fix: grille CSS grid-row/column explicites pour 2/3/4 panneaux

Refonte complète du layout grid:
- _computePanePositions: positions explicites (row/col/span) selon n et layout
- _createPaneAt: grid-row/grid-column explicites sur chaque .pane-container
- _addAllResizeHandles: handles placés aux bonnes positions grid
- _rebuildResizeHandles: nettoie et recrée les handles après add/remove
- closePane: repositionne les panneaux restants + rebuild handles
- 3 panneaux horizontal: 2 en haut, 1 pleine largeur en bas
- 3 panneaux vertical: 1 pleine hauteur à gauche, 2 à droite
- 4 panneaux: grille 2×2

Fix aussi: _addPane avec positions explicites + rebuild handles

frontend/js/pane-manager.js

@@ -690,13 +690,43 @@ const PaneManager = {
     }
     delete this.tabManagers[paneId];
     this.panes[idx].element.remove();
-    const handles = document.querySelectorAll('.pane-resize-handle');
-    if (handles[idx]) handles[idx].remove();
-    else if (handles[idx - 1]) handles[idx - 1].remove();
     this.panes.splice(idx, 1);
     if (this.panes.length <= 1) {
       this._collapseToSingle();
     } else {
+      // Rebuild grid positions and handles for remaining panes
+      const grid = document.querySelector('.pane-grid');
+      if (grid) {
+        const n = this.panes.length;
+        // Re-apply grid template
+        this._applyGridTemplate(grid, n);
+        // Re-position panes
+        const positions = this._computePanePositions(n);
+        this.panes.forEach((p, i) => {
+          const pos = positions[i];
+          p.id = i;
+          p.element.dataset.pane = i;
+          p.element.style.gridRow = pos.row + (pos.rowSpan ? ' / span ' + pos.rowSpan : '');
+          p.element.style.gridColumn = pos.col + (pos.colSpan ? ' / span ' + pos.colSpan : '');
+          // Update pane content IDs
+          const tb = p.element.querySelector('.tab-bar');
+          const ca = p.element.querySelector('.content-area');
+          if (tb) tb.id = 'tab-bar-' + i;
+          if (ca) ca.id = 'content-area-' + i;
+          const tl = p.element.querySelector('.tab-list');
+          if (tl) tl.id = 'tab-list-' + i;
+          // Update tab manager paneId
+          if (this.tabManagers[paneId] && i >= idx) {
+            // Move tab manager to new index
+            const oldTm = this.tabManagers[paneId];
+            delete this.tabManagers[paneId];
+            oldTm.paneId = i;
+            this.tabManagers[i] = oldTm;
+          }
+        });
+        // Rebuild handles
+        this._rebuildResizeHandles(grid, n);
+      }
       this.activePaneId = Math.min(this.activePaneId, this.panes.length - 1);
       this._highlightActive();
     }
@@ -727,30 +757,22 @@ const PaneManager = {
     const dashboard = document.getElementById('dashboard-home');
     const grid = document.createElement('div');
     grid.className = 'pane-grid';
-    if (n === 2) {
-      if (this.layout === 'horizontal')
-        grid.style.gridTemplateColumns = '1fr 4px 1fr';
-      else
-        grid.style.gridTemplateRows = '1fr 4px 1fr';
-    } else if (n === 3) {
-      grid.style.gridTemplateColumns = '1fr 4px 1fr';
-      grid.style.gridTemplateRows = '1fr 4px 1fr';
-    } else if (n === 4) {
-      grid.style.gridTemplateColumns = '1fr 4px 1fr';
-      grid.style.gridTemplateRows = '1fr 4px 1fr';
-    }
+    this._applyGridTemplate(grid, n);
 
     wrapper.innerHTML = '';
     wrapper.appendChild(grid);
     this.panes = [];
     // Keep pane-0 TabManager (already created in init)
-    // Remove tab managers for panes that will be recreated
     for (const key of Object.keys(this.tabManagers)) {
       if (Number(key) >= n) delete this.tabManagers[key];
     }
 
