kdesc --rewrite from the reflection klammerset; txt caption rules the block's width

Assembled from klammertext-dev e99530408517. The katom rewrite patterns
are rendered from ref/ (a table in dispatch order, patterns through @c),
the procedural listing having left mac/; a plain-text caption's rule is
as long as the table or listing it captions; the editor-support comments
name the tools' new dev/ location.

sks/target/phases.py

@@ -244,10 +244,29 @@ def txt_insert_captions(text, K):
     # "Listing 1", not "Listing 2".  It was one counter for every label.
     caption_numbers = {}
     width = int(K.Target_txt_width)
+    verbatim = txt_verbatim_marker()
+    def block_width(lines):
+        # The visible width of the laid-out block adjacent to a caption:
+        # its lines carry the verbatim marker, and the first line that does
+        # not (or a blank line) ends the block.
+        widest = 0
+        for line in lines:
+            if not line.startswith(verbatim) or not line.strip():
+                break
+            widest = max(widest, txt_visible_length(line))
+        return widest
     def replace(m):
         indent_run, name, text = m.groups()
         indent = len(indent_run) // len(nbsp)
         indented_width = max(1, width - indent)
+        # The block the caption belongs to: below a top caption, above a
+        # bottom one.  Its width is what the caption's rule is drawn to,
+        # so the rule under "Table 1 - Prices" is as long as the table's
+        # own rules, not as long as those words.  (Before the match sits
+        # the caption line's own verbatim marker: drop that line.)
+        after = m.string[m.end():].split("\n")[1:]
+        before = m.string[:m.start()].split("\n")[:-1]
+        block = max(block_width(after), block_width(reversed(before)))
         # An empty label means an unnumbered caption (":number false").  It
         # must NOT take a number from the sequence: a reader counting the
         # captions they can see would then find the next one a number
@@ -263,6 +282,7 @@ def txt_insert_captions(text, K):
         if txt_visible_length(caption) > indented_width:
             lines = txt_wrap(caption, indented_width)
         line_length = max(txt_visible_length(e) for e in lines)
+        line_length = max(line_length, block - indent)
         lines.append("-" * line_length)
         lead = txt_verbatim_marker() + indent_run
         # The first line's marker is already in the text, before the indent