feat: enable scratchpad tooling backend

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

AGENTS.md

@@ -154,7 +154,14 @@ Every interactive component must include basic accessibility:
 - Always commit completed repository changes before handing work off. If unrelated pre-existing changes are present in the worktree, stop and ask the user how to proceed before creating the commit.
 - Do not mark work as done until both the implementation and its verification are complete.
 
-## 8. Validation checklist
+## 8. Planning requirements
+
+- If a task spans both backend and frontend work, the implementation plan must be split into **Part 1 — Backend** and **Part 2 — Frontend**.
+- Backend work must be planned and executed first.
+- Before frontend work begins, backend work must produce a handover artifact in the session workspace `files\` directory. Do not put this handover document in the repository.
+- The frontend phase must consume that backend handover artifact and build on it rather than rediscovering backend contracts from scratch.
+
+## 9. Validation checklist
 
 Before every commit, run the following in order:
 

sidecar/src/Eryx.AgentHost/Services/CopilotAgentBundle.cs

@@ -28,8 +28,7 @@ internal sealed class CopilotAgentBundle : IAsyncDisposable
         List<IAsyncDisposable> disposables = [];
         List<AIAgent> agents = [];
         CopilotClientOptions clientOptions = CopilotCliPathResolver.CreateClientOptions();
-        bool isScratchpad = string.Equals(command.WorkspaceKind, "scratchpad", StringComparison.OrdinalIgnoreCase);
+        SessionToolingBundle? toolingBundle = command.Tooling is null
-        SessionToolingBundle? toolingBundle = isScratchpad
             ? null
             : await SessionToolingBundle.CreateAsync(command.Tooling, command.ProjectPath, cancellationToken)
                 .ConfigureAwait(false);
@@ -58,22 +57,7 @@ internal sealed class CopilotAgentBundle : IAsyncDisposable
                 Streaming = true,
             };
 
-            if (isScratchpad)
+            ApplySessionTooling(sessionConfig, toolingBundle?.McpServers, toolingBundle?.Tools);
-            {
-                sessionConfig.AvailableTools = [];
-            }
-            else if (toolingBundle is not null)
-            {
-                if (toolingBundle.McpServers.Count > 0)
-                {
-                    sessionConfig.McpServers = toolingBundle.McpServers;
-                }
-
-                if (toolingBundle.Tools.Count > 0)
-                {
-                    sessionConfig.Tools = toolingBundle.Tools.ToList();
-                }
-            }
 
             GitHubCopilotAgent agent = new(
                 client,
@@ -92,6 +76,22 @@ internal sealed class CopilotAgentBundle : IAsyncDisposable
         return bundle;
     }
 
+    internal static void ApplySessionTooling(
+        SessionConfig sessionConfig,
+        Dictionary<string, object>? mcpServers,
+        IReadOnlyList<AIFunction>? tools)
+    {
+        if (mcpServers is { Count: > 0 })
+        {
+            sessionConfig.McpServers = mcpServers;
+        }
+
+        if (tools is { Count: > 0 })
+        {
+            sessionConfig.Tools = tools.ToList();
+        }
+    }
+
     public Workflow BuildWorkflow(PatternDefinitionDto pattern)
     {
         return pattern.Mode switch

