fix: improve error trace propagation for telemetry

- post_update_to_api: Attempts 2/3 now send medium_error (16KB truncated
  log) instead of short_error (generic description only). This is the
  primary fix — when attempt 1 fails (120KB payload too large/timeout),
  attempts 2/3 no longer discard all log data.

- _send_abort_telemetry: Increased container fallback from 20 to 200
  log lines (capped at 16KB). Added SILENT_LOGFILE as fallback source.
  Added exit code explanation header and error_category to payload.

- get_error_text/get_full_log: Added SILENT_LOGFILE as last-resort
  fallback when INSTALL_LOG, combined log, and BUILD_LOG are all
  empty/missing.

misc/api.func

@@ -393,6 +393,11 @@ get_error_text() {
     logfile="$BUILD_LOG"
   fi
 
+  # Try SILENT_LOGFILE as last resort (captures $STD command output)
+  if [[ -z "$logfile" || ! -s "$logfile" ]] && [[ -n "${SILENT_LOGFILE:-}" && -s "${SILENT_LOGFILE}" ]]; then
+    logfile="$SILENT_LOGFILE"
+  fi
+
   if [[ -n "$logfile" && -s "$logfile" ]]; then
     tail -n 20 "$logfile" 2>/dev/null | sed 's/\r$//' | sed 's/\x1b\[[0-9;]*[a-zA-Z]//g'
   fi
@@ -438,6 +443,13 @@ get_full_log() {
     fi
   fi
 
+  # Fall back to SILENT_LOGFILE (captures $STD command output)
+  if [[ -z "$logfile" || ! -s "$logfile" ]]; then
+    if [[ -n "${SILENT_LOGFILE:-}" && -s "${SILENT_LOGFILE}" ]]; then
+      logfile="$SILENT_LOGFILE"
+    fi
+  fi
+
   if [[ -n "$logfile" && -s "$logfile" ]]; then
     # Strip ANSI codes, carriage returns, and anonymize IP addresses (GDPR)
     sed 's/\r$//' "$logfile" 2>/dev/null |
@@ -876,7 +888,7 @@ post_update_to_api() {
   esac
 
   # For failed/unknown status, resolve exit code and error description
-  local short_error=""
+  local short_error="" medium_error=""
   if [[ "$pb_status" == "failed" ]] || [[ "$pb_status" == "unknown" ]]; then
     if [[ "$raw_exit_code" =~ ^[0-9]+$ ]]; then
       exit_code="$raw_exit_code"
@@ -896,6 +908,18 @@ post_update_to_api() {
     short_error=$(json_escape "$(explain_exit_code "$exit_code")")
     error_category=$(categorize_error "$exit_code")
     [[ -z "$error" ]] && error="Unknown error"
+
+    # Build medium error for attempt 2: explanation + last 100 log lines (≤16KB)
+    # This is the critical middle ground between full 120KB log and generic-only description
+    local medium_log=""
+    medium_log=$(get_full_log 16384) || true # 16KB max
+    if [[ -z "$medium_log" ]]; then
+      medium_log=$(get_error_text) || true
+    fi
+    local medium_full
+    medium_full=$(build_error_string "$exit_code" "$medium_log")
+    medium_error=$(json_escape "$medium_full")
+    [[ -z "$medium_error" ]] && medium_error="$short_error"
   fi
 
   # Calculate duration if timer was started
@@ -954,7 +978,7 @@ EOF
     return 0
   fi
 
-  # ── Attempt 2: Short error text (no full log) ──
+  # ── Attempt 2: Medium error text (truncated log ≤16KB instead of full 120KB) ──
   sleep 1
   local RETRY_PAYLOAD
   RETRY_PAYLOAD=$(
@@ -974,7 +998,7 @@ EOF
     "pve_version": "${pve_version}",
     "method": "${METHOD:-default}",
     "exit_code": ${exit_code},
-    "error": "${short_error}",
+    "error": "${medium_error}",
     "error_category": "${error_category}",
     "install_duration": ${duration},
     "cpu_vendor": "${cpu_vendor}",
@@ -997,7 +1021,7 @@ EOF
     return 0
   fi
 
