diff --git a/routes/chat_helpers.py b/routes/chat_helpers.py
index 22a334116..df7494a2a 100644
--- a/routes/chat_helpers.py
+++ b/routes/chat_helpers.py
@@ -9,7 +9,7 @@ import time
 from dataclasses import dataclass, field
 from typing import Any, Optional
 
-from core.models import ChatMessage
+from core.models import ChatMessage, get_session_manager_instance
 from core.database import SessionLocal
 from core.database import Session as DBSession, ModelEndpoint
 from src.llm_core import normalize_model_id
@@ -481,6 +481,29 @@ def add_user_message(sess, chat_handler, preprocessed: PreprocessedMessage, inco
     chat_handler.update_session_name_if_needed(sess, preprocessed.text_for_context)
 
 
+def replace_latest_user_message(sess, session_id: str, preprocessed: PreprocessedMessage) -> bool:
+    history = getattr(sess, "history", None)
+    if not history:
+        return False
+    latest = history[-1]
+    latest_role = latest.get("role") if isinstance(latest, dict) else getattr(latest, "role", None)
+    if latest_role != "user":
+        return False
+    user_meta = {"attachments": preprocessed.attachment_meta} if preprocessed.attachment_meta else None
+    replacement = ChatMessage("user", preprocessed.user_content, metadata=user_meta)
+    updated = list(history)
+    updated[-1] = replacement
+    manager = get_session_manager_instance()
+    if manager and getattr(manager, "replace_messages", None):
+        if manager.replace_messages(session_id, updated):
+            return True
+        logger.warning("Failed to persist regenerated user message for session %s", session_id)
+        return False
+    history[-1] = replacement
+    sess.message_count = len(history)
+    return True
+
+
 def fire_message_event(request, webhook_manager, session_id: str, sess, message: str, compare_mode: bool = False):
     """Fire webhook and event_bus events for a new user message."""
     if webhook_manager and not compare_mode:
@@ -687,6 +710,7 @@ async def build_chat_context(
     use_enhanced_message: bool = False,
     agent_mode: bool = False,
     allow_tool_preprocessing: bool = True,
+    regenerate: bool = False,
 ) -> ChatContext:
     """Build the full context (preface + messages) for an LLM call.
 
@@ -707,12 +731,23 @@ async def build_chat_context(
         allow_tool_preprocessing=allow_tool_preprocessing,
     )
 
+    raw_history = [] if incognito else (getattr(sess, "history", None) or [])
+    latest_raw = raw_history[-1] if raw_history else None
+    latest_raw_role = latest_raw.get("role") if isinstance(latest_raw, dict) else getattr(latest_raw, "role", None)
+    regenerate_reused_user = bool(
+        regenerate
+        and latest_raw_role == "user"
+    )
+
     # Add user message to history. Nobody/incognito uses a request-local
     # transcript store instead of session history so stale saved chats cannot
     # bleed into context and the turn is not persisted.
     if incognito:
         user_meta = {"attachments": preprocessed.attachment_meta} if preprocessed.attachment_meta else None
         _append_incognito_message(session_id, "user", preprocessed.user_content, user_meta)
+    elif regenerate_reused_user:
+        if not replace_latest_user_message(sess, session_id, preprocessed):
+            raise HTTPException(500, "Failed to update regenerated user message")
     else:
         add_user_message(sess, chat_handler, preprocessed, incognito=False)
 
@@ -808,7 +843,13 @@ async def build_chat_context(
     # Build messages. In Nobody/incognito mode, never read saved session
     # history: the session id may be a temporary wrapper or, in buggy clients, a
     # stale normal session id. Only the ephemeral incognito transcript is safe.
-    messages = preface + (_incognito_messages(session_id) if incognito else sess.get_context_messages())
+    context_history = _incognito_messages(session_id) if incognito else sess.get_context_messages()
+    if regenerate_reused_user:
+        context_history = list(context_history)
+        context_history[-1] = {"role": "user", "content": preprocessed.user_content}
+        if preprocessed.attachment_meta:
+            context_history[-1]["metadata"] = {"attachments": preprocessed.attachment_meta}
+    messages = preface + context_history
 
