Fire spawn listeners for a child that exits before its first poll pass (#1986)

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": []
+}

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);
   }

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);
+});

tests/harness/corpus-costs/7640-child-spawn-before-fast-exit.ts.json

@@ -0,0 +1 @@
+{ "plain": 2600, "san": 4000 }