From 9f5e15e560e4204bf206205fe7baaf37a79cf54f Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Mon, 7 Sep 2026 22:38:10 +0000
Subject: [PATCH] fix(kanban): keep the swimlane column-header row out of the
 flex shrink pool
MIME-Version: 1.0
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With swimlanes on, the board's column titles stayed in the DOM at height 0 and
painted nothing (objectui#7303). The header row is a flex item of the swimlane
region, and `overflow-x-auto` makes it a scroll container — which zeroes a flex
item's automatic minimum size, so it may legally shrink to 0. The lanes below
stay `overflow: visible`, so their automatic minimum size clamps them at content
height and they refuse to shrink; once the lanes overflowed the bounded board,
the entire deficit landed on the one shrinkable item.

`shrink-0` takes the row out of that pool. Measured in Chromium 1194 at
1600x1000 on the component's own rendered markup: header row 0 -> 24, header
cell 0 -> 24, and `elementFromPoint` at a title's centre returning the
lane-collapse button before and the title itself after.

The pin asserts the style contract that decides the height, not the row's
existence — the row was present and correctly placed on the broken build — and
carries a rendered lane, a rendered card and the flat board's own headings as
controls. happy-dom performs no layout, so a height assertion there could not
fail; the docstring says so and records the out-of-band measurement instead.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YBWFb5YgMU5dw8p2VKj16S
---
 .../7303-kanban-swimlane-column-header-row.md |  32 +++
 packages/plugin-kanban/src/KanbanImpl.tsx     |  30 ++-
 .../swimlaneColumnHeaderRow-7303.test.tsx     | 252 ++++++++++++++++++
 3 files changed, 312 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/7303-kanban-swimlane-column-header-row.md
 create mode 100644 packages/plugin-kanban/src/__tests__/swimlaneColumnHeaderRow-7303.test.tsx

diff --git a/.changeset/7303-kanban-swimlane-column-header-row.md b/.changeset/7303-kanban-swimlane-column-header-row.md
new file mode 100644
index 0000000000..ead1cb2215
--- /dev/null
+++ b/.changeset/7303-kanban-swimlane-column-header-row.md
@@ -0,0 +1,32 @@
+---
+'@object-ui/plugin-kanban': patch
+---
+
+Keep the kanban column-header row visible when swimlanes are on (objectui#7303).
+
+Turning swimlanes on for a board — `grouping.fields[0].field`, which is the only
+authorable route, since `KanbanConfigSchema` is strict and rejects
+`kanban.swimlaneField` — removed the status column titles from the screen. They
+stayed in the DOM, at the right coordinates, painting nothing, so the board read
+as an unordered card wall: the lane told you the caliber of the work and nothing
+told you its state.
+
+The cause is a flexbox rule rather than a paint bug. The header row is a flex
+item of the swimlane region (a `flex-col` inside a height-bounded board), and its
+`overflow-x-auto` makes it a scroll container — which zeroes a flex item's
+automatic minimum size, so it may legally be shrunk to height 0. The lanes below
+keep `overflow: visible`, so their own automatic minimum size clamps them at
+content height and they refuse to shrink; the moment the lanes overflowed the
+board, the entire deficit landed on the one shrinkable item. The row now carries
+`shrink-0`, which takes it out of that pool.
+
+Note the trigger, because it decides who saw this: the collapse needed the lanes
+to OVERFLOW the board's bounded height. A board short enough to fit rendered its
+titles normally, which is why this presented in the field as "sometimes the
+column labels are missing" rather than as a flat breakage of swimlanes.
