From 6d0c98ee5e8367ad07ec7b933b64d73118d607b1 Mon Sep 17 00:00:00 2001
From: Cameron <cameron@pfiffer.org>
Date: Mon, 12 Jan 2026 15:37:51 -0800
Subject: [PATCH] feat: add LETTA_BACKFILL env var to disable message history
 backfilling (#504)

---
 src/agent/check-approval.ts | 23 +++++++++++++++++++++++
 src/cli/App.tsx             | 23 +++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/src/agent/check-approval.ts b/src/agent/check-approval.ts
index d785794..fa02ef8 100644
--- a/src/agent/check-approval.ts
+++ b/src/agent/check-approval.ts
@@ -10,6 +10,16 @@ import { debugWarn } from "../utils/debug";
 // Number of recent messages to backfill when resuming a session
 const MESSAGE_HISTORY_LIMIT = 15;
 
+/**
+ * Check if message backfilling is enabled via LETTA_BACKFILL env var.
+ * Defaults to true. Set LETTA_BACKFILL=0 or LETTA_BACKFILL=false to disable.
+ */
+function isBackfillEnabled(): boolean {
+  const val = process.env.LETTA_BACKFILL;
+  // Default to enabled (true) - only disable if explicitly set to "0" or "false"
+  return val !== "0" && val !== "false";
+}
+
 export interface ResumeData {
   pendingApproval: ApprovalRequest | null; // Deprecated: use pendingApprovals
   pendingApprovals: ApprovalRequest[];
@@ -63,6 +73,14 @@ export async function getResumeData(
         "check-approval",
         `No in-context messages (message_ids empty/null) - no pending approvals`,
       );
+      // Skip backfill if disabled via LETTA_BACKFILL=false
+      if (!isBackfillEnabled()) {
+        return {
+          pendingApproval: null,
+          pendingApprovals: [],
+          messageHistory: [],
+        };
+      }
       const historyCount = Math.min(MESSAGE_HISTORY_LIMIT, messages.length);
       let messageHistory = messages.slice(-historyCount);
       if (messageHistory[0]?.message_type === "tool_return_message") {
@@ -198,6 +216,11 @@ export async function getResumeData(
     }
 
     // Get last N messages for backfill (always use cursor messages for history)
+    // Skip backfill if disabled via LETTA_BACKFILL=false
+    if (!isBackfillEnabled()) {
+      return { pendingApproval, pendingApprovals, messageHistory: [] };
+    }
+
     const historyCount = Math.min(MESSAGE_HISTORY_LIMIT, messages.length);
     let messageHistory = messages.slice(-historyCount);
 
diff --git a/src/cli/App.tsx b/src/cli/App.tsx
index 959aaca..d705b55 100644
--- a/src/cli/App.tsx
+++ b/src/cli/App.tsx
@@ -6718,11 +6718,13 @@ Plan file path: ${planFilePath}`;
       });
       buffersRef.current.order.push(statusId);
       refreshDerived();
+      commitEligibleLines(buffersRef.current);
     }
   }, [
     loadingState,
     continueSession,
     messageHistory.length,
+    commitEligibleLines,
     columns,
     agentProvenance,
     agentState,
@@ -7145,6 +7147,27 @@ Plan file path: ${planFilePath}`;
                 </Box>
               )}
 
+              {/* Fallback approval UI when backfill is disabled (no liveItems) */}
+              {liveItems.length === 0 && currentApproval && (
+                <Box flexDirection="column">
+                  <InlineGenericApproval
+                    toolName={currentApproval.toolName}
+                    toolArgs={currentApproval.toolArgs}
+                    onApprove={() => handleApproveCurrent()}
+                    onApproveAlways={(scope) => handleApproveAlways(scope)}
+                    onDeny={(reason) => handleDenyCurrent(reason)}
+                    onCancel={handleCancelApprovals}
+                    isFocused={true}
+                    approveAlwaysText={
+                      currentApprovalContext?.approveAlwaysText
+                    }
+                    allowPersistence={
+                      currentApprovalContext?.allowPersistence ?? true
+                    }
+                  />
+                </Box>
+              )}
+
               {/* Subagent group display - shows running/completed subagents */}
               <SubagentGroupDisplay />
             </AnimationProvider>