diff --git a/.codespellrc b/.codespellrc
index 8809455..0269020 100644
--- a/.codespellrc
+++ b/.codespellrc
@@ -73,7 +73,12 @@ ignore-words-list = bessel,ist,sinces,nd,te,inout,nin,numer,neet,anc,sinks,doubl
     labelled,labelling,labels,labelled,
     fulfil,fulfils,fulfilled,fulfilling,
     endcode,
-    deklaration,deklarationen
+    deklaration,deklarationen,
+    recognise,recognised,recognises,recognising,recognisation,
+    signalled,signalling,
+    travelled,travelling,
+    cancelled,cancelling,
+    modelled,modelling
 
 # Words we explicitly DO want flagged (override the default skip list).
 # Keep empty for now; add as we hit real-but-not-flagged typos.
diff --git a/.editorconfig b/.editorconfig
new file mode 100644
index 0000000..26750ba
--- /dev/null
+++ b/.editorconfig
@@ -0,0 +1,56 @@
+# conformallab++ EditorConfig
+#
+# Honoured natively by VSCode (with the EditorConfig extension), CLion,
+# Vim, Emacs, Sublime, …  Covers the basics that .clang-format /
+# .cmake-format don't catch (Markdown, Python, YAML, shell, JSON, …)
+# and acts as a cross-IDE fallback when clang-format isn't installed.
+#
+# Authoritative formatting for C++ source still comes from .clang-format;
+# this file just keeps the editor's defaults from fighting it.
+
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+indent_style = space
+indent_size = 4
+
+# C++ — match .clang-format
+[*.{h,hpp,cpp,c,cc}]
+indent_size = 4
+max_line_length = 100
+
+# CMake — match .cmake-format.yaml
+[{CMakeLists.txt,*.cmake}]
+indent_size = 4
+max_line_length = 100
+
+# Python — PEP-8 default
+[*.py]
+indent_size = 4
+max_line_length = 100
+
+# Shell — Google shell style
+[*.sh]
+indent_size = 4
+max_line_length = 100
+
+# YAML — community convention
+[*.{yml,yaml}]
+indent_size = 2
+
+# JSON
+[*.json]
+indent_size = 2
+
+# Markdown — preserve trailing spaces (used for line breaks); don't strip
+[*.md]
+trim_trailing_whitespace = false
+max_line_length = off
+
+# Makefiles must use tabs
+[Makefile]
+indent_style = tab
diff --git a/code/CMakeLists.txt b/code/CMakeLists.txt
index 88278d7..b3dce95 100644
--- a/code/CMakeLists.txt
+++ b/code/CMakeLists.txt
@@ -55,8 +55,26 @@ if(NOT CMAKE_BUILD_TYPE)
 endif()
 
 if(CMAKE_CXX_COMPILER_ID MATCHES "Clang|GNU")
+  # ─── Compiler-warning policy ─────────────────────────────────────────────
+  # `-Wall -Wextra -Wpedantic` is the project default for first-party code.
+  # Vendored deps under code/deps/ get a separate, looser policy (handled
+  # via per-target SYSTEM include marking when they are pulled in).
+  #
+  # `CONFORMALLAB_WARNINGS_AS_ERRORS=ON` flips on `-Werror` — used in CI's
+  # promotion-track and by `scripts/quality/sanitizers.sh` to make sure no
+  # new warning class slips in unannounced.  Off by default so regular
+  # builds on slightly older toolchains aren't broken by a new GCC's
+  # added warning.
+  option(CONFORMALLAB_WARNINGS_AS_ERRORS
+    "Treat compiler warnings as errors (-Werror)." OFF)
+
   add_compile_options(-Wall -Wextra -Wpedantic)
 
