Handle shutdown signals gracefully in MCP server (#4227)

## Summary

- Add signal handling for SIGINT and SIGTERM in MCP server
- Call `Shutdown()` method when signals are received
- Exit cleanly with code 0 instead of crashing

## Problem

When Claude Agent SDK terminates the MCP server process, the Go process
doesn't handle signals gracefully. This causes the process to crash
during cleanup, resulting in "Command failed with exit code 1" error
that propagates back to the SDK.

This is a known issue pattern documented in:
- anthropics/claude-code#7718 (SIGABRT during
MCP shutdown)
- anthropics/claude-code#5506 (MCP Server
Shutdown Failure)

## Solution

Run the server in a goroutine and wait for either:
1. Server completion (EOF, error, or context cancellation)
2. Shutdown signal (SIGINT or SIGTERM)

When a signal is received, cancel the context and call `Shutdown()` to
clean up resources gracefully.

## Test plan

- [x] Build succeeds
- [ ] Manual test with Claude Agent SDK - verify no "exit code 1" errors
on session end

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: keugenek

experimental/apps-mcp/cmd/apps_mcp.go

@@ -1,6 +1,11 @@
 package mcp
 
 import (
+	"context"
+	"os"
+	"os/signal"
+	"syscall"
+
 	mcplib "github.com/databricks/cli/experimental/apps-mcp/lib"
 	"github.com/databricks/cli/experimental/apps-mcp/lib/server"
 	"github.com/databricks/cli/libs/log"
@@ -25,7 +30,13 @@ The server communicates via stdio using the Model Context Protocol.`,
 		Example: `  # Start MCP server with required warehouse
   databricks experimental apps-mcp --warehouse-id abc123`,
 		RunE: func(cmd *cobra.Command, args []string) error {
-			ctx := cmd.Context()
+			// Create cancellable context for graceful shutdown
+			ctx, cancel := context.WithCancel(cmd.Context())
+			defer cancel()
+
+			// Handle shutdown signals (SIGINT, SIGTERM)
+			sigCh := make(chan os.Signal, 1)
+			signal.Notify(sigCh, syscall.SIGINT, syscall.SIGTERM)
 
 			// Build MCP config from flags
 			cfg := &mcplib.Config{}
@@ -41,8 +52,29 @@ The server communicates via stdio using the Model Context Protocol.`,
 				return err
 			}
 
-			// Run server
-			return srv.Run(ctx)
+			// Run server in goroutine so we can handle signals
+			errCh := make(chan error, 1)
+			go func() {
+				errCh <- srv.Run(ctx)
+			}()
+
+			// Wait for either server error or shutdown signal
+			select {
+			case err := <-errCh:
+				// Server stopped (EOF, error, or context cancelled)
+				if shutdownErr := srv.Shutdown(ctx); shutdownErr != nil {
+					log.Warnf(ctx, "Shutdown error: %v", shutdownErr)
+				}
+				return err
+			case sig := <-sigCh:
+				// Received shutdown signal - exit gracefully
+				log.Infof(ctx, "Received signal %v, shutting down gracefully", sig)
+				cancel() // Cancel context to stop server.Run()
+				if shutdownErr := srv.Shutdown(ctx); shutdownErr != nil {
+					log.Warnf(ctx, "Shutdown error: %v", shutdownErr)
+				}
+				return nil
+			}
 		},
 	}