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

docs/claude/build-and-run.md

@@ -279,8 +279,12 @@ number of *figure rows* (the host's `RowSet::row_count()` is the plot count, `fi
 rows). `plot(i)`, `link_x()` and the crosshair's hovered index all take the **flattened** plot index.
 Cell widths use the height scheme: a floor of **64 px logical** per cell, the weights share the rest,
 the last cell closes the row exactly, and a figure too narrow for the floors shrinks the cells
-proportionally and drops the column gap. Only the bottom row's cells carry x labels and the x title
-(every other plot gets `XStrip::None`), and the left y gutter stays one maximum over the whole figure.
+proportionally and drops the column gap. The x labels and title follow the **column structure**: a row
+hides its x strip (`XStrip::None`) only when the row directly below has the *same columns* (same cell
+count, same normalised cell weights within 1e-4, empty weights = equal), so `[1][2]/[3][4]` has an axis
+under 3 and 4 only while `[1][2]/[3]` has one under 1, 2 and 3; the rule is structural, transitive down a
+chain and decided before the measurement pass (`same_columns()` in `figure.cpp`); `set_x_labels_only_on_bottom(false)`
+labels every row. The left y gutter stays one maximum over the whole figure.
 
 The cells of a figure row can **share one y range**, symmetric to the x link
 (`docs/superpowers/specs/2026-11-03-split-shared-y-design.md`):
@@ -303,6 +307,11 @@ The cells of a figure row can **share one y range**, symmetric to the x link
   share the rest by the existing `floor + extra * w / total` rule, the floors applying to plot widths.
   Equal weights give equal plot areas; the first cell's rect is gutter plus its plot width and the rects
   still tile the row exactly.
+- **The right gutter belongs to the last cell.** In a shared-y split row only the last cell gets
+  `set_right_gutter()`; it is taken off the row beside the y gutter (capped so both fit in half the row
+  and never beyond the figure's right gutter) and the last cell's rect grows right by it. The gap between
+  two plot frames is then exactly `col_gap` rather than `col_gap` plus a gutter; unsplit rows and rows
+  with sharing off lay out as before (`figure_split_row_gap_*`, `figure_row_gutter_without_sharing_is_the_old_layout`).
 
 In the GTK4 and GLFW adapters the pointer is routed by **cell rect** (`row_in(rows, x, y)`: the
 containing cell, else the nearest by squared distance), one `input::Controller` per plot. The tests are

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,