From 2fc3be34d0256fd0d6d57895930ce25175d9fe67 Mon Sep 17 00:00:00 2001
From: littensy <56808540+littensy@users.noreply.github.com>
Date: Wed, 30 Sep 2026 19:20:51 -0700
Subject: [PATCH] fix(charm-sync): preserve global patch list order for nil
 patches

Resolves #67
---
 packages/charm-sync/src/server.luau       |  6 +++---
 packages/charm-sync/test/server.test.luau | 21 +++++++++++++++++++++
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/packages/charm-sync/src/server.luau b/packages/charm-sync/src/server.luau
index 0494804..6485e18 100644
--- a/packages/charm-sync/src/server.luau
+++ b/packages/charm-sync/src/server.luau
@@ -125,8 +125,8 @@ local function diffGlobalUpdateBuffer(): { any }
 	local patchCount = #globalUpdates
 	local patches = table.create(patchCount)
 
-	for _, update in globalUpdates do
-		table.insert(patches, patch.diff(update.oldValue, update.newValue))
+	for index, update in globalUpdates do
+		patches[index] = patch.diff(update.oldValue, update.newValue)
 	end
 
 	return patches
@@ -146,7 +146,7 @@ local function selectFromGlobalPatchList(client: any, globalPatches: { any }): {
 	for index, update in globalUpdates do
 		local patchData = globalPatches[index]
 
-		if not patchData then
+		if patchData == nil then
 			continue
 		end
 
diff --git a/packages/charm-sync/test/server.test.luau b/packages/charm-sync/test/server.test.luau
index d43e7b8..d24970c 100644
--- a/packages/charm-sync/test/server.test.luau
+++ b/packages/charm-sync/test/server.test.luau
@@ -403,6 +403,27 @@ test.describe("historical", function()
 		server.flush()
 		assert(#payloads == 0, "Expected no payloads to be sent for unchanged state")
 	end)
+
+	test("should maintain patch list order for stale update", function()
+		local a = Charm.atom({ x = 1 })
+		local b = Charm.atom({ y = 1 })
+		local payloads
+
+		server.connect(function(_client, _payloads)
+			payloads = _payloads
+		end)
+
+		server.addSignalsToClient("client", { a = a, b = b })
+		server.flush()
+
+		payloads = nil
+		a({ x = 1 }) -- new table, same contents: diff is nil
+		b({ y = 2 })
+		server.flush()
+		assert(payloads, "Expected payloads to be sent")
+		assert(payloads[1].type == "patch", "Expected payload to be patch")
+		assert(payloads[1].data.b.y == 2, "Expected payload to contain atom 'b'")
+	end)
 end)
 
 test("addSignalsToClient should ignore tracking context", function()