feat: fill test coverage gaps + fix \sdcol i18n labels

- examples/subst-chain.tex: substitution walkthrough with \sdbox/\sdsubst/\sdstep
- examples/antipatterns.tex: four compile-clean-but-teach-false figures
- tests/invalid/step-outside-row.tex, empty-row.tex, undeclared-role.tex,
  two-contrast-pkg.tex: negative fixtures for package-level warnings
- test.sh: add tests/invalid/ loop
- build.sh: allow superderive-build: allow directive to suppress
  intentional warnings in antipatterns galleries
- superderive.sty: \sdcol respects [en] option for illegal/legal labels
- references/api.md: complete rewrite, all ~12 macros documented

examples/antipatterns.tex

@@ -0,0 +1,46 @@
+% Anti-patterns -- figures that compile cleanly and still teach something false.
+%   ../scripts/build.sh antipatterns.tex
+% superderive-lint: allow-multiple-contrast
+% superderive-build: allow
+\documentclass[border=10pt]{standalone}
+\usepackage[cjk]{superderive}
+
+\begin{document}
+\begin{tikzpicture}
+\sdstage{AP}{四张反例}
+\sdrow{R1}
+  % AP1: \sdsubst 只填了 from，to 也是同一个 -- 改写没有产生任何变化
+  \sdsubst[role=rewrite]{ap1}{x+y}{x+y}
+  \sdreason{ap1}{subst 的 from 和 to 相同，改写为空}
+\sdrowend
+
+\sdrow{R2}
+  % AP2: \sdcancel 划线后旁边又写了一遍同样的东西 -- 读者不知道划掉的是哪一部分
+  \sdcancel[role=cancel]{ap2a}{x+y}
+  \sdbox[role=keep]{ap2b}{x+y}
+  \sdreason{ap2a}{cancel 后面紧跟同一式子，等于没有 cancel}
+\sdrowend
+
+\sdrow{R3}
+  % AP3: 同一行里塞了五组 role，hue budget 超了
+  \sdbox[role=keep]{ap3a}{a}
+  \sdbox[role=rewrite]{ap3b}{b}
+  \sdbox[role=cancel]{ap3c}{c}
+  \sdbox[role=intro]{ap3d}{d}
+  \sdbox[role=neutral]{ap3e}{e}
+\sdrowend
+
+\sdrow{R4}
+  % AP4: 两个 contrast pair，第二个是多余的
+  \sdcol{ap4a}{x+y}{x+y}
+  \sdcol{ap4b}{a+b}{a+b}
+\sdrowend
+
+\sdbbox{all}
+\sdtopformula{F}{反例见 \texttt{references/antipatterns.md}}
+\sdmeaningbox{mb}{140mm}{all}
+  {subst from=to；cancel 后重复；row 内五色；两个 sdcol}
+  {每一行都符合语法，但每一行都在说谎}
+  {参考 antipatterns.md 的对应规则}
+\end{tikzpicture}
+\end{document}

examples/subst-chain.tex

@@ -0,0 +1,23 @@
+% Golden example -- a subst chain that must be seen, not just aligned.
+%   ../scripts/build.sh subst-chain.tex
+\documentclass[border=10pt]{standalone}
+\usepackage[cjk]{superderive}
+
+\sdsetrole{live}{sdTeal}
+
+\begin{document}
+\begin{tikzpicture}
+\sdstage{D1}{换元让积分内部对齐}
+\sdrow{R1}
+  \sdbox[role=keep]{x}{$u$}
+  \sdsubst[role=live]{s1}{u}{x^2}
+  \sdstep[role=rewrite]{s2}{\int_0^1 x\,e^{x^2}\,dx}{\tfrac12\int_0^1 e^u\,du}
+\sdrowend
+\sdbbox{all}
+\sdtopformula{F}{$\int_0^1 x\,e^{x^2}\,dx = \tfrac12\int_0^1 e^u\,du$}
+\sdmeaningbox{mb}{120mm}{all}
+  {换元是恒等改写，不改值}
+  {令 $u=x^2$，则 $du=2x\,dx$}
+  {上下限随 $u$ 一起换掉}
+\end{tikzpicture}
+\end{document}

references/api.md

@@ -1,7 +1,101 @@
-# API
+# superderive.sty API
 
-`\usepackage[cjk]{superderive}` or `[en]`.
+```tex
+\documentclass[border=10pt]{standalone}
+\usepackage[cjk]{superderive}     % cjk: ctex + fandol (XeLaTeX). en: English meaning-box and sdcol labels.
+```
 
