Fix: clicking on history item now shows diff for that revision

- Modified ui.js displayHistory() to pass previous revision to click handler
- Added showHistoryItemDiff() method in app.js to generate and display diff
- Diff compares selected revision with previous revision (Option A)
- First revision shows message instead of diff (no previous to compare)

ui/app.js

@@ -158,6 +158,36 @@ class CVSRepositoryBrowser {
         }
     }
 
+    /**
+     * Show diff for a history item (comparing with previous revision)
+     * @param {string} filePath - Path to the file
+     * @param {string} currentRevision - Current revision
+     * @param {string} previousRevision - Previous revision (or null if this is the first)
+     */
+    async showHistoryItemDiff(filePath, currentRevision, previousRevision) {
+        if (!filePath) return;
+
+        try {
+            ui.diffContent.innerHTML = '<div class="loading">Generating diff...</div>';
+            
+            if (!previousRevision) {
+                // If there's no previous revision, show a message
+                ui.diffContent.innerHTML = '<div class="loading">This is the first revision - no previous version to compare</div>';
+                ui.showView(ui.diffView);
+                return;
+            }
+
+            // Generate diff between previous and current revision
+            const diffResult = await api.getDiff(filePath, previousRevision, currentRevision);
+            const diffText = diffResult.diff || diffResult;
+            ui.displayDiff(diffText);
+        } catch (error) {
+            console.error('Error generating history item diff:', error);
+            ui.diffContent.innerHTML = `<div class="loading" style="color: #991b1b;">Error generating diff: ${error.message}</div>`;
+            ui.showView(ui.diffView);
+        }
+    }
+
     /**
      * Show patchsets view
      */