fix(kanban): disable card drag-reorder while a filter is active

Context:
In board view, item drag-drop computes the drop index by scanning the rendered
[data-item-id] cards (handleItemDrop), then passes that index to moveItem, which
splices into the lane's full, stored items array. Dragging was already disabled
for non-manual sort modes via disableDrag={!isManualSort}, because a sorted view
reorders the cards relative to storage.

Problem:
A text filter (filterItems) also makes the rendered cards a subset of the lane's
items, but drag stayed enabled in manual sort mode. With a filter active, the
drop index (a position among the visible/filtered cards) was spliced into the
unfiltered array, so the dragged card landed at the wrong position. applyChange
then serialized and persisted the corrupted order to the .kanban file. The
cross-lane drop path was affected identically.

Solution:
- Add a pure `canReorderItems(sortMode, filterQuery)` helper: reorder is valid
  only when sort is manual AND no filter is active (rendered order == stored
  order).
- Wire it in KanbanView as `disableDrag={!canReorder}`. KanbanCard already maps
  disableDrag to draggable=false and drops the dragstart handler, so no drag
  begins and handleItemDrop's `if (!dragItemId) return` guard short-circuits.

Behavior:
- Manual sort + no filter: drag-reorder works (unchanged).
- Manual sort + active filter: cards are no longer draggable (no silent
  misplacement / file corruption).
- Non-manual sort: drag stays disabled (unchanged).

Files:
- src/lib/plugins/kanban/kanban.logic.ts:688-700 — `canReorderItems` helper.
- src/lib/plugins/kanban/KanbanView.svelte:43,162-165,525 — import, `canReorder`
  derived, `disableDrag={!canReorder}`.
- src/tests/lib/plugins/kanban/kanban.logic.test.ts — canReorderItems cases
  (manual/no-filter true; filtered false; sorted false).
- tasks/todo/bug-hunt-fixes.md — H6 marked done.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: diegorv

src/lib/plugins/kanban/KanbanView.svelte

@@ -40,6 +40,7 @@
 		setSortMode,
 		filterItems,
 		setViewMode,
+		canReorderItems,
 	} from './kanban.logic';
 	import type { KanbanBoard, KanbanSortMode, KanbanViewMode } from './kanban.types';
 	import { kanbanStore } from './kanban.store.svelte';
@@ -159,6 +160,10 @@
 
 	let currentSortMode = $derived(board.settings.sortMode ?? 'manual');
 	let isManualSort = $derived(currentSortMode === 'manual');
+	// Manual card drag-reorder is only valid when the rendered order matches the
+	// stored order: manual sort AND no active filter. Otherwise a drop index among
+	// the filtered/sorted cards would misplace cards in the full lane list.
+	let canReorder = $derived(canReorderItems(currentSortMode, kanbanStore.filterQuery));
 
 	function handleSetSortMode(mode: KanbanSortMode) {
 		applyChange(setSortMode(board, mode));
@@ -519,7 +524,7 @@
 			atLimit={isLaneAtLimit(board, lane.title)}
 			autoComplete={isLaneAutoComplete(board, lane.title)}
 			tagColors={board.settings.tagColors ?? {}}
-			disableDrag={!isManualSort}
+			disableDrag={!canReorder}
 			{dragItemId}
 			isDragOver={dragOverLaneId === lane.id}
 			{dropIndicatorIndex}

src/lib/plugins/kanban/kanban.logic.ts

@@ -685,6 +685,20 @@ export function filterItems(items: KanbanItem[], query: string): KanbanItem[] {
 	return items.filter((item) => item.text.toLowerCase().includes(q));
 }
 
