Improve error handling and logging for LXC builds (#12208)

Prevent host-side error_handler from being triggered during in-container install/recovery by delaying re-enabling set -Eeuo pipefail and the ERR trap in misc/build.func until after install/recovery completes; add explanatory comments. Update misc/error_handler.func to fall back to BUILD_LOG if container-internal log path is unavailable, show the last 20 log lines when present, refine container vs host detection (check INSTALL_LOG file and /root), copy INSTALL_LOG into /root and write a .failed flag with the exit code for host-side detection, and ensure full-log output and container removal prompt are shown appropriately in host context. Tweak misc/core.func silent() output to include a "Full log" path and adjust formatting.

misc/build.func

@@ -4055,8 +4055,9 @@ EOF'
   lxc-attach -n "$CTID" -- bash -c "$(curl -fsSL https://raw.githubusercontent.com/community-scripts/ProxmoxVE/main/install/${var_install}.sh)"
   local lxc_exit=$?
 
-  set -Eeuo pipefail       # Re-enable error handling
-  trap 'error_handler' ERR # Restore ERR trap
+  # Keep error handling DISABLED during failure detection and recovery
+  # Re-enabling it here would cause any pct exec/pull failure to trigger
+  # error_handler() on the host, bypassing the recovery menu entirely
 
   # Check for error flag file in container (more reliable than lxc-attach exit code)
   local install_exit_code=0
@@ -4484,6 +4485,10 @@ EOF'
 
     exit $install_exit_code
   fi
+
+  # Re-enable error handling after successful install or recovery menu completion
+  set -Eeuo pipefail
+  trap 'error_handler' ERR
 }
 
 destroy_lxc() {

misc/core.func

@@ -524,7 +524,8 @@ silent() {
     if [[ -s "$logfile" ]]; then
       echo -e "\n${TAB}--- Last 10 lines of log ---"
       tail -n 10 "$logfile"
-      echo -e "${TAB}-----------------------------------\n"
+      echo -e "${TAB}-----------------------------------"
+      echo -e "${TAB}📋 Full log: ${logfile}\n"
     fi
 
     exit "$rc"

misc/error_handler.func

@@ -236,27 +236,37 @@ error_handler() {
     active_log="$SILENT_LOGFILE"
   fi
 
+  # If active_log points to a container-internal path that doesn't exist on host,
+  # fall back to BUILD_LOG (host-side log)
+  if [[ -n "$active_log" && ! -s "$active_log" && -n "${BUILD_LOG:-}" && -s "${BUILD_LOG}" ]]; then
+    active_log="$BUILD_LOG"
+  fi
+
+  # Show last log lines if available
   if [[ -n "$active_log" && -s "$active_log" ]]; then
     echo -e "\n${TAB}--- Last 20 lines of log ---"
     tail -n 20 "$active_log"
     echo -e "${TAB}-----------------------------------\n"
+  fi
 
-    # Detect context: Container (INSTALL_LOG set + /root exists) vs Host (BUILD_LOG)
-    if [[ -n "${INSTALL_LOG:-}" && -d /root ]]; then
+  # Detect context: Container (INSTALL_LOG set + inside container /root) vs Host
+  if [[ -n "${INSTALL_LOG:-}" && -f "${INSTALL_LOG:-}" && -d /root ]]; then
     # CONTAINER CONTEXT: Copy log and create flag file for host
     local container_log="/root/.install-${SESSION_ID:-error}.log"
-      cp "$active_log" "$container_log" 2>/dev/null || true
+    cp "${INSTALL_LOG}" "$container_log" 2>/dev/null || true
 
     # Create error flag file with exit code for host detection
     echo "$exit_code" >"/root/.install-${SESSION_ID:-error}.failed" 2>/dev/null || true
     # Log path is shown by host as combined log - no need to show container path
   else
     # HOST CONTEXT: Show local log path and offer container cleanup
+    if [[ -n "$active_log" && -s "$active_log" ]]; then
       if declare -f msg_custom >/dev/null 2>&1; then
         msg_custom "📋" "${YW}" "Full log: ${active_log}"
       else
         echo -e "${YW}Full log:${CL} ${BL}${active_log}${CL}"
       fi
+    fi
 
     # Offer to remove container if it exists (build errors after container creation)
     if [[ -n "${CTID:-}" ]] && command -v pct &>/dev/null && pct status "$CTID" &>/dev/null; then
@@ -314,7 +324,6 @@ error_handler() {
       fi
     fi
   fi
-  fi
 
   exit "$exit_code"
 }