-Layout: `\sdstage{n}{text}` `\sdrow[height]{name}` … `\sdrowend` `\sdbbox{all}` `\sdtopformula{F}{math}`.
+Build with `./scripts/build.sh fig.tex` — it puts `assets/` on `TEXINPUTS`, so the package
+does not need to be installed into your texmf tree.
 
-Call `\sdtopformula` after the last `\sdrowend`.
+The build first runs `scripts/lint.py`. It rejects raw TikZ drawing, a formula placed
+before the last row, more than one `\sdcol` contrast pair, and more than four active hue
+families in the figure. Intentional galleries/tests may put
+`% superderive-lint: allow-raw-tikz` near the top; do not add an exemption to a
+deliverable merely to make it pass.
+
+## Ledgers
+
+```tex
+\sdsetrole{keep}{sdTeal}        % role -> color. Macros take a ROLE, never a color.
+\sdsetlabels{Idea}{Rewrite}{Caveat}  % override the three meaning-box rail labels
+```
+
+Colors: `sdTeal sdOrange sdCoral sdViolet sdGray sdInk`. An unknown role falls back to
+gray **and emits a package warning**, which `build.sh` turns into a failed build.
+Redeclaring a role with the same value is harmless; changing its value emits a warning
+and keeps the original mapping.
+
+## Flow layout
+
+**This is the default.** `\sdrow` opens a band, every object inside is placed at the
+cursor, `\sdrowend` closes it. Hand-written offsets are the main source of layout bugs.
+
+```tex
+\sdstage{D1}{stage heading}       % on the left rail, below the previous band
+\sdrow[16mm]{R1}                  % open a band; height default is 16mm
+  \sdbox[role=keep]{x}{$u$}      % existing term, kept as-is
+  \sdsubst[role=live]{s1}{$u$}{$x^2$}     % from->to with a strike on the from
+  \sdstep[role=rewrite]{s2}{QK^\top}{QK^\top/\sqrt{d_k}}  % lhs -> rhs
+  \sdreason{s1}{§3.2.1}          % justification note, anchored to s1
+\sdrowend                         % fit the band
+```
+
+| macro | does |
+|---|---|
+| `\sdstage{name}{text}` | stage heading on the left rail, below all ink so far |
+| `\sdrow[height]{name}` | open a band; optional height defaults to 16mm |
+| `\sdrowend` | `fit` the band, warn if empty, close it |
+| `\sdstep[keys]{name}{lhs}{rhs}` | one rewrite step: two term boxes with an arrow |
+| `\sdcancel[keys]{name}{math}` | one term, struck through |
+| `\sdsubst[keys]{name}{from}{to}` | from-term struck through, to-term in role hue |
+| `\sdbox[keys]{name}{math}` | plain term, no arrow, no strike |
+| `\sdreason{step-name}{text}` | justification note anchored to a named step |
+| `\sdcol{name}{illegal}{legal}` | one contrast pair per figure — second is a warning |
+| `\sdbbox{all}` | everything drawn so far, as one node, for `\sdmeaningbox` |
+| `\sdtopformula{F}{math}` | the claim line, centered on what was actually drawn |
+| `\sdtrack{node}` | fold a hand-placed node into the bbox and the vertical cursor |
+| `\sdvgap{4mm}` / `\sdgap{4mm}` | one-off extra space, vertical / horizontal |
+| `\sdleftrail{x}` / `\sdlayoutreset` | move the rail / start over |
+
+### Keys for step/cancel/subst/box
+
+| key | default | meaning |
+|---|---|---|
+| `role=` | `rewrite` for step/subst, `cancel` for cancel, `keep` for box | hue, via `\sdsetrole` |
+| `level=` | `2` | lightness level 0–3 for the fill |
+| `gap=` | `\sdgutter` | space *before* this object; `gap=0pt` = exactly adjacent |
+
+Authors can declare their own roles: `\sdsetrole{live}{sdTeal}`.
+
+## Contrast column
+
+`\sdcol{name}{illegal}{legal}` draws two boxes side by side: the left in `sdCoral!30`
+struck, labelled **illegal** (or **非法** in `[cjk]` mode — never both); the right in
+`sdTeal!30`, labelled **legal** (or **合法**). The budget is **one per figure**; a second
+`\sdcol` triggers a package warning → build failure.
+
+## Bottom
+
+```tex
+\sdbbox{all}
+\sdtopformula{F}{$\mathrm{Attention}(Q,K,V)=\mathrm{softmax}(QK^\top/\sqrt{d_k})V$}
+\sdmeaningbox{mb}{120mm}{all}{Idea text}{Rewrite text}{Caveat text}
+\sdsignature{scaled-dot-product attention}{mb}   % optional
+```
+
+Arg 2 of `\sdmeaningbox` is the total box width; arg 3 is the node it hangs below.
+Arg 4/5/6 are the three rail rows; an empty `{}` row is dropped.
+
+`\sdsignature` renders only its subject; it has no author or handle mechanism. Its node
+is named `(#2-sig)` from the anchor.
+
+## Gotchas
+
+- `\sdrow`, `\sdrowend`, `\sdstage` must appear outside any other flow object.
+- A band that overflows its declared height triggers `Package superderive Warning` →
+  build failure.
+- `\sdcheckrole` never redefines an existing role. Use `\sdsetrole{name}{newColor}`
+  to change the mapping for subsequent figures in the same document.
+- `\sdcol` labels are **not** customizable via `\sdsetlabels` — they depend only on the
+  package option `[en]`/`[cjk]`.

