docs: split rows share one y axis

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/claude/probe-readings.md

@@ -2853,19 +2853,19 @@ inside the panel does not close it), `click_outside_closes=1` (a click on the pl
 
 ```
 [split-probe] start          plots=1 frows=1 cells=[1] widths=[756] tile=1 x_equal=1 cursors_aligned=1 weights=[-] traces=[1:sine,square,ramp,noise]
-[split-probe] split          plots=2 frows=1 cells=[2] widths=[376,376] tile=1 x_equal=1 cursors_aligned=1 weights=[-] traces=[1a:sine|1b:square]
-[split-probe] weights 3:1    plots=2 frows=1 cells=[2] widths=[533,220] tile=1 x_equal=1 cursors_aligned=1 weights=[3,1] traces=[1a:sine|1b:square]
+[split-probe] split          plots=2 frows=1 cells=[2] widths=[403,350] tile=1 x_equal=1 cursors_aligned=1 weights=[-] traces=[1a:sine|1b:square]
+[split-probe] weights 3:1    plots=2 frows=1 cells=[2] widths=[546,207] tile=1 x_equal=1 cursors_aligned=1 weights=[3,1] traces=[1a:sine|1b:square]
 [split-probe] caps-calls      insert_cell=[1,1,0] refused_cell=1 insert_row=[1,1,0] refused_row=1 plots=8
 [split-probe] roundtrip       rt=1 expect=r0(h=2.0000)[w=1.0000:sine] r1(h=1.0000)[w=3.0000:square][w=1.0000:ramp] got=r0(h=2.0000)[w=1.0000:sine] r1(h=1.0000)[w=3.0000:square][w=1.0000:ramp]
 [split-probe] ruler-labels    split=[row 1,row 2] mixed=[row 0,row 2]
 [split-probe] shared-y        y_shared=1 y_gutter=1 y_fit=1 ruler_mirror=1 ranges=[A=-3.000000..7.000000 B=-3.000000..7.000000 | fit A=-1.04..1.04 B=-1.04..1.04 data=-1..1] axes_w=[642.4,642.4] auto=1
 ```
 
-`UDPSCOPE_PROBE_SPLIT_MS` (stderr; see [verification.md](verification.md)). Nineteen steps, 250 ms apart;
+`UDPSCOPE_PROBE_SPLIT_MS` (stderr; see [verification.md](verification.md)). 23 steps, 250 ms apart;
 each restructures and the *next* step reports the frame that was laid out with it, so a line's label
 names the arrangement the line **reads**, not the call that made it. The state lines share one format:
 `plots` (`row_count()`), `frows` (`figure_row_count()`), `cells=[..]` (per figure row), `widths=[..]`
-(logical pixels of each cell, `|` between rows), `weights=[..]` (the stored cell weights, `-` for a row with
+(logical pixels of each cell rect, `|` between rows; the first cell's rect includes the row's y gutter, ~52 px here, and the others have none, so equal weights read `[403,350]` -- equal *plot* widths, not equal rects), `weights=[..]` (the stored cell weights, `-` for a row with
 none), `traces=[label:signals|..]` with the labels `plot_label()` gives (`1`, `1a`, `2b`). Every state line
 carries the same three assertions:
 
@@ -2879,22 +2879,22 @@ The other lines, in order:
 
