From acac0b865ea74d2aa6928f35c6b1c8bade99eee2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ralph=20K=C3=BCpper?= <ralph@skelpo.com>
Date: Sat, 5 Sep 2026 13:33:25 +0200
Subject: [PATCH] test: synchronize stdin lifecycle input with child readiness

---
 changelog.d/9783-stdin-fixture-handshake.md   |  3 ++
 ...t_gap_9676_stdin_unref_ref_keeps_reader.ts | 32 +++++++++++++------
 2 files changed, 25 insertions(+), 10 deletions(-)
 create mode 100644 changelog.d/9783-stdin-fixture-handshake.md

diff --git a/changelog.d/9783-stdin-fixture-handshake.md b/changelog.d/9783-stdin-fixture-handshake.md
new file mode 100644
index 0000000000..e2dafb7879
--- /dev/null
+++ b/changelog.d/9783-stdin-fixture-handshake.md
@@ -0,0 +1,3 @@
+Make the stdin lifecycle parity fixture wait for each child to finish its toggle
+and GC churn before sending the second input chunk. Removing the four fixed
+2.5-second waits lets the Node oracle finish within the suite's 10-second budget.
diff --git a/test-files/test_gap_9676_stdin_unref_ref_keeps_reader.ts b/test-files/test_gap_9676_stdin_unref_ref_keeps_reader.ts
index 2a11c08adc..dc280056f2 100644
--- a/test-files/test_gap_9676_stdin_unref_ref_keeps_reader.ts
+++ b/test-files/test_gap_9676_stdin_unref_ref_keeps_reader.ts
@@ -76,6 +76,10 @@ function runRole(name: string, onFirst: (s: any) => void, doChurn: boolean): voi
       console.log(name + " phase1: true");
       onFirst(s);
       if (doChurn) console.log(name + " churn: " + (churn(300000) > 0));
+      // The parent sends TWO only after the toggle and all churn complete.
+      // A fixed delay cannot prove this ordering and four sequential 2.5s
+      // waits alone exceed the parity suite's 10s per-process budget (#9783).
+      console.log(name + " ready: true");
     } else if (phase === 1 && text.indexOf("TWO") >= 0) {
       clearInterval(ticker);
       finish(name + " phase2: true");
@@ -110,9 +114,24 @@ if (role === "unref-ref") {
     new Promise<void>((resolve) => {
       const child = spawn(process.execPath, childArgs, {
         env: { ...process.env, [ROLE_ENV]: name },
-        stdio: ["pipe", "inherit", "inherit"],
+        stdio: ["pipe", "pipe", "inherit"],
       });
       let settled = false;
+      let output = "";
+      let sentSecond = false;
+      child.stdout!.on("data", (chunk: any) => {
+        process.stdout.write(chunk);
+        output += String(chunk);
+        // stdout may split the readiness line across arbitrary chunks.
+        if (!sentSecond && output.includes(name + " ready: true\n")) {
+          sentSecond = true;
+          try {
+            child.stdin!.write("TWO\n");
+          } catch {
+            /* child already gone */
+          }
+        }
+      });
       const watchdog = setTimeout(() => {
         if (settled) return;
         settled = true;
@@ -120,7 +139,8 @@ if (role === "unref-ref") {
         child.kill("SIGKILL");
         resolve();
       }, WATCHDOG_MS);
-      child.on("exit", (code) => {
+      // Drain the piped stdout before printing the role's exit summary.
+      child.on("close", (code) => {
         if (settled) return;
         settled = true;
         clearTimeout(watchdog);
@@ -134,14 +154,6 @@ if (role === "unref-ref") {
           /* child already gone */
         }
       }, 120);
-      // Late enough that the churn role has finished collecting first.
-      setTimeout(() => {
-        try {
-          child.stdin!.write("TWO\n");
-        } catch {
-          /* child already gone */
-        }
-      }, 2500);
     });
 
   (async () => {