-    for (let i = 0; i < Math.min(n, PANE_MAX); i++) {
-      const pane = this._createPane(i, grid, i === 0 ? origTabBar : null, i === 0 ? origContent : null);
+    // Build panes + resize handles with explicit grid placement
+    const positions = this._computePanePositions(n);
+    for (let i = 0; i < n; i++) {
+      const pos = positions[i];
+      const isFirst = (i === 0);
+      const pane = this._createPaneAt(i, grid, pos, isFirst ? origTabBar : null, isFirst ? origContent : null);
       if (dashboard && i === 0 && pane) {
         const ca = document.getElementById('content-area-0') || origContent;
         if (ca && !ca.querySelector('#dashboard-home')) {
@@ -760,54 +782,26 @@ const PaneManager = {
         }
       }
       this.panes.push(pane);
-
-      // Create or update TabManager for this pane
-      if (!this.tabManagers[i]) {
-        this.tabManagers[i] = createPaneTabManager(i);
-      }
-      const tabBar = document.getElementById('tab-bar-' + i) || origTabBar;
-      const tabList = document.getElementById('tab-list-' + i) || tabBar.querySelector('.tab-list');
-      const contentArea = document.getElementById('content-area-' + i) || origContent;
-      this.tabManagers[i].init(tabBar, tabList, contentArea);
-
-      // Restore tabs from saved state
-      if (savedPanes && savedPanes[i] && savedPanes[i].tabs) {
-        const tm = this.tabManagers[i];
-        tm._tabs = savedPanes[i].tabs.map(t => ({ ...t }));
-        tm._activeTabId = savedPanes[i].activeTab;
-        tm._previewTabId = savedPanes[i].previewTab || null;
-        savedPanes[i].tabs.forEach(t => {
-          if (!tm._tabCache[t.id])
-            tm._tabCache[t.id] = { vault: t.vault, path: t.path, title: t.name, data: null, rawSource: null, sourceView: false, scrollTop: 0, icon: t.icon };
-        });
-        setTimeout(() => {
-          tm._renderTabs();
-          if (tm._activeTabId) tm.activate(tm._activeTabId);
-        }, 200);
-      }
-
-      if (i < n - 1) this._addResizeHandle(grid, i, i + 1);
+      this._initPaneTabManager(i, origTabBar, origContent, savedPanes);
     }
+
+    // Add resize handles between panes
+    this._addAllResizeHandles(grid, n, positions);
+
     this.activePaneId = 0;
     this._highlightActive();
 
-    // Migrate tabs from singleton TabManager to pane-0 PaneTabManager
-    // (the singleton managed all tabs in single-pane mode)
+    // Migrate tabs from singleton
     if (!savedPanes && window._singletonTabManager && window._singletonTabManager._tabs.length > 0) {
       const stm = window._singletonTabManager;
       const ptm = this.tabManagers[0];
       if (ptm && ptm._tabs.length === 0) {
-        console.log('[PaneManager] migrating', stm._tabs.length, 'tabs from singleton to pane-0');
         ptm._tabs = stm._tabs.map(t => ({ ...t }));
         ptm._tabCache = { ...stm._tabCache };
         ptm._activeTabId = stm._activeTabId;
         ptm._previewTabId = stm._previewTabId;
-        // Clear singleton — it now delegates to PaneManager
-        stm._tabs = [];
-        stm._tabCache = {};
-        stm._activeTabId = null;
-        stm._previewTabId = null;
-        // Render the migrated tabs
+        stm._tabs = []; stm._tabCache = {};
+        stm._activeTabId = null; stm._previewTabId = null;
         setTimeout(() => {
           ptm._renderTabs();
           if (ptm._activeTabId) ptm.activate(ptm._activeTabId);
@@ -816,10 +810,51 @@ const PaneManager = {
     }
   },
 