+  if(CONFORMALLAB_WARNINGS_AS_ERRORS)
+    add_compile_options(-Werror)
+    message(STATUS "Warnings-as-errors mode active (-Werror).")
+  endif()
+
   # AddressSanitizer only in Debug (gtest_discover_tests runs the binary at
   # configure time and hangs with ASan enabled).
   if(CMAKE_BUILD_TYPE STREQUAL "Debug" AND NOT BUILD_TESTING)
diff --git a/doc/architecture/dependencies.md b/doc/architecture/dependencies.md
new file mode 100644
index 0000000..a68277e
--- /dev/null
+++ b/doc/architecture/dependencies.md
@@ -0,0 +1,151 @@
+# Dependencies & standalone-ness
+
+This document is the single source of truth for "what does conformallab++
+**require** vs. what does it **optionally** use".  Anyone evaluating the
+project for inclusion (CGAL submission, downstream consumer, Linux
+distribution package, reviewer audit) should be able to read this page
+and know exactly which dev tools are mandatory, which are nice-to-have,
+and which can be skipped or replaced.
+
+## TL;DR
+
+| Layer | What is required | What is optional |
+|---|---|---|
+| **Library use** (header-only, end-user code includes our headers) | C++17 compiler, CMake ≥ 3.20, Eigen ≥ 3.4 (headers), CGAL ≥ 5.6 (headers), Boost ≥ 1.74 (headers — needed by CGAL's BGL adapters) | — |
+| **Test build + run** | the above + GTest (auto-fetched by CMake `FetchContent`, no system install needed) | — |
+| **Documentation build** | Doxygen ≥ 1.10 | Graphviz (call graphs), MathJax (renders inline) |
+| **Local quality gates** (`scripts/quality/`) | nothing the library doesn't already need | every gate is **independent**; each one not installed is **skipped**, not failed |
+| **Optional viewer** (`-DWITH_VIEWER=ON`) | GLFW (vendored under `code/deps/glfw-3.4`), libigl, OpenGL system headers | — |
+
+The library itself is **header-only**.  There is no compiled `.so` /
+`.a` / `.lib` we ship; consumers just `#include` and let their build
+system do the rest.
+
+## Library deps (required to build/use the C++ headers)
+
+| Dep | Version | Header-only? | Purchase | Required by |
+|---|---|---|---|---|
+| **C++17 compiler** | g++ ≥ 11, clang++ ≥ 14, AppleClang ≥ 14 | n/a | system / brew / apt | everything |
+| **CMake** | ≥ 3.20 | n/a | system / brew / apt | build orchestration |
+| **Eigen** | ≥ 3.4 (header-only) | yes | system (`apt install libeigen3-dev`) or vendored under `code/deps/eigen-*/` | every functional & solver |
+| **CGAL** | ≥ 5.6 (header-only) | yes | system (`apt install libcgal-dev`) or downloaded tarball | `code/include/CGAL/*` wrappers + Surface_mesh |
+| **Boost** | ≥ 1.74 (header-only) | yes | system (`apt install libboost-dev`) | only when `WITH_CGAL_TESTS=ON` or `WITH_CGAL=ON`, because CGAL's BGL adapters pull in `boost::graph_traits` |
+| **GTest** | 1.14 | yes (auto-fetched) | `FetchContent_Declare` in `code/CMakeLists.txt` — never installed system-wide | tests only |
+
+Notes:
+- The library headers in `code/include/*.hpp` use only Eigen + STL.
+- The CGAL wrapper headers in `code/include/CGAL/*.h` add CGAL + Boost
+  (transitively).
+- `code/deps/single_includes/json.hpp` is the vendored
+  [nlohmann/json](https://github.com/nlohmann/json) header — used by
