fix: scope mouse selection to focused pane in split mode

src/app/linux_input.c

@@ -736,6 +736,16 @@ static void mouseButtonCallback(GLFWwindow* w, int button, int action, int mods)
             row -= g_grid_top_offset;
             if (row < 0) row = 0;
 
+            // Clamp to focused pane bounds when splits are active
+            if (g_split_active && g_pane_rect_rows > 0) {
+                int pr = g_pane_rect_row, pc = g_pane_rect_col;
+                int pe = pr + g_pane_rect_rows, pce = pc + g_pane_rect_cols;
+                if (row < pr) row = pr;
+                if (row >= pe) row = pe - 1;
+                if (col < pc) col = pc;
+                if (col >= pce) col = pce - 1;
+            }
+
             // Ctrl+click opens hyperlink
             if (mods & GLFW_MOD_CONTROL) {
                 int cols = g_cols, nrows = g_rows;
@@ -982,6 +992,17 @@ static void cursorPosCallback(GLFWwindow* w, double mx, double my) {
         mouseToCell(mx, my, &col, &row);
         row -= g_grid_top_offset;
         if (row < 0) row = 0;
+
+        // Clamp to focused pane bounds when splits are active
+        if (g_split_active && g_pane_rect_rows > 0) {
+            int pr = g_pane_rect_row, pc = g_pane_rect_col;
+            int pe = pr + g_pane_rect_rows, pce = pc + g_pane_rect_cols;
+            if (row < pr) row = pr;
+            if (row >= pe) row = pe - 1;
+            if (col < pc) col = pc;
+            if (col >= pce) col = pce - 1;
+        }
+
         if (col == g_sel_end_col && row == g_sel_end_row) return;
 
         if (g_click_count >= 3) {

src/app/linux_render_util.c

@@ -175,8 +175,8 @@ int emitString(Vertex* v, int i, GlyphCache* gc,
 
 int cellIsSelected(int row, int col) {
     if (!g_sel_active) return 0;
-    // In copy mode with splits, clip selection to focused pane rect
-    if (g_copy_mode && g_pane_rect_rows > 0) {
+    // With splits, clip selection to focused pane rect
+    if ((g_copy_mode || g_split_active) && g_pane_rect_rows > 0) {
         int pr = g_pane_rect_row, pc = g_pane_rect_col;
         if (row < pr || row >= pr + g_pane_rect_rows || col < pc || col >= pc + g_pane_rect_cols) return 0;
     }

src/app/macos_input.m

@@ -372,6 +372,16 @@ - (void)mouseDown:(NSEvent *)event {
     row -= g_grid_top_offset;
     if (row < 0) row = 0;
 
+    // Clamp to focused pane bounds when splits are active
+    if (g_split_active && g_pane_rect_rows > 0) {
+        int pr = g_pane_rect_row, pc = g_pane_rect_col;
+        int pe = pr + g_pane_rect_rows, pce = pc + g_pane_rect_cols;
+        if (row < pr) row = pr;
+        if (row >= pe) row = pe - 1;
+        if (col < pc) col = pc;
+        if (col >= pce) col = pce - 1;
+    }
+
     if (event.modifierFlags & NSEventModifierFlagCommand) {
         int cols = g_cols, rows_n = g_rows;
         if (g_cells && col >= 0 && col < cols && row >= 0 && row < rows_n) {
@@ -664,6 +674,17 @@ - (void)mouseDragged:(NSEvent *)event {
         mouseCell0(event, self, &col, &row);
         row -= g_grid_top_offset;
         if (row < 0) row = 0;
+
+        // Clamp to focused pane bounds when splits are active
+        if (g_split_active && g_pane_rect_rows > 0) {
+            int pr = g_pane_rect_row, pc = g_pane_rect_col;
+            int pe = pr + g_pane_rect_rows, pce = pc + g_pane_rect_cols;
+            if (row < pr) row = pr;
+            if (row >= pe) row = pe - 1;
+            if (col < pc) col = pc;
+            if (col >= pce) col = pce - 1;
+        }
+
         if (col == g_sel_end_col && row == g_sel_end_row) return;
 
         if (_clickCount >= 3) {

src/app/macos_renderer_draw.m

@@ -9,8 +9,8 @@
 
 static BOOL cellIsSelected(int row, int col) {
     if (!g_sel_active) return NO;
-    // In copy mode with splits, clip selection to focused pane rect
-    if (g_copy_mode && g_pane_rect_rows > 0) {
+    // With splits, clip selection to focused pane rect
+    if ((g_copy_mode || g_split_active) && g_pane_rect_rows > 0) {
         int pr = g_pane_rect_row, pc = g_pane_rect_col;
         int pe = pr + g_pane_rect_rows, pce = pc + g_pane_rect_cols;
         if (row < pr || row >= pe || col < pc || col >= pce) return NO;

src/app/ui/selection.zig

@@ -21,11 +21,18 @@ pub fn copySelection(is_block: bool) void {
     const total_lines = sb_count + grid_rows;
     if (total_lines <= 0) return;
 
-    // Read and normalize selection bounds (viewport-relative)
+    // Read and normalize selection bounds (viewport-relative).
+    // In split mode, coords are in global content-space — convert to pane-local.
     var sr: i32 = c.g_sel_start_row;
     var sc: i32 = c.g_sel_start_col;
     var er: i32 = c.g_sel_end_row;
     var ec: i32 = c.g_sel_end_col;
+    if (c.g_split_active != 0 and c.g_pane_rect_rows > 0) {
+        sr -= c.g_pane_rect_row;
+        er -= c.g_pane_rect_row;
+        sc -= c.g_pane_rect_col;
+        ec -= c.g_pane_rect_col;
+    }
     if (sr > er or (sr == er and sc > ec)) {
         const tr = sr;
         const tc = sc;