From c8080a09f7d0d3443826fb7b6b5a90a038cdcf79 Mon Sep 17 00:00:00 2001
From: Danny Avila <danny@librechat.ai>
Date: Thu, 13 Aug 2026 07:44:37 -0400
Subject: [PATCH] fix(api): reanchor substantial text boundaries

---
 .../src/agents/activityPhases/runtime.spec.ts | 10 +++++--
 .../api/src/agents/activityPhases/runtime.ts  | 30 ++++++++++++++++++-
 2 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/packages/api/src/agents/activityPhases/runtime.spec.ts b/packages/api/src/agents/activityPhases/runtime.spec.ts
index fe9490a78d..da1b640335 100644
--- a/packages/api/src/agents/activityPhases/runtime.spec.ts
+++ b/packages/api/src/agents/activityPhases/runtime.spec.ts
@@ -24,7 +24,9 @@ const batch = (id: string): PostToolBatchHookInput =>
     ],
   }) as PostToolBatchHookInput;
 
-const substantialText = (prefix: string): string => `${prefix} ${'x'.repeat(201)}`;
+const SUBSTANTIAL_TEXT_CHARS = 200;
+const substantialText = (prefix: string): string =>
+  `${prefix} ${'x'.repeat(SUBSTANTIAL_TEXT_CHARS + 1)}`;
 
 async function flushDetached(): Promise<void> {
   for (let i = 0; i < 4; i += 1) {
@@ -40,7 +42,7 @@ describe('createActivityPhaseWiring', () => {
     const generatePhase = jest.fn(async () => ({ label: 'Resolved the release compatibility' }));
     const wiring = createActivityPhaseWiring({
       getContentParts: () => parts,
-      getStepIndex: (stepId) => (stepId === 'final-step' ? 2 : undefined),
+      getStepIndex: (stepId) => (stepId === 'final-step' ? 1 : undefined),
       bumpIndexOffset: jest.fn(),
       emitLabelEvent,
       trackPendingFill: jest.fn(),
@@ -96,7 +98,9 @@ describe('createActivityPhaseWiring', () => {
       GraphEvents.ON_MESSAGE_DELTA,
       {
         id: 'final-step',
-        delta: { content: { type: ContentTypes.TEXT, text: 'A'.repeat(201) } },
+        delta: {
+          content: { type: ContentTypes.TEXT, text: 'A'.repeat(SUBSTANTIAL_TEXT_CHARS + 1) },
+        },
       },
       undefined,
       undefined,
diff --git a/packages/api/src/agents/activityPhases/runtime.ts b/packages/api/src/agents/activityPhases/runtime.ts
index c0a1ec5dd0..0176e97b01 100644
--- a/packages/api/src/agents/activityPhases/runtime.ts
+++ b/packages/api/src/agents/activityPhases/runtime.ts
@@ -364,6 +364,27 @@ function findReasoningStart(
   return startIndex ?? findLastPartIndex(parts, ContentTypes.THINK);
 }
 
+function findTextBoundary(
+  parts: ReadonlyArray<LooseContentPart | null | undefined>,
+  text: string,
+  stepIndex?: number,
+): number | undefined {
+  const needle = text.trim().slice(-REASONING_ANCHOR_CHARS);
+  const matches = (part: LooseContentPart | null | undefined) =>
+    part?.type === ContentTypes.TEXT && textValue(part.text).includes(needle);
+  if (stepIndex != null && matches(parts[stepIndex])) {
+    return stepIndex;
+  }
+  const indices = definedPartIndices(parts);
+  for (let position = indices.length - 1; position >= 0; position -= 1) {
+    const index = indices[position];
+    if (matches(parts[index])) {
+      return index;
+    }
+  }
+  return undefined;
+}
+
 /** Persists Open Responses text-phase metadata onto LibreChat text parts.
  *  Installed for existing batch labels too, so commentary can supply intent
  *  even when parent phase summaries are disabled. */
@@ -992,7 +1013,14 @@ export function createActivityPhaseWiring(deps: ActivityPhaseHostDeps): Activity
               contextEntry.text = `${contextEntry.text}${text}`.slice(-MAX_EXCERPT_CHARS);
             }
             const result = messageHandler.handle(event, data, metadata, graph);
-            const boundaryIndex = id ? deps.getStepIndex?.(id) : undefined;
+            const boundaryIndex =
+              id && contextEntry != null
+                ? findTextBoundary(
+                    deps.getContentParts(),
+                    contextEntry.text,
+                    deps.getStepIndex?.(id),
+                  )
+                : undefined;
             if (
               contextEntry != null &&
               contextEntry.text.trim().length > SUBSTANTIAL_TEXT_CHARS &&