sidecar/tests/Eryx.AgentHost.Tests/CopilotAgentBundleTests.cs

@@ -0,0 +1,73 @@
+using System.Reflection;
+using Eryx.AgentHost.Services;
+using GitHub.Copilot.SDK;
+using Microsoft.Extensions.AI;
+
+namespace Eryx.AgentHost.Tests;
+
+public sealed class CopilotAgentBundleTests
+{
+    [Fact]
+    public void ApplySessionTooling_MapsMcpServersAndToolsOntoTheSessionConfig()
+    {
+        SessionConfig sessionConfig = new()
+        {
+            AvailableTools = ["glob"],
+        };
+        Dictionary<string, object> mcpServers = new(StringComparer.OrdinalIgnoreCase)
+        {
+            ["Git MCP"] = new McpLocalServerConfig
+            {
+                Type = "local",
+                Command = "node",
+                Args = ["server.js"],
+                Tools = ["git.status"],
+            },
+        };
+        AIFunction tool = CreateTool();
+
+        CopilotAgentBundle.ApplySessionTooling(sessionConfig, mcpServers, [tool]);
+
+        Assert.Same(mcpServers, sessionConfig.McpServers);
+        Assert.NotNull(sessionConfig.Tools);
+        AIFunction configuredTool = Assert.Single(sessionConfig.Tools);
+        Assert.Same(tool, configuredTool);
+        Assert.Equal(["glob"], sessionConfig.AvailableTools);
+    }
+
+    [Fact]
+    public void ApplySessionTooling_LeavesSessionConfigUnsetWhenNoToolingIsProvided()
+    {
+        SessionConfig sessionConfig = new()
+        {
+            AvailableTools = ["glob", "view"],
+        };
+
+        CopilotAgentBundle.ApplySessionTooling(sessionConfig, null, []);
+
+        Assert.Null(sessionConfig.McpServers);
+        Assert.Null(sessionConfig.Tools);
+        Assert.Equal(["glob", "view"], sessionConfig.AvailableTools);
+    }
+
+    private static AIFunction CreateTool()
+    {
+        ToolTarget target = new();
+        MethodInfo method = typeof(ToolTarget).GetMethod(nameof(ToolTarget.Echo))
+            ?? throw new InvalidOperationException("Expected test method to exist.");
+
+        return AIFunctionFactory.Create(
+            method,
+            target,
+            new AIFunctionFactoryOptions
+            {
+                Name = "echo",
+                Description = "Echo test tool",
+            });
+    }
+
+    private sealed class ToolTarget
+    {
+        public string Echo() => "ok";
+    }
+}

src/main/EryxAppService.ts

@@ -6,8 +6,6 @@ import { dialog } from 'electron';
 import type {
   AgentActivityEvent,
   ApprovalRequestedEvent,
-  RunTurnLspProfileConfig,
-  RunTurnMcpServerConfig,
   RunTurnToolingConfig,
   SidecarCapabilities,
   TurnDeltaEvent,
@@ -89,6 +87,10 @@ import { WorkspaceRepository } from '@main/persistence/workspaceRepository';
 import { SecretStore } from '@main/secrets/secretStore';
 import { SidecarClient } from '@main/sidecar/sidecarProcess';
 import { GitService } from '@main/git/gitService';
+import {
+  buildRunTurnToolingConfig as buildSessionToolingConfig,
+  validateSessionToolingSelectionIds,
+} from '@main/sessionToolingConfig';
 
 type AppServiceEvents = {
   'workspace-updated': [WorkspaceState];
@@ -493,7 +495,7 @@ export class EryxAppService extends EventEmitter<AppServiceEvents> {
           workspaceKind,
           pattern: effectivePattern,
           messages: session.messages,
-          tooling: this.buildRunTurnToolingConfig(workspace, project, session),
+          tooling: this.buildRunTurnToolingConfig(workspace, session),
         },
         async (event) => {
           await this.applyTurnDelta(workspace, session.id, requestId, event);
@@ -650,7 +652,7 @@ export class EryxAppService extends EventEmitter<AppServiceEvents> {
   ): Promise<WorkspaceState> {
     const workspace = await this.loadWorkspace();
     const session = this.requireSession(workspace, sessionId);
-    const project = this.requireProject(workspace, session.projectId);
+    this.requireProject(workspace, session.projectId);
 
