fix sandbox app script loading and timer execution

- Add relative path resolution for filesystem-loaded documents in kernel.cpp
  - SetDocumentBasePath() tracks document directory for relative resource resolution
  - ResolvePath() resolves relative paths like "app.lua" against document base path
- Fix RmlUi context name lookup in sandbox test app (use "default" not "main")
- Add debug logging to timer_manager.cpp to trace timer creation and execution

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

core/src/sandbox/timer_manager.cpp

@@ -2,6 +2,13 @@
 
 #include <lua.hpp>
 #include <algorithm>
+#ifdef __ANDROID__
+#include <android/log.h>
+#define TIMER_LOG(...) __android_log_print(ANDROID_LOG_INFO, "MosisOS", __VA_ARGS__)
+#else
+#include <cstdio>
+#define TIMER_LOG(...) printf(__VA_ARGS__)
+#endif
 
 namespace mosis {
 
@@ -64,8 +71,12 @@ TimerId TimerManager::SetInterval(lua_State* L, const std::string& app_id,
                                    int callback_ref, int interval_ms) {
     std::lock_guard<std::mutex> lock(m_mutex);
 
+    TIMER_LOG("[Timer] SetInterval called: app=%s, interval=%dms, ref=%d",
+              app_id.c_str(), interval_ms, callback_ref);
+
     // Check per-app limit
     if (m_app_timer_counts[app_id] >= MAX_TIMERS_PER_APP) {
+        TIMER_LOG("[Timer] REJECTED: timer limit exceeded for %s", app_id.c_str());
         luaL_unref(L, LUA_REGISTRYINDEX, callback_ref);
         return 0;
     }
@@ -89,6 +100,9 @@ TimerId TimerManager::SetInterval(lua_State* L, const std::string& app_id,
     m_app_timer_counts[app_id]++;
     m_app_timer_ids[app_id].insert(timer.id);
 
+    TIMER_LOG("[Timer] Created interval timer id=%llu for %s (total: %zu)",
+              timer.id, app_id.c_str(), m_timers.size());
+
     return timer.id;
 }
 
@@ -158,9 +172,13 @@ void TimerManager::ClearAppTimers(const std::string& app_id) {
 
 void TimerManager::FireTimer(Timer& timer) {
     if (timer.cancelled || timer.callback_ref == LUA_NOREF || !timer.L) {
+        TIMER_LOG("[Timer] FireTimer skipped: cancelled=%d, ref=%d, L=%p",
+                  timer.cancelled, timer.callback_ref, timer.L);
         return;
     }
 
+    TIMER_LOG("[Timer] Firing timer id=%llu for %s", timer.id, timer.app_id.c_str());
+
     lua_State* L = timer.L;
 
     // Get the callback from registry
@@ -170,10 +188,15 @@ void TimerManager::FireTimer(Timer& timer) {
         // Call the callback with protected call
         int result = lua_pcall(L, 0, 0, 0);
         if (result != LUA_OK) {
-            // Log error but don't propagate
+            // Log the error
+            const char* err = lua_tostring(L, -1);
+            TIMER_LOG("[Timer] ERROR in callback: %s", err ? err : "(unknown)");
             lua_pop(L, 1);
+        } else {
+            TIMER_LOG("[Timer] Callback completed successfully");
         }
     } else {
+        TIMER_LOG("[Timer] ERROR: callback ref is not a function!");
         lua_pop(L, 1);
     }
 }
@@ -209,6 +232,12 @@ int TimerManager::ProcessTimers() {
                 }
             }
         }
+
+        // Log only when we have timers to fire (to avoid spam)
+        if (!to_fire.empty()) {
+            TIMER_LOG("[Timer] ProcessTimers: %zu ready to fire out of %zu total",
+                      to_fire.size(), m_timers.size());
+        }
     }
 
     // Fire timers outside the lock to allow callbacks to create new timers