fix(debug): pass workspace folder to startDebugging

src/test/suite/debug.test.ts

@@ -298,6 +298,22 @@ suite('Debug Tools Tests', () => {
     }
   });
 
+  test('should start debug session with a preLaunchTask', async () => {
+    const result = await callTool('debug_startSession', {
+      configuration: 'Debug With PreLaunchTask',
+      format: 'detailed',
+    });
+
+    // A preLaunchTask only resolves when startDebugging is given the
+    // owning workspace folder. Without it, VS Code reports
+    // "Could not find the task 'prelaunch-noop'" and startDebugging
+    // returns false.
+    assert.ok(!result.error, `Should not have error: ${result.error}`);
+    assert.strictEqual(result.success, true, 'Debug session should start');
+
+    await vscode.debug.stopDebugging();
+  });
+
   // Skip debug session tests for now as they require more setup
   test.skip('should start debug session', async () => {
     const result = await callTool('debug_startSession', {

src/tools/debug/startDebugSession.ts

@@ -24,7 +24,14 @@ export const debug_startSessionTool: Tool = {
   handler: async (args) => {
     const { configuration, format = 'compact' } = args;
 
-    const configs = vscode.workspace.getConfiguration('launch').get<any[]>('configurations') || [];
+    // Single-root only: a multi-root workspace can host per-folder launch
+    // configs and tasks, which this does not resolve.
+    const workspaceFolder = vscode.workspace.workspaceFolders?.[0];
+
+    const configs =
+      vscode.workspace
+        .getConfiguration('launch', workspaceFolder?.uri)
+        .get<any[]>('configurations') || [];
 
     if (configs.length === 0) {
       return format === 'compact'
@@ -46,7 +53,9 @@ export const debug_startSessionTool: Tool = {
       configToUse = found;
     }
 
-    const success = await vscode.debug.startDebugging(undefined, configToUse);
+    // The workspace folder must be passed so VS Code can resolve a
+    // preLaunchTask and folder-scoped variables like ${workspaceFolder}.
+    const success = await vscode.debug.startDebugging(workspaceFolder, configToUse);
 
     if (format === 'compact') {
       return { started: success, config: configToUse.name };

test-workspace/.vscode/launch.json

@@ -20,6 +20,15 @@
       "args": ["--timeout", "999999", "--colors", "${file}"],
       "internalConsoleOptions": "openOnSessionStart",
       "skipFiles": ["<node_internals>/**"]
+    },
+    {
+      "type": "node",
+      "request": "launch",
+      "name": "Debug With PreLaunchTask",
+      "program": "${workspaceFolder}/src/noop.cjs",
+      "preLaunchTask": "prelaunch-noop",
+      "internalConsoleOptions": "neverOpen",
+      "skipFiles": ["<node_internals>/**"]
     }
   ]
 }

test-workspace/.vscode/tasks.json

@@ -0,0 +1,15 @@
+{
+  "version": "2.0.0",
+  "tasks": [
+    {
+      "label": "prelaunch-noop",
+      "type": "shell",
+      "command": "node",
+      "args": ["-e", "process.exit(0)"],
+      "presentation": {
+        "reveal": "never"
+      },
+      "problemMatcher": []
+    }
+  ]
+}

test-workspace/src/noop.cjs

@@ -0,0 +1,3 @@
+// Minimal program launched by the preLaunchTask debug regression test.
+// Exits on its own so the debug session does not linger.
+setTimeout(() => process.exit(0), 200);