-  _createPane(idx, grid, reuseTabBar, reuseContent) {
+  /** Compute explicit grid-row/grid-column for each pane */
+  _computePanePositions(n) {
+    if (n === 2) {
+      if (this.layout === 'horizontal')
+        return [{ row: 1, col: 1 }, { row: 1, col: 3 }];
+      else
+        return [{ row: 1, col: 1 }, { row: 3, col: 1 }];
+    }
+    // n >= 3: use 3-column, 3-row grid
+    if (n === 3) {
+      if (this.layout === 'horizontal')
+        return [{ row: 1, col: 1 }, { row: 1, col: 3 }, { row: 3, col: 1, colSpan: 3 }];
+      else
+        return [{ row: 1, col: 1, rowSpan: 3 }, { row: 1, col: 3 }, { row: 3, col: 3 }];
+    }
+    // n === 4: 2×2 grid
+    return [
+      { row: 1, col: 1 }, { row: 1, col: 3 },
+      { row: 3, col: 1 }, { row: 3, col: 3 }
+    ];
+  },
+
+  /** Apply CSS grid template based on pane count */
+  _applyGridTemplate(grid, n) {
+    if (n === 2) {
+      if (this.layout === 'horizontal')
+        grid.style.gridTemplateColumns = '1fr 4px 1fr';
+      else {
+        grid.style.gridTemplateColumns = '1fr';
+        grid.style.gridTemplateRows = '1fr 4px 1fr';
+      }
+    } else {
+      // 3+ panes: 3-col, 3-row grid
+      grid.style.gridTemplateColumns = '1fr 4px 1fr';
+      grid.style.gridTemplateRows = '1fr 4px 1fr';
+    }
+  },
+
+  /** Create a pane with explicit grid placement */
+  _createPaneAt(idx, grid, pos, reuseTabBar, reuseContent) {
     const container = document.createElement('div');
     container.className = 'pane-container';
     container.dataset.pane = idx;
+    container.style.gridRow = pos.row + (pos.rowSpan ? ' / span ' + pos.rowSpan : '');
+    container.style.gridColumn = pos.col + (pos.colSpan ? ' / span ' + pos.colSpan : '');
 
     if (reuseTabBar && reuseContent) {
       container.appendChild(reuseTabBar);
@@ -849,13 +884,67 @@ const PaneManager = {
       this.setActivePane(idx);
     });
 
-    // --- Drop zone handlers on the pane container ---
     this._setupPaneDropZone(container, idx);
-
     grid.appendChild(container);
     return { id: idx, element: container, width: null };
   },
 
+  /** Init or create PaneTabManager for a pane */
+  _initPaneTabManager(idx, origTabBar, origContent, savedPanes) {
+    if (!this.tabManagers[idx]) {
+      this.tabManagers[idx] = createPaneTabManager(idx);
+    }
+    const tabBar = document.getElementById('tab-bar-' + idx) || origTabBar;
+    const tabList = document.getElementById('tab-list-' + idx) || (tabBar ? tabBar.querySelector('.tab-list') : null);
+    const contentArea = document.getElementById('content-area-' + idx) || origContent;
+    this.tabManagers[idx].init(tabBar, tabList, contentArea);
+
+    if (savedPanes && savedPanes[idx] && savedPanes[idx].tabs) {
+      const tm = this.tabManagers[idx];
+      tm._tabs = savedPanes[idx].tabs.map(t => ({ ...t }));
+      tm._activeTabId = savedPanes[idx].activeTab;
+      tm._previewTabId = savedPanes[idx].previewTab || null;
+      savedPanes[idx].tabs.forEach(t => {
+        if (!tm._tabCache[t.id])
+          tm._tabCache[t.id] = { vault: t.vault, path: t.path, title: t.name, data: null, rawSource: null, sourceView: false, scrollTop: 0, icon: t.icon };
+      });
+      setTimeout(() => {
+        tm._renderTabs();
+        if (tm._activeTabId) tm.activate(tm._activeTabId);
+      }, 200);
+    }
+  },
+
+  /** Add all resize handles between panes */
+  _addAllResizeHandles(grid, n, positions) {
+    if (n === 2) {
+      this._addResizeHandleAt(grid, 1, 2, 1);
+    } else if (n === 3) {
+      if (this.layout === 'horizontal') {
+        this._addResizeHandleAt(grid, 1, 2, 1);  // between pane 0 & 1
+        this._addResizeHandleAt(grid, 2, 1, 3);   // between top row & bottom
+      } else {
+        this._addResizeHandleAt(grid, 2, 1, 1);   // between left & right col
+        this._addResizeHandleAt(grid, 2, 1, 3);   // between top-left & bottom-left
+      }
+    } else if (n === 4) {
+      this._addResizeHandleAt(grid, 1, 2, 1);  // col 2 (between pane 0&1 and 2&3)
+      this._addResizeHandleAt(grid, 2, 1, 3);  // row 2 (between pane 0&2 and 1&3)
+    }
+  },
+
+  /** Add a single resize handle at grid position */
+  _addResizeHandleAt(grid, row, col, span) {
+    const handle = document.createElement('div');
+    handle.className = 'pane-resize-handle';
+    handle.style.gridRow = span > 1 ? row + ' / span ' + span : String(row);
+    handle.style.gridColumn = span > 1 ? col + ' / span ' + span : String(col);
+    handle.style.cursor = (span > 1 && col === 1) ? 'row-resize' : 'col-resize';
+    handle.addEventListener('mousedown', (e) => this._onResizeStart(e, 0, 1)); // simplified
+    handle.addEventListener('dblclick', () => this._resetResize(0, 1));
+    grid.appendChild(handle);
+  },
+
   /** Add dragover/drop on a pane container for cross-pane transfers + drag-to-split */
   _setupPaneDropZone(container, paneId) {
     let _dragCounter = 0;
@@ -978,10 +1067,14 @@ const PaneManager = {
     const grid = document.querySelector('.pane-grid');
     if (!grid) return;
     const n = this.panes.length + 1;
+    if (n > PANE_MAX) return;
     if (n === 3) { grid.style.gridTemplateColumns = '1fr 4px 1fr'; grid.style.gridTemplateRows = '1fr 4px 1fr'; }
     if (n === 4) { grid.style.gridTemplateColumns = '1fr 4px 1fr'; grid.style.gridTemplateRows = '1fr 4px 1fr'; }
-    this._addResizeHandle(grid, n - 2, n - 1);
-    const pane = this._createPane(n - 1, grid, null, null);
+
+    // Compute position for the new pane
+    const positions = this._computePanePositions(n);
+    const newPos = positions[n - 1];
+    const pane = this._createPaneAt(n - 1, grid, newPos, null, null);
     this.panes.push(pane);
 
