feat(mdviewer): add reload support and source-line-based scroll restore

- Reload button clears file cache and re-renders, restoring scroll
  position and edit mode
- Scroll save/restore now uses data-source-line elements instead of
  pixel positions, making it immune to image loading layout shifts

Author: abose

src-mdviewer/src/bridge.js

@@ -13,6 +13,7 @@ let _syncId = 0;
 let _lastReceivedSyncId = -1;
 let _suppressContentChange = false;
 let _baseURL = "";
+let _pendingReloadScroll = null; // { filePath, scrollPos, editMode } for scroll restore after reload
 
 /**
  * Check if a URL is absolute (not relative to the document).
@@ -126,6 +127,9 @@ export function initBridge() {
             case "MDVIEWR_CLOSE_FILE":
                 handleCloseFile(data);
                 break;
+            case "MDVIEWR_RELOAD_FILE":
+                handleReloadFile(data);
+                break;
             case "MDVIEWR_SET_THEME":
                 handleSetTheme(data);
                 break;
@@ -362,12 +366,45 @@ function handleSwitchFile(data) {
         docCache.createEntry(filePath, markdown, parseResult);
         docCache.switchTo(filePath);
 
-        setState({
-            currentContent: markdown,
-            parseResult: parseResult
-        });
+        // Restore scroll position from reload if applicable
+        if (_pendingReloadScroll && _pendingReloadScroll.filePath === filePath) {
+            const entry = docCache.getEntry(filePath);
+            if (entry) {
+                entry._scrollSourceLine = _pendingReloadScroll.scrollSourceLine;
+                entry._editMode = _pendingReloadScroll.editMode;
+            }
+            const restoreEditMode = _pendingReloadScroll.editMode;
+            _pendingReloadScroll = null;
+
+            setState({
+                currentContent: markdown,
+                parseResult: parseResult
+            });
+            emit("file:rendered", parseResult);
+
+            // Scroll to source line element after render
+            if (entry && entry._scrollSourceLine) {
+                requestAnimationFrame(() => {
+                    const els = entry.dom.querySelectorAll("[data-source-line]");
+                    for (const el of els) {
+                        if (parseInt(el.getAttribute("data-source-line"), 10) === entry._scrollSourceLine) {
+                            el.scrollIntoView({ behavior: "instant", block: "start" });
+                            break;
+                        }
+                    }
+                });
+            }
 
-        emit("file:rendered", parseResult);
+            if (restoreEditMode) {
+                setState({ editMode: true });
+            }
+        } else {
+            setState({
+                currentContent: markdown,
+                parseResult: parseResult
+            });
+            emit("file:rendered", parseResult);
+        }
     }
 
     _suppressContentChange = false;
@@ -395,6 +432,35 @@ function handleCloseFile(data) {
     }
 }
 
+/**
+ * Reload a specific file: save scroll position, clear its cache entry,
+ * so the next SWITCH_FILE will re-render from scratch.
+ */
+function handleReloadFile(data) {
+    const { filePath } = data;
+    if (!filePath) return;
+
+    const entry = docCache.getEntry(filePath);
+    const savedScrollPos = entry ? entry.scrollPos : 0;
+    const wasEditMode = entry ? entry._editMode : false;
+
+    // If this is the active file, save current scroll
+    if (docCache.getActiveFilePath() === filePath) {
+        docCache.saveActiveScrollPos();
+        const activeEntry = docCache.getEntry(filePath);
+        if (activeEntry) {
+            const scrollSourceLine = activeEntry._scrollSourceLine;
+            if (getState().editMode) {
+                setState({ editMode: false });
+            }
+            docCache.removeEntry(filePath);
+            _pendingReloadScroll = { filePath, scrollSourceLine, editMode: wasEditMode };
+        }
+    } else {
+        docCache.removeEntry(filePath);
+    }
+}
+
 // --- Theme, edit mode, locale ---
 
 function handleSetTheme(data) {

src-mdviewer/src/core/doc-cache.js

@@ -148,8 +148,18 @@ export function switchTo(filePath) {
 
     activeFilePath = filePath;
 
-    // Restore scroll position after layout
+    // Restore scroll position after layout using source-line element if available
     requestAnimationFrame(() => {
+        if (entry._scrollSourceLine) {
+            const elements = entry.dom.querySelectorAll("[data-source-line]");
+            for (const el of elements) {
+                if (parseInt(el.getAttribute("data-source-line"), 10) === entry._scrollSourceLine) {
+                    el.scrollIntoView({ behavior: "instant", block: "start" });
+                    return;
+                }
+            }
+        }
+        // Fallback to pixel position
         viewerContainer.scrollTop = entry.scrollPos;
     });
 
@@ -158,12 +168,30 @@ export function switchTo(filePath) {
 
 /**
  * Save the current scroll position for the active document.
+ * Saves both pixel position and the source line visible at the top of the viewport,
+ * so scroll can be restored even when images haven't loaded yet.
  */
 export function saveActiveScrollPos() {
     if (!activeFilePath) return;
     const entry = cache.get(activeFilePath);
-    if (entry) {
-        entry.scrollPos = viewerContainer.scrollTop;
+    if (!entry) return;
+
+    entry.scrollPos = viewerContainer.scrollTop;
+
+    // Find the source line element closest to the top of the viewport
+    const elements = entry.dom.querySelectorAll("[data-source-line]");
+    const containerTop = viewerContainer.getBoundingClientRect().top;
+    let bestEl = null;
+    let bestDist = Infinity;
+    for (const el of elements) {
+        const dist = Math.abs(el.getBoundingClientRect().top - containerTop);
+        if (dist < bestDist) {
+            bestDist = dist;
+            bestEl = el;
+        }
+    }
+    if (bestEl) {
+        entry._scrollSourceLine = parseInt(bestEl.getAttribute("data-source-line"), 10);
     }
 }
 

src/extensionsIntegrated/Phoenix-live-preview/MarkdownSync.js

@@ -593,7 +593,26 @@ define(function (require, exports, module) {
         return _doc._masterEditor._codeMirror;
     }
 
+    /**
+     * Clear the current file's cache in the mdviewer iframe and force re-render.
+     * Called on reload button click.
+     */
+    function reloadCurrentFile() {
+        if (!_active || !_iframeReady || !_doc) {
+            return;
+        }
+        const iframeWindow = _getIframeWindow();
+        if (!iframeWindow) {
+            return;
+        }
+        iframeWindow.postMessage({
+            type: "MDVIEWR_RELOAD_FILE",
+            filePath: _doc.file.fullPath
+        }, "*");
+    }
+
     exports.activate = activate;
     exports.deactivate = deactivate;
     exports.isActive = isActive;
+    exports.reloadCurrentFile = reloadCurrentFile;
 });

src/extensionsIntegrated/Phoenix-live-preview/main.js

@@ -865,6 +865,10 @@ define(function (require, exports, module) {
 
         if (_isMdviewrActive) {
             // Mdviewr iframe already loaded, just update the sync for the new document
+            if (force) {
+                // Reload: clear this file's cache and force re-render
+                MarkdownSync.reloadCurrentFile();
+            }
             MarkdownSync.activate(currentDoc, $iframe, baseURL);
             return;
         }