diff --git a/chat/server.js b/chat/server.js
index 5f42b87..aaf3ff5 100644
--- a/chat/server.js
+++ b/chat/server.js
@@ -16906,7 +16906,15 @@ async function handleNewMessage(req, res, sessionId, userId) {
     if (body.originalMessageId) message.originalMessageId = body.originalMessageId;
     // Preserve opencodeSessionId for session continuity in retries/continuations
     // Also prioritize body.opencodeSessionId over session.opencodeSessionId for explicit continuation
-    if (body.opencodeSessionId) {
+    // CRITICAL: If session.opencodeSessionId is null (session was reset), ignore body.opencodeSessionId
+    // to prevent reusing a corrupted session that was previously reset
+    if (session.opencodeSessionId === null && body.opencodeSessionId) {
+      log('Ignoring body opencodeSessionId because session was reset', { 
+        bodySessionId: body.opencodeSessionId,
+        reason: 'Session was reset due to corruption/undo failure - forcing new session creation'
+      });
+      // Don't set message.opencodeSessionId - let ensureOpencodeSession create a new one
+    } else if (body.opencodeSessionId) {
       message.opencodeSessionId = body.opencodeSessionId;
       log('Using explicit opencodeSessionId from request body', { opencodeSessionId: body.opencodeSessionId });
     } else if (session.opencodeSessionId) {