[code-simplifier] refactor(tree): clarify array-node event delta logic

Overview

This PR makes small readability-focused refactors in the recently-updated array-node change event wiring, without changing runtime behavior.

Files Simplified

• packages/dds/tree/src/simple-tree/api/treeNodeApi.ts
  • Simplifies the shallow-change guard for array-node nodeChanged to make the early-return condition more direct.
• packages/dds/tree/src/simple-tree/core/unhydratedFlexTree.ts
  • Extracts the fieldMarks map construction into a named local for clarity.

Why

These areas were recently updated to include delta payloads for array-node events; the refactors make the intent easier to read while preserving the exact semantics (including the marks === undefined fallback behavior).

Changes Based On

• #26927 - array node treeChanged delta payload and unhydrated node fix

Testing

• ✅ corepack pnpm -C packages/dds/tree run build:test:esm
• ✅ corepack pnpm -C packages/dds/tree run build:test:cjs
• ✅ corepack pnpm -C packages/dds/tree run eslint
• ✅ corepack pnpm -C packages/dds/tree run check:biome

Review Focus

• Confirm behavior is unchanged (only refactors).
• Sanity-check the array-node nodeChanged early-return logic readability.

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From 4f67235bd1565c21b7c452fc5c2062a14685ff5a Mon Sep 17 00:00:00 2001
From: tylerbutler <tylerbutler@users.noreply.github.com>
Date: Wed, 15 Apr 2026 09:53:30 +0000
Subject: [PATCH] refactor(tree): clarify array-node event delta logic

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 packages/dds/tree/src/simple-tree/api/treeNodeApi.ts      | 8 ++++----
 .../dds/tree/src/simple-tree/core/unhydratedFlexTree.ts   | 3 ++-
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/packages/dds/tree/src/simple-tree/api/treeNodeApi.ts b/packages/dds/tree/src/simple-tree/api/treeNodeApi.ts
index c1d40d2..88d2a0e 100644
--- a/packages/dds/tree/src/simple-tree/api/treeNodeApi.ts
+++ b/packages/dds/tree/src/simple-tree/api/treeNodeApi.ts
@@ -284,10 +284,10 @@ export const treeNodeApi: TreeNodeApi = {
 						// internal passes), we conservatively fire nodeChanged rather than silently
 						// dropping the event, even though the underlying change may have been
 						// purely deep. This is a known limitation of the current eventing stack.
-						const hasShallowChange =
-							marks === undefined ||
-							marks.some((m) => m.attach !== undefined || m.detach !== undefined);
-						if (!hasShallowChange) {
+						if (
+							marks !== undefined &&
+							!marks.some((m) => m.attach !== undefined || m.detach !== undefined)
+						) {
 							return;
 						}
 						// `marks` is undefined when the field was modified across multiple batches
diff --git a/packages/dds/tree/src/simple-tree/core/unhydratedFlexTree.ts b/packages/dds/tree/src/simple-tree/core/unhydratedFlexTree.ts
index 9df6bce..39340b4 100644
--- a/packages/dds/tree/src/simple-tree/core/unhydratedFlexTree.ts
+++ b/packages/dds/tree/src/simple-tree/core/unhydratedFlexTree.ts
@@ -289,9 +289,10 @@ export class UnhydratedFlexTreeNode
 	 * When omitted (e.g. for non-sequence fields), `fieldMarks` is empty.
 	 */
 	public emitChangedEvent(key: FieldKey, marks?: readonly DeltaMark[]): void
... (truncated)

Read packages/dds/tree/src/simple-tree/api/treeNodeApi.ts and packages/dds/tree/src/simple-tree/core/unhydratedFlexTree.ts, focusing on the array-node event wiring and fieldMarks construction. Run the targeted package build, eslint, and Biome checks listed in the issue; done means the refactor preserves the existing marks === undefined behavior and runtime semantics.