File list: Shift+nav uses toggle-and-fill model

- Each Shift+arrow/Page/Home/End independently toggles the cursor's old item, then sets every item the cursor jumps over to that state. The landing item is included only when the jump overflowed (intended distance > actual distance because of a list-boundary clamp).
- Mouse Shift+click keeps the prior anchor/end semantics (renamed to `handleShiftMouseNavigation`); keyboard goes through the new `handleShiftKeyboardNavigation(oldCursor, newCursor, overflow, hasParent)`.
- `..` is never selected; with cursor on `..`, keyboard fills default to "select" so Shift+End from `..` selects everything else.
- `handleNavigationShortcut` and `BriefList.handleKeyNavigation` now return `{ newIndex, overflow }`. Home/End always overflow; Page/Brief Left/Right overflow when clamped.
- Full-mode Shift+Left/Right acts as Shift+Home/End (always overflow).
- Intentionally asymmetric: Shift+Down 3× then Shift+Up 3× doesn't restore the start — each press independently toggles.

Author: vdavid

apps/desktop/src/lib/file-explorer/CLAUDE.md

@@ -10,10 +10,17 @@ Dual-pane file explorer with keyboard-driven navigation, file selection, sorting
 - **Insert**: toggle selection at cursor and move cursor down (Total Commander style). `..` isn't selectable, but the
   cursor still advances. At the last row the cursor stays put. No physical Insert key on Apple keyboards — users can
   remap via Karabiner-Elements, plug in a PC USB keyboard, or rebind in Settings → Shortcuts.
-- **Shift+click / Shift+arrow**: range selection with anchor (A) and end (B). If anchor already selected, range
+- **Shift+click**: mouse range selection with anchor (A) and end (B). If anchor was already selected, the range
   deselects.
+- **Shift+arrow / Shift+Page / Shift+Home/End / Shift+Left/Right (Brief)**: keyboard toggle-and-fill. Toggles the item
+  at the cursor's _old_ position, then sets (not toggles) every item the cursor jumps over to that toggled state. The
+  landing item is included only when the jump **overflowed** (intended distance > actual distance because of a list
+  boundary clamp). Home/End always overflow; arrows overflow when pressed at a boundary (no movement);
+  PageUp/PageDown/Brief Left/Right overflow when clamped. Full-mode Shift+Left/Right behave like Shift+Home/End. The
+  model is intentionally asymmetric: Shift+Down 3× then Shift+Up 3× does NOT restore the start state — each press
+  independently toggles the cursor's item.
 - **Cmd+A / Cmd+Shift+A**: select all / deselect all
-- **".." entry can't be selected**
+- **".." entry can't be selected**: keyboard fills from `..` default to "select" (so Shift+End from `..` selects).
 - **Cleared on navigation**: selection is per-directory
 
 ### Implementation
@@ -40,7 +47,8 @@ Dual-pane file explorer with keyboard-driven navigation, file selection, sorting
 ### Gotchas
 
 - **Parent offset**: when `hasParent`, frontend indices = backend indices + 1
-- **Range shrinking**: moving cursor back toward anchor removes items no longer in range
+- **Range shrinking (mouse Shift+click only)**: moving cursor back toward anchor removes items no longer in range. The
+  keyboard path is stateless (toggle-and-fill) and doesn't shrink.
 - **Optimization flag**: `allSelected: true` avoids sending 500k indices over IPC
 - **`allSelected` + cancel**: calls `selectAll()` for move/delete/trash (source listing changed), leaves untouched for
   copy (source listing unchanged)

apps/desktop/src/lib/file-explorer/navigation/CLAUDE.md

@@ -112,6 +112,11 @@ Meta+Home/End is intentionally not handled (passes to OS). Returns `null` for un
 
 Brief PageUp/PageDown lands on the **bottom row** of the target column (TUI convention).
 
+`NavigationResult` also carries an `overflow: boolean` field: `true` when the requested step was clamped at a list
+boundary (intended distance > actual distance). Home/End are always overflow. PageUp/PageDown are overflow when the page
+step would cross 0 or `totalCount - 1`. Callers wiring keyboard Shift+nav use this to decide whether to include the
+landing item in the toggle-and-fill range — see `file-explorer/CLAUDE.md` § Selection.
+
 ## `VolumeBreadcrumb.svelte`
 
 Pure presentational component. Reads the volume list from the shared `volume-store.svelte.ts` (no fetching, no event

apps/desktop/src/lib/file-explorer/navigation/keyboard-shortcuts.test.ts

@@ -22,16 +22,16 @@ describe('handleNavigationShortcut', () => {
       totalCount: 100,
     }
 
-    it('handles Option+ArrowUp as Home', () => {
+    it('handles Option+ArrowUp as Home (always overflow)', () => {
       const event = createKeyboardEvent('ArrowUp', { altKey: true })
       const result = handleNavigationShortcut(event, context)
-      expect(result).toEqual({ newIndex: 0, handled: true })
+      expect(result).toEqual({ newIndex: 0, handled: true, overflow: true })
     })
 
