Fix double expansion in slash command arguments (#152)

* Initial plan

* Add tests to verify single expansion issue

Co-authored-by: alexec <1142830+alexec@users.noreply.github.com>

* Fix double expansion: parse task before expanding

Co-authored-by: alexec <1142830+alexec@users.noreply.github.com>

* Improve comment clarity per code review feedback

Co-authored-by: alexec <1142830+alexec@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: alexec <1142830+alexec@users.noreply.github.com>

Author: Copilot

integration_test.go

@@ -1230,3 +1230,69 @@ This rule is from a remote directory.
 		t.Errorf("task not found in stdout. Output:\n%s", output)
 	}
 }
+
+// TestSingleExpansion verifies that content is expanded only once in the full flow
+func TestSingleExpansion(t *testing.T) {
+	dirs := setupTestDirs(t)
+
+	// Create a task that uses a parameter with expansion syntax
+	taskFile := filepath.Join(dirs.tasksDir, "test-expand.md")
+	taskContent := `Task with parameter: ${param1}
+
+And a value that looks like expansion syntax but should not be expanded: ${"nested"}`
+	if err := os.WriteFile(taskFile, []byte(taskContent), 0644); err != nil {
+		t.Fatalf("failed to create task file: %v", err)
+	}
+
+	// Run with param1 set to a value that contains expansion syntax
+	output := runTool(t, "-C", dirs.tmpDir, "-p", "param1=!`echo hello`", "test-expand")
+
+	// The param1 should be replaced with the literal string "!`echo hello`"
+	// It should NOT be expanded again (that would execute the command)
+	if !strings.Contains(output, "!`echo hello`") {
+		t.Errorf("Expected param1 to be replaced with literal value, got: %s", output)
+	}
+
+	// Verify "hello" is not in output (which would indicate the command was executed)
+	// Note: there may be other "hello" strings, so check for the specific context
+	if strings.Contains(output, "Task with parameter: hello") {
+		t.Errorf("Parameter value was re-expanded (command was executed), got: %s", output)
+	}
+}
+
+// TestCommandExpansionOnce verifies that command files are expanded only once
+func TestCommandExpansionOnce(t *testing.T) {
+	dirs := setupTestDirs(t)
+	commandsDir := filepath.Join(dirs.tmpDir, ".agents", "commands")
+	if err := os.MkdirAll(commandsDir, 0o755); err != nil {
+		t.Fatalf("failed to create commands dir: %v", err)
+	}
+
+	// Create a command file with a parameter
+	commandFile := filepath.Join(commandsDir, "test-cmd.md")
+	commandContent := `Command param: ${cmd_param}`
+	if err := os.WriteFile(commandFile, []byte(commandContent), 0644); err != nil {
+		t.Fatalf("failed to create command file: %v", err)
+	}
+
+	// Create a task that calls the command with a param containing expansion syntax
+	taskFile := filepath.Join(dirs.tasksDir, "test-cmd-task.md")
+	taskContent := `/test-cmd cmd_param="!` + "`echo injected`" + `"`
+	if err := os.WriteFile(taskFile, []byte(taskContent), 0644); err != nil {
+		t.Fatalf("failed to create task file: %v", err)
+	}
+
+	// Run the task
+	output := runTool(t, "-C", dirs.tmpDir, "test-cmd-task")
+
+	// The command parameter should be replaced with the literal string "!`echo injected`"
+	// It should NOT be expanded again (that would execute the command)
+	if !strings.Contains(output, "!`echo injected`") {
+		t.Errorf("Expected command param to be replaced with literal value, got: %s", output)
+	}
+
+	// Verify "injected" is not in output (which would indicate the command was executed)
+	if strings.Contains(output, "Command param: injected") {
+		t.Errorf("Command parameter value was re-expanded (command was executed), got: %s", output)
+	}
+}

pkg/codingcontext/context.go

@@ -193,21 +193,25 @@ func (cc *Context) findTask(taskName string) error {
 			cc.agent = agent
 		}
 
-		// Expand parameters only if expand_params is not explicitly set to false
-		contentToProcess := md.Content
-		if shouldExpandParams(frontMatter.ExpandParams) {
-			contentToProcess = cc.expandParams(md.Content, nil)
-		}
-
-		task, err := ParseTask(contentToProcess)
+		// Parse the task content first to separate text blocks from slash commands
+		task, err := ParseTask(md.Content)
 		if err != nil {
 			return err
 		}
 
+		// Build the final content by processing each block
+		// Text blocks are expanded if expand_params is not false
+		// Slash command arguments are NOT expanded here - they are passed as literals
+		// to command files where they may be substituted via ${param} templates
 		finalContent := strings.Builder{}
 		for _, block := range task {
 			if block.Text != nil {
-				finalContent.WriteString(block.Text.Content())
+				textContent := block.Text.Content()
+				// Expand parameters in text blocks only if expand_params is not explicitly set to false
+				if shouldExpandParams(frontMatter.ExpandParams) {
+					textContent = cc.expandParams(textContent, nil)
+				}
+				finalContent.WriteString(textContent)
 			} else if block.SlashCommand != nil {
 				commandContent, err := cc.findCommand(block.SlashCommand.Name, block.SlashCommand.Params())
 				if err != nil {