     # Current date/time — injected as a standalone *user*-role context message
     # placed immediately before the latest user turn, NOT folded into the
diff --git a/routes/chat_routes.py b/routes/chat_routes.py
index b081d5f1c..89180bd4f 100644
--- a/routes/chat_routes.py
+++ b/routes/chat_routes.py
@@ -600,6 +600,7 @@ def setup_chat_routes(
         use_research = chat_request.use_research
         time_filter = chat_request.time_filter
         preset_id = chat_request.preset_id
+        regenerate = bool(chat_request.regenerate)
 
         # Verify the caller owns this session before loading it.
         # Without this, any authenticated user can post into another user's chat.
@@ -648,6 +649,7 @@ def setup_chat_routes(
             time_filter=time_filter,
             webhook_manager=webhook_manager,
             allow_tool_preprocessing=allow_tool_preprocessing,
+            regenerate=regenerate,
         )
 
         # Research injection
@@ -732,6 +734,7 @@ def setup_chat_routes(
         search_context = form_data.get("search_context")  # pre-fetched web search results (compare mode)
         compare_mode = str(form_data.get("compare_mode", "")).lower() == "true"
         incognito = str(form_data.get("incognito", "")).lower() == "true"
+        regenerate = str(form_data.get("regenerate") or (body or {}).get("regenerate") or "").lower() == "true"
         plan_mode = str(form_data.get("plan_mode") or (body or {}).get("plan_mode") or "").lower() == "true"
         chat_mode = str(form_data.get("mode", "")).lower()  # 'chat' or 'agent'
         # Workspace: confine the agent's file/shell tools to this folder.
@@ -992,6 +995,7 @@ def setup_chat_routes(
             # index would be useless / unwanted noise.
             agent_mode=(chat_mode == "agent"),
             allow_tool_preprocessing=allow_tool_preprocessing,
+            regenerate=regenerate,
         )
 
         _research_flags = {"do": do_research}  # Mutable container for generator scope
diff --git a/src/request_models.py b/src/request_models.py
index f7755b1d4..ca6d48b0d 100644
--- a/src/request_models.py
+++ b/src/request_models.py
@@ -12,6 +12,7 @@ class ChatRequest(BaseModel):
     use_research: Optional[bool] = Field(default=False, description="Enable deep research")
     time_filter: Optional[str] = Field(default=None, description="Time filter for search")
     preset_id: Optional[str] = Field(default=None, description="Preset identifier")
+    regenerate: Optional[bool] = Field(default=False, description="Reuse the retained latest user turn")
     
     @field_validator('message')
     @classmethod
diff --git a/static/js/chat.js b/static/js/chat.js
index df4550d8d..54b19bffc 100644
--- a/static/js/chat.js
+++ b/static/js/chat.js
@@ -1424,6 +1424,8 @@ import { wireArrowUpRecall, getUserMessagesFromChatHistory } from './composerArr
       _displayOverride = null;
       const skipBubble = _hideUserBubble;
       _hideUserBubble = false;
+      const regenerateSend = _pendingRegenerateSend;
+      _pendingRegenerateSend = false;
       // Auto-recovery counter: carries across a turn's auto-continues, but resets
       // when the user genuinely sends a new message (so each task gets a fresh cap).
       // A real user turn (visible bubble) ALWAYS resets the budget — even if a
@@ -1627,6 +1629,7 @@ import { wireArrowUpRecall, getUserMessagesFromChatHistory } from './composerArr
       const fd = new FormData();
       fd.append('message', _finalMsgWithInject);
       fd.append('session', streamSessionId);
+      if (regenerateSend) fd.append('regenerate', 'true');
       if (selectedRouteForSend.model) fd.append('selected_model', selectedRouteForSend.model);
       if (selectedRouteForSend.endpoint_url) fd.append('selected_endpoint_url', selectedRouteForSend.endpoint_url);
       if (selectedRouteForSend.endpoint_id) fd.append('selected_endpoint_id', selectedRouteForSend.endpoint_id);
@@ -4934,6 +4937,7 @@ import { wireArrowUpRecall, getUserMessagesFromChatHistory } from './composerArr
           sibling = next;
         }
         _hideUserBubble = true;
+        _pendingRegenerateSend = true;
       }
       _pendingRegenAttachments = _ids;
 
