debugger: lazily wait for initial break output

[trivikr]

Fix a flaky test-debugger-run-after-quit-restart failure where the debugger
REPL could display debug> before the initial break output had been rendered.

The startup path now waits for the first local --inspect-brk pause render to
finish before completing REPL startup, but only when that pause render is
observed during startup initialization. This preserves the prompt ordering fix
without hanging when the debug target exits or disconnects before producing an
initial pause event.

Refs:

• https://github.com/nodejs/node/actions/runs/27582782593/job/81546582775
• https://github.com/nodejs/node/actions/runs/27608332546/job/81625923848
• https://github.com/nodejs/node/actions/runs/27702868250/job/81943652942
• https://github.com/nodejs/node/actions/runs/27582782593/job/81546582775

Error Log

=== release test-debugger-run-after-quit-restart ===
Path: parallel/test-debugger-run-after-quit-restart
Error: --- stderr ---
/Users/runner/work/node/node/dir%20with $unusual"chars?'åß∂ƒ©∆¬…`/test/common/debugger.js:92
        const timeoutErr = new Error(`Timeout (${TIMEOUT}) while waiting for ${pattern}`);
                           ^

Error: Timeout (15000) while waiting for /break (?:on start )?in/i
    at /Users/runner/work/node/node/dir%20with $unusual"chars?'åß∂ƒ©∆¬…`/test/common/debugger.js:92:28
    at new Promise (<anonymous>)
    at Object.waitFor (/Users/runner/work/node/node/dir%20with $unusual"chars?'åß∂ƒ©∆¬…`/test/common/debugger.js:67:14)
    at Object.waitForInitialBreak (/Users/runner/work/node/node/dir%20with $unusual"chars?'åß∂ƒ©∆¬…`/test/common/debugger.js:116:18)
    at Object.<anonymous> (/Users/runner/work/node/node/dir%20with $unusual"chars?'åß∂ƒ©∆¬…`/test/parallel/test-debugger-run-after-quit-restart.js:18:7)
    at Module._compile (node:internal/modules/cjs/loader:1947:14)
    at Object..js (node:internal/modules/cjs/loader:2087:10)
    at Module.load (node:internal/modules/cjs/loader:1669:32)
    at Module._load (node:internal/modules/cjs/loader:1450:12)
    at wrapModuleLoad (node:internal/modules/cjs/loader:260:19) {
  output: '< Debugger listening on ws://127.0.0.1:62970/019e6944-4d82-44b5-956b-e4505af5b290\n' +
    '< For help, see: https://nodejs.org/learn/getting-started/debugging\n' +
    '< \n' +
    '\n' +
    '\n' +
    'connecting to 127.0.0.1:62970 ...\n' +
    '< Debugger attached.\n' +
    '< \n' +
    '\n' +
    ' ok\n' +
    '\n' +
    'debug> '
}

---

Assisted-by: openai:gpt-5.5

[inoway46]

This direction looks good to me. It matches the hypothesis in #64005 (comment)

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/74335/

[mcollina]

lgtm

[nodejs-github-bot]

Landed in 1f806f2