+/**
+ * Whether manual drag-reordering of cards is valid for the current view.
+ *
+ * Drop positions are computed from the rendered (filtered + sorted) cards, but
+ * moveItem splices into the lane's full, stored item list. That mapping is only
+ * 1:1 when the rendered order equals the stored order: manual sort mode AND no
+ * active filter. When the board is sorted or filtered, the rendered cards are a
+ * reordered/subset view, so a drop index among them would misplace and persist
+ * cards. Callers disable item dragging when this returns false.
+ */
+export function canReorderItems(sortMode: KanbanSortMode, filterQuery: string): boolean {
+	return sortMode === 'manual' && filterQuery.trim() === '';
+}
+
 // ── View mode ───────────────────────────────────────────────────────
 
 /** Sets the board view mode */

src/tests/lib/plugins/kanban/kanban.logic.test.ts

@@ -46,6 +46,7 @@ import {
 	setSortMode,
 	filterItems,
 	setViewMode,
+	canReorderItems,
 } from '$lib/plugins/kanban/kanban.logic';
 import type { KanbanBoard, KanbanSettings } from '$lib/plugins/kanban/kanban.types';
 
@@ -1519,3 +1520,23 @@ describe('setViewMode', () => {
 		expect(parsed.settings.viewMode).toBe('list');
 	});
 });
+
+describe('canReorderItems', () => {
+	it('allows manual reorder when sort is manual and no filter is active', () => {
+		expect(canReorderItems('manual', '')).toBe(true);
+		expect(canReorderItems('manual', '   ')).toBe(true);
+	});
+
+	it('blocks reorder when a filter is active (visible order != stored order)', () => {
+		// Drop positions are computed among the filtered DOM cards; mapping them
+		// into the lane's full item array misplaces and persists cards.
+		expect(canReorderItems('manual', 'x')).toBe(false);
+		expect(canReorderItems('manual', ' fix ')).toBe(false);
+	});
+
+	it('blocks reorder when the board is sorted (non-manual)', () => {
+		expect(canReorderItems('date-asc', '')).toBe(false);
+		expect(canReorderItems('text-desc', '')).toBe(false);
+		expect(canReorderItems('checked', 'x')).toBe(false);
+	});
+});

tasks/todo/bug-hunt-fixes.md

@@ -12,7 +12,7 @@ This batch fixes the **7 HIGH** bugs (one commit each). Medium + Low are backlog
 - [x] H3: collection parser — method/field chaining on a function-call result broken (`now().format()`, `today().date()`). `src/lib/features/collection/expression/parser.ts:130-143,206-212`. Fix: structural `methodCall` node holding receiver ASTNode, not flattened dotted string.
 - [x] H4: collection filter — single-row `not` group collapses to bare positive expression, inverting filter + persisting inverted YAML. `src/lib/features/collection/toolbar/filter.logic.ts:146-148`. Fix: shortcut only when `conjunction !== 'not'`.
 - [x] H5: properties panel crashes (Svelte `each_key_duplicate`) when frontmatter has alias + canonical twin (`color` + `_color`). `src/lib/features/properties/PropertiesView.svelte:92-96,221`. Fix: `dedupeCanonicalKeys` on parse path (or key=index).
-- [ ] H6: kanban drag-drop misplaces cards (DOM filtered index spliced into full array) when a filter is active -> corrupts `.kanban`. `src/lib/plugins/kanban/KanbanView.svelte:372-393`. Fix: disable drag while filtered, or map filtered->absolute index.
+- [x] H6: kanban drag-drop misplaces cards (DOM filtered index spliced into full array) when a filter is active -> corrupts `.kanban`. `src/lib/plugins/kanban/KanbanView.svelte:372-393`. Fix: disable drag while filtered, or map filtered->absolute index.
 - [ ] H7: Table of Contents empty for CRLF files (`\r` breaks HEADING_RE). `src/lib/plugins/table-of-contents/toc.logic.ts:63-93` (root: `wikilink/navigation.logic.ts:2`). Fix: split `/\r?\n/` or strip `\r`; also fixes wikilink `#heading` jump on CRLF docs.
 
 ## Backlog — MEDIUM (22)