+  `serialization.hpp` only.  No system install needed.
+
+## Build modes — what each requires
+
+| Mode | CMake invocation | Extra system deps |
+|---|---|---|
+| **Fast / pure-math tests** (default) | `cmake -S code -B build` | none beyond C++17 + CMake |
+| **CGAL headless tests** | `cmake -S code -B build -DWITH_CGAL_TESTS=ON` | Boost headers |
+| **Full build** (CLI + viewer) | `cmake -S code -B build -DWITH_CGAL=ON` | Boost + Wayland/X11 dev headers |
+| **Coverage / sanitizers / etc.** | see `scripts/quality/` | per-script (each documents its prereqs and skips if missing) |
+
+The `-DWITH_*` flags **all default to OFF**.  A fresh checkout +
+`cmake -S code -B build` works with nothing but a C++17 compiler and
+CMake — useful for evaluating the math without taking on the full CGAL
+toolchain.
+
+## Local quality gates — all optional, each independently skippable
+
+`scripts/quality/` contains 12 gate scripts.  None of them is wired
+into the regular CMake build; each is a standalone shell or Python
+invocation.  When the underlying tool is not installed, the script
+exits with **code 2** and a clear message; `scripts/quality/run-all.sh`
+recognises this as **SKIP**, not FAIL.
+
+| Tool | Used by | Install (macOS) | Install (Debian/Ubuntu) | Behaviour if missing |
+|---|---|---|---|---|
+| `clang-format` ≥ 15 | `clang-format.sh` | `brew install clang-format` | `apt install clang-format` | gate prints install hint, exits 2 → SKIP |
+| `clang-tidy` ≥ 14 | `clang-tidy.sh` | `brew install llvm` (then PATH-prepend `$(brew --prefix llvm)/bin`) | `apt install clang-tidy` | SKIP |
+| `cmake-format` / `cmake-lint` | `cmake-format.sh` | `pip3 install --user cmakelang` + PATH-prepend `~/.local/bin` | `pip3 install --user cmakelang` | SKIP |
+| `codespell` | `codespell.sh` | `brew install codespell` | `apt install codespell` (or `pip3 install codespell`) | SKIP |
+| `shellcheck` | `shellcheck.sh` | `brew install shellcheck` | `apt install shellcheck` | SKIP |
+| `cppcheck` | `cppcheck.sh` | `brew install cppcheck` | `apt install cppcheck` | SKIP |
+| `lcov` (+ `gcov` from the compiler) | `coverage.sh` | `brew install lcov` | `apt install lcov` | SKIP |
+| second `g++` or `clang++` | `multi-compiler.sh` | `brew install gcc` or `brew install llvm` | `apt install g++` / `clang++-N` | runs against whatever compilers it finds; WARNING if < 2 |
+| extra CGAL source trees | `cgal-version-matrix.sh` | manually `git clone` under `~/cgal/<ver>/` (or pass `CGAL_ROOTS=...`) | same | exits 2 → SKIP with explicit recovery hint |
+
+### How to disable a gate temporarily
+
+Two options:
+
+1. **Don't install the tool** — `run-all.sh` skips it.
+2. **Remove the line from `GATES_FAST` / `GATES_SLOW` in `run-all.sh`** —
+   the script is a 5-line edit; no separate "disabled" flag system.
+
+There is no global "disable all quality gates" switch by design.  If
+the gates feel heavy, run only the fast subset (`run-all.sh --fast`,
+~5 seconds wall-time when all tools are present); if even that is too
+much, invoke the one gate you care about directly.
+
+### `CONFORMALLAB_WARNINGS_AS_ERRORS` — the only CMake-level quality flag
+
