Images in plain text and the terminal; bounded build parallelism (from dev 16f82cc887af)

- @image under txt and ansi is a picture in characters, in five styles
  (Image_txt_style: halfblock the default, shade, ascii, quadrant,
  braille), sized to the terminal's width less a margin when ktext runs
  in one, every cell in its own colours under ansi; a figure's caption
  is centred under it and no txt caption is ruled off any more.
- The build compiles as many files at once as the machine has cores
  (JOBS; make -C com JOBS=1 for a small machine): the sub-makes' bare -j
  meant unlimited parallelism and exhausted 8 GB machines. The three
  install pages say "make -C com".

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

sks/target/phases.py

@@ -75,20 +75,43 @@ _STYLE_MARKER_RGX = re.compile(
     "|".join(re.escape(txt_style_marker(s, on))
              for s in TXT_STYLES for on in (True, False)))
 
+# A COLOUR marker carries its colour: __KTEXTFG<rrggbb>__ opens a foreground
+# colour, __KTEXTFGOFF__ restores the default (SGR 39, never a blanket reset).
+# Used by @image under txt/ansi (2026-09-27, Andy's terminal images): the
+# character carries the luminance and the colour the hue, so stripping the
+# escapes still leaves a monochrome picture -- the invariant kept.
+def txt_color_marker(rgb=None, background=False):
+    """A foreground colour marker, or with background=True a background one
+    (__KTEXTBG<rrggbb>__ / __KTEXTBGOFF__, SGR 48;2 and 49): the quadrant
+    and halfblock image styles set two colours per cell."""
+    ground = "BG" if background else "FG"
+    if rgb is None:
+        return f"__KTEXT{ground}OFF__"
+    r, g, b = rgb
+    return f"__KTEXT{ground}{int(r):02X}{int(g):02X}{int(b):02X}__"
+
+_COLOR_MARKER_RGX = re.compile(r"__KTEXT(FG|BG)(?:([0-9A-F]{6})|OFF)__")
+
 def txt_strip_styles(text, K):
-    return _STYLE_MARKER_RGX.sub("", text)
+    return _COLOR_MARKER_RGX.sub("", _STYLE_MARKER_RGX.sub("", text))
 
 def ansi_resolve_styles(text, K):
     for style, (on, off) in TXT_STYLES.items():
         text = text.replace(txt_style_marker(style), on)
         text = text.replace(txt_style_marker(style, False), off)
-    return text
+    def color(m):
+        ground, hex6 = m.group(1), m.group(2)
+        code = 38 if ground == "FG" else 48
+        if hex6 is None:
+            return f"\033[{code + 1}m"       # 39 / 49: the default fore-/background
+        return f"\033[{code};2;{int(hex6[0:2], 16)};{int(hex6[2:4], 16)};{int(hex6[4:6], 16)}m"
+    return _COLOR_MARKER_RGX.sub(color, text)
 
 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).replace(txt_verbatim_marker(), "")
+    s = _COLOR_MARKER_RGX.sub("", _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=""):
@@ -257,6 +280,10 @@ def txt_insert_captions(text, K):
         return widest
     def replace(m):
         indent_run, name, text = m.groups()
+        # The name may carry flags after "+": "center" sets the caption
+        # centred on its block (a figure's, as in html and tex).
+        name, _, flags = name.partition("+")
+        centered = "center" in flags.split("+")
         indent = len(indent_run) // len(nbsp)
         indented_width = max(1, width - indent)
         # The block the caption belongs to: below a top caption, above a
@@ -278,12 +305,16 @@ def txt_insert_captions(text, K):
         else:
             caption = text
         # Visible widths throughout: a caption may carry style markers.
+        # NO RULE under (or over) a caption: none of the targets draws one
+        # (Andy, 2026-09-28 -- the rule this pass drew since 2026-08 was a
+        # txt invention; a table's rules are its own :hline, a listing's its
+        # own frame).  A centred caption is set on the block's width.
         lines = [caption]
         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)
+        if centered:
+            measure = max(block - indent, max(txt_visible_length(e) for e in lines))
+            lines = [" " * max(0, (measure - txt_visible_length(e)) // 2) + e for e in lines]
         lead = txt_verbatim_marker() + indent_run
         # The first line's marker is already in the text, before the indent
         # run this match begins with (add_caption); the others get theirs.