Make simulation block submission idempotent

api/QuestionsApi.Tests/ExamSimulationTests.cs

@@ -111,6 +111,16 @@ public sealed class ExamSimulationTests
         Assert.False(ExamSimulationStore.TryDecodeHistoryCursor("not-a-cursor", out _));
     }
 
+    [Theory]
+    [InlineData(ExamSimulationStates.BetweenBlocks, true)]
+    [InlineData(ExamSimulationStates.Completed, true)]
+    [InlineData(ExamSimulationStates.BlockActive, false)]
+    [InlineData(ExamSimulationStates.Abandoned, false)]
+    public void RepeatedBlockSubmissionIsIdempotentOnlyAfterSubmission(string state, bool expected)
+    {
+        Assert.Equal(expected, ExamSimulationStore.IsAlreadySubmittedState(state));
+    }
+
     private static List<ExamSimulationItem> BuildItems(int count, bool wasSeen = false) =>
         Enumerable.Range(0, count).Select(index => new ExamSimulationItem
         {

api/QuestionsApi/Services/ExamSimulationStore.cs

@@ -354,6 +354,8 @@ public class ExamSimulationStore
 
     public async Task<ExamSimulation> SubmitBlockAsync(ExamSimulation simulation, bool expired = false)
     {
+        if (IsAlreadySubmittedState(simulation.State))
+            return simulation;
         if (simulation.State != ExamSimulationStates.BlockActive)
             throw new InvalidOperationException("There is no active block to submit.");
         if (!expired && simulation.BlockDeadlineUtc is not null)
@@ -370,6 +372,9 @@ public class ExamSimulationStore
         return simulation;
     }
 
+    public static bool IsAlreadySubmittedState(string state) =>
+        state is ExamSimulationStates.BetweenBlocks or ExamSimulationStates.Completed;
+
     public async Task AbandonAsync(ExamSimulation simulation)
     {
         simulation.State = ExamSimulationStates.Abandoned;

scripts/autoload/exam_simulation_service.gd

@@ -154,6 +154,8 @@ func _on_request_completed(result: int, response_code: int, _headers: PackedStri
 	if response_code == 401:
 		AuthState.handle_unauthorized(request_access_token)
 	if result != HTTPRequest.RESULT_SUCCESS or response_code < 200 or response_code >= 300:
+		if _is_stale_submit_failure(action):
+			return
 		var server_message := body.get_string_from_utf8().strip_edges()
 		var error_parsed: Variant = JSON.parse_string(server_message)
 		if typeof(error_parsed) == TYPE_DICTIONARY:
@@ -205,6 +207,10 @@ func _on_request_completed(result: int, response_code: int, _headers: PackedStri
 	state_changed.emit()
 
 
+func _is_stale_submit_failure(action: String) -> bool:
+	return action == "submit" and str(simulation.get("state", "")) in ["between_blocks", "completed"]
+
+
 func _process_request_queue() -> void:
 	if is_loading or request_queue.is_empty():
 		return

scripts/ui/question_player.gd

@@ -1190,6 +1190,9 @@ func _on_simulation_state_changed() -> void:
 func _on_simulation_request_failed(message: String) -> void:
 	if BlockSessionService.session_kind != "simulation":
 		return
+	if str(ExamSimulationService.simulation.get("state", "")) in ["between_blocks", "completed"]:
+		simulation_submit_pending = false
+		return
 	simulation_submit_pending = false
 	if ExamSimulationService.last_failed_action != "submit":
 		# A per-question autosave failing shouldn't interrupt a timed exam with a

tests/simulation_history_ui_test.gd

@@ -15,6 +15,11 @@ func _run() -> void:
 	service.simulation = {"id": "active", "state": "between_blocks", "currentBlock": 2, "totalBlocks": 12, "createdUtc": "2026-07-16T22:04:00Z"}
 	service.history = [{"id": "completed", "state": "completed", "currentBlock": 11, "totalBlocks": 12, "createdUtc": "2026-07-15T20:35:00Z", "predictedScore": 236, "rangeLow": 221, "rangeHigh": 248, "passProbability": 0.82}]
 	service.history_next_cursor = "next-page"
+	_assert(service._is_stale_submit_failure("submit"), "a submit failure after reaching between-block state should be ignored")
+	service.simulation["state"] = "completed"
+	_assert(service._is_stale_submit_failure("submit"), "a submit failure after completion should be ignored")
+	_assert(not service._is_stale_submit_failure("save"), "non-submit failures should still be surfaced")
+	service.simulation["state"] = "between_blocks"
 	var host := Control.new()
 	host.size = Vector2(1400, 800)
 	root.add_child(host)