diff --git a/CHANGELOG.md b/CHANGELOG.md
index d639484..6cc57c8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -26,8 +26,8 @@ All notable changes to this project will be documented in this file.
   17 functions → `mqlaunch/lib/network.sh`), the fzf interactive pickers
   (git log/branch, kill process/port, run snippet, recent files, 6 functions →
   `mqlaunch/lib/fzf-pickers.sh`), and diagnostics (version reporting,
-  self-check, debug bundle, release notes, 5 functions →
-  `mqlaunch/lib/diagnostics.sh`). No behavior change; the launcher drops ~430
+  self-check, debug bundle, release notes, plus the system check, 6 functions →
+  `mqlaunch/lib/diagnostics.sh`). No behavior change; the launcher drops ~530
   lines and each concern now has a named owner. Guarded by
   `tests/monolith-delayer-smoke.sh`, a table-driven check that fails if any
   extracted function is redefined in the monolith or a lib source is dropped.
diff --git a/docs/AUTHORITY_MAP.md b/docs/AUTHORITY_MAP.md
index e0afdc3..28343c9 100644
--- a/docs/AUTHORITY_MAP.md
+++ b/docs/AUTHORITY_MAP.md
@@ -72,7 +72,7 @@ Reached through other live paths:
 | `mqlaunch/lib/mqobsidian/*` | `terminal/menus/mq-obsidian-menu.sh` |
 | `mqlaunch/lib/network.sh` | `terminal/launchers/mqlaunch.sh` (sourced) — network concern de-layered out of the monolith (Step 11a) |
 | `mqlaunch/lib/fzf-pickers.sh` | `terminal/launchers/mqlaunch.sh` (sourced) — fzf interactive pickers de-layered out of the monolith (Step 11a) |
-| `mqlaunch/lib/diagnostics.sh` | `terminal/launchers/mqlaunch.sh` (sourced) — version/self-check/debug-bundle/release-notes de-layered out of the monolith (Step 11a) |
+| `mqlaunch/lib/diagnostics.sh` | `terminal/launchers/mqlaunch.sh` (sourced) — version/self-check/debug-bundle/release-notes/system-check de-layered out of the monolith (Step 11a) |
 