+By default the build adds `-Wall -Wextra -Wpedantic` but does **not**
+fail on warnings.  Set `-DCONFORMALLAB_WARNINGS_AS_ERRORS=ON` for a
+strict build (intended for CI promotion-track and for sanitizer runs).
+Defaulting to off keeps the build green on slightly-newer toolchains
+that may flag new warning classes we haven't yet annotated.
+
+## CI gates (active on every PR via `.gitea/workflows/`)
+
+These run inside the `git.eulernest.eu/conformallab/ci-cpp:latest`
+container, so the tools are baked into the image — contributors do not
+need any of them locally:
+
+| Gate | Workflow file |
+|---|---|
+| ctest (fast + CGAL suites) | `cpp-tests.yml` |
+| test-count consistency | same |
+| End-to-end `try_it.sh` | same |
+| Markdown link check | `markdown-links.yml` |
+| Doxygen build + Codeberg Pages publish | `doxygen-pages.yml` |
+| Mirror to Codeberg | `mirror-to-codeberg.yml` |
+
+The local quality gates under `scripts/quality/` are **not** in CI
+today.  Each one's promotion path is documented in
+`scripts/quality/README.md`.
+
+## Verification of the standalone claim
+
+Test recipe (any UNIX, ~30 s):
+
+```bash
+# Strip PATH down to system + brew core (no quality tools).
+env -i PATH="/usr/bin:/bin:/opt/homebrew/bin" HOME="$HOME" \
+    cmake -S code -B /tmp/build-standalone
+
+# Build the fast test suite.
+cmake --build /tmp/build-standalone --target conformallab_tests
+
+# Run them.
+ctest --test-dir /tmp/build-standalone -E "^cgal\."
+```
+
+If this passes, the library is genuinely independent of every quality
+tool listed above.  Tested locally on macOS-arm64 — green.
+
+For the CGAL-mode equivalent (adds Boost headers as a system dep):
+
+```bash
+env -i PATH="/usr/bin:/bin:/opt/homebrew/bin" HOME="$HOME" \
+    cmake -S code -B /tmp/build-cgal -DWITH_CGAL_TESTS=ON
+cmake --build /tmp/build-cgal --target conformallab_cgal_tests
+ctest --test-dir /tmp/build-cgal -R "^cgal\."
+```
+
+## What is **not** in this repo (out of scope)
+
+- No package-manager metadata (Debian `.deb`, RPM, Conan, vcpkg, …) —
+  yet.  Adding them is downstream work; the header-only nature makes
+  each trivial.
+- No language bindings (Python, …) — out of scope; the library is C++.
+- No GPU compute path — out of scope; numerical work is CPU-only.
diff --git a/scripts/quality/README.md b/scripts/quality/README.md
index 5fe0fb8..12ad35e 100644
--- a/scripts/quality/README.md
+++ b/scripts/quality/README.md
@@ -23,6 +23,8 @@ consistency + markdown links + end-to-end smoke via `try_it.sh`).
 | `clang-format.sh` | every C++ source matches `.clang-format` (dry-run by default; `--fix` to apply) | ~2 s | `clang-format` ≥ 15 |
 | `cmake-format.sh` | every `CMakeLists.txt` matches `.cmake-format.yaml` + passes `cmake-lint` | ~2 s | `cmake-format` (pip: cmakelang) |
 | `codespell.sh` | typo check across docs + source comments + script messages | ~1 s | `codespell` |
+| `shellcheck.sh` | static analysis of every `scripts/**/*.sh` | ~1 s | `shellcheck` |
+| `cppcheck.sh` | second-opinion static analyser over `code/include/` | ~5 s | `cppcheck` |
 | `../check-markdown-links.py` | every internal markdown link resolves | ~2 s | `python3` |
 
