[sedax90]

Summary

• Selecting two or more rows shows the focused column's sum, average and count in the bottom bar of a table tab, an editor result and a Redis key tab. The popover lists count, numbers, empty, not-a-number, sum, average, minimum and maximum, each with a Copy button that copies plain text with no grouping.
• Exact arithmetic on the values as their cells show them: integers of any width, decimals by their digits (SqlDecimal::parts, new in core), floats by the shortest text the cell shows. Sum, minimum and maximum keep the widest scale and at least the column's declared one; the average carries four more digits. No digit caps.
• A number column sums (a value that is not a number, such as NaN, counts as one); a column of no declared type sums text that reads as a number, Value::Other included; any other column only counts. NULL and a cell left to its default count as empty. Rows marked for deletion are left out, also after a failed save.
• The summed column is the last focused data column, so the readout stays while the focus is in its popover or Row Details. A hidden column is not summed.
• The sum runs off the GTK thread on the grid's Tasks, once per main-loop turn, over the summed column alone, sharing the page's cells. A newer selection or closing the grid stops a run still out; Copy is off while one is out.
• Closing a grid also stops a find-bar search still out.
• Structure tab: Discard on a table that changed elsewhere shows the definition as last read while it reads the table again, and through a failed read, instead of the discarded edits.
• The change tracker keeps pending drafts in an IndexMap by id, so reading every draft of a 100,000-row paste (the summary, copy, find, duplicate) or undoing it no longer scans every draft per row.
• Stock widgets only: a GtkMenuButton with can-shrink, so a narrow bar ellipsizes the sentence and keeps the arrow, inside a slide-right GtkRevealer, which keeps the bar's height while hidden. The popover is built once and updated in place.
• The browse tab hides the readout behind its error and loading pages, as it does the selected-row count.
• The editor result footer is now a fixed 34 px (the button's height) instead of 22 px, so selecting a second row no longer shifts the grid.

Screenshots

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Before
After

Test plan

• services::grid::selection_summary::tests (11): exact decimal, float32 and float64 sums, widths past i128, a 1,500-digit decimal, the declared scale, rounding, NULL and NaN, untyped text and Value::Other, the rule per column type, cancellation.
• ui::data_grid::tests::summary (11): sums the focused column, a text column only counts, one row hides it, an edit counts while the focus is elsewhere, deleted rows left out after a failed save, a hidden column, constant height, the popover's figures and Copy's plain text, a long figure on one line, the readout freed with its grid, closing the grid stops the run.
• ui::data_grid::tracked_values::tests: a column snapshot reads a pending edit, a draft's cell, and a default as NULL.
• ui::data_grid::find_bar::tests::closing_the_grid_stops_the_search_still_running. It and the summary's closing test fail with the two stop() lines taken out of dispose.
• ui::structure_tab::tests::a_discard_whose_read_fails_leaves_the_discarded_column_out; a_discard_after_a_save_found_the_table_changed_reads_it_again no longer races the read.
• services::change_tracker::tests::the_largest_paste_reads_back_and_undoes_without_a_scan_per_draft: 100,000 drafts read back and undone in under 2 s.
• ui::browse_tab::tests::load::the_selection_summary_hides_behind_the_error_page, ui::key_tab::tests::the_footer_sums_the_selected_entries (also checks the popover's first Copy button takes the focus).
• value::decimal::tests::parts_round_trip_through_from_parts.
• verify.sh --platform linux test tablepro: 2,561 of 2,563 passed; the other two are fixed here, after which ui::structure_tab and ui::data_grid (416) pass. lint: clean.