refactor(desktop): move transfer browser column resize onto its state

The three resize handlers only read and wrote self.transfer.browser, so
they now take &mut TransferBrowserState and the NyaTermApp methods are
forwarders that own the redraw. The update and finish helpers return
whether anything changed so the forwarder can skip a needless notify.

TransferBrowserColumnResizeState no longer leaks into the transfers page
module, which is what the narrower receiver buys.

crates/nyaterm-desktop/src/features/pages/transfers/browser_columns.rs

@@ -7,12 +7,9 @@ impl NyaTermApp {
         event: &MouseDownEvent,
         cx: &mut Context<Self>,
     ) {
-        self.transfer.browser.column_resize = Some(TransferBrowserColumnResizeState {
-            column,
-            start_x: event.position.x,
-            start_width: self.transfer.browser.column_widths.get(column),
-        });
-        self.transfer.browser.status = format!("resizing {} column", column.label().to_lowercase());
+        self.transfer
+            .browser
+            .start_column_resize(column, event.position.x);
         cx.notify();
     }
 
@@ -21,18 +18,9 @@ impl NyaTermApp {
         event: &MouseMoveEvent,
         cx: &mut Context<Self>,
     ) {
-        let Some(state) = self.transfer.browser.column_resize else {
-            return;
-        };
-        let next_width = state.start_width + (event.position.x - state.start_x);
-        self.transfer
-            .browser
-            .column_widths
-            .set(state.column, next_width);
-        let width = f32::from(self.transfer.browser.column_widths.get(state.column)).round();
-        self.transfer.browser.status =
-            format!("{} column: {width}px", state.column.label().to_lowercase());
-        cx.notify();
+        if self.transfer.browser.update_column_resize(event.position.x) {
+            cx.notify();
+        }
     }
 
     pub(in crate::features) fn finish_transfer_browser_column_resize(
@@ -40,8 +28,7 @@ impl NyaTermApp {
         _event: &MouseUpEvent,
         cx: &mut Context<Self>,
     ) {
-        if self.transfer.browser.column_resize.take().is_some() {
-            self.transfer.browser.status = "file column width updated".to_string();
+        if self.transfer.browser.finish_column_resize() {
             cx.notify();
         }
     }

crates/nyaterm-desktop/src/features/pages/transfers/mod.rs

@@ -14,7 +14,7 @@ use std::collections::{HashSet, VecDeque};
 use std::time::Duration;
 
 use crate::models::{
-    TransferBrowserColumnResizeState, TransferBrowserColumnWidths, TransferBrowserContextMenuState,
+    TransferBrowserColumnWidths, TransferBrowserContextMenuState,
     TransferBrowserDragSelectionState, TransferBrowserFavoritesMenuState,
     TransferBrowserPendingRenameState, TransferBrowserSessionCacheState, TransferBrowserSortColumn,
     TransferBrowserSortDirection, TransferBrowserUploadMenuState, TransferDeleteState,

crates/nyaterm-desktop/src/features/transfers/state.rs

@@ -9,7 +9,7 @@ use std::collections::{HashMap, HashSet, VecDeque};
 use std::sync::mpsc;
 use std::time::Instant;
 
-use gpui::{FocusHandle, WindowHandle};
+use gpui::{FocusHandle, Pixels, WindowHandle};
 use nyaterm_transport::{SftpDuplicatePolicy, SftpFileEntry};
 
 use crate::features::{TransferExternalSyncWindow, TransferJobResult};
@@ -268,3 +268,43 @@ impl TransferFeatureState {
         }
     }
 }
+
+/// Column resize is self-contained: it only reads and writes browser geometry.
+///
+/// Keeping it here rather than on `NyaTermApp` means a drag cannot reach any
+/// other app state; the page-level handlers are forwarders that own the redraw.
+impl TransferBrowserState {
+    pub(in crate::features) fn start_column_resize(
+        &mut self,
+        column: TransferBrowserSortColumn,
+        position_x: Pixels,
+    ) {
+        self.column_resize = Some(TransferBrowserColumnResizeState {
+            column,
+            start_x: position_x,
+            start_width: self.column_widths.get(column),
+        });
+        self.status = format!("resizing {} column", column.label().to_lowercase());
+    }
+
+    /// Returns false when no resize is in flight, so the caller can skip the redraw.
+    pub(in crate::features) fn update_column_resize(&mut self, position_x: Pixels) -> bool {
+        let Some(state) = self.column_resize else {
+            return false;
+        };
+        let next_width = state.start_width + (position_x - state.start_x);
+        self.column_widths.set(state.column, next_width);
+        let width = f32::from(self.column_widths.get(state.column)).round();
+        self.status = format!("{} column: {width}px", state.column.label().to_lowercase());
+        true
+    }
+
+    /// Returns false when no resize was in flight, so the caller can skip the redraw.
+    pub(in crate::features) fn finish_column_resize(&mut self) -> bool {
+        if self.column_resize.take().is_none() {
+            return false;
+        }
+        self.status = "file column width updated".to_string();
+        true
+    }
+}