Add tests for PatchSet and ServeSession functionality

- Introduced comprehensive tests for the `PatchSet` module, covering methods such as `hasRemoves`, `hasAdditions`, `hasUpdates`, and various ID and instance checks.
- Added a new test suite for `ServeSession`, focusing on WebSocket message handling and confirmation behavior, ensuring correct merging and application of patches.
- Implemented edge case tests in `ChangeBatcher` to verify data integrity during rapid changes and instance removals.
- Enhanced `applyPatch` tests to handle scenarios involving missing instances and ignored class names, ensuring robust patch application logic.

plugin/src/App/init.lua

@@ -714,6 +714,8 @@ function App:startSession()
 		end
 	end)
 
+	local initialSyncConfirmed = false
+
 	serveSession:setConfirmCallback(function(instanceMap, patch, serverInfo)
 		-- Filter out the DataModel name change from the patch
 		-- The project name (DataModel.Name) is managed by Studio independently
@@ -721,6 +723,17 @@ function App:startSession()
 
 		local isOneShotMode = Settings:get("oneShotSync")
 
+		-- ONE-SHOT MODE: After the initial sync is confirmed, skip any
+		-- subsequent patches entirely. These are server echoes from processing
+		-- our pull request (e.g. VFS re-snapshots after file deletions).
+		-- The session is about to disconnect — applying them is pointless,
+		-- and without this guard the echo triggers a second confirmation
+		-- dialog that races with endSession() and gets stuck.
+		if isOneShotMode and initialSyncConfirmed then
+			Log.info("One-shot mode: skipping post-initial-sync echo patch")
+			return "Skip"
+		end
+
 		-- ONE-SHOT MODE: Never auto-accept, always require explicit confirmation
 		-- This ensures nothing can "sneak through" without user review
 		if not isOneShotMode then
@@ -796,6 +809,7 @@ function App:startSession()
 		-- The actual disconnect is handled by setInitialSyncCompleteCallback
 		-- to ensure any pending writes complete first
 		if Settings:get("oneShotSync") then
+			initialSyncConfirmed = true
 			return result
 		end