feat(install): add conflict detection with override/link/abort options

When a tool already exists in PATH:
- override: download new binary, replace existing
- link: wrap existing binary with anycli middleware (no download)
- abort: cancel installation

Supports -y flag for non-interactive mode (defaults to link).
Supports -m flag to specify mode directly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: wenfengwang

cmd/install.go

@@ -1,9 +1,12 @@
 package cmd
 
 import (
+	"bufio"
 	"fmt"
 	"os"
+	"os/exec"
 	"path/filepath"
+	"strings"
 
 	"github.com/shipbase/anycli/definitions"
 	"github.com/shipbase/anycli/internal/config"
@@ -19,8 +22,10 @@ var installCmd = &cobra.Command{
 	Args:  cobra.ExactArgs(1),
 	RunE: func(cmd *cobra.Command, args []string) error {
 		name := args[0]
+		yes, _ := cmd.Flags().GetBool("yes")
+		mode, _ := cmd.Flags().GetString("mode")
 
-		// Check if already installed
+		// Check if already installed in anycli
 		if _, err := registry.Load(name); err == nil {
 			fmt.Printf("%s is already installed\n", name)
 			return nil
@@ -43,13 +48,46 @@ var installCmd = &cobra.Command{
 			def = d
 		}
 
-		// Download the real binary if source is configured
+		// Check if the tool already exists in PATH
+		if mode == "" {
+			existingPath, err := findExistingBinary(name)
+			if err == nil && existingPath != "" {
+				if yes {
+					// Non-interactive: default to link
+					mode = "link"
+					fmt.Printf("found existing %s at %s, linking\n", name, existingPath)
+				} else {
+					m, err := promptConflict(name, existingPath)
+					if err != nil {
+						return err
+					}
+					mode = m
+				}
+			}
+		}
+
+		if mode == "abort" {
+			fmt.Println("installation aborted")
+			return nil
+		}
+
+		if mode == "link" {
+			// Link mode: wrap existing binary, skip download
+			existingPath, err := findExistingBinary(name)
+			if err != nil {
+				return fmt.Errorf("cannot find existing %s: %w", name, err)
+			}
+			def.Resolve = existingPath
+			def.Source = nil // don't download
+			fmt.Printf("linking to existing %s at %s\n", name, existingPath)
+		}
+
+		// Download the real binary if source is configured (override mode or no conflict)
 		if def.Source != nil {
 			result, err := installer.Install(def)
 			if err != nil {
 				return fmt.Errorf("failed to install %s: %w", name, err)
 			}
-			// Set resolve to the installed binary path
 			def.Resolve = result.BinaryPath
 			fmt.Printf("downloaded %s v%s\n", name, result.Version)
 		}
@@ -69,6 +107,46 @@ var installCmd = &cobra.Command{
 	},
 }
 
+// findExistingBinary searches PATH for an existing binary, skipping the anycli shim dir.
+func findExistingBinary(name string) (string, error) {
+	shimDir := config.BinDir()
+	pathEnv := os.Getenv("PATH")
+	for _, dir := range filepath.SplitList(pathEnv) {
+		if dir == shimDir {
+			continue
+		}
+		candidate := filepath.Join(dir, name)
+		if info, err := os.Stat(candidate); err == nil && !info.IsDir() {
+			return candidate, nil
+		}
+	}
+	return "", exec.ErrNotFound
+}
+
+// promptConflict asks the user how to handle an existing binary.
+func promptConflict(name, existingPath string) (string, error) {
+	fmt.Printf("found existing %s at %s\n", name, existingPath)
+	fmt.Println("  [o]verride  - download new binary, replace existing")
+	fmt.Println("  [l]ink      - wrap existing binary with anycli middleware")
+	fmt.Println("  [a]bort     - cancel installation")
+	fmt.Print("choose [o/l/a]: ")
+
+	reader := bufio.NewReader(os.Stdin)
+	input, _ := reader.ReadString('\n')
+	input = strings.TrimSpace(strings.ToLower(input))
+
+	switch input {
+	case "o", "override":
+		return "override", nil
+	case "l", "link":
+		return "link", nil
+	case "a", "abort", "":
+		return "abort", nil
+	default:
+		return "abort", nil
+	}
+}
+
 func loadFromFile(path string) (*registry.Definition, error) {
 	data, err := os.ReadFile(path)
 	if err != nil {
@@ -108,5 +186,7 @@ func createShim(name string) error {
 
 func init() {
 	installCmd.Flags().String("from", "", "install from a local JSON definition file")
+	installCmd.Flags().StringP("mode", "m", "", "conflict resolution: override, link, or abort")
+	installCmd.Flags().BoolP("yes", "y", false, "non-interactive mode (defaults to link on conflict)")
 	rootCmd.AddCommand(installCmd)
 }