 ### Correctness / quality gates (run before tagging or reviewer demos)
diff --git a/scripts/quality/cgal-version-matrix.sh b/scripts/quality/cgal-version-matrix.sh
index 5e215f3..55e4ef7 100755
--- a/scripts/quality/cgal-version-matrix.sh
+++ b/scripts/quality/cgal-version-matrix.sh
@@ -73,7 +73,11 @@ echo "  versions tested:"
 echo "$AVAILABLE" | sed 's/^/    /'
 echo "========================================"
 
-overall=0
+# Failures are recorded in $ROOT/.cgal-matrix-failures because the
+# while-loop runs in a subshell (consequence of the pipe from echo), so
+# a plain `overall=0; overall=1` would not survive back to the parent.
+rm -f "$ROOT/.cgal-matrix-failures"
+
 echo "$AVAILABLE" | while IFS= read -r cgal_root; do
     [ -z "$cgal_root" ] && continue
     ver="$(basename "$cgal_root")"
diff --git a/scripts/quality/clang-format.sh b/scripts/quality/clang-format.sh
index 4d3d58d..a515a30 100755
--- a/scripts/quality/clang-format.sh
+++ b/scripts/quality/clang-format.sh
@@ -23,7 +23,7 @@
 
 set -uo pipefail
 ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
-cd "$ROOT"
+cd "$ROOT" || exit 2
 
 command -v clang-format >/dev/null 2>&1 || {
     echo "FAIL: clang-format not in PATH." >&2
diff --git a/scripts/quality/clang-tidy.sh b/scripts/quality/clang-tidy.sh
index 584ecdf..1e1ba39 100755
--- a/scripts/quality/clang-tidy.sh
+++ b/scripts/quality/clang-tidy.sh
@@ -40,20 +40,39 @@ TARGET_DIR="${1:-code/include}"
 [ -d "$TARGET_DIR" ] || { echo "FAIL: $TARGET_DIR is not a directory" >&2; exit 2; }
 
 # Generate compile_commands.json (clang-tidy needs it for include paths).
+# Enable WITH_CGAL_TESTS so the CGAL include directories are part of at
+# least one compile entry — clang-tidy walks those when linting headers
+# that don't appear in compile_commands.json directly.
 cmake -S code -B "$BUILD_DIR" \
     -DCMAKE_EXPORT_COMPILE_COMMANDS=ON \
+    -DWITH_CGAL_TESTS=ON \
     -DCMAKE_BUILD_TYPE=Release \
     -Wno-dev >/dev/null
 
+# ── macOS workaround: brew-installed clang-tidy doesn't know where the
+# Apple Command-Line-Tools SDK lives, so it can't find <cmath>, <complex>,
+# <CGAL/...>, etc.  Pass `--extra-arg=-isysroot ...` to teach it.
+EXTRA_ARGS=()
+if [ "$(uname -s)" = "Darwin" ]; then
+    SDK="$(xcrun --show-sdk-path 2>/dev/null || true)"
+    if [ -n "$SDK" ]; then
+        EXTRA_ARGS+=(--extra-arg=-isysroot --extra-arg="$SDK")
+    fi
+fi
+
 mkdir -p "$BUILD_DIR"
 : > "$LOG"
 
-# Find every .h / .hpp under TARGET_DIR (skip deps + macOS dup files).
+# Find every .h / .hpp under TARGET_DIR (skip deps + macOS dup files +
+# viewer-only headers — those need `-DWITH_VIEWER=ON` plus a system
+# GLFW/libigl that we don't drag into the lint build).
 HEADERS=$(find "$TARGET_DIR" \
     \( -name "*.h" -o -name "*.hpp" \) \
     -type f \
     | grep -v "code/deps/" \
     | grep -v " 2\." \
+    | grep -v "viewer_utils\.h$" \
+    | grep -v "mesh_utils\.hpp$" \
     | sort)
 
 echo "========================================"
@@ -72,6 +91,7 @@ for h in $HEADERS; do
     # generated" boilerplate.  Pipe through tee for the log file.
     clang-tidy --quiet \
         -p "$BUILD_DIR" \
+        "${EXTRA_ARGS[@]}" \
         "$h" 2>&1 | tee -a "$LOG" || true
 done
 
diff --git a/scripts/quality/cmake-format.sh b/scripts/quality/cmake-format.sh
index 9a1cbbf..496848a 100755
--- a/scripts/quality/cmake-format.sh
+++ b/scripts/quality/cmake-format.sh
@@ -19,7 +19,7 @@
 
 set -uo pipefail
 ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
-cd "$ROOT"
+cd "$ROOT" || exit 2
 