@@ -5053,6 +5057,7 @@ import { wireArrowUpRecall, getUserMessagesFromChatHistory } from './composerArr
       _hideUserBubble = true;
       const messageInput = uiModule.el('message');
       messageInput.value = userText;
+      _pendingRegenerateSend = true;
       const submitBtn = document.querySelector('.send-btn');
       if (submitBtn) submitBtn.click();
 
@@ -5068,6 +5073,7 @@ import { wireArrowUpRecall, getUserMessagesFromChatHistory } from './composerArr
   // File-ids carried over from the original user message during a regen, so
   // photos / OCR overrides survive into the new send. Consumed once.
   let _pendingRegenAttachments = null;
+  let _pendingRegenerateSend = false;
 
   /**
    * Called after streaming completes to attach variant navigation if this was a regen.
diff --git a/tests/test_chat_helpers.py b/tests/test_chat_helpers.py
index 16cb38c01..cb7145408 100644
--- a/tests/test_chat_helpers.py
+++ b/tests/test_chat_helpers.py
@@ -580,3 +580,196 @@ async def test_build_chat_context_keeps_cookie_user_owner_scope(monkeypatch):
         "preface_owner": "bob",
         "compact_owner": "bob",
     }
+
+
+@pytest.mark.asyncio
+async def test_build_chat_context_regenerate_reuses_latest_user_without_persisting_duplicate(monkeypatch):
+    async def fake_preprocess(chat_handler, message, att_ids, sess, **kwargs):
+        return PreprocessedMessage(
+            enhanced_message=message,
+            user_content=[{"type": "text", "text": message}],
+            text_for_context=message,
+            youtube_transcripts=[],
+            attachment_meta=[{"id": "file-1", "name": "scan.png"}],
+        )
+
+    monkeypatch.setattr(chat_helpers, "preprocess", fake_preprocess)
+    monkeypatch.setattr(chat_helpers, "extract_preset", lambda *_args, **_kwargs: PresetInfo(0.7, 1024, None, None))
+    monkeypatch.setattr(chat_helpers, "load_prefs_for_user", lambda _user: {})
+    monkeypatch.setattr(chat_helpers, "effective_user", lambda _request: "alice")
+    monkeypatch.setattr(chat_helpers, "_normalize_model_id_from_cache", lambda _sess: None)
+    monkeypatch.setattr(chat_helpers, "normalize_model_id", lambda *_args, **_kwargs: None)
+    async def fake_maybe_compact(sess, endpoint_url, model, messages, headers, owner=None):
+        return messages, 8192, False
+
+    monkeypatch.setattr(chat_helpers, "maybe_compact", fake_maybe_compact)
+    monkeypatch.setattr(chat_helpers, "trim_for_context", lambda messages, _context_length: messages)
+
+    adds = []
+    monkeypatch.setattr(chat_helpers, "add_user_message", lambda *_args, **_kwargs: adds.append(1))
+    replacements = []
+
+    class FakeManager:
+        def replace_messages(self, session_id, messages):
+            replacements.append((session_id, messages))
+            sess.history = list(messages)
+            return True
+
+    monkeypatch.setattr(chat_helpers, "get_session_manager_instance", lambda: FakeManager())
+
+    sess = SimpleNamespace(
+        endpoint_url="http://model.local/v1/chat/completions",
+        model="test-model",
+        headers={},
+        history=[chat_helpers.ChatMessage("user", "stale OCR", metadata={"attachments": [{"id": "old-file"}]})],
+    )
+    sess.get_context_messages = lambda: [m.to_dict() for m in sess.history]
+
+    ctx = await build_chat_context(
+        sess=sess,
+        request=SimpleNamespace(),
+        chat_handler=SimpleNamespace(),
+        chat_processor=SimpleNamespace(build_context_preface=lambda **_kwargs: ([], [], [])),
+        message="original prompt",
+        session_id="session-1",
+        regenerate=True,
+        agent_mode=True,
+    )
+
+    assert adds == []
+    assert replacements[0][0] == "session-1"
+    assert [(m.role, m.content, m.metadata) for m in sess.history] == [(
+        "user",
+        [{"type": "text", "text": "original prompt"}],
+        {"attachments": [{"id": "file-1", "name": "scan.png"}]},
+    )]
+    user_messages = [m for m in ctx.messages if m.get("role") == "user"]
+    assert user_messages == [{
+        "role": "user",
+        "content": [{"type": "text", "text": "original prompt"}],
+        "metadata": {"attachments": [{"id": "file-1", "name": "scan.png"}]},
+    }]
+
+
+@pytest.mark.asyncio
+async def test_build_chat_context_regenerate_replaces_persisted_user_row(monkeypatch):
+    import core.database as cdb
+    import core.session_manager as sm
+    from tests.helpers.sqlite_db import make_temp_sqlite
+
+    session_local, _engine, _tmpdb = make_temp_sqlite(cdb.Base.metadata)
+    monkeypatch.setattr(sm, "SessionLocal", session_local)
+
+    manager = sm.SessionManager.__new__(sm.SessionManager)
+    manager.sessions = {}
+    manager.upload_handler = None
+
+    sid = "regen-" + uuid.uuid4().hex[:8]
