diff --git a/src/lib/components/chat/Chat.svelte b/src/lib/components/chat/Chat.svelte
index 751c49bed9..44dabafeb2 100644
--- a/src/lib/components/chat/Chat.svelte
+++ b/src/lib/components/chat/Chat.svelte
@@ -58,6 +58,7 @@
 		copyToClipboard,
 		getMessageContentParts,
 		createMessagesList,
+		sanitizeHistory,
 		getPromptVariables,
 		processDetails,
 		removeAllDetails,
@@ -1379,29 +1380,9 @@
 						? chatContent.history
 						: convertMessagesToHistory(chatContent.messages);
 
-				// Sanitize history: repair orphaned references from failed regenerations (#24424)
-				for (const message of Object.values(history.messages)) {
-					if (message.childrenIds) {
-						message.childrenIds = message.childrenIds.filter(
-							(childId) => history.messages[childId]
-						);
-					}
-				}
-				if (history.currentId && !history.messages[history.currentId]) {
-					const messageIds = Object.keys(history.messages);
-					let lastMessageId = null;
-					for (const messageId of messageIds) {
-						const message = history.messages[messageId];
-						if (
-							(message.childrenIds ?? []).length === 0 &&
-							(!lastMessageId ||
-								(message.timestamp ?? 0) > (history.messages[lastMessageId].timestamp ?? 0))
-						) {
-							lastMessageId = messageId;
-						}
-					}
-					history.currentId = lastMessageId ?? messageIds[0] ?? null;
-				}
+				// Sanitize history: repair orphaned references and structurally-malformed
+				// nodes from failed regenerations (#24424, #24157, #20474)
+				sanitizeHistory(history);
 
 				chatTitle.set(chatContent.title);
 
diff --git a/src/lib/utils/index.ts b/src/lib/utils/index.ts
index 91cfa2b688..b4009f198a 100644
--- a/src/lib/utils/index.ts
+++ b/src/lib/utils/index.ts
@@ -225,6 +225,81 @@ export const convertMessagesToHistory = (messages) => {
 	return history;
 };
 
+// Repair structurally-malformed history nodes from failed regenerations.
+// A lost assistant placeholder may exist under its map key with only
+// completion fields (content/done/error), missing id/role/parentId.
+// Reconstruct graph fields so already-corrupted chats recover on open.
+export const sanitizeHistory = (history) => {
+	if (!history?.messages || typeof history.messages !== 'object') return;
+
+	// Purge entries that aren't usable objects
+	for (const [id, message] of Object.entries(history.messages)) {
+		if (!message || typeof message !== 'object') {
+			delete history.messages[id];
+		}
+	}
+
+	// Ensure every surviving node has its canonical id and a childrenIds array
+	for (const [id, message] of Object.entries(history.messages)) {
+		if (message.id !== id) message.id = id;
+		if (!Array.isArray(message.childrenIds)) message.childrenIds = [];
+	}
+
+	// Build reverse lookup: parent, indexed by child id
+	const parentByChildId = {};
+	for (const [id, message] of Object.entries(history.messages)) {
+		for (const childId of message.childrenIds) {
+			parentByChildId[childId] = id;
+		}
+	}
+
+	// Reconstruct missing parentId and role
+	for (const [id, message] of Object.entries(history.messages)) {
+		// Well-formed: has role and explicit parentId (null is valid for root)
+		if (message.role && message.parentId !== undefined) continue;
+
+		if (message.parentId === undefined) {
+			message.parentId = parentByChildId[id] ?? null;
+		}
+
+		if (!message.role) {
+			const parent = message.parentId ? history.messages[message.parentId] : null;
+			message.role =
+				parent?.role === 'user'
+					? 'assistant'
+					: parent?.role === 'assistant'
+						? 'user'
+						: message.model || message.usage || message.done !== undefined
+							? 'assistant'
+							: 'user';
+		}
+	}
+
+	// Prune childrenIds referencing deleted/missing nodes
+	for (const message of Object.values(history.messages)) {
+		message.childrenIds = message.childrenIds.filter(
+			(childId) => history.messages[childId]
+		);
+	}
+
+	// Recover currentId if it points to a missing or incomplete node
+	const currentMessage = history.messages?.[history.currentId];
+	if (!currentMessage?.id || !currentMessage?.role) {
+		let latestLeafId = null;
+		let latestTimestamp = -1;
+		for (const [id, message] of Object.entries(history.messages)) {
+			if (
+				message.childrenIds.length === 0 &&
+				(message.timestamp ?? 0) > latestTimestamp
+			) {
+				latestLeafId = id;
+				latestTimestamp = message.timestamp ?? 0;
+			}
+		}
+		history.currentId = latestLeafId ?? Object.keys(history.messages)[0] ?? null;
+	}
+};
+
 export const getGravatarURL = (email) => {
 	// Trim leading and trailing whitespace from
 	// an email address and force all characters