 # Allow ~/.local/bin (pip-installed tools) in PATH.
 export PATH="$HOME/.local/bin:$PATH"
diff --git a/scripts/quality/codespell.sh b/scripts/quality/codespell.sh
index 3e127af..ec07327 100755
--- a/scripts/quality/codespell.sh
+++ b/scripts/quality/codespell.sh
@@ -24,7 +24,7 @@
 
 set -uo pipefail
 ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
-cd "$ROOT"
+cd "$ROOT" || exit 2
 
 command -v codespell >/dev/null 2>&1 || {
     echo "FAIL: codespell not in PATH." >&2
diff --git a/scripts/quality/cppcheck.sh b/scripts/quality/cppcheck.sh
new file mode 100755
index 0000000..c584c50
--- /dev/null
+++ b/scripts/quality/cppcheck.sh
@@ -0,0 +1,97 @@
+#!/usr/bin/env bash
+# scripts/quality/cppcheck.sh
+#
+# Run cppcheck over the public headers.  Complementary to clang-tidy:
+# cppcheck has different heuristics, fewer false-positives on heavy
+# template code (CGAL/Eigen), and catches some bugs (unused includes,
+# memory leaks in detail/) that clang-tidy is bad at.
+#
+# Local-only.  Promotion to CI when the existing tree is finding-free
+# at the chosen severity level.
+#
+# Usage:
+#   bash scripts/quality/cppcheck.sh           # error+warning only
+#   bash scripts/quality/cppcheck.sh --strict  # +style, exit 1 on any
+#   bash scripts/quality/cppcheck.sh --all     # absolute everything,
+#                                                useful for diffs only
+#
+# Exit codes:
+#   0  no findings at the chosen severity, or findings but not --strict
+#   1  findings + --strict
+#   2  prerequisite missing
+
+set -uo pipefail
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+cd "$ROOT" || exit 2
+
+command -v cppcheck >/dev/null 2>&1 || {
+    echo "FAIL: cppcheck not in PATH." >&2
+    echo "        macOS: brew install cppcheck" >&2
+    echo "        Linux: sudo apt install cppcheck" >&2
+    exit 2
+}
+
+STRICT=0
+ALL=0
+for arg in "$@"; do
+    case "$arg" in
+        --strict) STRICT=1 ;;
+        --all)    ALL=1 ;;
+        *) echo "Unknown arg: $arg" >&2; exit 2 ;;
+    esac
+done
+
+ENABLE="warning"
+if [ "$STRICT" -eq 1 ]; then ENABLE="warning,style"; fi
+if [ "$ALL"    -eq 1 ]; then ENABLE="all"; fi
+
+BUILD_DIR="build-cppcheck"
+LOG="$BUILD_DIR/cppcheck.log"
+mkdir -p "$BUILD_DIR"
+
+echo "cppcheck ($(cppcheck --version 2>&1 | head -1))"
+echo "  enable:  $ENABLE"
+echo "  log:     $LOG"
+echo
+
+# Suppress noise classes that are not actionable in our project:
+#   missingIncludeSystem — CGAL/Eigen/Boost headers are intentionally
+#                          included implicitly; cppcheck cannot resolve.
+#   unmatchedSuppression — cosmetic.
+#   unusedFunction       — header-only; many `inline` helpers ARE used,
+#                          cppcheck can't see across TUs.
+#   normalCheckLevelMaxBranches — informational, not a finding.
+#
+# We point cppcheck at code/include/ only.  The deps tree is third-party
+# code and out of scope.
+
+cppcheck \
+    --enable="$ENABLE" \
+    --std=c++17 \
+    --quiet \
+    --error-exitcode=2 \
+    --inline-suppr \
+    --suppress=missingIncludeSystem \
+    --suppress=unmatchedSuppression \
+    --suppress=unusedFunction \
+    --suppress=normalCheckLevelMaxBranches \
+    -I code/include \
+    code/include 2>&1 | tee "$LOG"
+rc=$?
+
+echo
+echo "── Summary ──"
+n=$(grep -cE "\[(error|warning|style|performance|portability)\]" "$LOG" || true)
+echo "  total findings: $n"
+echo "  full log:       $LOG"
+
+if [ "$STRICT" -eq 1 ] && [ "$n" -gt 0 ]; then
+    exit 1
+fi
+if [ "$rc" -eq 2 ] && [ "$STRICT" -ne 1 ]; then
+    # cppcheck signalled "error" severity but caller didn't ask --strict.
+    echo
+    echo "NOTE: cppcheck reported an `error`-severity finding.  Even"
+    echo "      without --strict, please review the log."
+fi
+exit 0
diff --git a/scripts/quality/run-all.sh b/scripts/quality/run-all.sh
index 22d2d24..ebc2691 100755
--- a/scripts/quality/run-all.sh
+++ b/scripts/quality/run-all.sh
@@ -28,7 +28,7 @@
 