+    db = session_local()
+    try:
+        db.add(cdb.Session(
+            id=sid,
+            owner="alice",
+            name="chat",
+            model="test-model",
+            endpoint_url="http://model.local/v1/chat/completions",
+            archived=False,
+            message_count=1,
+        ))
+        db.add(cdb.ChatMessage(
+            id="stale-user",
+            session_id=sid,
+            role="user",
+            content="stale OCR",
+        ))
+        db.commit()
+    finally:
+        db.close()
+
+    sess = manager.get_session(sid)
+
+    async def fake_preprocess(chat_handler, message, att_ids, sess, **kwargs):
+        return PreprocessedMessage(
+            enhanced_message=message,
+            user_content=[{"type": "text", "text": message}],
+            text_for_context=message,
+            youtube_transcripts=[],
+            attachment_meta=[{"id": "file-1", "name": "scan.png"}],
+        )
+
+    async def fake_maybe_compact(sess, endpoint_url, model, messages, headers, owner=None):
+        return messages, 8192, False
+
+    monkeypatch.setattr(chat_helpers, "preprocess", fake_preprocess)
+    monkeypatch.setattr(chat_helpers, "extract_preset", lambda *_args, **_kwargs: PresetInfo(0.7, 1024, None, None))
+    monkeypatch.setattr(chat_helpers, "load_prefs_for_user", lambda _user: {})
+    monkeypatch.setattr(chat_helpers, "effective_user", lambda _request: "alice")
+    monkeypatch.setattr(chat_helpers, "_normalize_model_id_from_cache", lambda _sess: None)
+    monkeypatch.setattr(chat_helpers, "normalize_model_id", lambda *_args, **_kwargs: None)
+    monkeypatch.setattr(chat_helpers, "maybe_compact", fake_maybe_compact)
+    monkeypatch.setattr(chat_helpers, "trim_for_context", lambda messages, _context_length: messages)
+    monkeypatch.setattr(chat_helpers, "get_session_manager_instance", lambda: manager)
+
+    ctx = await build_chat_context(
+        sess=sess,
+        request=SimpleNamespace(),
+        chat_handler=SimpleNamespace(),
+        chat_processor=SimpleNamespace(build_context_preface=lambda **_kwargs: ([], [], [])),
+        message="current OCR",
+        session_id=sid,
+        regenerate=True,
+        agent_mode=True,
+    )
+    manager.add_message(sid, chat_helpers.ChatMessage("assistant", "new answer"))
+
+    db = session_local()
+    try:
+        rows = db.query(cdb.ChatMessage).filter(cdb.ChatMessage.session_id == sid).order_by(cdb.ChatMessage.timestamp).all()
+        assert [(row.role, row.content) for row in rows] == [
+            ("user", "current OCR\n[Attachment: scan.png | id=file-1 | mime=application/octet-stream]"),
+            ("assistant", "new answer"),
+        ]
+    finally:
+        db.close()
+
+    manager.sessions.clear()
+    reloaded = manager.get_session(sid)
+    assert [m["content"] for m in reloaded.get_context_messages()] == [
+        "current OCR\n[Attachment: scan.png | id=file-1 | mime=application/octet-stream]",
+        "new answer",
+    ]
+    assert [m for m in ctx.messages if m.get("role") == "user"] == [{
+        "role": "user",
+        "content": [{"type": "text", "text": "current OCR"}],
+        "metadata": {"attachments": [{"id": "file-1", "name": "scan.png"}]},
+    }]
+
+
+@pytest.mark.asyncio
+async def test_build_chat_context_regenerate_fails_when_user_row_replacement_fails(monkeypatch):
+    async def fake_preprocess(chat_handler, message, att_ids, sess, **kwargs):
+        return PreprocessedMessage(message, message, message, [], [])
+
+    class FakeManager:
+        def replace_messages(self, session_id, messages):
+            return False
+
+    monkeypatch.setattr(chat_helpers, "preprocess", fake_preprocess)
+    monkeypatch.setattr(chat_helpers, "extract_preset", lambda *_args, **_kwargs: PresetInfo(0.7, 1024, None, None))
+    monkeypatch.setattr(chat_helpers, "get_session_manager_instance", lambda: FakeManager())
+
+    sess = SimpleNamespace(
+        history=[chat_helpers.ChatMessage("user", "stale")],
+        get_context_messages=lambda: [{"role": "user", "content": "stale"}],
+    )
+
+    with pytest.raises(HTTPException):
+        await build_chat_context(
+            sess=sess,
+            request=SimpleNamespace(),
+            chat_handler=SimpleNamespace(),
+            chat_processor=SimpleNamespace(build_context_preface=lambda **_kwargs: ([], [], [])),
+            message="current",
+            session_id="session-1",
+            regenerate=True,
+        )
diff --git a/tests/test_chat_route_tool_policy.py b/tests/test_chat_route_tool_policy.py
index babf85f6e..21ea53f52 100644
--- a/tests/test_chat_route_tool_policy.py
+++ b/tests/test_chat_route_tool_policy.py
@@ -79,6 +79,29 @@ def test_allow_web_search_reads_from_body_as_fallback():
     )
 