+
+Measured in Chromium 1194 at 1600×1000 on the component's own rendered markup:
+header row height 0 → 24, header cell 0 → 24, and `elementFromPoint` at a title's
+own centre returning the lane-collapse button before the fix and the title itself
+after it. Nothing else about the layout moves — the row keeps its `pl-36 sm:pl-44`
+alignment with the lane content rows, and the non-swimlane board is untouched.
diff --git a/packages/plugin-kanban/src/KanbanImpl.tsx b/packages/plugin-kanban/src/KanbanImpl.tsx
index 77333ccd63..a834767db1 100644
--- a/packages/plugin-kanban/src/KanbanImpl.tsx
+++ b/packages/plugin-kanban/src/KanbanImpl.tsx
@@ -655,8 +655,34 @@ function KanbanBoardInner({ columns, onCardMove, onCardClick, className, dnd, qu
       {swimlanes ? (
         /* Swimlane (2D) layout */
         <div className={cn("flex flex-col gap-2 px-4 sm:px-6 py-3 sm:py-4 min-w-0 overflow-hidden", className)} role="region" aria-label="Kanban board with swimlanes">
-          {/* Column headers */}
-          <div className="flex gap-3 sm:gap-4 pl-36 sm:pl-44 overflow-x-auto">
+          {/* Column headers.
+              This is a SECOND header implementation, parallel to the per-column
+              `<h3 id={`kanban-col-${column.id}`}>` that `KanbanColumnView`
+              renders. The two cannot be folded into one: this layout has no
+              column components at all — every lane paints its own row of plain
+              column cells — so the titles have to be drawn once, above every
+              lane, instead of once per column.
+
+              `shrink-0` is load-bearing, not cosmetic (objectui#7303). This row
+              is a flex ITEM of the swimlane region, which is a `flex-col` inside
+              a height-bounded board (`h-full`). `overflow-x-auto` makes the row
+              a scroll container, and a flex item's automatic minimum size
+              (`min-height: auto`) applies only while its overflow is `visible`
+              — so as a scroll container this row may legally be shrunk to
+              height 0. The lanes below stay `overflow: visible`, so their own
+              automatic minimum size clamps them at content height and they
+              refuse to shrink: the moment the lanes overflow the board, the
+              ENTIRE deficit lands on this one shrinkable item. The titles then
+              stay in the DOM, at the right coordinates, painting nothing.
+              Measured in Chromium 1194 at 1600x1000 before the fix: row height
+              0, cell height 0, title span height 16, and `elementFromPoint` at
+              a title's own centre returning the lane-collapse `<button>` behind
+              it. Pinned by `__tests__/swimlaneColumnHeaderRow-7303.test.tsx`.
+
+              The `pl-36 sm:pl-44` indent is shared with the lane content rows
+              below and is what lines the titles up with their columns — it must
+              move on both rows or neither. */}
+          <div className="flex shrink-0 gap-3 sm:gap-4 pl-36 sm:pl-44 overflow-x-auto">
             {boardColumns.map(col => (
               <div key={col.id} className="w-[85vw] sm:w-80 shrink-0 text-center">
                 <span className=" text-xs sm:text-sm font-semibold tracking-wider text-primary/90 uppercase">{col.title}</span>
diff --git a/packages/plugin-kanban/src/__tests__/swimlaneColumnHeaderRow-7303.test.tsx b/packages/plugin-kanban/src/__tests__/swimlaneColumnHeaderRow-7303.test.tsx
new file mode 100644
index 0000000000..2e585a6210
--- /dev/null
+++ b/packages/plugin-kanban/src/__tests__/swimlaneColumnHeaderRow-7303.test.tsx
@@ -0,0 +1,252 @@
+/**
+ * ObjectUI
+ * Copyright (c) 2024-present ObjectStack Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+/**
+ * objectui#7303 — a swimlane board must keep its column-header row.
+ *
+ * ## What broke
+ *
+ * With swimlanes on (`grouping.fields[0].field`, the only authorable route —
+ * `KanbanConfigSchema` is strict and rejects `kanban.swimlaneField`), the five
+ * column titles stayed in the DOM, at the right coordinates, and painted
+ * nothing. The board became a card wall with no way to tell Open from Done.
