                     }
 
-                    var function = services.GetKeyedService<AITool>(use) ?? services.GetKeyedService<AIFunction>(use);
-                    if (function is not null)
-                    {
-                        contexts.Add(new AIContext { Tools = [function] });
-                        continue;
-                    }
-
                     if (configuration.GetSection("ai:context:" + use) is { } ctxSection &&
                         ctxSection.Get<AIContextConfiguration>() is { } ctxConfig)
                     {
@@ -161,7 +156,7 @@ public override IAsyncEnumerable<AgentRunResponseUpdate> RunStreamingAsync(IEnum
                             {
                                 var tool = services.GetKeyedService<AITool>(toolName) ??
                                     services.GetKeyedService<AIFunction>(toolName) ??
-                                    throw new InvalidOperationException($"Specified tool '{toolName}' for AI context '{ctxSection.Path}:tools' is not registered, and is required by agent section '{configSection.Path}'.");
+                                    throw new InvalidOperationException($"Specified tool '{toolName}' for AI context '{ctxSection.Path}:tools' is not registered as a keyed {nameof(AITool)} or {nameof(AIFunction)}, and is required by agent section '{configSection.Path}'.");
 
                                 configured.Tools ??= [];
                                 configured.Tools.Add(tool);
@@ -172,7 +167,16 @@ public override IAsyncEnumerable<AgentRunResponseUpdate> RunStreamingAsync(IEnum
                         continue;
                     }
 
-                    throw new InvalidOperationException($"Specified AI context '{use}' for agent '{name}' is not registered as either {nameof(AIContent)}, {nameof(AITool)} or configuration section 'ai:context:{use}'.");
+                    throw new InvalidOperationException($"Specified AI context '{use}' for agent '{name}' is not registered as either {nameof(AIContent)} or configuration section 'ai:context:{use}'.");
+                }
+
+                foreach (var toolName in options.Tools ?? [])
+                {
+                    var tool = services.GetKeyedService<AITool>(toolName) ??
+                        services.GetKeyedService<AIFunction>(toolName) ??
+                        throw new InvalidOperationException($"Specified tool '{toolName}' for agent '{section}' is not registered as a keyed {nameof(AITool)} or {nameof(AIFunction)}.");
+
+                    contexts.Add(new AIContext { Tools = [tool] });
                 }
 
                 options.AIContextProviderFactory = _ => new CompositeAIContextProvider(contexts);
@@ -215,7 +219,9 @@ void OnReload(object? state)
     internal class AgentClientOptions : ChatClientAgentOptions
     {
         public string? Client { get; set; }
+        public string? Model { get; set; }
         public IList<string>? Use { get; set; }
+        public IList<string>? Tools { get; set; }
     }
 }
 

src/Agents/ConfigurableAIAgent.cs

@@ -539,7 +539,7 @@ public async Task UseAIToolFromKeyedServiceAsync()
             [ai.agents.chat]
             description = "Chat agent."
             client = "openai"
-            use = ["get_date"]
+            tools = ["get_date"]
             """");
 
         AITool tool = AIFunctionFactory.Create(() => DateTimeOffset.Now, "get_date");
@@ -561,6 +561,32 @@ public async Task UseAIToolFromKeyedServiceAsync()
         Assert.Same(tool, context.Tools[0]);
     }
 
+    [Fact]
+    public async Task MissingAIToolFromKeyedServiceThrows()
+    {
+        var builder = new HostApplicationBuilder();
+
+        builder.Configuration.AddToml(
+            $$"""
+            [ai.clients.openai]
+            modelid = "gpt-4.1"
+            apikey = "sk-asdf"
+
+            [ai.agents.chat]
+            description = "Chat agent."
+            client = "openai"
+            tools = ["get_date"]
+            """);
+
+        builder.AddAIAgents();
+        var app = builder.Build();
+
+        var exception = Assert.ThrowsAny<Exception>(() => app.Services.GetRequiredKeyedService<AIAgent>("chat"));
+
+        Assert.Contains("get_date", exception.Message);
+        Assert.Contains("ai:agents:chat", exception.Message);
+    }
+
     [Fact]
     public async Task UseAIContextFromSection()
     {
@@ -668,5 +694,57 @@ public async Task UnknownUseThrows()
 
         Assert.Contains("foo", exception.Message);
     }
+
+    [Fact]
+    public async Task OverrideModelFromAgentChatOptions()
+    {
+        var builder = new HostApplicationBuilder();
+
+        builder.Configuration.AddToml(
+            $$"""
+            [ai.clients.openai]
+            modelid = "gpt-4.1"
+            apikey = "sk-asdf"
+
+            [ai.agents.chat]
+            description = "Chat"
+            client = "openai"
+            options = { modelid = "gpt-5" }
+            """);
+
+        builder.AddAIAgents();
+        var app = builder.Build();
+
+        var agent = app.Services.GetRequiredKeyedService<AIAgent>("chat");
+        var options = agent.GetService<ChatClientAgentOptions>();
+
+        Assert.Equal("gpt-5", options?.ChatOptions?.ModelId);
+    }
+
+    [Fact]
+    public async Task OverrideModelFromAgentModel()
+    {
+        var builder = new HostApplicationBuilder();
+
+        builder.Configuration.AddToml(
+            $$"""
+            [ai.clients.openai]
+            modelid = "gpt-4.1"
+            apikey = "sk-asdf"
+
+            [ai.agents.chat]
+            description = "Chat"
+            client = "openai"
+            model = "gpt-5"
+            """);
+
+        builder.AddAIAgents();
+        var app = builder.Build();
+
+        var agent = app.Services.GetRequiredKeyedService<AIAgent>("chat");
+        var options = agent.GetService<ChatClientAgentOptions>();
+
+        Assert.Equal("gpt-5", options?.ChatOptions?.ModelId);
+    }
 }