 | line | value it must read | the defect a wrong reading names |
 | --- | --- | --- |
-| `start` / `split` | `cells=[1]` then `[2]` with `widths=[376,376]` (equal halves of 756) and the traces on `1a`/`1b`; a second cell starts **empty**, the probe assigns it | a split that moved or dropped the first cell's traces, or unequal default cells |
-| `weights 3:1` | `widths=[533,220]`, **not** 3:1, and `tile=1` | not a defect: the plotter's 64 px floor per cell is taken off first and the weights share the remainder, so the shares read compressed; a result of exactly 3:1 would be the floor missing |
+| `start` / `split` | `cells=[1]` then `[2]` with `widths=[403,350]` (equal plot widths of 350.4 px; the first rect is 52 px wider by the y gutter it alone carries) and the traces on `1a`/`1b`; a second cell starts **empty**, the probe assigns it | a split that moved or dropped the first cell's traces, or unequal default plot widths (`[376,376]` is the pre-sharing reading: a second cell that still has its own gutter) |
+| `weights 3:1` | `widths=[546,207]`, **not** 3:1, and `tile=1` | not a defect: the row's y gutter and the plotter's 64 px floor per plot are taken off first and the weights share the remainder, so the shares read compressed; a result of exactly 3:1 would be the floor missing |
 | `row+cell` | `cells=[2,2]`, `weights=[3,1\|-]` | row 0's cell weights lost or moved when a row and a cell were inserted below it (they belong to the figure row) |
 | `caps-calls` | `insert_cell=[1,1,0] refused_cell=1 insert_row=[1,1,0] refused_row=1 plots=8` | a cap that is not reached or not held: row 0 starts with two cells and takes two more, refusing the third call at 4; two rows then fit before the plot total reaches 8 and the third is refused; `plots` must stop at **8** |
 | `caps` | `plots=8 frows=4 cells=[4,2,1,1]`, `tile=1` | a ninth plot, or a fifth cell in a row |
 | `remove` | `plots=7 cells=[3,2,1,1]` | `remove_cell()` on a multi-cell row that removed the row, or that dropped a neighbour's traces |
 | `roundtrip-io` | `wrote=1 read=1 plots_in_file=3` | a save that was refused, or a file that lost a `[[plot]]` table |
-| `roundtrip` (state line) | `cells=[1,2] widths=[756\|533,220] weights=[-\|3,1]` and the three traces on `1`, `2a`, `2b` | the arrangement did not survive `collect_layout()` -> file -> `apply_layout()` |
+| `roundtrip` (state line) | `cells=[1,2] widths=[756\|546,207] weights=[-\|3,1]` and the three traces on `1`, `2a`, `2b` | the arrangement did not survive `collect_layout()` -> file -> `apply_layout()` |
 | `roundtrip rt=` | **`rt=1`** with `got=` equal to `expect=` (row weights `h=`, cell weights `w=` and each cell's trace, read back at the file's `%.4f`) | **`rt=0`** names the difference: a weight written per plot index instead of per figure row, widths applied before the arrangement (which resets them), or a trace that moved to another cell |
 | `legacy-io` | `read=1 plots_in_file=3 row_unset=1` | the stripped file still carrying a `row`, which would make the next line test nothing |
 | `legacy` | `cells=[1,1,1]`, `frows=3`, `widths=[756\|756\|756]`, `traces=[1:sine\|2:square\|3:ramp]` | a session from before the split that did not open as one cell per row, or lost its signals |
 | `invalid-rows` | `ok=1 frows/plots=[5/5 3/3 3/3 3/3]` | one of four unusable `row` sequences (five cells in a row; a skipped row; a row that goes back; a first row that is not 0) that was refused, or kept as a split instead of loading one cell per row |
-| `editor-on` -> `cell-split` | `cells=[1]` then `cell-split-ck cells=2` and `cell-split` with `widths=[376,376]`, the new `1b` empty | the editor's cell `+` not reaching `insert_cell()`, or the figure not re-pointed after it |
+| `editor-on` -> `cell-split` | `cells=[1]` then `cell-split-ck cells=2` and `cell-split` with `widths=[403,350]`, the new `1b` empty | the editor's cell `+` not reaching `insert_cell()`, or the figure not re-pointed after it |
 | `cell-assigned` | `1a:sine\|1b:square` | an assignment into the new cell that landed on another plot |
-| `col-drag` | `ok=1 left_gt_right=1 follows_80=1 relative=1 sum_80=1 right_floor=1 left_floor=1 sum_ext=1 both_above_min=1 tile=1`, then `d80=[376.5,376.5]->[456.5,296.5]` and `ext=[657.0,96.0\|96.0,657.0]` (all logical px, 753 px pair) | `ok` is the AND of the checks. `follows_80=0`: the drag of +80 did not put the left cell within 1 px of `start + 80` (the weights were taken as proportional to widths and the plotter's 64 px floor ignored -- an old reading was `[442.9,310.1]`); `relative=0`: three updates (+30, +60, +80) from one begin did not land at +80, i.e. the drag read the live weights instead of the begin snapshot `layout_col_drag_start`; `sum_80=0` / `sum_ext=0`: the pair's total changed instead of being redistributed; `right_floor=0` / `left_floor=0`: after +10000 / -10000 the shrinking cell does not read `kMinCellPx` (96) within 1 px; `both_above_min=0`: a cell below 96 px; `tile=1` is `split_probe_tile()`, the same check the state lines print. `left_gt_right` is `d80.l > d80.r` (after +80 from equal halves the left is the wider). The probe goes through `layout_col_drag_begin()` + `layout_col_apply()`, the pair the gesture calls |
-| `pre-insert0` (state line) | after the extreme drags `widths=[96,657]` | the last extreme drag was -10000: the left cell sits on the 96 px floor and the right takes the rest of the pair. A left cell reading 144 is the old floor-ignoring weights (`weights=[0.25,1.75]`); correct weights read `[0.1,1.9]` |
