From 8e77c5e58d13accea1dfd96b2c384f9b85ffa83b Mon Sep 17 00:00:00 2001
From: Virgil <virgil@lethean.io>
Date: Thu, 2 Apr 2026 12:56:30 +0000
Subject: [PATCH] feat(mcp): auto-select unix socket transport

Co-Authored-By: Virgil <virgil@lethean.io>
---
 cmd/mcpcmd/cmd_mcp.go          | 11 +++++---
 pkg/mcp/mcp.go                 |  7 +++++
 pkg/mcp/transport_unix_test.go | 47 ++++++++++++++++++++++++++++++++++
 3 files changed, 62 insertions(+), 3 deletions(-)
 create mode 100644 pkg/mcp/transport_unix_test.go

diff --git a/cmd/mcpcmd/cmd_mcp.go b/cmd/mcpcmd/cmd_mcp.go
index 392f0d8..cb2b3ad 100644
--- a/cmd/mcpcmd/cmd_mcp.go
+++ b/cmd/mcpcmd/cmd_mcp.go
@@ -10,10 +10,10 @@ import (
 	"os/signal"
 	"syscall"
 
-	"forge.lthn.ai/core/cli/pkg/cli"
 	"dappco.re/go/mcp/pkg/mcp"
 	"dappco.re/go/mcp/pkg/mcp/agentic"
 	"dappco.re/go/mcp/pkg/mcp/brain"
+	"forge.lthn.ai/core/cli/pkg/cli"
 )
 
 var workspaceFlag string
@@ -27,13 +27,18 @@ var mcpCmd = &cli.Command{
 var serveCmd = &cli.Command{
 	Use:   "serve",
 	Short: "Start the MCP server",
-	Long: `Start the MCP server on stdio (default) or TCP.
+	Long: `Start the MCP server on stdio (default), TCP, Unix socket, or HTTP.
 
 The server provides file operations, RAG tools, and metrics tools for AI assistants.
 
 Environment variables:
   MCP_ADDR    TCP address to listen on (e.g., "localhost:9999")
-              If not set, uses stdio transport.
+  MCP_UNIX_SOCKET
+              Unix socket path to listen on (e.g., "/tmp/core-mcp.sock")
+              Selected after MCP_ADDR and before stdio.
+  MCP_HTTP_ADDR
+              HTTP address to listen on (e.g., "127.0.0.1:9101")
+              Selected before MCP_ADDR and stdio.
 
 Examples:
   # Start with stdio transport (for Claude Code integration)
diff --git a/pkg/mcp/mcp.go b/pkg/mcp/mcp.go
index 29107b4..dc2b94e 100644
--- a/pkg/mcp/mcp.go
+++ b/pkg/mcp/mcp.go
@@ -716,6 +716,10 @@ func supportedLanguages() []LanguageInfo {
 //	os.Setenv("MCP_ADDR", "127.0.0.1:9100")
 //	svc.Run(ctx)
 //
+//	// Unix socket (set MCP_UNIX_SOCKET):
+//	os.Setenv("MCP_UNIX_SOCKET", "/tmp/core-mcp.sock")
+//	svc.Run(ctx)
+//
 //	// HTTP (set MCP_HTTP_ADDR):
 //	os.Setenv("MCP_HTTP_ADDR", "127.0.0.1:9101")
 //	svc.Run(ctx)
@@ -726,6 +730,9 @@ func (s *Service) Run(ctx context.Context) error {
 	if addr := core.Env("MCP_ADDR"); addr != "" {
 		return s.ServeTCP(ctx, addr)
 	}
+	if socketPath := core.Env("MCP_UNIX_SOCKET"); socketPath != "" {
+		return s.ServeUnix(ctx, socketPath)
+	}
 	return s.ServeStdio(ctx)
 }
 
diff --git a/pkg/mcp/transport_unix_test.go b/pkg/mcp/transport_unix_test.go
new file mode 100644
index 0000000..c5446f9
--- /dev/null
+++ b/pkg/mcp/transport_unix_test.go
@@ -0,0 +1,47 @@
+package mcp
+
+import (
+	"context"
+	"net"
+	"testing"
+	"time"
+)
+
+func TestRun_Good_UnixTrigger(t *testing.T) {
+	s, err := New(Options{})
+	if err != nil {
+		t.Fatalf("Failed to create service: %v", err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	socketPath := shortSocketPath(t, "run")
+	t.Setenv("MCP_UNIX_SOCKET", socketPath)
+	t.Setenv("MCP_HTTP_ADDR", "")
+	t.Setenv("MCP_ADDR", "")
+
+	errCh := make(chan error, 1)
+	go func() {
+		errCh <- s.Run(ctx)
+	}()
+
+	var conn net.Conn
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		conn, err = net.DialTimeout("unix", socketPath, 200*time.Millisecond)
+		if err == nil {
+			break
+		}
+		time.Sleep(50 * time.Millisecond)
+	}
+	if err != nil {
+		t.Fatalf("Failed to connect to Unix socket at %s: %v", socketPath, err)
+	}
+	conn.Close()
+
+	cancel()
+	if err := <-errCh; err != nil {
+		t.Fatalf("Run failed: %v", err)
+	}
+}