feat: add scratchpad chat sessions

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

sidecar/src/Kopaya.AgentHost/Contracts/ProtocolModels.cs

@@ -71,6 +71,7 @@ public sealed class RunTurnCommandDto : SidecarCommandEnvelope
 {
     public string SessionId { get; init; } = string.Empty;
     public string ProjectPath { get; init; } = string.Empty;
+    public string WorkspaceKind { get; init; } = "project";
     public PatternDefinitionDto Pattern { get; init; } = new();
     public IReadOnlyList<ChatMessageDto> Messages { get; init; } = [];
 }

sidecar/src/Kopaya.AgentHost/Services/AgentInstructionComposer.cs

@@ -7,12 +7,22 @@ internal static class AgentInstructionComposer
     public static string Compose(
         PatternDefinitionDto pattern,
         PatternAgentDefinitionDto agent,
-        int agentIndex)
+        int agentIndex,
+        string workspaceKind = "project")
     {
         string baseInstructions = agent.Instructions.Trim();
+        string workspaceGuidance = string.Equals(workspaceKind, "scratchpad", StringComparison.OrdinalIgnoreCase)
+            ? """
+              You are operating in scratchpad mode.
+              Treat this session as pure ad-hoc Q&A rather than repository automation.
+              Do not inspect, modify, create, or delete files, and do not behave as though you are working inside a user project.
+              Answer conversationally and focus on the user's question directly.
+              """
+            : string.Empty;
+
         if (!string.Equals(pattern.Mode, "handoff", StringComparison.OrdinalIgnoreCase))
         {
-            return baseInstructions;
+            return JoinInstructionBlocks(baseInstructions, workspaceGuidance);
         }
 
         string runtimeGuidance = agentIndex == 0
@@ -28,8 +38,13 @@ internal static class AgentInstructionComposer
               Do not push the actual work back to triage unless you are blocked or the request is clearly outside your specialty.
               """;
 
-        return string.IsNullOrWhiteSpace(baseInstructions)
-            ? runtimeGuidance
-            : $"{baseInstructions}\n\n{runtimeGuidance}";
+        return JoinInstructionBlocks(baseInstructions, workspaceGuidance, runtimeGuidance);
+    }
+
+    private static string JoinInstructionBlocks(params string[] blocks)
+    {
+        return string.Join(
+            "\n\n",
+            blocks.Where(block => !string.IsNullOrWhiteSpace(block)).Select(block => block.Trim()));
     }
 }

sidecar/src/Kopaya.AgentHost/Services/CopilotWorkflowRunner.cs

@@ -40,7 +40,7 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
             throw new InvalidOperationException(validationError.Message);
         }
 
-        await using AgentBundle bundle = await AgentBundle.CreateAsync(command.Pattern, command.ProjectPath, cancellationToken);
+        await using AgentBundle bundle = await AgentBundle.CreateAsync(command, cancellationToken);
         Workflow workflow = bundle.BuildWorkflow(command.Pattern);
         List<ChatMessage> inputMessages = command.Messages.Select(ToChatMessage).ToList();
 
@@ -436,15 +436,15 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
         public IReadOnlyList<AIAgent> Agents { get; }
 
         public static async Task<AgentBundle> CreateAsync(
-            PatternDefinitionDto pattern,
-            string projectPath,
+            RunTurnCommandDto command,
             CancellationToken cancellationToken)
         {
             List<IAsyncDisposable> disposables = [];
             List<AIAgent> agents = [];
             CopilotClientOptions clientOptions = CopilotCliPathResolver.CreateClientOptions();
+            bool isScratchpad = string.Equals(command.WorkspaceKind, "scratchpad", StringComparison.OrdinalIgnoreCase);
 
-            foreach ((PatternAgentDefinitionDto definition, int agentIndex) in pattern.Agents.Select((definition, index) => (definition, index)))
+            foreach ((PatternAgentDefinitionDto definition, int agentIndex) in command.Pattern.Agents.Select((definition, index) => (definition, index)))
             {
                 CopilotClient client = new(clientOptions);
                 await client.StartAsync(cancellationToken).ConfigureAwait(false);
@@ -455,13 +455,18 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
                     ReasoningEffort = definition.ReasoningEffort,
                     SystemMessage = new SystemMessageConfig
                     {
-                        Content = AgentInstructionComposer.Compose(pattern, definition, agentIndex),
+                        Content = AgentInstructionComposer.Compose(command.Pattern, definition, agentIndex, command.WorkspaceKind),
                     },
-                    WorkingDirectory = projectPath,
+                    WorkingDirectory = command.ProjectPath,
                     OnPermissionRequest = ApprovePermissionAsync,
                     Streaming = true,
                 };
 
+                if (isScratchpad)
+                {
+                    sessionConfig.AvailableTools = [];
+                }
+
                 GitHubCopilotAgent agent = new(
                     client,
                     sessionConfig,