plugin-gantt: summary bars lack resize/link affordances; last-row tooltip flicker; horizontal scrollbar unreachable (clipped + overlay engines); locked-bar cursor #2676

Found while building the 排班计划甘特图 (4-level tree: project/product group rows → self-dated summary plan bars → locked dispatch leaf bars) on @objectstack/console 15.1.1 / objectui main, all reproduced live.

1. Self-dated summary bars are not editable (spec gap)

canDrag = !!onTaskUpdate && !row.isSummary && !isLocked gates ALL edit affordances off for summary rows, even when the summary's own dates are authoritative (summaryExtent: 'self' + hasOwnDates). Such a bar gets no edge-resize grips and no drag-to-link connector dots — dependencies can only be created through the context menu. This breaks the standard manual-scheduling model (MS Project "Manually Scheduled", Bryntum manuallyScheduled, Syncfusion taskMode: Manual): a parent whose dates are its own should edit like a task bar, while rollup summaries (derived dates, nothing to persist) stay move-only.

Also missing at the component level: per-interaction switches (DHTMLX drag_move/drag_resize/drag_progress/drag_links model) and a pre-commit veto hook (beforeTaskDrag/beforeTaskEdit pattern) so hosts can express rules like "moves allowed, durations pinned".

2. Last-row tooltip flickers in a loop (最后一行悬浮狂闪)

The hover tooltip renders downward (top: rowHeight - 8). On one of the LAST rows it pokes past the rows box, growing the scroller's scrollHeight while shown; with the user scrolled to the bottom, browser scroll clamping/anchoring re-adjusts scrollTop on every tooltip mount/unmount — the bar slides under the stationary cursor, hover re-fires, and the tooltip strobes.

3. Horizontal scrollbar unreachable / doubled

Two stacked causes:

• ObjectGantt sizes the pane with h-[calc(100vh-200px)], a viewport guess that overshoots whenever the chrome above (tabs, toolbar, quick filters) exceeds 200px; the overflow-hidden host then clips the pane's bottom edge (53px in the console layout), swallowing the scrollbar area entirely.
• The ::-webkit-scrollbar theming intended to force a classic always-visible bar is silently ignored by overlay-scrollbar engines (macOS "show while scrolling", embedded Chromium): the rules match (6 rules present) yet offsetHeight - clientHeight === 0. Worse, once the clipping is fixed those engines still flash their own auto-hiding bar on scroll, stacking a second bar under any custom one (双滚动条).

4. Locked summary bars advertise a grab cursor

locked (仅查看) summary rows are unmovable — beginDrag rejects them — but the bar still shows cursor: grab instead of not-allowed (🚫), unlike leaf bars.

Fix direction (PR follows)

• Editability follows date ownership: summaryExtent 'self' + own dates + !locked → resize grips, connector dots, edge-zone drag on summary bars; middle drag still group-moves the subtree; rollup summaries unchanged.
• interactions: { move, resize, progress, link } view-config switches (default all on, narrow-only) + onBeforeTaskUpdate async veto on the central commit belt (undo/redo exempt).
• Bottom rows flip the tooltip above the bar — upward absolute overflow never extends the scrollable area, removing the feedback loop.
• ObjectGantt fills its host flex cell (flex-1 min-h-0) instead of the viewport calc; native timeline scrollbars fully hidden (scrollbar-width: none, honored by overlay engines) and replaced by self-drawn track+thumb bars on both axes (drag + track-click jump, auto-hidden when content fits, task-list lockstep preserved).
• Locked summaries fold !isLocked into the movable flag → not-allowed cursor.

All verified live against a real 4-level dataset (edge-resize persists only the plan's own dates; connector-dot link writes the dependency field; group move skips locked children; conflict dialog, context menus, locked rows regress clean). plugin-gantt suite: 323 tests green.