From eb2fa3c829fff0433b890cf92bc41690d63bde6e Mon Sep 17 00:00:00 2001
From: Chris Tate <chris@ctate.dev>
Date: Fri, 23 Oct 2026 05:14:51 -0500
Subject: [PATCH] Fire spawn listeners for a child that exits before its first
 poll pass

A child spawned from a listener that runs during a poll pass, such as a
'close' listener, can exit before the next pass fires its 'spawn'
listeners. The same pass's waitpid loop then settled it with 'spawn' never
emitted. Settling an exited child now fires its pending 'spawn' listeners
first, before its stream data and 'exit', as Node emits them.
---
 .../7640-child-spawn-before-fast-exit.ts.json |  6 ++++++
 packages/runtime/src/scr_child.c              | 10 +++++++---
 .../7640-child-spawn-before-fast-exit.ts      | 20 +++++++++++++++++++
 .../7640-child-spawn-before-fast-exit.ts.json |  1 +
 4 files changed, 34 insertions(+), 3 deletions(-)
 create mode 100644 packages/compiler/test/ts7/baselines/order-parity/tests/corpus/7640-child-spawn-before-fast-exit.ts.json
 create mode 100644 tests/corpus/7640-child-spawn-before-fast-exit.ts
 create mode 100644 tests/harness/corpus-costs/7640-child-spawn-before-fast-exit.ts.json

diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/7640-child-spawn-before-fast-exit.ts.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/7640-child-spawn-before-fast-exit.ts.json
new file mode 100644
index 000000000..0b82f6091
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/7640-child-spawn-before-fast-exit.ts.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/7640-child-spawn-before-fast-exit.ts"
+ ],
+ "diags": []
+}
diff --git a/packages/runtime/src/scr_child.c b/packages/runtime/src/scr_child.c
index df7543500..a70b10894 100644
--- a/packages/runtime/src/scr_child.c
+++ b/packages/runtime/src/scr_child.c
@@ -2780,7 +2780,8 @@ static void scr_child_settle(ScrChild *c) {
     scr_children_reffed_n--;
   }
   if (c->state == SCR_CHILD_EXITED) {
-    scr_child_stream_drain_now(c->out_stream);
+    if (!c->spawn_done) scr_child_fire_spawn(c);
+    if (!scr_exc_pending()) scr_child_stream_drain_now(c->out_stream);
     if (!scr_exc_pending()) scr_child_stream_drain_now(c->err_stream);
     if (!scr_exc_pending()) scr_ipc_settle(c->ipc);
   }
@@ -5607,9 +5608,12 @@ static void scr_child_settle(ScrChild *c) {
   /* Streams first, settled after: an exit listener registered from a
    * draining 'data'/'end' callback still fires below, like Node's. The
    * SPAWN-FAILURE path skips the drain — Node fires 'error' first and
-   * the streams' immediate EOF delivers 'end' on the next turn. */
+   * the streams' immediate EOF delivers 'end' on the next turn. A child
+   * spawned during this pass can exit before the next pass fires 'spawn';
+   * Node emits 'spawn' before any data or 'exit', so it fires here first. */
   if (c->state == SCR_CHILD_EXITED) {
-    scr_child_stream_drain_now(c->out_stream);
+    if (!c->spawn_done) scr_child_fire_spawn(c);
+    if (!scr_exc_pending()) scr_child_stream_drain_now(c->out_stream);
     if (!scr_exc_pending()) scr_child_stream_drain_now(c->err_stream);
     if (!scr_exc_pending()) scr_ipc_settle(c->ipc);
   }
diff --git a/tests/corpus/7640-child-spawn-before-fast-exit.ts b/tests/corpus/7640-child-spawn-before-fast-exit.ts
new file mode 100644
index 000000000..9c232d96c
--- /dev/null
+++ b/tests/corpus/7640-child-spawn-before-fast-exit.ts
@@ -0,0 +1,20 @@
+// A child spawned from a 'close' listener that exits before the listener
+// returns still emits 'spawn' before 'exit'.
+import { spawn } from "node:child_process";
+
+function busyWait(ms: number): void {
+  const end = Date.now() + ms;
+  while (Date.now() < end) {}
+}
+
+const events: string[] = [];
+spawn("sh", ["-c", "exit 0"], { stdio: "ignore" }).on("close", () => {
+  const child = spawn("sh", ["-c", "exit 4"], { stdio: "ignore" });
+  child.on("spawn", () => events.push("spawn"));
+  child.on("exit", (code) => events.push(`exit ${code}`));
+  child.on("close", (code) => {
+    events.push(`close ${code}`);
+    console.log(events.join(", "));
+  });
+  busyWait(300);
+});
diff --git a/tests/harness/corpus-costs/7640-child-spawn-before-fast-exit.ts.json b/tests/harness/corpus-costs/7640-child-spawn-before-fast-exit.ts.json
new file mode 100644
index 000000000..b56ad904d
--- /dev/null
+++ b/tests/harness/corpus-costs/7640-child-spawn-before-fast-exit.ts.json
@@ -0,0 +1 @@
+{ "plain": 2600, "san": 4000 }