feat(candidate): support cross-page arrow navigation

- move down from the last candidate to the next page
- move up from the first candidate to the previous page
- preserve selection when expanding initial candidates
- keep navigation bounded at the first and last candidates
- add regression tests for cross-page selection

server/src/global/globals.h

@@ -1,4 +1,5 @@
 #pragma once
+#include <algorithm>
 #include <string>
 #include <string_view>
 #include <unordered_set>
@@ -132,18 +133,26 @@ struct CandidateUiState
 
     bool move_selection(int offset)
     {
+        if (page_size <= 0)
+        {
+            page_index = 0;
+            selected_index_in_page = 0;
+            return false;
+        }
         const int count = current_page_count();
         if (count <= 0)
         {
             selected_index_in_page = 0;
             return false;
         }
-        const int next = selected_index_in_page + offset;
-        if (next < 0 || next >= count)
+        selected_index_in_page = std::clamp(selected_index_in_page, 0, count - 1);
+        const int next = current_page_start() + selected_index_in_page + offset;
+        if (next < 0 || next >= item_total_count)
         {
             return false;
         }
-        selected_index_in_page = next;
+        page_index = next / page_size;
+        selected_index_in_page = next % page_size;
         return true;
     }
 

server/src/ipc/event_listener.cpp

@@ -2391,11 +2391,11 @@ void HandleImeKey(uint64_t client_id, uint64_t activation_epoch, uint64_t reques
         UINT result = Global::DataFromServerMsgType::NavigationIgnored;
         bool refresh = false;
 
-        const auto move_page = [&](int offset, UINT response_type) {
-            result = response_type;
-            if (offset > 0 && ui.page_index == 0 && g_inputSession->expand_initial_candidates())
+        const auto expand_initial_candidates = [&] {
+            if (g_inputSession->expand_initial_candidates())
             {
                 const int current_page = ui.page_index;
+                const int current_selection = ui.selected_index_in_page;
                 auto expanded = g_inputSession->get_candidates();
                 user_dictionary::apply_fixed_positions(
                     user_dictionary::default_user_db_path(), CurrentRankingContextKey(), expanded, true,
@@ -2404,6 +2404,16 @@ void HandleImeKey(uint64_t client_id, uint64_t activation_epoch, uint64_t reques
                     });
                 ui.set_items(std::move(expanded));
                 ui.page_index = current_page;
+                ui.selected_index_in_page = current_selection;
+                return true;
+            }
+            return false;
+        };
+        const auto move_page = [&](int offset, UINT response_type) {
+            result = response_type;
+            if (offset > 0 && ui.page_index == 0)
+            {
+                expand_initial_candidates();
             }
             if (offset < 0 ? ui.has_prev_page() : ui.has_next_page())
             {
@@ -2413,6 +2423,10 @@ void HandleImeKey(uint64_t client_id, uint64_t activation_epoch, uint64_t reques
         };
         const auto move_selection = [&](int offset, UINT response_type) {
             result = response_type;
+            if (offset > 0 && ui.selected_index_in_page + 1 >= ui.current_page_count())
+            {
+                expand_initial_candidates();
+            }
             if (ui.move_selection(offset))
             {
                 refresh = true;

server/tests/CMakeLists.txt

@@ -14,6 +14,7 @@ set(TEST_SOURCE_FILES
     "${CMAKE_CURRENT_SOURCE_DIR}/src/test_input_key_policy.cpp"
     "${CMAKE_CURRENT_SOURCE_DIR}/src/test_candidate_ui_owner.cpp"
     "${CMAKE_CURRENT_SOURCE_DIR}/src/test_candidate_ui_action_policy.cpp"
+    "${CMAKE_CURRENT_SOURCE_DIR}/src/test_candidate_ui_state.cpp"
     "${CMAKE_CURRENT_SOURCE_DIR}/src/test_ipc_protocol_constants.cpp"
     "${CMAKE_CURRENT_SOURCE_DIR}/src/test_floating_toolbar_visibility_policy.cpp"
     "${CMAKE_CURRENT_SOURCE_DIR}/src/test_terminal_deactivation_policy.cpp"

server/tests/src/test_candidate_ui_state.cpp

@@ -0,0 +1,49 @@
+#include "global/globals.h"
+#include "tests/includes/test_framework.h"
+
+namespace
+{
+Global::CandidateUiState MakeCandidateUiState(int item_count, int page_size)
+{
+    Global::CandidateUiState state;
+    state.item_total_count = item_count;
+    state.page_size = page_size;
+    return state;
+}
+}
+
+TEST_CASE(candidate_ui_selection_moves_from_page_end_to_next_page_start)
+{
+    auto state = MakeCandidateUiState(8, 3);
+    state.page_index = 0;
+    state.selected_index_in_page = 2;
+
+    REQUIRE(state.move_selection(1));
+    REQUIRE_EQ(state.page_index, 1);
+    REQUIRE_EQ(state.selected_index_in_page, 0);
+}
+
+TEST_CASE(candidate_ui_selection_moves_from_page_start_to_previous_page_end)
+{
+    auto state = MakeCandidateUiState(8, 3);
+    state.page_index = 1;
+    state.selected_index_in_page = 0;
+
+    REQUIRE(state.move_selection(-1));
+    REQUIRE_EQ(state.page_index, 0);
+    REQUIRE_EQ(state.selected_index_in_page, 2);
+}
+
+TEST_CASE(candidate_ui_selection_stops_at_first_and_last_candidate)
+{
+    auto state = MakeCandidateUiState(8, 3);
+    REQUIRE(!state.move_selection(-1));
+    REQUIRE_EQ(state.page_index, 0);
+    REQUIRE_EQ(state.selected_index_in_page, 0);
+
+    state.page_index = 2;
+    state.selected_index_in_page = 1;
+    REQUIRE(!state.move_selection(1));
+    REQUIRE_EQ(state.page_index, 2);
+    REQUIRE_EQ(state.selected_index_in_page, 1);
+}