Verbatim-safe typography, ^-punctuation quoting, full-range ^UUUU^, polyglot html

Typographic transforms (---, quote pairs, ~) no longer touch verbatim
text: @c/@code/@source_listing content and ^'...'^ spans show exactly the
characters written. "^" before any punctuation character quotes it in
every target (the apostrophe excepted: ^' opens a literal span), with the
new :resolve option on @@@target declaring per-target renderings. The
^UUUU^ code-point form accepts 4-6 hex digits, the full Unicode range.
The html output and transform spellings are polyglot (XML-valid), in
preparation for an EPUB target. New suites: transform_test, character_test
(engine), typography_test (SKS).

(from dev 07ce5ea86a0a)

tst/escape_test.sh

@@ -183,6 +183,33 @@ check_eq "25. a real literal klammer still works after a comment naming it" \
 
 rm -f "$ERR"
 
+echo
+echo "-- 26-29: a general body escapes only its OWN literal text, never a --"
+echo "-- substituted argument value (ordering defect fixed 2026-08-19)    --"
+# An argument value is writer text already escaped at the top level (KTESC
+# markers, idempotent) PLUS final target markup from klammers the writer
+# nested in the argument.  apply_klammer used to substitute values first and
+# escape the general body after, so that markup was swept as if it were the
+# body's literal text: "@sig @b Andy @ @" emitted BSLtextbf{Andy}.  The escape
+# now runs before substitution.  BOLD is a target-specific nested klammer
+# (case 7/9 pattern) whose raw output must survive untouched.
+BOLD='@@b.k s : d @@ @@b.t :: \textbf{*s*} @@'
+check_eq "26. substituted klammer output NOT re-escaped" \
+    'Sincerely, \textbf{Andy}' --klammersets none -t t \
+    -s "$T $BOLD @@sig name : Sincerely, *name* @@ @sig @b Andy @ @"
+check_eq "27. ... while the body's own literal & still IS escaped" \
+    'Fish AMP \textbf{Chips}' --klammersets none -t t \
+    -s "$T $BOLD @@sig2 name : Fish & *name* @@ @sig2 @b Chips @ @"
+check_eq "28. writer specials in the argument still escaped (markers)" \
+    'Sincerely, a AMP b' --klammersets none -t t \
+    -s "$T @@sig name : Sincerely, *name* @@ @sig a & b @"
+# The variable shares one text katom with literal specials on both sides:
+# the katom's literal "_"s must be escaped and the value spliced in raw
+# afterwards -- the ordering this section exists to pin.
+check_eq "29. mixed katom: literal specials escaped, spliced value raw" \
+    'AUND\textbf{Q}UNDB' --klammersets none -t t \
+    -s "$T $BOLD @@w s : A_*s*_B @@ @w @b Q @ @"
+
 echo
 echo "============================================"
 echo "Results: ${green}$PASS passed${reset}, ${red}$FAIL failed${reset}"