+| `col-drag` | `ok=1 left_gt_right=1 follows_80=1 relative=1 sum_80=1 right_floor=1 left_floor=1 sum_ext=1 both_above_min=1 tile=1`, then `d80=[350.4,350.4]->[430.4,270.4]`, `ext=[604.8,96.0\|96.0,604.8]` and `gutter0=52.2` (all logical **plot** widths, `axes.w` plus the right gutter of the two plots, measured after a `layout()` on the new weights; 700.8 px pair) | `ok` is the AND of the checks. The compared widths are plot widths and not cell rects, because only the first cell carries the y gutter (`gutter0=` is its rect width minus its plot width, printed so a reader can tell the two apart): a drag that equates the rect widths moves the divider ~17 px more than the pointer (the gutter's share is treated as weight; `d80=[350.4,350.4]->[447.6,253.2]`, +97.2 for +80) and reaches the left floor at 145.5 instead of 96 (`ext=[607.5,93.3\|93.3,607.5]` or `[659.7,93.3\|145.5,607.5]`), which reads `follows_80=0 relative=0 left_floor=0 right_floor=0 both_above_min=0`. `gutter0=` itself should read the y gutter (about 52 px; 0 means the first cell lost its gutter, a value near the cell width means the plot area collapsed). `follows_80=0`: the drag of +80 did not put the left cell within 1 px of `start + 80` (the weights were taken as proportional to widths and the plotter's 64 px floor ignored -- an old reading was `[442.9,310.1]`); `relative=0`: three updates (+30, +60, +80) from one begin did not land at +80, i.e. the drag read the live weights instead of the begin snapshot `layout_col_drag_start`; `sum_80=0` / `sum_ext=0`: the pair's total changed instead of being redistributed; `right_floor=0` / `left_floor=0`: after +10000 / -10000 the shrinking cell does not read `kMinCellPx` (96) within 1 px; `both_above_min=0`: a cell below 96 px; `tile=1` is `split_probe_tile()`, the same check the state lines print. `left_gt_right` is `d80.l > d80.r` (after +80 from equal halves the left is the wider). The probe goes through `layout_col_drag_begin()` + `layout_col_apply()`, the pair the gesture calls |
+| `pre-insert0` (state line) | after the extreme drags `widths=[148,605]`, `weights=[0.111732,1.88827]` | the last extreme drag was -10000: the left *plot* sits on the 96 px floor (the rect reads 148 = 96 plus the 52 px y gutter) and the right takes the rest of the pair. A left rect reading 144 is the old floor-ignoring weights (`weights=[0.25,1.75]`); `[146,607]` / `[96,657]` are the readings of the drag before it measured plot widths and before the sharing (floor 93 px / 96 px rect) |
 | `insert0-move` | `move_ok=1 before=[sine,square] after=[,sine,square]` | an insert at the left edge that renumbered the cells instead of moving their traces right with them |
 | `remove-mid` | `rm_ok=1 after=[,square]` | removing a middle cell that dropped or shifted the wrong neighbour |
 | `row-weights` | `wt_ok=1 before=[3,1,1] after=[1,1]` | the row weights not following an insert or removal of a *figure row* (the vector had the plot-count length once and drifted off the rows) |
@@ -2905,7 +2905,7 @@ The other lines, in order:
 | `assign-1b` / `drop-2b` | `assigned=1 notice='plotting 'sine' on plot 1b'`; `dropped=1 notice='plotting 'square' on plot 2b'` | a notice that names the plot by number alone |
 | `after-assign` (state line) | `traces=[1a:-\|1b:sine\|2a:-\|2b:square]` | the signal went to a neighbouring cell |
 | `ruler-labels` | `split=[row 1,row 2]` and, with cells `{1,2}`, `mixed=[row 0,row 2]` | the cursors pane's ruler lines (a label read through the pane's own widgets): **one line per figure row**, because the cells of a split row share their y axis and so their rulers. A split row is `row <figure row, from 1>` and sits on its first cell; an unsplit row keeps `row <plot index>` (**0-based**, as it always was -- `row 0` is the first plot, not a defect). One line per cell (`plot 1a,plot 1b,...`) is the pre-sharing reading |
-| `shared-y` | `y_shared=1 y_gutter=1 y_fit=1 ruler_mirror=1`, `ranges=[A=-3..7 B=-3..7 | fit A=B]`, `axes_w` equal to within a pixel, `auto=1` | a row of two cells with a trace each. `y_shared`: a `set_y_range(-3, 7)` on cell A is B's after one frame. `y_gutter`: only cell A has a y gutter (B's `y_axis_width` and `y_label_area.w` are 0) and the two plots are equally wide. `y_fit`: `fit_all()` leaves both cells on one range that covers both traces (not the manual one). `ruler_mirror`: a ruler written on A and read back by `sync_cursors(0)` is B's too. A 0 in the first two is `set_share_row_y(true)` not reaching the figure; in `y_fit`, no frame between `fit_all()` and the read (the probe restructures to pump one) or a group that did not follow the flag |
+| `shared-y` | `y_shared=1 y_gutter=1 y_fit=1 ruler_mirror=1`, `ranges=[A=-3..7 B=-3..7 \| fit A=B]`, `axes_w` equal to within a pixel, `auto=1` | a row of two cells with a trace each. `y_shared`: a `set_y_range(-3, 7)` on cell A is B's after one frame. `y_gutter`: only cell A has a y gutter (B's `y_axis_width` and `y_label_area.w` are 0) and the two plots are equally wide. `y_fit`: `fit_all()` leaves both cells on one range that covers both traces (not the manual one). `ruler_mirror`: a ruler written on A and read back by `sync_cursors(0)` is B's too. A 0 in the first two is `set_share_row_y(true)` not reaching the figure; in `y_fit`, no frame between `fit_all()` and the read (the probe restructures to pump one) or a group that did not follow the flag |
 
 The run ends with the usual `gtk warnings: 0` and no `Gtk-CRITICAL`. `x_equal=1` and `cursors_aligned=1` on every state line are
 the only readings of the shared time window across cells.