     if (session.status === 'running') {
       throw new Error('Wait for the current response to finish before changing session tools.');
@@ -660,34 +662,7 @@ export class EryxAppService extends EventEmitter<AppServiceEvents> {
       enabledMcpServerIds,
       enabledLspProfileIds,
     });
-
+    validateSessionToolingSelectionIds(workspace.settings.tooling, selection);
-    if (
-      isScratchpadProject(project)
-      && (selection.enabledMcpServerIds.length > 0 || selection.enabledLspProfileIds.length > 0)
-    ) {
-      throw new Error('Scratchpad sessions do not support MCP or LSP tools.');
-    }
-
-    const knownMcpServerIds = new Set(
-      workspace.settings.tooling.mcpServers.map((server) => server.id),
-    );
-    const knownLspProfileIds = new Set(
-      workspace.settings.tooling.lspProfiles.map((profile) => profile.id),
-    );
-
-    const unknownMcpServerIds = selection.enabledMcpServerIds.filter(
-      (id) => !knownMcpServerIds.has(id),
-    );
-    if (unknownMcpServerIds.length > 0) {
-      throw new Error(`Unknown MCP server "${unknownMcpServerIds[0]}".`);
-    }
-
-    const unknownLspProfileIds = selection.enabledLspProfileIds.filter(
-      (id) => !knownLspProfileIds.has(id),
-    );
-    if (unknownLspProfileIds.length > 0) {
-      throw new Error(`Unknown LSP profile "${unknownLspProfileIds[0]}".`);
-    }
 
     session.tooling = selection;
     session.updatedAt = nowIso();
@@ -700,7 +675,7 @@ export class EryxAppService extends EventEmitter<AppServiceEvents> {
   ): Promise<WorkspaceState> {
     const workspace = await this.loadWorkspace();
     const session = this.requireSession(workspace, sessionId);
-    const project = this.requireProject(workspace, session.projectId);
+    this.requireProject(workspace, session.projectId);
 
     if (session.status === 'running') {
       throw new Error('Wait for the current response to finish before changing session approval settings.');
@@ -710,14 +685,6 @@ export class EryxAppService extends EventEmitter<AppServiceEvents> {
       autoApprovedToolNames === undefined ? undefined : { autoApprovedToolNames },
     );
 
-    if (
-      isScratchpadProject(project)
-      && settings
-      && settings.autoApprovedToolNames.length > 0
-    ) {
-      throw new Error('Scratchpad sessions do not support tool auto-approval settings.');
-    }
-
     const knownToolNames = new Set(await this.listKnownApprovalToolNames(workspace));
     const unknownToolName = settings?.autoApprovedToolNames.find((toolName) => !knownToolNames.has(toolName));
     if (unknownToolName) {
@@ -1227,82 +1194,11 @@ export class EryxAppService extends EventEmitter<AppServiceEvents> {
 
   private buildRunTurnToolingConfig(
     workspace: WorkspaceState,
-    project: ProjectRecord,
     session: SessionRecord,
   ): RunTurnToolingConfig | undefined {
-    if (isScratchpadProject(project)) {
-      return undefined;
-    }
-
     const selection = resolveSessionToolingSelection(session);
-    const mcpServersById = new Map<string, McpServerDefinition>(
+    validateSessionToolingSelectionIds(workspace.settings.tooling, selection);
-      workspace.settings.tooling.mcpServers.map((server) => [server.id, server]),
+    return buildSessionToolingConfig(workspace.settings.tooling, selection);
-    );
-    const lspProfilesById = new Map<string, LspProfileDefinition>(
-      workspace.settings.tooling.lspProfiles.map((profile) => [profile.id, profile]),
-    );
-
-    const mcpServers = selection.enabledMcpServerIds.flatMap((id): RunTurnMcpServerConfig[] => {
-      const server = mcpServersById.get(id);
-      if (!server) {
-        return [];
-      }
-
-      if (server.transport === 'local') {
-        return [
-          {
-            id: server.id,
-            name: server.name,
-            transport: 'local',
-            tools: [...server.tools],
-            timeoutMs: server.timeoutMs,
-            command: server.command,
-            args: [...server.args],
-            cwd: server.cwd,
-          },
-        ];
-      }
-
-      return [
-        {
-          id: server.id,
-          name: server.name,
-          transport: server.transport,
-          tools: [...server.tools],
-          timeoutMs: server.timeoutMs,
-          url: server.url,
-        },
-      ];
-    });
-
-    const lspProfiles = selection.enabledLspProfileIds.flatMap(
-      (id): RunTurnLspProfileConfig[] => {
-        const profile = lspProfilesById.get(id);
-        if (!profile) {
-          return [];
-        }
-
-        return [
-          {
-            id: profile.id,
-            name: profile.name,
-            command: profile.command,
-            args: [...profile.args],
-            languageId: profile.languageId,
-            fileExtensions: [...profile.fileExtensions],
-          },
-        ];
-      },
-    );
-
-    if (mcpServers.length === 0 && lspProfiles.length === 0) {
-      return undefined;
-    }
-
-    return {
-      mcpServers,
-      lspProfiles,
-    };
   }
 