-    it('handles Home key', () => {
+    it('handles Home key (always overflow)', () => {
       const event = createKeyboardEvent('Home')
       const result = handleNavigationShortcut(event, context)
-      expect(result).toEqual({ newIndex: 0, handled: true })
+      expect(result).toEqual({ newIndex: 0, handled: true, overflow: true })
     })
 
     it('does not handle Home with metaKey', () => {
@@ -47,16 +47,16 @@ describe('handleNavigationShortcut', () => {
       totalCount: 100,
     }
 
-    it('handles Option+ArrowDown as End', () => {
+    it('handles Option+ArrowDown as End (always overflow)', () => {
       const event = createKeyboardEvent('ArrowDown', { altKey: true })
       const result = handleNavigationShortcut(event, context)
-      expect(result).toEqual({ newIndex: 99, handled: true })
+      expect(result).toEqual({ newIndex: 99, handled: true, overflow: true })
     })
 
-    it('handles End key', () => {
+    it('handles End key (always overflow)', () => {
       const event = createKeyboardEvent('End')
       const result = handleNavigationShortcut(event, context)
-      expect(result).toEqual({ newIndex: 99, handled: true })
+      expect(result).toEqual({ newIndex: 99, handled: true, overflow: true })
     })
 
     it('does not handle End with metaKey', () => {
@@ -72,12 +72,12 @@ describe('handleNavigationShortcut', () => {
       }
       const event = createKeyboardEvent('End')
       const result = handleNavigationShortcut(event, emptyContext)
-      expect(result).toEqual({ newIndex: 0, handled: true })
+      expect(result).toEqual({ newIndex: 0, handled: true, overflow: true })
     })
   })
 
   describe('PageUp in Full mode', () => {
-    it('moves up by visible items', () => {
+    it('moves up by visible items (no overflow)', () => {
       const context: NavigationContext = {
         currentIndex: 50,
         totalCount: 100,
@@ -86,7 +86,7 @@ describe('handleNavigationShortcut', () => {
       const event = createKeyboardEvent('PageUp')
       const result = handleNavigationShortcut(event, context)
       // pageSize = max(1, 20 - 1) = 19
-      expect(result).toEqual({ newIndex: 31, handled: true })
+      expect(result).toEqual({ newIndex: 31, handled: true, overflow: false })
     })
 
     it('uses default page size when visibleItems not provided', () => {
@@ -97,23 +97,35 @@ describe('handleNavigationShortcut', () => {
       const event = createKeyboardEvent('PageUp')
       const result = handleNavigationShortcut(event, context)
       // pageSize defaults to 20
-      expect(result).toEqual({ newIndex: 30, handled: true })
+      expect(result).toEqual({ newIndex: 30, handled: true, overflow: false })
     })
 
-    it('clamps to 0', () => {
+    it('clamps to 0 (overflow=true)', () => {
       const context: NavigationContext = {
         currentIndex: 5,
         totalCount: 100,
         visibleItems: 20,
       }
       const event = createKeyboardEvent('PageUp')
       const result = handleNavigationShortcut(event, context)
-      expect(result).toEqual({ newIndex: 0, handled: true })
+      expect(result).toEqual({ newIndex: 0, handled: true, overflow: true })
+    })
+
+    it('exact boundary (raw = 0) is not overflow', () => {
+      const context: NavigationContext = {
+        currentIndex: 19,
+        totalCount: 100,
+        visibleItems: 20,
+      }
+      // pageSize = 19, raw = 19 - 19 = 0 → not clamped
+      const event = createKeyboardEvent('PageUp')
+      const result = handleNavigationShortcut(event, context)
+      expect(result).toEqual({ newIndex: 0, handled: true, overflow: false })
     })
   })
 
   describe('PageDown in Full mode', () => {
-    it('moves down by visible items', () => {
+    it('moves down by visible items (no overflow)', () => {
       const context: NavigationContext = {
         currentIndex: 50,
         totalCount: 100,
@@ -122,7 +134,7 @@ describe('handleNavigationShortcut', () => {
       const event = createKeyboardEvent('PageDown')
       const result = handleNavigationShortcut(event, context)
       // pageSize = max(1, 20 - 1) = 19
-      expect(result).toEqual({ newIndex: 69, handled: true })
+      expect(result).toEqual({ newIndex: 69, handled: true, overflow: false })
     })
 
     it('uses default page size when visibleItems not provided', () => {
@@ -132,19 +144,30 @@ describe('handleNavigationShortcut', () => {
       }
       const event = createKeyboardEvent('PageDown')
       const result = handleNavigationShortcut(event, context)
-      // pageSize defaults to 20
-      expect(result).toEqual({ newIndex: 70, handled: true })
+      expect(result).toEqual({ newIndex: 70, handled: true, overflow: false })
     })
 