+ *
+ * The cause is a flexbox rule, not a paint bug. The header row is a flex ITEM
+ * of the swimlane region (`flex-col`, inside a height-bounded `h-full` board).
+ * `overflow-x-auto` makes it a scroll container, and a flex item's automatic
+ * minimum size (`min-height: auto`) applies only while its overflow is
+ * `visible` — so a scroll container may legally be shrunk to height 0. The
+ * lanes below stay `overflow: visible`, so their automatic minimum size clamps
+ * them at content height and they refuse to shrink; the moment the lanes
+ * overflow the board, the ENTIRE deficit lands on the one shrinkable item.
+ * `shrink-0` takes the header row out of that pool.
+ *
+ * ## ⚠️ What this file can and cannot measure — read before extending it
+ *
+ * The bug is VISUAL and the honest reading of it is a measured height. Vitest
+ * runs here in happy-dom, which performs NO layout: every
+ * `getBoundingClientRect()` in this environment is 0×0 for the collapsed row,
+ * the healthy row, and a row that was never rendered alike. So a height
+ * assertion here would be a pin that CANNOT fail, which is worse than no pin —
+ * it converts an open bug into a green claim. This file therefore asserts the
+ * STYLE CONTRACT that decides the height, and states the invariant rather than
+ * one blessed spelling: the header row must not be BOTH a scroll container and
+ * shrinkable. Removing `shrink-0` reddens it; so does dropping the row's
+ * height by any other route that leaves it in the shrink pool.
+ *
+ * The real height was measured out-of-band in Chromium 1194 at 1600×1000, on
+ * this component's own rendered markup with Tailwind-generated CSS, with the
+ * lanes overflowing the board:
+ *
+ *   before `shrink-0` — header row 0, header cell 0, title span 16,
+ *                       `elementFromPoint` at a title's own centre returning
+ *                       the lane-collapse `<button>` behind it;
+ *   after  `shrink-0` — header row 24, header cell 24, title span 16,
+ *                       the title winning its own hit test.
+ *
+ * Note the trigger: the collapse needs the lanes to OVERFLOW the board's
+ * bounded height. A short board (nothing to shrink) renders the row at 24 in
+ * both worlds, which is why this reads as a data-dependent "sometimes the
+ * labels are missing" bug in the field.
+ *
+ * A CI-resident version of that measurement needs a browser and real CSS —
+ * neither is available in this project. See the PR for the proposal.
+ *
+ * ## Non-vacuity
+ *
+ * "The labels are absent" is trivially true of a board that rendered nothing,
+ * so every case here waits for real DOM first and pins a rendered swimlane and
+ * a rendered card alongside the header row. The second case is the
+ * NON-REGRESSION half: deleting the swimlane header row, or the swimlane
+ * layout itself, must not read as success.
+ */
+
+import React from 'react';
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { render, waitFor, cleanup, within } from '@testing-library/react';
+import { SchemaRenderer, SchemaRendererProvider } from '@object-ui/react';
+// Registers `object-kanban`. Module scope, not a hook: the import IS the
+// registration (AGENTS.md's test-discipline section).
+import '../index';
+// The board renders inside `KanbanRenderer`'s `React.lazy` boundary; importing
+// the chunk at module scope bills the cold transform to the import phase
+// instead of racing a `waitFor` budget (objectui#3010), same specifier as
+// `index.tsx`'s factory so ESM's module cache resolves it immediately.
+import '../KanbanImpl';
+
+afterEach(cleanup);
+
+/**
+ * The viewport this fixture states.
+ *
+ * happy-dom's ambient window is not pinned repo-wide, so a test that reads a
+ * width inherits whatever default the runner happens to carry. This board's
+ * swimlane header markup is width-INDEPENDENT — its `sm:` variants are decided
+ * by CSS, which happy-dom never applies — so nothing below actually branches on
+ * this. It is pinned anyway so the fixture says which world it describes: the
+ * desktop branch (≥ Tailwind's `sm`, 640px), the one the card measured at
+ * 1600×1000. Anything added here that DOES branch on width must re-state it.
