Width and height argtypes, kdesc --argtypes from ref/, txt @define/@left_right/@columns, kdiag --check value validation (from dev d6993110e9b3)

Also: the klammertext argtype (descriptions kept as source), txt table
wrapping and :hpos/:offset, @c between ‹ ›, txt section headings, the
ktext newline-only trim, capitalize(), and the argtype test suite.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

sks/target/phases.py

@@ -25,6 +25,26 @@ def txt_vspace_marker():
 def txt_nbsp_marker():
     return "__KTEXTNBSP__"
 
+# A ZERO-WIDTH mark that says "this line is already laid out" (2026-09-16).
+# The justification pass takes a paragraph beginning with a space or the
+# nbsp marker as verbatim, and until now that was the only way a block
+# could say so -- which broke the moment a block was flush left: a @table
+# with :hpos left :offset 0 (what @columns emits) began with its first
+# cell, so its rows were re-flowed into one line.  A block that lays itself
+# out puts this at the start of every line (txt_lay_out); it is nothing to
+# txt_visible_length and is removed at the end of txt_justify_blocks.
+def txt_verbatim_marker():
+    return "__KTEXTVERBATIM__"
+
+def txt_lay_out(text):
+    """text with every line marked as already laid out."""
+    mark = txt_verbatim_marker()
+    return "\n".join(mark + line for line in text.split("\n"))
+
+def txt_is_laid_out(par):
+    """True for a paragraph the justification pass must leave alone."""
+    return par.startswith((" ", txt_nbsp_marker(), txt_verbatim_marker()))
+
 # The type-style markers, emitted by @b.txt, @i.txt, @u.txt and @ri.txt
 # (sks/font/font.k) around their text.  Plain text has no bold, but a
 # terminal does: the txt target STRIPS these in its last phase
@@ -68,7 +88,7 @@ def txt_visible_length(s):
     """How many columns s occupies once its markers resolve: a KTESC
     marker is one glyph, an nbsp marker one space, a style marker nothing.
     len() is the wrong measure for anything laid out (see txt_util)."""
-    s = _STYLE_MARKER_RGX.sub("", s)
+    s = _STYLE_MARKER_RGX.sub("", s).replace(txt_verbatim_marker(), "")
     return len(klammer_base.unescape_ktesc(s).replace(txt_nbsp_marker(), " "))
 
 def txt_wrap(text, width, subsequent_indent=""):
@@ -159,7 +179,7 @@ def txt_justify_blocks(text, K):
         # branch that had nothing to do also did not copy the text through.
         # An indented paragraph vanished from the output with no error.
         nbsp = txt_nbsp_marker()
-        if par and par[0] != ' ' and not par.startswith(nbsp):
+        if par and not txt_is_laid_out(par):
             label = re.match("(?:" + re.escape(nbsp) + r")*\[\d+\] ", par)
             par = "\n".join(txt_wrap(
                 par, int(K.Target_txt_width),
@@ -167,6 +187,7 @@ def txt_justify_blocks(text, K):
         result += par + "\n\n"
     result = re.sub(" *" + txt_vspace_marker() + " *", "\n", result)
     result = re.sub(r"\n? *" + txt_nl_marker() + r" *\n?", "\n", result)
+    result = result.replace(txt_verbatim_marker(), "")
     result = result.replace(txt_nbsp_marker(), " ")
     return result