-    it('clamps to totalCount - 1', () => {
+    it('clamps to totalCount - 1 (overflow=true)', () => {
       const context: NavigationContext = {
         currentIndex: 95,
         totalCount: 100,
         visibleItems: 20,
       }
       const event = createKeyboardEvent('PageDown')
       const result = handleNavigationShortcut(event, context)
-      expect(result).toEqual({ newIndex: 99, handled: true })
+      expect(result).toEqual({ newIndex: 99, handled: true, overflow: true })
+    })
+
+    it('exact boundary (raw = totalCount-1) is not overflow', () => {
+      const context: NavigationContext = {
+        currentIndex: 80,
+        totalCount: 100,
+        visibleItems: 20,
+      }
+      // pageSize = 19, raw = 80 + 19 = 99 = lastIndex → not clamped
+      const event = createKeyboardEvent('PageDown')
+      const result = handleNavigationShortcut(event, context)
+      expect(result).toEqual({ newIndex: 99, handled: true, overflow: false })
     })
   })
 
@@ -153,7 +176,7 @@ describe('handleNavigationShortcut', () => {
     // itemsPerColumn = 10, visibleColumns = 3
     // Layout: Col0[0-9], Col1[10-19], Col2[20-29], Col3[30-39], etc.
 
-    it('moves left by visible columns minus 1', () => {
+    it('moves left by visible columns minus 1 (no overflow)', () => {
       const context: NavigationContext = {
         currentIndex: 35, // Column 3, row 5
         totalCount: 50,
@@ -165,10 +188,10 @@ describe('handleNavigationShortcut', () => {
       // columnsToMove = max(1, 3 - 1) = 2
       // currentColumn = 3, targetColumn = 1
       // targetColumnStart = 10, bottommost = min(49, 10 + 10 - 1) = 19
-      expect(result).toEqual({ newIndex: 19, handled: true })
+      expect(result).toEqual({ newIndex: 19, handled: true, overflow: false })
     })
 
-    it('jumps to first item when near start', () => {
+    it('jumps to first item when near start (overflow=true)', () => {
       const context: NavigationContext = {
         currentIndex: 5, // Column 0, row 5
         totalCount: 50,
@@ -178,10 +201,10 @@ describe('handleNavigationShortcut', () => {
       const event = createKeyboardEvent('PageUp')
       const result = handleNavigationShortcut(event, context)
       // targetColumn would be -2, which is <= 0, so jump to 0
-      expect(result).toEqual({ newIndex: 0, handled: true })
+      expect(result).toEqual({ newIndex: 0, handled: true, overflow: true })
     })
 
-    it('jumps to first item from column 1', () => {
+    it('jumps to first item from column 1 (overflow=true)', () => {
       const context: NavigationContext = {
         currentIndex: 15, // Column 1, row 5
         totalCount: 50,
@@ -191,12 +214,12 @@ describe('handleNavigationShortcut', () => {
       const event = createKeyboardEvent('PageUp')
       const result = handleNavigationShortcut(event, context)
       // targetColumn = 1 - 2 = -1, which is <= 0
-      expect(result).toEqual({ newIndex: 0, handled: true })
+      expect(result).toEqual({ newIndex: 0, handled: true, overflow: true })
     })
   })
 
   describe('PageDown in Brief mode', () => {
-    it('moves right by visible columns minus 1', () => {
+    it('moves right by visible columns minus 1 (no overflow)', () => {
       const context: NavigationContext = {
         currentIndex: 15, // Column 1, row 5
         totalCount: 50,
@@ -209,10 +232,10 @@ describe('handleNavigationShortcut', () => {
       // currentColumn = 1, targetColumn = 3
       // totalColumns = ceil(50/10) = 5, so 3 < 4 (last column index)
       // targetColumnStart = 30, bottommost = min(49, 30 + 10 - 1) = 39
-      expect(result).toEqual({ newIndex: 39, handled: true })
+      expect(result).toEqual({ newIndex: 39, handled: true, overflow: false })
     })
 
-    it('jumps to last item when near end', () => {
+    it('jumps to last item when near end (overflow=true)', () => {
       const context: NavigationContext = {
         currentIndex: 35, // Column 3, row 5
         totalCount: 50,
@@ -222,10 +245,10 @@ describe('handleNavigationShortcut', () => {
       const event = createKeyboardEvent('PageDown')
       const result = handleNavigationShortcut(event, context)
       // totalColumns = 5, targetColumn = 3 + 2 = 5 >= 4 (last column index)
-      expect(result).toEqual({ newIndex: 49, handled: true })
+      expect(result).toEqual({ newIndex: 49, handled: true, overflow: true })
     })
 
-    it('handles partial last column', () => {
+    it('handles partial last column (overflow=true)', () => {
       const context: NavigationContext = {
         currentIndex: 25, // Column 2, row 5
         totalCount: 45, // Last column only has 5 items
@@ -236,7 +259,7 @@ describe('handleNavigationShortcut', () => {
       const result = handleNavigationShortcut(event, context)
       // totalColumns = ceil(45/10) = 5, targetColumn = 2 + 2 = 4 (last column)
       // 4 >= 4, so jump to last item
-      expect(result).toEqual({ newIndex: 44, handled: true })
+      expect(result).toEqual({ newIndex: 44, handled: true, overflow: true })
     })
   })