 ## Bridges
 
diff --git a/mqlaunch/lib/diagnostics.sh b/mqlaunch/lib/diagnostics.sh
index c25dd1f..1587ce0 100755
--- a/mqlaunch/lib/diagnostics.sh
+++ b/mqlaunch/lib/diagnostics.sh
@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
-# mqlaunch diagnostics — version reporting, self-check, debug bundle, and
-# release notes.
+# mqlaunch diagnostics — version reporting, self-check, debug bundle, release
+# notes, and the system check.
 #
 # Extracted from terminal/launchers/mqlaunch.sh as part of Step 11a (monolith
 # de-layering, audit P4). Sourced into the launcher's scope, so it relies on the
@@ -135,3 +135,110 @@ show_release_notes() {
   print_footer
   pause_enter
 }
+
+# Coordinates system check behavior.
+system_check() {
+  local prompt_count="0"
+  local resolved_prompt_dir=""
+  local ai_status=""
+  local link_target=""
+  local active_cmd=""
+
+  resolved_prompt_dir="$(resolve_prompt_dir 2>/dev/null || true)"
+  ai_status="$(resolve_ai_status)"
+
+  if [[ -n "$resolved_prompt_dir" ]]; then
+    prompt_count="$(find "$resolved_prompt_dir" -maxdepth 1 -type f 2>/dev/null | wc -l | tr -d ' ')"
+  fi
+
+  if [[ -L "$BIN_LINK" ]]; then
+    link_target="$(readlink "$BIN_LINK" 2>/dev/null || true)"
+  fi
+
+  active_cmd="$(command -v mqlaunch 2>/dev/null || true)"
+
+  print_header
+  row "SYSTEM CHECK"
+  empty_row
+
+  if [[ -d "$BASE_DIR" ]]; then
+    row "[OK]   Base dir found"
+  else
+    row "[FAIL] Base dir missing"
+  fi
+
+  if [[ -x "$MQ_SCRIPT" ]]; then
+    row "[OK]   mqlaunch.sh executable"
+  elif [[ -e "$MQ_SCRIPT" ]]; then
+    row "[FAIL] mqlaunch.sh found but not executable"
+  else
+    row "[FAIL] mqlaunch.sh missing"
+  fi
+
+  case "$ai_status" in
+    OK)
+      row "[OK]   AI backend executable"
+      ;;
+    FOUND_NOT_EXECUTABLE)
+      row "[FAIL] AI backend found but not executable"
+      ;;
+    MISSING)
+      row "[FAIL] AI backend missing"
+      ;;
+  esac
+
+  if [[ -n "$resolved_prompt_dir" ]]; then
+    row "[OK]   Prompt dir found"
+    row "       $resolved_prompt_dir"
+  else
+    row "[FAIL] Prompt dir missing"
+  fi
+
+  if [[ -f "$TERMINAL_GUIDE_HTML" ]]; then
+    row "[OK]   Terminal guide local file found"
+  else
+    row "[FAIL] Terminal guide local file missing"
+  fi
+
+  if [[ -L "$BIN_LINK" ]]; then
+    if [[ "$link_target" == "$BASE_DIR/bin/mqlaunch" || "$link_target" == "$MQ_SCRIPT" ]]; then
+      row "[OK]   ~/bin/mqlaunch symlink correct"
+    else
+      row "[FAIL] ~/bin/mqlaunch points elsewhere"
+      row "       $link_target"
+    fi
+  elif [[ -e "$BIN_LINK" ]]; then
+    row "[FAIL] ~/bin/mqlaunch exists but is not a symlink"
+  else
+    row "[FAIL] ~/bin/mqlaunch missing"
+  fi
+
+  if [[ -n "$active_cmd" ]]; then
+    row "[OK]   mqlaunch command resolves"
+    row "       $active_cmd"
+  else
+    row "[FAIL] mqlaunch command not found in PATH"
+  fi
+
+  if command -v git >/dev/null 2>&1; then
+    row "[OK]   git available"
+  else
+    row "[FAIL] git missing"
+  fi
+
+  if command -v open >/dev/null 2>&1; then
+    row "[OK]   open command available"
+  else
+    row "[FAIL] open command missing"
+  fi
+
+  if command -v pbcopy >/dev/null 2>&1; then
+    row "[OK]   pbcopy available"
+  else
+    row "[FAIL] pbcopy missing"
+  fi
+
+  row "Prompt files: $prompt_count"
+  print_footer
+  pause_enter
+}
diff --git a/terminal/launchers/mqlaunch.sh b/terminal/launchers/mqlaunch.sh
index 51d5076..487f211 100755
--- a/terminal/launchers/mqlaunch.sh
+++ b/terminal/launchers/mqlaunch.sh
@@ -604,113 +604,6 @@ open_terminal_guide() {
   fi
 }
 
