Harden \stgroup and tighten the callout budget (review follow-up)

- Bracket ink is part of the fit: \st@facebody drops -inkw/-inke extreme
  coordinates and \stface/\ststack register them with the enclosing
  group/col/row fit, so a group outline can no longer be crossed by a
  member's bracket arms
- \stlink inside \stgroup or \stcol is now a package error: sub-flow
  members never terminate a pending connector, so the arrow was dropped
  silently while the label still rendered
- \stgroup requires role= (explicit role=neutral for mixed groups) and
  must bind at least two members or one \stcol partition; a lone stack
  or face inside a group is a dirty-build warning
- lint: default budget is one \stcallout per figure; the
  allow-multiple-callouts directive relaxes it to one per band
- build.sh: clean-build hint no longer names hue budget (lint owns it)
- tests/group-callout.tex reworked: multi-member group with a bracketed
  member as a regression probe, single callout; new negative fixtures
  group-link, group-norole, group-single, callout-budget
- api.md, checklist.md, style.md, layout.md, SKILL.md updated to match

tests/group-callout.tex

@@ -1,7 +1,9 @@
 % Regression test for \stgroup and \stcallout.
-%   - a group over one stack (the three sheets are one composite object),
-%   - a group over two adjacent shards (the pair is one partitioned parent),
-%   - a side card hanging off the right edge of each band.
+%   - a group over three adjacent head faces (the trio is one composite q);
+%     the first face carries bracket=true, probing that bracket ink is part
+%     of the group's fit -- the outline must clear the bracket arms,
+%   - a group over a \stcol partition (two shards tiling one parent W),
+%   - one side card for the whole figure, hanging off a finished band.
 % No absolute coordinate appears anywhere in this figure.
 %   ../scripts/build.sh group-callout.tex
 \documentclass[border=10pt]{standalone}
@@ -9,9 +11,7 @@
 
 \stsetrole{act}{stTeal}
 \stsetrole{w}{stOrange}
-\stsetrole{q}{stTeal}
-\stsetrole{k}{stViolet}
-\stsetrole{v}{stCoral}
+\stsetrole{q}{stViolet}
 
 \stdim{T}{7}
 \stdim{d}{5}
@@ -20,27 +20,18 @@
 \begin{document}
 \begin{tikzpicture}
 
-\ststage{S1}{一、分组框：把已经排好的面命名为一个复合对象}
+\ststage{S1}{一、分组框：三个相邻的头合起来是一个复合对象}
 \strow{R1}{T}
   \stface[role=act, bracket=true]{X}{}{T}{d}
-  \stlink{l1}{三路投影}
+  \stlink{l1}{按头切分}
   \stgroup[role=q]{QG}
-    \ststack[role=q]{Q}{}{T}{dh}{3}
-  \stgroupend
-  \stgroup[role=k]{KG}
-    \ststack[role=k]{K}{}{T}{dh}{3}
-  \stgroupend
-  \stgroup[role=v]{VG}
-    \ststack[role=v]{V}{}{T}{dh}{3}
+    \stface[role=q, bracket=true]{Q1}{}{T}{dh}
+    \stface[role=q, gap=2mm]{Q2}{}{T}{dh}
+    \stface[role=q, gap=2mm]{Q3}{}{T}{dh}
   \stgroupend
 \strowend
 \stcaption{X}{$\mathbf X$}{$T\times d$}
 \stcaption{QG}{$\mathbf q$}{$h\times T\times d_h$}
-\stcaption{KG}{$\mathbf k$}{$h\times T\times d_h$}
-\stcaption{VG}{$\mathbf v$}{$h\times T\times d_h$}
-\stcallout{N1}{4.2cm}{R1}{分组框在说什么}%
-  {外框与里面的面同色，因为它圈的是同一个对象的多头视图，不是一个新张量。
-   框的内边距计入行的包围盒，所以下面的符号轨仍然从框底起算。}
 
 \ststage{S2}{二、分组框圈住两片相邻的分片，标注它们合起来是谁}
 \strow{R2}{T}
@@ -58,8 +49,10 @@
 \stcaption{H}{$\mathbf H$}{$T\times d$}
 \stcaption{WG}{$\mathbf W$}{$d\times T$}
 \stcaption{Z}{$\mathbf Z$}{$T\times T$}
-\stcallout{N2}{4.2cm}{R2}{一行一张卡}%
-  {同一个 band 上挂两张卡会被 lint 拒绝：并排的说明卡是仪表盘，不是图。}
+\stcallout{N1}{4.2cm}{R2}{分组框在说什么}%
+  {外框与成员同色，因为它圈的是同一个对象的分片视图，不是一个新张量。
+   括号等装饰墨迹也计入外框的包围盒，所以框永远不会被成员的括号穿过；
+   整张图默认只允许一张这样的卡片，再多就是仪表盘。}
 
