fix: create MCP toolset even when command binary is unavailable

When EnsureCommand fails (binary not on PATH, no aqua package, etc.),
createMCPTool now logs a warning and creates the toolset with the
original command string instead of returning an error.

Previously, the error caused the toolset to be discarded entirely at
config-load time, so it was never added to the agent's toolset list.
The Start() retry (from the previous commit) was never reached because
there was no toolset object to retry.

Now the toolset is always created. On the first conversation turn,
Start() detects the missing binary and returns errServerUnavailable
(keeping started=false). On subsequent turns, ensureToolSetsAreStarted
retries Start() — once the binary is available, the MCP server connects
successfully.

Assisted-By: docker-agent

Author: simonferquel-clanker

pkg/teamloader/registry.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"log/slog"
 	"os"
 	"path/filepath"
 	"time"
@@ -268,10 +269,15 @@ func createMCPTool(ctx context.Context, toolset latest.Toolset, _ string, runCon
 
 	// STDIO MCP Server from shell command
 	case toolset.Command != "":
-		// Auto-install missing command binary if needed
+		// Auto-install missing command binary if needed.
+		// If EnsureCommand fails (binary not on PATH, no aqua package, etc.),
+		// treat as transient: create the toolset with the original command
+		// and let mcp.Toolset.Start() retry on each conversation turn.
 		resolvedCommand, err := toolinstall.EnsureCommand(ctx, toolset.Command, toolset.Version)
 		if err != nil {
-			return nil, fmt.Errorf("resolving command %q: %w", toolset.Command, err)
+			slog.Warn("MCP command not yet available, will retry on next turn",
+				"command", toolset.Command, "error", err)
+			resolvedCommand = toolset.Command
 		}
 
 		env, err := environment.ExpandAll(ctx, environment.ToValues(toolset.Env), envProvider)

pkg/teamloader/registry_test.go

@@ -3,11 +3,13 @@ package teamloader
 import (
 	"testing"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
 	"github.com/docker/docker-agent/pkg/config"
 	"github.com/docker/docker-agent/pkg/config/latest"
 	"github.com/docker/docker-agent/pkg/environment"
+	"github.com/docker/docker-agent/pkg/tools"
 )
 
 func TestCreateShellTool(t *testing.T) {
@@ -26,3 +28,45 @@ func TestCreateShellTool(t *testing.T) {
 	require.NoError(t, err)
 	require.NotNil(t, tool)
 }
+
+func TestCreateMCPTool_CommandNotFound_CreatesToolsetAnyway(t *testing.T) {
+	t.Setenv("DOCKER_AGENT_TOOLS_DIR", t.TempDir())
+
+	toolset := latest.Toolset{
+		Type:    "mcp",
+		Command: "./bin/nonexistent-mcp-server",
+	}
+
+	registry := NewDefaultToolsetRegistry()
+
+	runConfig := &config.RuntimeConfig{
+		Config:              config.Config{WorkingDir: t.TempDir()},
+		EnvProviderForTests: environment.NewOsEnvProvider(),
+	}
+
+	tool, err := registry.CreateTool(t.Context(), toolset, ".", runConfig, "test-agent")
+	require.NoError(t, err)
+	require.NotNil(t, tool)
+	assert.Equal(t, "mcp(stdio cmd=./bin/nonexistent-mcp-server)", tools.DescribeToolSet(tool))
+}
+
+func TestCreateMCPTool_BareCommandNotFound_CreatesToolsetAnyway(t *testing.T) {
+	t.Setenv("DOCKER_AGENT_TOOLS_DIR", t.TempDir())
+
+	toolset := latest.Toolset{
+		Type:    "mcp",
+		Command: "some-nonexistent-mcp-binary",
+	}
+
+	registry := NewDefaultToolsetRegistry()
+
+	runConfig := &config.RuntimeConfig{
+		Config:              config.Config{WorkingDir: t.TempDir()},
+		EnvProviderForTests: environment.NewOsEnvProvider(),
+	}
+
+	tool, err := registry.CreateTool(t.Context(), toolset, ".", runConfig, "test-agent")
+	require.NoError(t, err)
+	require.NotNil(t, tool)
+	assert.Equal(t, "mcp(stdio cmd=some-nonexistent-mcp-binary)", tools.DescribeToolSet(tool))
+}