enhance: send MCP errors back to the LLM so it can correct if possible (#974)

Signed-off-by: Donnie Adams <[email protected]>

Author: thedadams

pkg/engine/cmd.go

@@ -65,7 +65,7 @@ func compressEnv(envs []string) (result []string) {
 	return
 }
 
-func (e *Engine) runCommand(ctx Context, tool types.Tool, input string, toolCategory ToolCategory) (cmdOut string, cmdErr error) {
+func (e *Engine) runCommand(ctx Context, tool types.Tool, input string) (cmdOut string, cmdErr error) {
 	id := counter.Next()
 
 	var combinedOutput string
@@ -128,7 +128,7 @@ func (e *Engine) runCommand(ctx Context, tool types.Tool, input string, toolCate
 
 	cmd, stop, err := e.newCommand(commandCtx, extraEnv, tool, input, true)
 	if err != nil {
-		if toolCategory == NoCategory && ctx.Parent != nil {
+		if ctx.ToolCategory == NoCategory && ctx.Parent != nil {
 			return fmt.Sprintf("ERROR: got (%v) while parsing command", err), nil
 		}
 		return "", fmt.Errorf("got (%v) while parsing command", err)
@@ -167,7 +167,7 @@ func (e *Engine) runCommand(ctx Context, tool types.Tool, input string, toolCate
 
 	if err := cmd.Run(); err != nil && (commandCtx.Err() == nil || ctx.Ctx.Err() != nil) {
 		// If the command failed and the context hasn't been canceled, then return the error.
-		if toolCategory == NoCategory && ctx.Parent != nil {
+		if ctx.ToolCategory == NoCategory && ctx.Parent != nil {
 			// If this is a sub-call, then don't return the error; return the error as a message so that the LLM can retry.
 			return fmt.Sprintf("ERROR: got (%v) while running tool, OUTPUT: %s", err, stdoutAndErr), nil
 		}

pkg/engine/engine.go

@@ -45,7 +45,7 @@ type Engine struct {
 }
 
 type MCPRunner interface {
-	Run(ctx context.Context, progress chan<- types.CompletionStatus, tool types.Tool, input string) (string, error)
+	Run(ctx Context, progress chan<- types.CompletionStatus, tool types.Tool, input string) (string, error)
 }
 
 type State struct {
@@ -313,7 +313,7 @@ func populateMessageParams(ctx Context, completion *types.CompletionRequest, too
 }
 
 func (e *Engine) runMCPInvoke(ctx Context, tool types.Tool, input string) (*Return, error) {
-	output, err := e.MCPRunner.Run(ctx.Ctx, e.Progress, tool, input)
+	output, err := e.MCPRunner.Run(ctx, e.Progress, tool, input)
 	if err != nil {
 		return nil, fmt.Errorf("failed to run MCP invoke: %w", err)
 	}
@@ -335,7 +335,7 @@ func (e *Engine) runCommandTools(ctx Context, tool types.Tool, input string) (*R
 	} else if tool.IsCall() {
 		return e.runCall(ctx, tool, input)
 	}
-	s, err := e.runCommand(ctx, tool, input, ctx.ToolCategory)
+	s, err := e.runCommand(ctx, tool, input)
 	return &Return{
 		Result: &s,
 	}, err

pkg/mcp/runner.go

@@ -1,16 +1,16 @@
 package mcp
 
 import (
-	"context"
 	"encoding/json"
 	"fmt"
 	"strings"
 
+	"github.com/gptscript-ai/gptscript/pkg/engine"
 	"github.com/gptscript-ai/gptscript/pkg/types"
 	"github.com/mark3labs/mcp-go/mcp"
 )
 
-func (l *Local) Run(ctx context.Context, _ chan<- types.CompletionStatus, tool types.Tool, input string) (string, error) {
+func (l *Local) Run(ctx engine.Context, _ chan<- types.CompletionStatus, tool types.Tool, input string) (string, error) {
 	fields := strings.Fields(tool.Instructions)
 	if len(fields) < 2 {
 		return "", fmt.Errorf("invalid mcp call, invalid number of fields in %s", tool.Instructions)
@@ -41,8 +41,16 @@ func (l *Local) Run(ctx context.Context, _ chan<- types.CompletionStatus, tool t
 	request.Params.Name = toolName
 	request.Params.Arguments = arguments
 
-	result, err := session.Client.CallTool(ctx, request)
+	result, err := session.Client.CallTool(ctx.Ctx, request)
 	if err != nil {
+		if ctx.ToolCategory == engine.NoCategory && ctx.Parent != nil {
+			var output []byte
+			if result != nil {
+				output, _ = json.Marshal(result)
+			}
+			// If this is a sub-call, then don't return the error; return the error as a message so that the LLM can retry.
+			return fmt.Sprintf("ERROR: got (%v) while running tool, OUTPUT: %s", err, string(output)), nil
+		}
 		return "", fmt.Errorf("failed to call tool %s: %w", toolName, err)
 	}