 \sttopformula{F}{$\displaystyle \mathbf Z=\mathbf H\,\mathbf W,\qquad
   \mathbf W=\begin{bmatrix}\mathbf W_a\\ \mathbf W_b\end{bmatrix}$}
@@ -69,10 +62,9 @@
   {$T$ 序列长，$d$ 模型维，$d_h$ 头宽，$h$ 头数}
   {}
   {分组框是横向的子流：成员写在块里，所以它只能圈住相邻的对象；
-   两侧的内边距各占一份宽度，箭头也接在外框上而不是成员上——
-   否则连接线会穿过一个并非自己端点的框。
-   说明卡挂在 band 右侧，并把纵向游标压到自己底边以下，所以卡片过高只会撑开空白，
-   不会压住下一段。}
+   它必须绑定至少两个成员或一个 \texttt{stcol} 分片，单个对象外再画框是装饰。
+   连接线不能在框内起止——\texttt{stlink} 写在组里是构建错误，
+   闭合后箭头接在外框上，而不是穿过一个并非自己端点的边。}
 
 \end{tikzpicture}
 \end{document}

tests/invalid/group-link.tex

@@ -0,0 +1,16 @@
+% \stlink inside a group: members never terminate a pending connector, so the
+% arrow would be dropped silently. The package must error rather than build a
+% figure whose label appears but whose arrow does not.
+\documentclass[border=2pt]{standalone}
+\usepackage[en]{supertensor}
+\stsetrole{x}{stTeal}
+\stdim{T}{4}
+\begin{document}\begin{tikzpicture}
+  \strow{R1}{T}
+    \stgroup[role=x]{G}
+      \stface[role=x]{A}{}{T}{T}
+      \stlink{l1}{lost arrow}
+      \stface[role=x]{B}{}{T}{T}
+    \stgroupend
+  \strowend
+\end{tikzpicture}\end{document}

tests/invalid/group-norole.tex

@@ -0,0 +1,14 @@
+% A group with no role would silently fall back to neutral gray, violating
+% the "outline in the composite's own hue" rule. The package must error.
+\documentclass[border=2pt]{standalone}
+\usepackage[en]{supertensor}
+\stsetrole{x}{stTeal}
+\stdim{T}{4}
+\begin{document}\begin{tikzpicture}
+  \strow{R1}{T}
+    \stgroup{G}
+      \stface[role=x]{A}{}{T}{T}
+      \stface[role=x]{B}{}{T}{T}
+    \stgroupend
+  \strowend
+\end{tikzpicture}\end{document}

tests/invalid/group-single.tex

@@ -0,0 +1,13 @@
+% A group around a single object is decoration: the stack already reads as
+% one composite. The package must reject this with a dirty-build warning.
+\documentclass[border=2pt]{standalone}
+\usepackage[en]{supertensor}
+\stsetrole{x}{stTeal}
+\stdim{T}{4}
+\begin{document}\begin{tikzpicture}
+  \strow{R1}{T}
+    \stgroup[role=x]{G}
+      \ststack[role=x]{Q}{}{T}{T}{3}
+    \stgroupend
+  \strowend
+\end{tikzpicture}\end{document}

tests/lint-invalid/callout-budget.tex

@@ -0,0 +1,17 @@
+% One card per band, but a card on EVERY band, is still a dashboard. The
+% default budget is one callout per figure; this must fail lint without the
+% allow-multiple-callouts exemption.
+\documentclass{standalone}
+\usepackage[en]{supertensor}
+\stdim{T}{4}
+\begin{document}\begin{tikzpicture}
+  \strow{R1}{T}
+    \stface{A}{}{T}{T}
+  \strowend
+  \stcallout{N1}{3cm}{R1}{first}{one per figure}
+  \strow{R2}{T}
+    \stface{B}{}{T}{T}
+  \strowend
+  \stcallout{N2}{3cm}{R2}{second}{this one belongs in the meaning box}
+  \sttopformula{F}{$A,B$}
+\end{tikzpicture}\end{document}