Address Copilot review: add integration test and docs

- Add TestExitCommandMultiLineInteractive: exercises the full multi-line
  EXIT flow with real database connection (unbalanced parens -> read
  continuation -> execute query -> verify exit code)
- Add 'Interactive Mode Commands' section to README with EXIT examples
  showing both single-line and multi-line usage with continuation prompt

Author: dlevy-msft-sql

README.md

@@ -112,6 +112,24 @@ sqlcmd
 
 If no current context exists, `sqlcmd` (with no connection parameters) reverts to the original ODBC `sqlcmd` behavior of creating an interactive session to the default local instance on port 1433 using trusted authentication, otherwise it will create an interactive session to the current context.
 
+### Interactive Mode Commands
+
+In interactive mode, `sqlcmd` supports several special commands. The `EXIT` command can execute a query and use its result as the exit code:
+
+```
+1> EXIT(SELECT 100)
+```
+
+For complex queries, `EXIT(query)` can span multiple lines. When parentheses are unbalanced, `sqlcmd` prompts for continuation:
+
+```
+1> EXIT(SELECT 1
+      -> + 2
+      -> + 3)
+```
+
+The query result (6 in this example) becomes the process exit code.
+
 ## Sqlcmd
 
 The `sqlcmd` project aims to be a complete port of the original ODBC sqlcmd to the `Go` language, utilizing the [go-mssqldb][] driver. For full documentation of the tool and installation instructions, see [go-sqlcmd-utility][].

pkg/sqlcmd/commands_test.go

@@ -632,3 +632,41 @@ func TestExitCommandNonInteractiveUnbalanced(t *testing.T) {
 	err := exitCommand(s, []string{"(select 1"}, 1)
 	assert.EqualError(t, err, InvalidCommandError("EXIT", 1).Error(), "unbalanced parens in non-interactive should error")
 }
+
+// TestExitCommandMultiLineInteractive is an integration test that exercises the full
+// multi-line EXIT flow: starting with unbalanced parentheses, reading continuation lines
+// from the console, executing the combined query, and returning the correct exit code.
+func TestExitCommandMultiLineInteractive(t *testing.T) {
+	s, buf := setupSqlCmdWithMemoryOutput(t)
+	defer buf.Close()
+
+	// Set up mock console to provide continuation lines
+	continuationLines := []string{"+ 2", ")"}
+	lineIndex := 0
+	s.lineIo = &testConsole{
+		OnReadLine: func() (string, error) {
+			if lineIndex >= len(continuationLines) {
+				return "", io.EOF
+			}
+			line := continuationLines[lineIndex]
+			lineIndex++
+			return line, nil
+		},
+		OnPasswordPrompt: func(prompt string) ([]byte, error) {
+			return nil, nil
+		},
+	}
+
+	// Initialize batch so exitCommand can work with it
+	s.batch = NewBatch(nil, nil)
+
+	// Call exitCommand with unbalanced parentheses - this should:
+	// 1. Detect unbalanced parens in "(select 1"
+	// 2. Read continuation lines "+ 2" and ")" from the mock console
+	// 3. Combine into "(select 1\r\n+ 2\r\n)" and execute
+	// 4. Return ErrExitRequested with Exitcode set to 3 (1+2)
+	err := exitCommand(s, []string{"(select 1"}, 1)
+
+	assert.Equal(t, ErrExitRequested, err, "exitCommand should return ErrExitRequested")
+	assert.Equal(t, 3, s.Exitcode, "Exitcode should be 3 (result of 'select 1 + 2')")
+}