scripts/build.sh

@@ -35,10 +35,14 @@ if grep -qE "^(Overfull|Underfull) \\\\[hv]box" "$LOG"; then
   status=1
 fi
 if grep -q "Package superderive Warning" "$LOG"; then
+  if grep -q "^% superderive-build: allow" "$SRC"; then
+    echo "   superderive warnings present (suppressed by superderive-build: allow)" >&2
+  else
     echo "!! superderive warnings:" >&2
     grep -m5 -A2 "Package superderive Warning" "$LOG" >&2
     status=1
   fi
+fi
 
 if command -v pdftocairo >/dev/null 2>&1; then
   echo "==> exporting svg / png"

scripts/test.sh

@@ -22,6 +22,16 @@ for f in "$ROOT"/tests/lint-invalid/*.tex; do
     echo "  ok    $name (rejected by lint)"
   fi
 done
+for f in "$ROOT"/tests/invalid/*.tex; do
+  [[ -e "$f" ]] || continue
+  name="$(basename "$f")"
+  if "$ROOT/scripts/build.sh" "$f" >/dev/null 2>&1; then
+    echo "  FAIL  $name (invalid fixture built)"
+    fail=$((fail+1))
+  else
+    echo "  ok    $name (rejected by package/build)"
+  fi
+done
 if [[ $fail -gt 0 ]]; then
   echo "$fail failing check(s)" >&2
   exit 1

tests/invalid/empty-row.tex

@@ -0,0 +1,5 @@
+\usepackage[en]{superderive}
+\begin{document}\begin{tikzpicture}
+\sdrow{R1}
+\sdrowend
+\end{tikzpicture}\end{document}

tests/invalid/step-outside-row.tex

@@ -0,0 +1,4 @@
+\usepackage[en]{superderive}
+\begin{document}\begin{tikzpicture}
+\sdstep{s1}{a}{b}
+\end{tikzpicture}\end{document}

tests/invalid/two-contrast-pkg.tex

@@ -0,0 +1,7 @@
+\usepackage[en]{superderive}
+\begin{document}\begin{tikzpicture}
+\sdrow{R1}
+  \sdcol{c1}{a}{b}
+  \sdcol{c2}{c}{d}
+\sdrowend
+\end{tikzpicture}\end{document}

tests/invalid/undeclared-role.tex

@@ -0,0 +1,6 @@
+\usepackage[en]{superderive}
+\begin{document}\begin{tikzpicture}
+\sdrow{R1}
+  \sdbox[role=nosuch]{a}{x}
+\sdrowend
+\end{tikzpicture}\end{document}