fix(11.1-07): check go fences, README src= and shell fences from the AST

- goLang follows the highlighter's chroma lookup, so golang and main.go need src=
- a src= fence in a module README is refused and never captioned
- shell fences inside callouts and lists are command-checked
- a fence with four or more leading spaces is an indented code block

internal/docsite/check_policy.go

@@ -2,7 +2,6 @@ package docsite
 
 import (
 	"fmt"
-	"regexp"
 	"slices"
 	"strings"
 
@@ -12,52 +11,63 @@ import (
 // calloutTypes are the only `> [!TYPE]` callouts the theme renders.
 var calloutTypes = []string{"NOTE", "TIP", "WARNING"}
 
-// calloutMarker matches the first line of a callout blockquote.
-var calloutMarker = regexp.MustCompile(`^\s{0,3}>\s?\[!([A-Za-z]+)\]\s*$`)
-
 // checkPolicy enforces the page content rules:
-//   - every go fence in a docs/ page carries src= (module READMEs are
-//     rendered as written, D-18);
+//   - every Go-lexer fence in a docs/ page carries src=, at any depth
+//     (module READMEs are rendered as written, D-18);
 //   - callouts are NOTE, TIP or WARNING;
 //   - docs/ headings are plain ASCII text without links or code spans.
-func (s *site) checkPolicy(docs []parsedDoc) []Problem {
+func (s *site) checkPolicy(docs []parsedDoc) ([]Problem, error) {
 	var problems []Problem
 	for _, d := range docs {
 		if d.page == nil {
 			continue
 		}
 		guide := d.page.Module == ""
-		lines := strings.Split(string(d.body), "\n")
-		fences := scanFences(lines)
-		inFence := make([]bool, len(lines))
-		for _, f := range fences {
-			end := f.close
-			if end < 0 {
-				end = len(lines) - 1
+		if guide {
+			fences, err := collectFences(d.doc, d.body)
+			if err != nil {
+				return nil, err
 			}
-			for i := f.open; i <= end; i++ {
-				inFence[i] = true
-			}
-			fields := strings.Fields(f.info)
-			if guide && len(fields) > 0 && fields[0] == "go" &&
-				!slices.ContainsFunc(fields[1:], func(f string) bool { return strings.HasPrefix(f, "src=") }) {
-				problems = append(problems, Problem{File: d.file, Line: d.line + f.open, Rule: "snippet",
-					Message: "go code block has no src= reference"})
-			}
-		}
-		for i, line := range lines {
-			if inFence[i] {
-				continue
-			}
-			if m := calloutMarker.FindStringSubmatch(line); m != nil && !slices.Contains(calloutTypes, m[1]) {
-				problems = append(problems, Problem{File: d.file, Line: d.line + i, Rule: "callout",
-					Message: fmt.Sprintf("unknown type %s (use NOTE, TIP or WARNING)", m[1])})
+			for _, f := range fences {
+				if _, hasSrc := ParseSrc(f.info); goLang(f.lang) && !hasSrc {
+					problems = append(problems, Problem{File: d.file, Line: d.line + f.line, Rule: "snippet",
+						Message: f.lang + " code block has no src= reference"})
+				}
 			}
 		}
+		problems = append(problems, calloutProblems(d)...)
 		if guide {
 			problems = append(problems, headingProblems(d)...)
 		}
 	}
+	return problems, nil
+}
+
+// calloutProblems reports blockquotes whose marker is not NOTE, TIP or
+// WARNING. calloutTransformer has already turned the known types into
+// callout nodes, so a remaining blockquote with a marker is unknown.
+// The marker is read from the AST, so a copy of it inside a code fence
+// is not a callout.
+func calloutProblems(d parsedDoc) []Problem {
+	var problems []Problem
+	_ = gast.Walk(d.doc, func(n gast.Node, entering bool) (gast.WalkStatus, error) {
+		bq, ok := n.(*gast.Blockquote)
+		if !entering || !ok {
+			return gast.WalkContinue, nil
+		}
+		para, ok := bq.FirstChild().(*gast.Paragraph)
+		if !ok || para.Lines().Len() == 0 {
+			return gast.WalkContinue, nil
+		}
+		first := para.Lines().At(0)
+		m := calloutLine.FindStringSubmatch(strings.TrimSpace(string(first.Value(d.body))))
+		if m == nil || slices.Contains(calloutTypes, m[1]) {
+			return gast.WalkContinue, nil
+		}
+		problems = append(problems, Problem{File: d.file, Line: lineOf(d.body, first.Start, d.line), Rule: "callout",
+			Message: fmt.Sprintf("unknown type %s (use NOTE, TIP or WARNING)", m[1])})
+		return gast.WalkContinue, nil
+	})
 	return problems
 }