Fix multiline detection for CRLF-terminated startup commands

Strip the entire CRLF terminator (or lone CR/LF) from startup commands
before checking if the body contains newline characters.

Previously, slicing off only the last character of a CRLF-terminated
command left a trailing CR in the body. This caused a single-line
command to be incorrectly categorized as multiline and wrapped in
bracketed paste.

src/shared/startup-command-submission.test.ts

@@ -17,6 +17,12 @@ describe('buildStartupCommandSubmission', () => {
     ).toBe('claude\n')
   })
 
+  it('treats a CRLF-terminated single-line command as single-line', () => {
+    expect(
+      buildStartupCommandSubmission('claude\r\n', { submit: '\r', bracketedPasteSafe: true })
+    ).toBe('claude\r\n')
+  })
+
   it('wraps a multiline command in bracketed paste with a trailing submit byte', () => {
     const command = "claude 'first\nsecond'"
     expect(buildStartupCommandSubmission(command, { submit: '\n', bracketedPasteSafe: true })).toBe(

src/shared/startup-command-submission.ts

@@ -32,8 +32,11 @@ export function buildStartupCommandSubmission(
   command: string,
   { submit, bracketedPasteSafe }: StartupCommandSubmissionOptions
 ): string {
-  const endsWithSubmit = command.endsWith('\r') || command.endsWith('\n')
-  const body = endsWithSubmit ? command.slice(0, -1) : command
+  // Strip a full CRLF (or lone CR/LF) terminator so a single-line command ending
+  // in \r\n isn't misread as multiline by the \r/\n body check below.
+  const trailingTerminator = /\r\n$|\r$|\n$/.exec(command)?.[0] ?? ''
+  const endsWithSubmit = trailingTerminator.length > 0
+  const body = endsWithSubmit ? command.slice(0, -trailingTerminator.length) : command
   if (bracketedPasteSafe && (body.includes('\n') || body.includes('\r'))) {
     return `${BRACKETED_PASTE_START}${body}${BRACKETED_PASTE_END}${submit}`
   }