fix: step text cursors by advance, not ink width

The date rendered as "16 /SEP /2026", each slash jammed against the
next glyph. measure() returns the ink width, which ignores leading and
trailing spaces because a space carries no ink, and clock.lua was using
it to advance a cursor. Measured: " / " covers 6px of ink but advances
14px, so every separator lost 8px.

Splits the two uses that were conflated in one function. measure() is
for centring and right-aligning, where ink width is what you want;
advance() returns x_advance and is for laying out runs of text left to
right. The clock's date now uses advance() and reads "16 / SEP / 2026"
with even gaps, verified by screenshot.

Worth the split rather than changing measure() in place: text_right is
a correct caller of the ink width, so one function cannot serve both
and silently returning the advance would have broken alignment
instead.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

3 files changed, 43 insertions, 6 deletions

diff --git a/docs/superpowers/plans/2026-09-16-conky-lua-dashboard.md b/docs/superpowers/plans/2026-09-16-conky-lua-dashboard.md
index 7d7573c..a77c30b 100644
--- a/docs/superpowers/plans/2026-09-16-conky-lua-dashboard.md
+++ b/docs/superpowers/plans/2026-09-16-conky-lua-dashboard.md
@@ -396,11 +396,31 @@ function M.text(cr, x, y, s)
   cairo_show_text(cr, s)
 end
 
--- Measured width and height of a string under the current font.
+-- One reused extents struct for every measurement, allocated at load.
+--
+-- Not per call: cairo_text_extents_t:create() leaks. 5000 allocations grow
+-- Lua's heap by ~182KB that collectgarbage() never reclaims, and calling
+-- :destroy() on each one does NOT help (measured: same 182KB either way).
+-- Reusing a single struct costs 0KB.
+local extents = cairo_text_extents_t:create()
+
+-- Ink size of a string: how much space the glyphs actually cover.
+-- Use this to CENTRE or RIGHT-ALIGN text, never to advance a cursor.
 function M.measure(cr, s)
-  local e = cairo_text_extents_t:create()
-  cairo_text_extents(cr, s, e)
-  return e.width, e.height
+  cairo_text_extents(cr, s, extents)
+  return extents.width, extents.height
+end
+
+-- How far the cursor moves after drawing a string. Use this to lay out runs of
+-- text left to right.
+--
+-- Not measure(): that returns the INK width, which ignores leading and
+-- trailing spaces because a space carries no ink. " / " measures 6px of ink
+-- against a 14px advance, so stepping a cursor by the ink width renders a
+-- segmented date as "16 /SEP /2026", each slash jammed into the next glyph.
+function M.advance(cr, s)
+  cairo_text_extents(cr, s, extents)
+  return extents.x_advance
 end
 
 -- Right-aligned text: x is the RIGHT edge.
@@ -974,7 +994,8 @@ function M.draw(cr, rect, colors)
   for _, p in ipairs(parts) do
     card.rgba(cr, p[2])
     card.text(cr, dx, dy, p[1])
-    dx = dx + card.measure(cr, p[1])
+    -- advance(), not measure(): the ink width of ' / ' omits its spaces.
+    dx = dx + card.advance(cr, p[1])
   end
 end
 
diff --git a/lib/card.lua b/lib/card.lua
index 474228d..4d94465 100644
--- a/lib/card.lua
+++ b/lib/card.lua
@@ -44,11 +44,26 @@ end
 -- values before the next call overwrites them.
 local extents = cairo_text_extents_t:create()
 
+-- Ink size of a string: how much space the glyphs actually cover.
+-- Use this to CENTRE or RIGHT-ALIGN text, never to advance a cursor.
 function M.measure(cr, s)
   cairo_text_extents(cr, s, extents)
   return extents.width, extents.height
 end
 
+-- How far the cursor moves after drawing a string. Use this to lay out runs of
+-- text left to right.
+--
+-- Not measure(): that returns the INK width, which ignores leading and
+-- trailing spaces because a space carries no ink. Stepping a cursor by the ink
+-- width collapses the gaps, and " / " measures 6px of ink against a 14px
+-- advance, so a date drawn in segments came out as "16 /SEP /2026" with each
+-- slash jammed into the next glyph.
+function M.advance(cr, s)
+  cairo_text_extents(cr, s, extents)
+  return extents.x_advance
+end
+
 -- Right-aligned text: x is the RIGHT edge.
 function M.text_right(cr, x, y, s)
   local w = M.measure(cr, s)
diff --git a/widgets/clock.lua b/widgets/clock.lua
index 10f1dd8..978715e 100644
--- a/widgets/clock.lua
+++ b/widgets/clock.lua
@@ -49,7 +49,8 @@ function M.draw(cr, rect, colors)
   for _, p in ipairs(parts) do
     card.rgba(cr, p[2])
     card.text(cr, dx, dy, p[1])
-    dx = dx + card.measure(cr, p[1])
+    -- advance(), not measure(): the ink width of ' / ' omits its spaces.
+    dx = dx + card.advance(cr, p[1])
   end
 end