Clear existing breakpoints in session when debugger starts

This change ensures that the breakpoints the user has in their runspace
correspond to the list of breakpoints that are enabled in the debug
adapter client.

Resolves PowerShell/vscode-powershell#625

Author: daviwil

src/PowerShellEditorServices.Protocol/Server/DebugAdapter.cs

@@ -182,6 +182,9 @@ private async Task HandleInitializeRequest(
             object shutdownParams,
             RequestContext<InitializeResponseBody> requestContext)
         {
+            // Clear any existing breakpoints before proceeding
+            await this.ClearSessionBreakpoints();
+
             // Now send the Initialize response to continue setup
             await requestContext.SendResult(
                 new InitializeResponseBody {
@@ -420,6 +423,9 @@ await requestContext.SendError(
                     return;
                 }
 
+                // Clear any existing breakpoints before proceeding
+                await this.ClearSessionBreakpoints();
+
                 // Execute the Debug-Runspace command but don't await it because it
                 // will block the debug adapter initialization process.  The
                 // InitializedEvent will be sent as soon as the RunspaceChanged
@@ -883,6 +889,18 @@ private void UnregisterEventHandlers()
             this.editorSession.PowerShellContext.DebuggerResumed -= this.powerShellContext_DebuggerResumed;
         }
 
+        private async Task ClearSessionBreakpoints()
+        {
+            try
+            {
+                await this.editorSession.DebugService.ClearAllBreakpoints();
+            }
+            catch (Exception e)
+            {
+                Logger.WriteException("Caught exception while clearing breakpoints from session", e);
+            }
+        }
+
         #endregion
 
         #region Event Handlers

src/PowerShellEditorServices/Debugging/DebugService.cs

@@ -660,6 +660,18 @@ public VariableScope[] GetVariableScopes(int stackFrameId)
             };
         }
 
+        /// <summary>
+        /// Clears all breakpoints in the current session.
+        /// </summary>
+        public async Task ClearAllBreakpoints()
+        {
+            PSCommand psCommand = new PSCommand();
+            psCommand.AddCommand(@"Microsoft.PowerShell.Utility\Get-PSBreakpoint");
+            psCommand.AddCommand(@"Microsoft.PowerShell.Utility\Remove-PSBreakpoint");
+
+            await this.powerShellContext.ExecuteCommand<object>(psCommand);
+        }
+
         #endregion
 
         #region Private Methods