Improve container build/install logging and error handling

Introduces distinct BUILD_LOG and INSTALL_LOG variables for host and container operations, ensuring logs are properly captured and retrievable. Refactors silent execution and error handling to use the active log file, improves log copying after failures, and enhances context detection for log management. Also adds fallback logic for INSTALL_LOG initialization in install.func.

misc/build.func

@@ -47,6 +47,7 @@ variables() {
   METHOD="default"                                  # sets the METHOD variable to "default", used for the API call.
   RANDOM_UUID="$(cat /proc/sys/kernel/random/uuid)" # generates a random UUID and sets it to the RANDOM_UUID variable.
   SESSION_ID="${RANDOM_UUID:0:8}"                   # Short session ID (first 8 chars of UUID) for log files
+  BUILD_LOG="/tmp/create-lxc-${SESSION_ID}.log"     # Host-side container creation log
   CTTYPE="${CTTYPE:-${CT_TYPE:-1}}"}
 
   # Get Proxmox VE version and kernel version
@@ -2206,6 +2207,8 @@ build_container() {
   export DIAGNOSTICS="$DIAGNOSTICS"
   export RANDOM_UUID="$RANDOM_UUID"
   export SESSION_ID="$SESSION_ID"
+  export BUILD_LOG="$BUILD_LOG"
+  export INSTALL_LOG="/root/.install-${SESSION_ID}.log"
   export CACHER="$APT_CACHER"
   export CACHER_IP="$APT_CACHER_IP"
   export tz="$timezone"
@@ -2576,10 +2579,12 @@ EOF'
   # Install SSH keys
   install_ssh_keys_into_ct
 
-  # Run application installer
+  # Run application installer (disable ERR trap to handle errors manually)
+  set +e
   lxc-attach -n "$CTID" -- bash -c "$(curl -fsSL https://raw.githubusercontent.com/community-scripts/ProxmoxVED/main/install/${var_install}.sh)"
   local lxc_exit=$?
-  
+  set -e
+
   # Check for error flag file in container (more reliable than lxc-attach exit code)
   local install_exit_code=0
   if [[ -n "${SESSION_ID:-}" ]]; then
@@ -2589,21 +2594,35 @@ EOF'
       pct exec "$CTID" -- rm -f "$error_flag" 2>/dev/null || true
     fi
   fi
-  
+
   # Fallback to lxc-attach exit code if no flag file
   if [[ $install_exit_code -eq 0 && $lxc_exit -ne 0 ]]; then
     install_exit_code=$lxc_exit
   fi
-  
+
   # Installation failed?
   if [[ $install_exit_code -ne 0 ]]; then
     msg_error "Installation failed in container ${CTID} (exit code: ${install_exit_code})"
 
-    # Try to copy installation log from container (without spinner/msg_info)
+    # Copy both logs from container before potential deletion
+    local build_log_copied=false
+    local install_log_copied=false
+
     if [[ -n "$CTID" && -n "${SESSION_ID:-}" ]]; then
-      if pct pull "$CTID" "/root/.install-${SESSION_ID}.log" "/tmp/install-${SESSION_ID}.log" 2>/dev/null; then
-        echo -e "${GN}✔${CL} Installation log: ${BL}/tmp/install-${SESSION_ID}.log${CL}"
+      # Copy BUILD_LOG (creation log) if it exists
+      if [[ -f "${BUILD_LOG}" ]]; then
+        cp "${BUILD_LOG}" "/tmp/create-lxc-${CTID}-${SESSION_ID}.log" 2>/dev/null && build_log_copied=true
       fi
+
+      # Copy INSTALL_LOG from container
+      if pct pull "$CTID" "/root/.install-${SESSION_ID}.log" "/tmp/install-lxc-${CTID}-${SESSION_ID}.log" 2>/dev/null; then
+        install_log_copied=true
+      fi
+
+      # Show available logs
+      echo ""
+      [[ $build_log_copied == true ]] && echo -e "${GN}✔${CL} Container creation log: ${BL}/tmp/create-lxc-${CTID}-${SESSION_ID}.log${CL}"
+      [[ $install_log_copied == true ]] && echo -e "${GN}✔${CL} Installation log: ${BL}/tmp/install-lxc-${CTID}-${SESSION_ID}.log${CL}"
     fi
 
     # Prompt user for cleanup with 60s timeout (plain echo - no msg_info to avoid spinner)