feat(pan): interactive PAN mode with left-drag (no middle button needed)

The PAN command/tool dispatched a command nobody handled, so it did
nothing. Combined with no middle mouse button on a trackpad/web client,
there was no way to pan at all (issue 164).

PAN (and the "P" alias) now enters a pan mode: a left-button drag pans the
view, reusing the existing middle-button pan path. Exit with Esc or by
starting another command. While active the crosshair is hidden and the
cursor becomes a hand (open when hovering, closed while dragging). PAN/P
are also added to command-line autocomplete.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/commands.rs

@@ -29,6 +29,9 @@ impl OpenCADStudio {
             self.tabs[i].scene.clear_preview_wire();
             self.tabs[i].active_cmd = None;
         }
+        // Starting any command leaves interactive PAN mode (the PAN arm below
+        // re-enables it).
+        self.tabs[i].pan_mode = false;
         // Reset the last committed point so the first click of the new command
         // is not constrained by ortho/polar relative to a previous command's endpoint.
         self.last_point = None;
@@ -5148,6 +5151,14 @@ impl OpenCADStudio {
                 self.command_line.push_output("Display regenerated.");
             }
 
+            // Interactive pan: left-drag pans the view until Esc. The only pan
+            // path when there is no middle mouse button (trackpad / web).
+            "PAN" | "P" => {
+                self.tabs[i].pan_mode = true;
+                self.command_line
+                    .push_output("PAN: drag with the left mouse button. Press Esc to exit.");
+            }
+
             // ── TABLE cell editing ─────────────────────────────────────────────
             // TABLE CELL <row> <col> <text> — set text for a cell in the selected Table
             cmd if cmd.starts_with("TABLE ") => {
@@ -5972,7 +5983,8 @@ inventory::submit!(crate::command::CommandRegistration {
         "LAYER", "LAYERS", "LAYISO", "LAYON", "LAYOUTMANAGER", "LAYOUTPANEL", "LAYOUTTAB", "LAYTHW",
         "LAYUNISO", "LI", "LINETYPE", "LIST", "LTSCALE", "LWDISPLAY", "MASSPROP", "MLEADERSTYLE",
         "MLSTYLE", "MS", "MSPACE", "NAVVCUBE", "NEW", "OBJIMPORT", "OPEN", "ORTHO",
-        "PAGESETUP", "PERF", "PERSP", "PLOT", "PLOTSTYLE", "PLOTSTYLEEDITOR", "PLOTSTYLEPANEL", "PR",
+        "P", "PAN", "PAGESETUP", "PERF", "PERSP", "PLOT", "PLOTSTYLE", "PLOTSTYLEEDITOR",
+        "PLOTSTYLEPANEL", "PR",
         "PRINT", "PROPERTIES", "PROPS", "PSPACE", "PURGE", "QS", "QSAVE", "QSELECT",
         "QUIT", "REDO", "REDRAW", "REDRWALL", "REGEN", "REGENALL", "RENAME", "REPORT",
         "SA", "SAVE", "SAVEAS", "SCALETEXT", "SELECTALL", "SELECTSIMILAR", "SELSIM", "SHEETSET",

src/app/document.rs

@@ -158,6 +158,11 @@ pub(super) struct DocumentTab {
     /// of the model-space shader. The scene is still constructed so the
     /// rest of the code can treat it as a normal tab when reading.
     pub(super) is_start: bool,
+    /// Interactive PAN mode (the PAN command / tool). While active, a left-
+    /// button drag pans the view instead of selecting — the only pan path on a
+    /// device with no middle mouse button (a trackpad / web client). Exited
+    /// with Esc or by starting another command.
+    pub(super) pan_mode: bool,
     /// Per-plugin document state (`plugin::BuiltinPlugin` manifest id → state).
     #[cfg_attr(target_arch = "wasm32", allow(dead_code))]
     pub(super) plugin_state: HashMap<&'static str, Box<dyn Any + Send + Sync>>,
@@ -377,6 +382,7 @@ impl DocumentTab {
             active_mleader_style: "Standard".to_string(),
             last_synced_camera_gen: 0,
             is_start: false,
+            pan_mode: false,
             plugin_state: HashMap::new(),
             suspended_cmd: None,
         }

src/app/update.rs

@@ -1835,6 +1835,18 @@ impl OpenCADStudio {
                     self.text_inline_cancel();
                     return self.post_editor_closed(false);
                 }
+                // Leave interactive PAN mode (and end any in-flight pan drag).
+                if self.tabs[self.active_tab].pan_mode {
+                    let i = self.active_tab;
+                    self.tabs[i].pan_mode = false;
+                    {
+                        let mut sel = self.tabs[i].scene.selection.borrow_mut();
+                        sel.middle_down = false;
+                        sel.middle_last_pos = None;
+                    }
+                    self.command_line.push_output("PAN ended.");
+                    return Task::none();
+                }
                 // Grip popup intercepts Escape — dismisses the menu
                 // without doing anything else.
                 if self.grip_popup.take().is_some() {
@@ -3217,6 +3229,16 @@ impl OpenCADStudio {
                 };
                 let (vw, vh) = vp_size;
 
