pin deps/plotter: per-column x axes, tighter cell gap; docs

docs/claude/invariants-plot-and-layout.md

@@ -134,9 +134,16 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
     per figure row**: `row N` with N the 1-based figure row for a split row, and the 0-based plot index
     for an unsplit row (the pane read that before splitting existed). Readouts and measurements stay per
     trace and per plot index; only the axis is shared.
-  - **Bottom-row x labels only.** The plotter gives every plot that is not in the last figure row
-    `XStrip::None`; the cells of the bottom row each keep their strip, so a middle-drag on the axis
-    works in any of them. The `t0` caption goes on those cells too.
+  - **The x axis is the bottom row's for every run of rows with the same columns.** A figure row gets
+    `XStrip::None` only if the row directly below has the same columns (same cell count and same
+    normalised cell weights); a row whose columns differ keeps its own strip under each of its cells
+    (`[1][2]/[3]` has axes on 1, 2 and 3), because the axis below is at another width and scale. The
+    rule is structural and transitive, never a function of content. Every cell that carries a strip is
+    a place a middle-drag on the axis works. The `t0` caption belongs on every cell that carries a strip,
+    not only the last figure row's.
+  - **The right gutter is the last cell's.** In a split row with a shared y the plotter gives
+    `right_gutter` to the last cell alone and takes it off the row like the y gutter, so the visible gap
+    between two plots is `col_gap` and equal weights give equal axes widths.
   - **One left gutter, on the first cell only.** The y gutter is one maximum for the whole figure with the
     same reserved floor as before (`Figure::set_min_y_gutter()`). It is carried by the first cell of each
     row alone: `Figure::layout` gives every other cell `YStrip::None` from its column index (structurally,