-# Coordinates system check behavior.
-system_check() {
-  local prompt_count="0"
-  local resolved_prompt_dir=""
-  local ai_status=""
-  local link_target=""
-  local active_cmd=""
-
-  resolved_prompt_dir="$(resolve_prompt_dir 2>/dev/null || true)"
-  ai_status="$(resolve_ai_status)"
-
-  if [[ -n "$resolved_prompt_dir" ]]; then
-    prompt_count="$(find "$resolved_prompt_dir" -maxdepth 1 -type f 2>/dev/null | wc -l | tr -d ' ')"
-  fi
-
-  if [[ -L "$BIN_LINK" ]]; then
-    link_target="$(readlink "$BIN_LINK" 2>/dev/null || true)"
-  fi
-
-  active_cmd="$(command -v mqlaunch 2>/dev/null || true)"
-
-  print_header
-  row "SYSTEM CHECK"
-  empty_row
-
-  if [[ -d "$BASE_DIR" ]]; then
-    row "[OK]   Base dir found"
-  else
-    row "[FAIL] Base dir missing"
-  fi
-
-  if [[ -x "$MQ_SCRIPT" ]]; then
-    row "[OK]   mqlaunch.sh executable"
-  elif [[ -e "$MQ_SCRIPT" ]]; then
-    row "[FAIL] mqlaunch.sh found but not executable"
-  else
-    row "[FAIL] mqlaunch.sh missing"
-  fi
-
-  case "$ai_status" in
-    OK)
-      row "[OK]   AI backend executable"
-      ;;
-    FOUND_NOT_EXECUTABLE)
-      row "[FAIL] AI backend found but not executable"
-      ;;
-    MISSING)
-      row "[FAIL] AI backend missing"
-      ;;
-  esac
-
-  if [[ -n "$resolved_prompt_dir" ]]; then
-    row "[OK]   Prompt dir found"
-    row "       $resolved_prompt_dir"
-  else
-    row "[FAIL] Prompt dir missing"
-  fi
-
-  if [[ -f "$TERMINAL_GUIDE_HTML" ]]; then
-    row "[OK]   Terminal guide local file found"
-  else
-    row "[FAIL] Terminal guide local file missing"
-  fi
-
-  if [[ -L "$BIN_LINK" ]]; then
-    if [[ "$link_target" == "$BASE_DIR/bin/mqlaunch" || "$link_target" == "$MQ_SCRIPT" ]]; then
-      row "[OK]   ~/bin/mqlaunch symlink correct"
-    else
-      row "[FAIL] ~/bin/mqlaunch points elsewhere"
-      row "       $link_target"
-    fi
-  elif [[ -e "$BIN_LINK" ]]; then
-    row "[FAIL] ~/bin/mqlaunch exists but is not a symlink"
-  else
-    row "[FAIL] ~/bin/mqlaunch missing"
-  fi
-
-  if [[ -n "$active_cmd" ]]; then
-    row "[OK]   mqlaunch command resolves"
-    row "       $active_cmd"
-  else
-    row "[FAIL] mqlaunch command not found in PATH"
-  fi
-
-  if command -v git >/dev/null 2>&1; then
-    row "[OK]   git available"
-  else
-    row "[FAIL] git missing"
-  fi
-
-  if command -v open >/dev/null 2>&1; then
-    row "[OK]   open command available"
-  else
-    row "[FAIL] open command missing"
-  fi
-
-  if command -v pbcopy >/dev/null 2>&1; then
-    row "[OK]   pbcopy available"
-  else
-    row "[FAIL] pbcopy missing"
-  fi
-
-  row "Prompt files: $prompt_count"
-  print_footer
-  pause_enter
-}
-
 # Opens downloads folder.
 open_downloads_folder() {
   open_folder_screen "OPEN DOWNLOADS FOLDER" "$HOME/Downloads" "Downloads folder missing:"
@@ -1123,8 +1016,9 @@ open_tools_menu() {
   fi
 }
 
-# Diagnostics — version reporting, self-check, debug bundle, and release notes
-# — live in a dedicated library (Step 11a monolith de-layering, audit P4).
+# Diagnostics — version reporting, self-check, debug bundle, release notes, and
+# the system check — live in a dedicated library (Step 11a monolith de-layering,
+# audit P4).
 # Sourced into this scope so they keep using the ambient UI helpers and
 # $BASE_DIR; no behavior change — the functions are verbatim moves.
 if [[ -f "$BASE_DIR/mqlaunch/lib/diagnostics.sh" ]]; then
diff --git a/tests/monolith-delayer-smoke.sh b/tests/monolith-delayer-smoke.sh
index d27802e..7caa5ff 100755
--- a/tests/monolith-delayer-smoke.sh
+++ b/tests/monolith-delayer-smoke.sh
@@ -16,7 +16,7 @@ fail() { printf '[FAIL] %s\n' "$1" >&2; exit 1; }
 CONCERNS=(
   "mqlaunch/lib/network.sh : network_default_interface network_service_name network_interface_ip network_dns_server network_gateway network_ssid network_ping_ms network_value network_report copy_network_info open_network_settings ping_test show_dns_gateway run_network_pulse run_network_ghost run_network_quality show_network_info"
   "mqlaunch/lib/fzf-pickers.sh : fzf_git_log fzf_git_branch fzf_kill_process fzf_kill_port fzf_run_snippet fzf_recent_files"
-  "mqlaunch/lib/diagnostics.sh : get_repo_version show_version_info run_self_check run_debug_bundle show_release_notes"
+  "mqlaunch/lib/diagnostics.sh : get_repo_version show_version_info run_self_check run_debug_bundle show_release_notes system_check"
 )
 
 total=0