[Flight] Fix stack overflow in visitAsyncNode with deep async chains (#35612)

Database libraries like Gel/EdgeDB can create very long linear chains of
async sequences through temporal async sequencing in connection pools.
The recursive traversal of `node.previous` chains in `visitAsyncNode`
causes stack overflow on these deep chains.

The fix converts the `previous` chain traversal from recursive to
iterative. We collect the chain into an array, then process from deepest
to shallowest.

The `awaited` traversal remains recursive since its depth is bounded by
promise dependency depth, not by the number of event loop turns. Each
`awaited` branch still benefits from the iterative `previous` handling
within its own traversal.

I've verified that this fixes the
[repro](https://github.com/jere-co/next-debug) provided in #35246.

closes #35246

packages/react-server/src/ReactFlightServer.js

@@ -2345,19 +2345,53 @@ function visitAsyncNode(
   >,
   cutOff: number,
 ): void | null | PromiseNode | IONode {
-  if (visited.has(node)) {
-    // It's possible to visit them same node twice when it's part of both an "awaited" path
-    // and a "previous" path. This also gracefully handles cycles which would be a bug.
-    return visited.get(node);
+  // Collect the previous chain iteratively instead of recursively to avoid
+  // stack overflow on deep chains. We process from deepest to shallowest so
+  // each node has its previousIONode available.
+  const chain: Array<AsyncSequence> = [];
+  let current: AsyncSequence | null = node;
+
+  while (current !== null) {
+    if (visited.has(current)) {
+      break;
+    }
+    chain.push(current);
+    current = current.previous;
   }
-  // Set it as visited early in case we see ourselves before returning.
-  visited.set(node, null);
-  const result = visitAsyncNodeImpl(request, task, node, visited, cutOff);
-  if (result !== null) {
-    // If we ended up with a value, let's use that value for future visits.
-    visited.set(node, result);
+
+  let previousIONode: void | null | PromiseNode | IONode =
+    current !== null ? visited.get(current) : null;
+
+  // Process from deepest to shallowest (reverse order).
+  for (let i = chain.length - 1; i >= 0; i--) {
+    const n = chain[i];
+    // Set it as visited early in case we see the node again before returning.
+    visited.set(n, null);
+
+    const result = visitAsyncNodeImpl(
+      request,
+      task,
+      n,
+      visited,
+      cutOff,
+      previousIONode,
+    );
+
+    if (result !== null) {
+      // If we ended up with a value, let's use that value for future visits.
+      visited.set(n, result);
+    }
+
+    if (result === undefined) {
+      // Undefined is used as a signal that we found a suitable aborted node
+      // and we don't have to find further aborted nodes.
+      return undefined;
+    }
+
+    previousIONode = result;
   }
-  return result;
+
+  return previousIONode;
 }
 
 function visitAsyncNodeImpl(
@@ -2369,6 +2403,7 @@ function visitAsyncNodeImpl(
     void | null | PromiseNode | IONode,
   >,
   cutOff: number,
+  previousIONode: void | null | PromiseNode | IONode,
 ): void | null | PromiseNode | IONode {
   if (node.end >= 0 && node.end <= request.timeOrigin) {
     // This was already resolved when we started this render. It must have been either something
@@ -2377,23 +2412,6 @@ function visitAsyncNodeImpl(
     return null;
   }
 
-  let previousIONode: void | null | PromiseNode | IONode = null;
-  // First visit anything that blocked this sequence to start in the first place.
-  if (node.previous !== null) {
-    previousIONode = visitAsyncNode(
-      request,
-      task,
-      node.previous,
-      visited,
-      cutOff,
-    );
-    if (previousIONode === undefined) {
-      // Undefined is used as a signal that we found a suitable aborted node and we don't have to find
-      // further aborted nodes.
-      return undefined;
-    }
-  }
-
   // `found` represents the return value of the following switch statement.
   // We can't use multiple `return` statements in the switch statement
   // since that prevents Closure compiler from inlining `visitAsyncImpl`