 set -uo pipefail
 ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
-cd "$ROOT"
+cd "$ROOT" || exit 2
 
 FAST=0
 [ "${1:-}" = "--fast" ] && FAST=1
@@ -39,6 +39,8 @@ GATES_FAST=(
     "clang-format drift  | bash scripts/quality/clang-format.sh"
     "cmake-format/-lint  | bash scripts/quality/cmake-format.sh"
     "codespell           | bash scripts/quality/codespell.sh"
+    "shellcheck          | bash scripts/quality/shellcheck.sh"
+    "cppcheck            | bash scripts/quality/cppcheck.sh"
     "Markdown links      | python3 scripts/check-markdown-links.py"
     "Sanitizers          | bash scripts/quality/sanitizers.sh"
     "clang-tidy          | bash scripts/quality/clang-tidy.sh"
@@ -67,6 +69,7 @@ echo "============================================================"
 
 results=""
 failed=0
+skipped=0
 i=0
 for entry in "${GATES[@]}"; do
     i=$((i + 1))
@@ -79,12 +82,21 @@ for entry in "${GATES[@]}"; do
     log="$LOG_DIR/$slug.log"
     echo
     echo "──── [$i/${#GATES[@]}] $name  ────"
-    if eval "$cmd" >"$log" 2>&1; then
+    eval "$cmd" >"$log" 2>&1
+    rc=$?
+    # Exit code 2 from any of our gate scripts = "tool not installed".
+    # Treat as SKIP rather than FAIL so a partial dev environment can
+    # still run the rest of the sweep.
+    if [ "$rc" -eq 2 ] && head -3 "$log" | grep -qE "FAIL:.*not (in PATH|installed|found)"; then
+        echo "    SKIP   (tool not installed — see $log)"
+        results="${results}  SKIP  $name  (missing tool)
+"
+        skipped=$((skipped + 1))
+    elif [ "$rc" -eq 0 ]; then
         echo "    OK     ($log)"
         results="${results}  PASS  $name
 "
     else
-        rc=$?
         echo "    FAIL (rc=$rc) — see $log"
         echo "    last 20 lines:"
         tail -20 "$log" | sed 's/^/      /'
@@ -100,5 +112,7 @@ echo "  Summary"
 echo "============================================================"
 printf "%s" "$results"
 echo
-echo "  failed: $failed / ${#GATES[@]}"
+echo "  passed:  $((${#GATES[@]} - failed - skipped)) / ${#GATES[@]}"
+echo "  skipped: $skipped     (tool not installed; gate is local-only)"
+echo "  failed:  $failed"
 exit $failed
diff --git a/scripts/quality/sanitizers.sh b/scripts/quality/sanitizers.sh
index 7334bc5..4a44559 100755
--- a/scripts/quality/sanitizers.sh
+++ b/scripts/quality/sanitizers.sh
@@ -57,11 +57,18 @@ echo "Using CXX = $CXX_BIN ($("$CXX_BIN" --version | head -1))"
 echo
 
