fix shell allowlist initialization and add guard tests

pkg/tools/shell.go

@@ -29,15 +29,21 @@ type ExecTool struct {
 }
 
 func NewExecTool(cfg config.ShellConfig, workspace string) *ExecTool {
-	denyPatterns := make([]*regexp.Regexp, 0)
+	denyPatterns := make([]*regexp.Regexp, 0, len(cfg.DeniedCmds))
 	for _, p := range cfg.DeniedCmds {
 		denyPatterns = append(denyPatterns, regexp.MustCompile(`\b`+regexp.QuoteMeta(p)+`\b`))
 	}
 
+	allowPatterns := make([]*regexp.Regexp, 0, len(cfg.AllowedCmds))
+	for _, p := range cfg.AllowedCmds {
+		allowPatterns = append(allowPatterns, regexp.MustCompile(`\b`+regexp.QuoteMeta(p)+`\b`))
+	}
+
 	return &ExecTool{
 		workingDir:          workspace,
 		timeout:             cfg.Timeout,
 		denyPatterns:        denyPatterns,
+		allowPatterns:       allowPatterns,
 		restrictToWorkspace: cfg.RestrictPath,
 		sandboxEnabled:      cfg.Sandbox.Enabled,
 		sandboxImage:        cfg.Sandbox.Image,

pkg/tools/shell_test.go

@@ -43,3 +43,21 @@ func TestAssessCommandRisk_GitCleanIsDestructive(t *testing.T) {
 		t.Fatalf("expected git clean to be destructive, got %s", assessment.Level)
 	}
 }
+
+func TestNewExecTool_LoadsAllowedCmdsIntoAllowPatterns(t *testing.T) {
+	tool := NewExecTool(config.ShellConfig{AllowedCmds: []string{"echo"}}, ".")
+	if len(tool.allowPatterns) != 1 {
+		t.Fatalf("expected one allow pattern, got %d", len(tool.allowPatterns))
+	}
+}
+
+func TestGuardCommand_BlocksCommandNotInAllowlist(t *testing.T) {
+	tool := NewExecTool(config.ShellConfig{AllowedCmds: []string{"echo"}}, ".")
+	if msg := tool.guardCommand("ls -la", "."); msg == "" {
+		t.Fatal("expected allowlist to block command not in allowed_cmds")
+	}
+
+	if msg := tool.guardCommand("echo hi", "."); msg != "" {
+		t.Fatalf("expected allowed command to pass guard, got %q", msg)
+	}
+}