fix(skill): sendwait refuses an empty prompt; verbs.md says it joins lines

A prompt made only of blank lines joined to nothing, and sendwait then sent
a bare Enter onto whatever sat on the worker's composer. It now refuses
with "sendwait: empty prompt" (the test fails without the check).
reference/verbs.md still said sendwait takes one line and a multi-line
prompt can sit unsent; it now says sendwait joins the lines with a space,
which loses their layout, so long multi-line content belongs in a file.
Plugin mirror regenerated.

Co-Authored-By: Christian Haberl <116439789+christianhaberl@users.noreply.github.com>
Co-Authored-By: Claude <noreply@anthropic.com>

test/agent-skill-sendwait.test.ts

@@ -47,6 +47,7 @@ function sentInput(prompt: string): string {
   `;
   try {
     execFileSync('bash', ['-c', script], {
+      stdio: ['ignore', 'pipe', 'pipe'],
       env: {
         PATH: process.env.PATH,
         HOME: process.env.HOME,
@@ -74,6 +75,10 @@ describe.skipIf(!hasJq)('preamble sendwait', () => {
     expect(sentInput(prompt)).toBe(toSingleLine(prompt) + '\r');
   });
 
+  it('refuses a prompt made only of blank lines instead of sending a bare Enter', () => {
+    expect(() => sentInput('  \n \t\n')).toThrow(/sendwait: empty prompt/);
+  });
+
   it('leaves a single-line prompt, glob characters included, as it was', () => {
     expect(sentInput('fix * in ?.ts  ')).toBe('fix * in ?.ts  \r');
   });