fix(chat): restore forked context

src/routes/chat.ts

@@ -19,6 +19,7 @@ import {
   extractLatestFrontendTurn,
   generateSessionTitle,
   shouldGenerateSessionTitle,
+  shouldRestoreConversationForRuntime,
 } from "./chatSession.js";
 import { registerChatAuxiliaryRoutes } from "./chatAuxiliaryRoutes.js";
 import { registerChatInteractionRoutes } from "./chatInteractionRoutes.js";
@@ -37,10 +38,8 @@ import {
   type StreamSubscriber,
   cancelBackendTodos,
   completeBackendProgress,
-  countFrontendUserMessages,
   createInitialStreamingMessages,
   isObjectRecord,
-  pruneBranchGroupsForMessageIndex,
   toFrontendPermission,
   toPermissionStatus,
   updateLastAssistantMessage,
@@ -56,7 +55,6 @@ const payloadSchema = z.object({
   session_id: z.string().max(128).optional(),
   model: z.enum(supportedModels).optional(),
   approval_mode: z.enum(["request", "always"]).optional().default("request"),
-  regenerate_from_message_index: z.coerce.number().int().min(0).optional(),
 });
 
 const createSessionPayloadSchema = z.object({
@@ -86,6 +84,17 @@ const toSessionUiStateContext = (sessionRecord: SessionRecord) => ({
 const getSessionRunStatus = (sessionId: string) =>
   activeRuns.get(sessionId)?.status ?? lastRunStatuses.get(sessionId);
 
+const runtimeHasConversation = async (
+  runtime: OpencodeRuntimeAdapter,
+  sessionId: string,
+) => {
+  const messages = await runtime.messages(sessionId, 1);
+  return messages.some(
+    (message) =>
+      message.info.role === "user" || message.info.role === "assistant",
+  );
+};
+
 export const buildChatRouter = (
   sessionBridge: ChatSessionBridge,
   runtime: OpencodeRuntimeAdapter,
@@ -555,6 +564,13 @@ export const buildChatRouter = (
           userId,
         });
       const activeSessionRecord = await sessionMetadataStore.touch(ensuredSessionRecord);
+      const hasRuntimeConversation = hadExistingRuntimeSession
+        ? await runtimeHasConversation(runtime, binding.sessionId)
+        : false;
+      const shouldRestoreConversation = shouldRestoreConversationForRuntime({
+        hadExistingSessionRecord: hadExistingRuntimeSession,
+        runtimeHasConversation: hasRuntimeConversation,
+      });
       const historyContext = {
         actorKey: requestContext.actorKey,
         clientSessionId: requestContext.clientSessionId,
@@ -565,20 +581,7 @@ export const buildChatRouter = (
         toSessionUiStateContext(activeSessionRecord),
       );
       const persistedMessages = initialSessionState?.messages ?? [];
-      const isRegenerate =
-        parsed.data.regenerate_from_message_index !== undefined;
-      const baseMessages =
-        isRegenerate
-          ? persistedMessages.slice(0, parsed.data.regenerate_from_message_index)
-          : persistedMessages;
-      const targetUserOrdinal = isRegenerate
-        ? countFrontendUserMessages(
-            persistedMessages.slice(
-              0,
-              (parsed.data.regenerate_from_message_index ?? 0) + 1,
-            ),
-          )
-        : undefined;
+      const baseMessages = persistedMessages;
       if (activeRuns.get(activeSessionRecord.sessionId)?.status === "running") {
         res.status(409).json({
           message: "session is already streaming",
@@ -586,15 +589,7 @@ export const buildChatRouter = (
         });
         return;
       }
-      if (isRegenerate) {
-        await sessionTranscriptStore.truncateThread(
-          historyContext,
-          parsed.data.regenerate_from_message_index ?? 0,
-        );
-      }
-      const recentTurns = isRegenerate
-        ? []
-        : await sessionTranscriptStore.getRecentTurns(historyContext, 8);
+      const recentTurns = await sessionTranscriptStore.getRecentTurns(historyContext, 8);
 
       logger.info(
         {
@@ -603,7 +598,6 @@ export const buildChatRouter = (
           created: created || sessionCreated,
           model: parsed.data.model,
           approvalMode: parsed.data.approval_mode,
-          regenerateFromMessageIndex: parsed.data.regenerate_from_message_index,
           traceId: requestContext.traceId,
           projectId: requestContext.projectId,
         },
@@ -625,10 +619,7 @@ export const buildChatRouter = (
         baseMessages,
         parsed.data.message,
       );
-      const branchGroups = pruneBranchGroupsForMessageIndex(
-        initialSessionState?.branchGroups ?? [],
-        parsed.data.regenerate_from_message_index,
-      );
+      const branchGroups = initialSessionState?.branchGroups ?? [];
       const activeRun: ActiveRun = {
         clientSessionId,
         controller: abortController,
@@ -815,15 +806,6 @@ export const buildChatRouter = (
       };
 
       try {
-        if (isRegenerate) {
-          if (!targetUserOrdinal || targetUserOrdinal < 1) {
-            throw new Error("target user message not found for regeneration");
-          }
-          await runtime.revertToUserMessage(binding.sessionId, {
-            userOrdinal: targetUserOrdinal,
-          });
-        }
-
         const preparedMessage = await buildPromptWithLearningContext(
           memoryStore,
           requestContext.actorKey,
@@ -832,7 +814,7 @@ export const buildChatRouter = (
             recentTurns,
             persistedMessages: baseMessages,
             message: parsed.data.message,
-            restoreConversation: !hadExistingRuntimeSession,
+            restoreConversation: shouldRestoreConversation,
           },
         );
         const streamResult = await streamPromptResponse({

src/routes/chatSession.ts

@@ -212,6 +212,11 @@ export const buildPromptWithLearningContext = async (
     .join("\n\n");
 };
 
+export const shouldRestoreConversationForRuntime = (options: {
+  hadExistingSessionRecord: boolean;
+  runtimeHasConversation: boolean;
+}) => !options.hadExistingSessionRecord || !options.runtimeHasConversation;
+
 const buildRestoredConversationContext = (recentTurns: SessionTurnRecord[]) => {
   const formattedTurns = recentTurns
     .slice(-RESTORE_TURN_LIMIT)

src/routes/chatUiState.ts

@@ -63,26 +63,6 @@ export const createInitialStreamingMessages = (
   ];
 };
 
-export const countFrontendUserMessages = (messages: unknown[]) =>
-  messages.filter(
-    (message) => isObjectRecord(message) && message.role === "user",
-  ).length;
-
-export const pruneBranchGroupsForMessageIndex = (
-  branchGroups: unknown[],
-  messageIndex: number | undefined,
-) => {
-  if (messageIndex === undefined) {
-    return branchGroups;
-  }
-  return branchGroups.filter(
-    (group) =>
-      !isObjectRecord(group) ||
-      typeof group.parentCount !== "number" ||
-      group.parentCount < messageIndex,
-  );
-};
-
 export const upsertBackendProgress = (
   progress: unknown,
   payload: Record<string, unknown>,