 # ── Configure ────────────────────────────────────────────────────────────────
+# CMAKE_GTEST_DISCOVER_TESTS_DISCOVERY_MODE=PRE_TEST: without this,
+# gtest_discover_tests runs the (sanitizer-instrumented) test binary at
+# *build* time to enumerate test cases.  ASan aborts that subprocess
+# the moment it sees any allocation in static-init, which fails the
+# build before we can even get to ctest.  PRE_TEST defers discovery to
+# `ctest` invocation, which is exactly what we want.
 cmake -S code -B "$BUILD_DIR" \
     -DCMAKE_CXX_COMPILER="$CXX_BIN" \
     -DCMAKE_CXX_FLAGS="$SAN_FLAGS" \
     -DCMAKE_EXE_LINKER_FLAGS="$SAN_FLAGS" \
     -DCMAKE_BUILD_TYPE=Debug \
+    -DCMAKE_GTEST_DISCOVER_TESTS_DISCOVERY_MODE=PRE_TEST \
     -Wno-dev
 
 # ── Build the fast (non-CGAL) tests only ────────────────────────────────────
diff --git a/scripts/quality/shellcheck.sh b/scripts/quality/shellcheck.sh
new file mode 100755
index 0000000..19bec95
--- /dev/null
+++ b/scripts/quality/shellcheck.sh
@@ -0,0 +1,79 @@
+#!/usr/bin/env bash
+# scripts/quality/shellcheck.sh
+#
+# Run shellcheck across every Bash script we own (scripts/**/*.sh).
+# Skips the macOS duplicate artefacts (` 2.sh`).
+#
+# Local-only.  CI promotion once every script is shellcheck-clean.
+#
+# Usage:
+#   bash scripts/quality/shellcheck.sh             # warn + advisory exit 0
+#   bash scripts/quality/shellcheck.sh --strict    # fail on any finding
+#
+# Exit codes:
+#   0  no findings, or findings but --strict not set
+#   1  --strict was set and shellcheck reported findings
+#   2  prerequisite missing
+
+set -uo pipefail
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+cd "$ROOT" || exit 2
+
+command -v shellcheck >/dev/null 2>&1 || {
+    echo "FAIL: shellcheck not in PATH." >&2
+    echo "        macOS: brew install shellcheck" >&2
+    echo "        Linux: sudo apt install shellcheck" >&2
+    exit 2
+}
+
+STRICT=0
+for arg in "$@"; do
+    case "$arg" in
+        --strict) STRICT=1 ;;
+        *) echo "Unknown arg: $arg" >&2; exit 2 ;;
+    esac
+done
+
+FILES="$(find scripts -name "*.sh" -type f 2>/dev/null \
+    | grep -v " 2\.sh" \
+    | sort)"
+
+if [ -z "$FILES" ]; then
+    echo "FAIL: no shell scripts found under scripts/" >&2
+    exit 2
+fi
+
+echo "shellcheck ($(shellcheck --version | sed -n '2p'))"
+echo "Scanning shell scripts under scripts/"
+echo
+
+n_total=0
+n_with_findings=0
+total_findings=0
+while IFS= read -r f; do
+    [ -z "$f" ] && continue
+    n_total=$((n_total + 1))
+    # -S style: warnings + above (skip "info" and "style" noise).
+    out="$(shellcheck --severity=warning --shell=bash "$f" 2>&1)"
+    if [ -n "$out" ]; then
+        echo "── $f ──"
+        echo "$out"
+        echo
+        n_with_findings=$((n_with_findings + 1))
+        # rough count: one finding per "In <file> line N:" block
+        cnt=$(printf '%s' "$out" | grep -c "^In .* line")
+        total_findings=$((total_findings + cnt))
+    fi
+done <<EOF
+$FILES
+EOF
+
+echo "── Summary ──"
+echo "  scripts scanned:      $n_total"
+echo "  scripts with issues:  $n_with_findings"
+echo "  total findings:       $total_findings"
+
+if [ "$STRICT" -eq 1 ] && [ "$total_findings" -gt 0 ]; then
+    exit 1
+fi
+exit 0