-  # ── Attempt 3: Minimal payload (bare minimum to set status) ──
+  # ── Attempt 3: Minimal payload with medium error (bare minimum to set status) ──
   sleep 2
   local MINIMAL_PAYLOAD
   MINIMAL_PAYLOAD=$(
@@ -1009,7 +1033,7 @@ EOF
     "nsapp": "${NSAPP:-unknown}",
     "status": "${pb_status}",
     "exit_code": ${exit_code},
-    "error": "${short_error}",
+    "error": "${medium_error}",
     "error_category": "${error_category}",
     "install_duration": ${duration}
 }

misc/error_handler.func

@@ -408,10 +408,29 @@ _send_abort_telemetry() {
   [[ "${DIAGNOSTICS:-no}" == "no" ]] && return 0
   [[ -z "${RANDOM_UUID:-}" ]] && return 0
 
-  # Collect last 20 log lines for error diagnosis (best-effort)
+  # Collect last 200 log lines for error diagnosis (best-effort)
+  # Container context has no get_full_log(), so we gather as much as possible
   local error_text=""
+  local logfile=""
   if [[ -n "${INSTALL_LOG:-}" && -s "${INSTALL_LOG}" ]]; then
-    error_text=$(tail -n 20 "$INSTALL_LOG" 2>/dev/null | sed 's/\x1b\[[0-9;]*[a-zA-Z]//g; s/\\/\\\\/g; s/"/\\"/g; s/\r//g' | tr '\n' '|' | sed 's/|$//' | tr -d '\000-\010\013\014\016-\037\177') || true
+    logfile="${INSTALL_LOG}"
+  elif [[ -n "${SILENT_LOGFILE:-}" && -s "${SILENT_LOGFILE}" ]]; then
+    logfile="${SILENT_LOGFILE}"
+  fi
+
+  if [[ -n "$logfile" ]]; then
+    error_text=$(tail -n 200 "$logfile" 2>/dev/null | sed 's/\x1b\[[0-9;]*[a-zA-Z]//g; s/\\/\\\\/g; s/"/\\"/g; s/\r//g' | tr '\n' '|' | sed 's/|$//' | head -c 16384 | tr -d '\000-\010\013\014\016-\037\177') || true
+  fi
+
+  # Prepend exit code explanation header (like build_error_string does on host)
+  local explanation=""
+  if declare -f explain_exit_code &>/dev/null; then
+    explanation=$(explain_exit_code "$exit_code" 2>/dev/null) || true
+  fi
+  if [[ -n "$explanation" && -n "$error_text" ]]; then
+    error_text="exit_code=${exit_code} | ${explanation}|---|${error_text}"
+  elif [[ -n "$explanation" && -z "$error_text" ]]; then
+    error_text="exit_code=${exit_code} | ${explanation}"
   fi
 
   # Calculate duration if start time is available
@@ -420,10 +439,17 @@ _send_abort_telemetry() {
     duration=$(($(date +%s) - DIAGNOSTICS_START_TIME))
   fi
 
+  # Categorize error if function is available (may not be in minimal container context)
+  local error_category=""
+  if declare -f categorize_error &>/dev/null; then
+    error_category=$(categorize_error "$exit_code" 2>/dev/null) || true
+  fi
+
   # Build JSON payload with error context
   local payload
   payload="{\"random_id\":\"${RANDOM_UUID}\",\"execution_id\":\"${EXECUTION_ID:-${RANDOM_UUID}}\",\"type\":\"${TELEMETRY_TYPE:-lxc}\",\"nsapp\":\"${NSAPP:-${app:-unknown}}\",\"status\":\"failed\",\"exit_code\":${exit_code}"
   [[ -n "$error_text" ]] && payload="${payload},\"error\":\"${error_text}\""
+  [[ -n "$error_category" ]] && payload="${payload},\"error_category\":\"${error_category}\""
   [[ -n "$duration" ]] && payload="${payload},\"duration\":${duration}"
   payload="${payload}}"