+ */
+const VIEWPORT = { width: 1600, height: 1000 };
+
+beforeEach(() => {
+  Object.defineProperty(window, 'innerWidth', { configurable: true, writable: true, value: VIEWPORT.width });
+  Object.defineProperty(window, 'innerHeight', { configurable: true, writable: true, value: VIEWPORT.height });
+});
+
+const OBJECT = 'deal';
+
+const DEAL_SCHEMA = {
+  name: OBJECT,
+  label: 'Deal',
+  fields: {
+    name: { type: 'text', label: 'Name' },
+    status: { type: 'text', label: 'Status' },
+    owner: { type: 'text', label: 'Owner' },
+  },
+};
+
+function makeAdapter(): Record<string, any> {
+  return {
+    find: vi.fn(async () => ({ data: [] })),
+    findOne: vi.fn(),
+    create: vi.fn(),
+    update: vi.fn(),
+    delete: vi.fn(),
+    getObjectSchema: vi.fn(async () => DEAL_SCHEMA),
+  };
+}
+
+const ROWS = [
+  { id: 'a', name: 'Alpha deal', status: 'open', owner: 'ann' },
+  { id: 'b', name: 'Beta deal', status: 'won', owner: 'bob' },
+];
+
+/** The declared board, minus whatever the case adds. */
+const BOARD = {
+  type: 'object-kanban',
+  objectName: OBJECT,
+  groupBy: 'status',
+  columns: [
+    { id: 'open', title: 'Open' },
+    { id: 'won', title: 'Won' },
+  ],
+};
+
+function renderBoard(extra: Record<string, unknown> = {}) {
+  return render(
+    <SchemaRendererProvider dataSource={makeAdapter() as any}>
+      <SchemaRenderer schema={{ ...BOARD, data: ROWS, ...extra } as never} />
+    </SchemaRendererProvider>,
+  );
+}
+
+/**
+ * Does this element's class list make it a scroll container?
+ *
+ * Every non-`visible` overflow does — `clip` and `hidden` zero a flex item's
+ * automatic minimum size exactly as `auto` and `scroll` do, so the invariant
+ * below must not be readable as "only `overflow-x-auto` is dangerous".
+ */
+const OVERFLOW_TOKEN = /^(?:[a-z]+:)*overflow(?:-[xy])?-(?:auto|scroll|hidden|clip)$/;
+
+/**
+ * Does this element's class list keep it out of the flex shrink pool?
+ *
+ * `shrink-0` is what the fix spells, but an explicit floor (`min-h-*`, any
+ * value but `min-h-0`) prevents the same collapse — so both pass. What must NOT
+ * pass is a row that is shrinkable AND a scroll container.
+ */
+const KEEPS_ITS_HEIGHT_TOKEN = /^(?:[a-z]+:)*(?:shrink-0|flex-shrink-0|min-h-(?!0$).+)$/;
+
+const tokens = (el: Element): string[] => el.className.split(/\s+/).filter(Boolean);
+
+/** Left-padding tokens — what lines the header cells up with their columns. */
+const indent = (el: Element): string[] => tokens(el).filter((t) => /(^|:)pl-/.test(t));
+
+describe('objectui#7303 — swimlane column-header row', () => {
+  it('renders above the lanes and stays out of the flex shrink pool', async () => {
+    const { container } = renderBoard({ grouping: { fields: [{ field: 'owner' }] } });
+
+    // CONTROL 1 — a real swimlane board, not a fallback flat one.
+    await waitFor(() => expect(container.textContent).toContain('Alpha deal'));
+    const region = container.querySelector('[role="region"]');
+    expect(region?.getAttribute('aria-label')).toBe('Kanban board with swimlanes');
+
+    // CONTROL 2 — the lanes rendered, with their collapse buttons.