+                // PAN mode: a left press begins a pan drag. Reuse the middle-
+                // button pan path (the move handler pans whenever `middle_down`),
+                // so no selection/pick logic runs while panning.
+                if self.tabs[i].pan_mode {
+                    let mut sel = self.tabs[i].scene.selection.borrow_mut();
+                    sel.middle_down = true;
+                    sel.middle_last_pos = Some(p);
+                    return Task::none();
+                }
+
                 if vw > 1.0 && vh > 1.0 {
                     let rot = self.tabs[i].scene.active_view_rotation_mat();
                     // Map the cursor into whichever area owns the cube (active
@@ -3382,6 +3404,15 @@ impl OpenCADStudio {
             Message::ViewportLeftRelease => {
                 let i = self.active_tab;
 
+                // PAN mode: end the pan drag but stay in pan mode for the next
+                // drag (exit is Esc / another command). Mirror of the press.
+                if self.tabs[i].pan_mode {
+                    let mut sel = self.tabs[i].scene.selection.borrow_mut();
+                    sel.middle_down = false;
+                    sel.middle_last_pos = None;
+                    return Task::none();
+                }
+
                 // End an in-flight tile-divider drag. Any tile that fell
                 // below the minimum (viewcube fits comfortably) gets
                 // absorbed into its longest-contact neighbour, so the

src/app/view.rs

@@ -263,6 +263,7 @@ impl OpenCADStudio {
                 tab.last_cursor_screen,
                 !is_paper && self.show_viewcube,
                 tile_edges,
+                tab.pan_mode,
             )
         };
 

src/ui/overlay.rs

@@ -129,6 +129,7 @@ pub fn selection_overlay<'a>(
     cursor_screen: Point,
     show_viewcube: bool,
     tile_edges: Vec<crate::scene::TileEdge>,
+    pan_mode: bool,
 ) -> Element<'a, Message> {
     canvas(SelectionCanvas {
         selection,
@@ -140,6 +141,7 @@ pub fn selection_overlay<'a>(
         cursor_screen,
         show_viewcube,
         tile_edges,
+        pan_mode,
     })
     .width(Length::Fill)
     .height(Length::Fill)
@@ -156,6 +158,9 @@ struct SelectionCanvas {
     cursor_screen: Point,
     show_viewcube: bool,
     tile_edges: Vec<crate::scene::TileEdge>,
+    /// Interactive PAN mode: the crosshair is hidden and the cursor becomes a
+    /// hand so the viewport reads as a draggable surface.
+    pan_mode: bool,
 }
 
 impl SelectionCanvas {
@@ -207,6 +212,15 @@ impl canvas::Program<Message> for SelectionCanvas {
         bounds: iced::Rectangle,
         cursor: mouse::Cursor,
     ) -> mouse::Interaction {
+        // PAN mode owns the whole viewport: an open hand when hovering, a
+        // closed hand while dragging.
+        if self.pan_mode && cursor.is_over(bounds) {
+            return if self.selection.middle_down {
+                mouse::Interaction::Grabbing
+            } else {
+                mouse::Interaction::Grab
+            };
+        }
         if self.show_viewcube {
             if let Some(pos) = cursor.position_in(bounds) {
                 use crate::scene::{VIEWCUBE_DRAW_PX, VIEWCUBE_PAD};
@@ -757,7 +771,8 @@ impl canvas::Program<Message> for SelectionCanvas {
         // arrow (see `mouse_interaction`); drawing the CAD crosshair on
         // top of it would double up the visual feedback.
         let over_divider = self.tile_edge_under(cursor, bounds).is_some();
-        if !over_viewcube && !over_divider {
+        // PAN mode replaces the crosshair with a hand cursor.
+        if !over_viewcube && !over_divider && !self.pan_mode {
             if let Some(cp) = self.selection.last_move_pos {
                 let color = Color {
                     r: 0.85,