   private updateSessionRun(

tests/main/sessionToolingConfig.test.ts

@@ -0,0 +1,100 @@
+import { describe, expect, test } from 'bun:test';
+
+import {
+  buildRunTurnToolingConfig,
+  validateSessionToolingSelectionIds,
+} from '@main/sessionToolingConfig';
+import type { SessionToolingSelection, WorkspaceToolingSettings } from '@shared/domain/tooling';
+
+const TIMESTAMP = '2026-03-25T00:00:00.000Z';
+
+const TOOLING: WorkspaceToolingSettings = {
+  mcpServers: [
+    {
+      id: 'mcp-git',
+      name: 'Git MCP',
+      transport: 'local',
+      command: 'node',
+      args: ['server.js'],
+      cwd: 'C:\\workspace\\repo',
+      tools: ['git.status'],
+      createdAt: TIMESTAMP,
+      updatedAt: TIMESTAMP,
+    },
+  ],
+  lspProfiles: [
+    {
+      id: 'lsp-ts',
+      name: 'TypeScript',
+      command: 'typescript-language-server',
+      args: ['--stdio'],
+      languageId: 'typescript',
+      fileExtensions: ['.ts', '.tsx'],
+      createdAt: TIMESTAMP,
+      updatedAt: TIMESTAMP,
+    },
+  ],
+};
+
+describe('session tooling config helpers', () => {
+  test('validates selected tooling ids against configured workspace tooling', () => {
+    const selection: SessionToolingSelection = {
+      enabledMcpServerIds: ['mcp-git'],
+      enabledLspProfileIds: ['lsp-ts'],
+    };
+
+    expect(() => validateSessionToolingSelectionIds(TOOLING, selection)).not.toThrow();
+    expect(() =>
+      validateSessionToolingSelectionIds(TOOLING, {
+        enabledMcpServerIds: ['missing-mcp'],
+        enabledLspProfileIds: [],
+      }),
+    ).toThrow('Unknown MCP server "missing-mcp".');
+    expect(() =>
+      validateSessionToolingSelectionIds(TOOLING, {
+        enabledMcpServerIds: [],
+        enabledLspProfileIds: ['missing-lsp'],
+      }),
+    ).toThrow('Unknown LSP profile "missing-lsp".');
+  });
+
+  test('builds a run-turn tooling config from selected MCP and LSP ids', () => {
+    expect(
+      buildRunTurnToolingConfig(TOOLING, {
+        enabledMcpServerIds: ['mcp-git'],
+        enabledLspProfileIds: ['lsp-ts'],
+      }),
+    ).toEqual({
+      mcpServers: [
+        {
+          id: 'mcp-git',
+          name: 'Git MCP',
+          transport: 'local',
+          tools: ['git.status'],
+          command: 'node',
+          args: ['server.js'],
+          cwd: 'C:\\workspace\\repo',
+        },
+      ],
+      lspProfiles: [
+        {
+          id: 'lsp-ts',
+          name: 'TypeScript',
+          command: 'typescript-language-server',
+          args: ['--stdio'],
+          languageId: 'typescript',
+          fileExtensions: ['.ts', '.tsx'],
+        },
+      ],
+    });
+  });
+
+  test('returns undefined when no session tooling is selected', () => {
+    expect(
+      buildRunTurnToolingConfig(TOOLING, {
+        enabledMcpServerIds: [],
+        enabledLspProfileIds: [],
+      }),
+    ).toBeUndefined();
+  });
+});