debugger: defer probe pause handling until startup

lib/internal/debugger/inspect_probe.js

@@ -599,6 +599,9 @@ class ProbeInspectorSession {
 
   async handlePaused(params) {
     if (this.finished) { return; }
+    // Keep the initial --inspect-brk pause held until breakpoint setup is
+    // complete. `Runtime.runIfWaitingForDebugger` releases startup execution.
+    if (!this.started) { return; }
 
     const hitBreakpoints = params.hitBreakpoints;
     if (hitBreakpoints === undefined || hitBreakpoints.length === 0) {
@@ -979,5 +982,6 @@ async function runProbeMode(stdout, probeOptions) {
 
 module.exports = {
   parseProbeTokens,
+  ProbeInspectorSession,
   runProbeMode,
 };

test/parallel/test-debugger-probe-startup-pause.js

@@ -0,0 +1,32 @@
+// Flags: --expose-internals
+// This tests that probe mode keeps the initial --inspect-brk pause held until
+// startup has finished binding breakpoints.
+'use strict';
+
+const common = require('../common');
+common.skipIfInspectorDisabled();
+
+const assert = require('assert');
+const { ProbeInspectorSession } = require('internal/debugger/inspect_probe');
+
+const session = new ProbeInspectorSession({
+  probes: [],
+});
+
+const cdpCalls = [];
+session.client = {
+  callMethod: common.mustCall(async (method) => {
+    cdpCalls.push(method);
+  }),
+};
+
+async function testStartupPauseHandling() {
+  await session.handlePaused({});
+  assert.deepStrictEqual(cdpCalls, []);
+
+  session.started = true;
+  await session.handlePaused({});
+  assert.deepStrictEqual(cdpCalls, ['Debugger.resume']);
+}
+
+testStartupPauseHandling().then(common.mustCall());