fix: use platform-aware shell detection for Windows compatibility

Replace hardcoded 'sh -c' and '$SHELL' fallbacks with shellpath.DetectShell()
in skill command expansion, script_shell tools, post-edit hooks, and the TUI
bang command. On Windows this resolves to PowerShell or cmd.exe instead of
failing to find /bin/sh.

Also aligns the post-edit hook env variable from 'path' to 'file', matching
the documented ${file} syntax and avoiding conflict with zsh's special $path
parameter (tied to $PATH).

Author: trungutt

pkg/app/app.go

@@ -24,6 +24,7 @@ import (
 	"github.com/docker/docker-agent/pkg/runtime"
 	"github.com/docker/docker-agent/pkg/session"
 	"github.com/docker/docker-agent/pkg/sessiontitle"
+	"github.com/docker/docker-agent/pkg/shellpath"
 	"github.com/docker/docker-agent/pkg/skills"
 	"github.com/docker/docker-agent/pkg/tools"
 	mcptools "github.com/docker/docker-agent/pkg/tools/mcp"
@@ -503,7 +504,8 @@ func (a *App) RunBangCommand(ctx context.Context, command string) {
 		return
 	}
 
-	out, err := exec.CommandContext(ctx, "/bin/sh", "-c", command).CombinedOutput()
+	shell, argsPrefix := shellpath.DetectShell()
+	out, err := exec.CommandContext(ctx, shell, append(argsPrefix, command)...).CombinedOutput()
 	output := "$ " + command + "\n" + string(out)
 	if err != nil && len(out) == 0 {
 		output = "$ " + command + "\nError: " + err.Error()

pkg/skills/expand.go

@@ -10,6 +10,8 @@ import (
 	"regexp"
 	"strings"
 	"time"
+
+	"github.com/docker/docker-agent/pkg/shellpath"
 )
 
 // commandTimeout is the maximum time allowed for a single command expansion.
@@ -47,7 +49,8 @@ func runCommand(ctx context.Context, command, workDir string) (string, error) {
 	ctx, cancel := context.WithTimeout(ctx, commandTimeout)
 	defer cancel()
 
-	cmd := exec.CommandContext(ctx, "sh", "-c", command)
+	shell, argsPrefix := shellpath.DetectShell()
+	cmd := exec.CommandContext(ctx, shell, append(argsPrefix, command)...)
 	cmd.Dir = workDir
 
 	var stderr bytes.Buffer

pkg/tools/builtin/filesystem.go

@@ -17,6 +17,7 @@ import (
 
 	"github.com/docker/docker-agent/pkg/chat"
 	"github.com/docker/docker-agent/pkg/fsx"
+	"github.com/docker/docker-agent/pkg/shellpath"
 	"github.com/docker/docker-agent/pkg/tools"
 )
 
@@ -354,9 +355,10 @@ func (t *FilesystemTool) executePostEditCommands(ctx context.Context, filePath s
 			continue
 		}
 
-		cmd := exec.CommandContext(ctx, "/bin/sh", "-c", postEdit.Cmd)
+		shell, argsPrefix := shellpath.DetectShell()
+		cmd := exec.CommandContext(ctx, shell, append(argsPrefix, postEdit.Cmd)...)
 		cmd.Env = cmd.Environ()
-		cmd.Env = append(cmd.Env, "path="+filePath)
+		cmd.Env = append(cmd.Env, "file="+filePath)
 
 		if err := cmd.Run(); err != nil {
 			return fmt.Errorf("post-edit command failed for %s: %w", filePath, err)

pkg/tools/builtin/filesystem_test.go

@@ -413,7 +413,7 @@ func main() {
 	postEditConfigs := []PostEditConfig{
 		{
 			Path: "*.go",
-			Cmd:  "touch $path.formatted",
+			Cmd:  "touch $file.formatted",
 		},
 	}
 	tool := NewFilesystemTool(tmpDir, WithPostEditCommands(postEditConfigs))

pkg/tools/builtin/script_shell.go

@@ -12,6 +12,7 @@ import (
 	"strings"
 
 	"github.com/docker/docker-agent/pkg/config/latest"
+	"github.com/docker/docker-agent/pkg/shellpath"
 	"github.com/docker/docker-agent/pkg/tools"
 )
 
@@ -137,10 +138,9 @@ func (t *ScriptShellTool) execute(ctx context.Context, toolConfig *latest.Script
 		}
 	}
 
-	// Use default shell
-	shell := cmp.Or(os.Getenv("SHELL"), "/bin/sh")
+	shell, argsPrefix := shellpath.DetectShell()
 
-	cmd := exec.CommandContext(ctx, shell, "-c", toolConfig.Cmd)
+	cmd := exec.CommandContext(ctx, shell, append(argsPrefix, toolConfig.Cmd)...)
 	cmd.Dir = toolConfig.WorkingDir
 	cmd.Env = t.env
 	for key, value := range params {