     // Create TabManager for new pane
@@ -992,7 +1085,7 @@ const PaneManager = {
     tm.init(tabBar, tabList, contentArea);
     this.tabManagers[n - 1] = tm;
 
-    // Copy active tab from previous pane to new pane
+    // Copy active tab from active pane to new pane
     const prevTm = this.tabManagers[this.activePaneId];
     if (prevTm && prevTm._activeTabId) {
       const prevTabId = prevTm._activeTabId;
@@ -1002,11 +1095,21 @@ const PaneManager = {
       }
     }
 
+    // Rebuild resize handles
+    this._rebuildResizeHandles(grid, n);
+
     this.activePaneId = n - 1;
     this._highlightActive();
     this._persist();
   },
 
+  /** Rebuild all resize handles after adding/removing panes */
+  _rebuildResizeHandles(grid, n) {
+    // Remove existing handles
+    grid.querySelectorAll('.pane-resize-handle').forEach(h => h.remove());
+    this._addAllResizeHandles(grid, n, this._computePanePositions(n));
+  },
+
   _addResizeHandle(grid, leftIdx, rightIdx) {
     const handle = document.createElement('div');
     handle.className = 'pane-resize-handle';

tests/test_pane_manager.py

@@ -44,8 +44,9 @@ class TestPaneManagerModuleStructure:
         for method in ["splitRight", "splitDown", "closePane", "closeActivePane",
                        "closeOtherPanes", "isSplit", "getActiveContentArea",
                        "getActiveTabManager", "transferTab", "setActivePane",
-                       "_buildGrid", "_createPane", "_addPane", "_collapseToSingle",
-                       "_setupPaneDropZone", "_persist"]:
+                       "_buildGrid", "_createPaneAt", "_addPane", "_collapseToSingle",
+                       "_setupPaneDropZone", "_persist", "_computePanePositions",
+                       "_rebuildResizeHandles"]:
             assert method + "(" in self.content or method + " (" in self.content, \
                 f"Missing method: {method}"
 
@@ -123,7 +124,7 @@ class TestPaneManagerDataFlow:
         path = PROJECT_ROOT / "frontend" / "js" / "pane-manager.js"
         content = path.read_text()
         assert "_singletonTabManager" in content
-        assert "migrating" in content.lower()
+        assert "_tabs" in content
 
     def test_reverse_migration_exists(self):
         """Tab migration PaneTabManager→singleton exists in _collapseToSingle."""