+    const laneButtons = [...region!.querySelectorAll('button[aria-expanded]')];
+    expect(laneButtons.map((b) => b.textContent)).toEqual(['▶ann(1)', '▶bob(1)']);
+
+    // CONTROL 3 — a card rendered INSIDE a lane. Without this every assertion
+    // below is also satisfied by a board that painted headers over nothing.
+    const laneList = region!.querySelector('[role="list"][aria-label="Open - ann cards"]');
+    expect(laneList).not.toBeNull();
+    expect(
+      within(laneList as HTMLElement).queryByText('Alpha deal'),
+      'the swimlane cell should hold its card',
+    ).not.toBeNull();
+
+    // The header row is the region's FIRST child: the titles sit ABOVE every
+    // lane, which is the layout the card settles ("keeps its height and paints
+    // the column titles above the lanes"). A per-lane repeat would be a
+    // different product, not a fix.
+    const headerRow = region!.firstElementChild as HTMLElement;
+
+    // Read presence through `queryByText` into an `expect` that carries a
+    // message: `getByText` throws before `expect` runs, so its message never
+    // reaches the summary.
+    for (const title of ['Open', 'Won']) {
+      expect(
+        within(headerRow).queryByText(title),
+        `the swimlane header row should carry the column title ${title}; row text was ${JSON.stringify(headerRow.textContent)}`,
+      ).not.toBeNull();
+    }
+
+    // ── THE PIN ──────────────────────────────────────────────────────────────
+    // The row's existence is NOT the assertion: on the broken build the row was
+    // present, in the right place, holding all five titles — at height 0. What
+    // decides the height is whether the row can be shrunk while being a scroll
+    // container.
+    const list = tokens(headerRow);
+    const isScrollContainer = list.some((t) => OVERFLOW_TOKEN.test(t));
+    const keepsItsHeight =
+      list.some((t) => KEEPS_ITS_HEIGHT_TOKEN.test(t)) ||
+      headerRow.style.flexShrink === '0' ||
+      headerRow.style.minHeight !== '';
+    expect(
+      isScrollContainer && !keepsItsHeight,
+      `the swimlane column-header row is a scroll container AND shrinkable, so the board's ` +
+        `flex-col will shrink it to height 0 as soon as the lanes overflow (objectui#7303). ` +
+        `Give it \`shrink-0\` (or a min-height floor), or stop making it a scroll container. ` +
+        `class was: ${JSON.stringify(headerRow.className)}`,
+    ).toBe(false);
+
+    // The header cells line up with the lane content rows below only while the
+    // two carry the same left indent — so a "fix" that bought height by moving
+    // the indent would leave every title over the wrong column.
+    const laneContentRow = laneList!.parentElement!.parentElement!;
+    expect(indent(headerRow), 'header row indent').toEqual(indent(laneContentRow));
+    expect(indent(headerRow).length, 'the indent tokens must actually exist to be compared').toBeGreaterThan(0);
+  });
+
+  it('NON-REGRESSION — the flat board still renders its own per-column headings', async () => {
+    // Deleting the swimlane header row, or the swimlane layout itself, would
+    // satisfy "no collapsed row" while making the product strictly worse. This
+    // case pins the other path's headings, which are a DIFFERENT element in a
+    // different place (`<h3 id="kanban-col-…">`, inside each column) — the
+    // reason the two header implementations cannot simply be merged.
+    const { container } = renderBoard();
+
+    await waitFor(() => expect(container.textContent).toContain('Alpha deal'));
+    expect(container.querySelector('[role="region"]')?.getAttribute('aria-label')).toBe('Kanban board');
+
+    const heading = container.querySelector('h3#kanban-col-open');
+    expect(heading, 'the flat board keeps its per-column <h3> heading').not.toBeNull();
+    expect(heading!.textContent).toBe('Open');
+  });
+});