 
+def test_regenerate_reads_from_body_as_fallback():
+    """chat_stream must honor JSON regenerate requests, not just FormData."""
+    source = _CHAT_ROUTES.read_text(encoding="utf-8")
+    tree = ast.parse(source)
+
+    chat_stream_func = next(
+        node for node in ast.walk(tree)
+        if isinstance(node, ast.AsyncFunctionDef) and node.name == "chat_stream"
+    )
+
+    found_body_fallback = False
+    for node in ast.walk(chat_stream_func):
+        if isinstance(node, ast.Assign):
+            for target in node.targets:
+                if isinstance(target, ast.Name) and target.id == "regenerate":
+                    src_segment = ast.get_source_segment(source, node)
+                    if src_segment and "body" in src_segment:
+                        found_body_fallback = True
+    assert found_body_fallback, (
+        "regenerate assignment in chat_stream must fall back to JSON body"
+    )
+
+
 def test_browser_form_followups_include_approval_and_send_phrases():
     """Short approval replies after a form/browser turn must keep browser tools available."""
     source = _CHAT_ROUTES.read_text(encoding="utf-8")
diff --git a/tests/test_resend_message_nondestructive.py b/tests/test_resend_message_nondestructive.py
index 426b7d4b2..7bb550953 100644
--- a/tests/test_resend_message_nondestructive.py
+++ b/tests/test_resend_message_nondestructive.py
@@ -43,18 +43,18 @@ def test_only_regenerate_callers_opt_into_replace_from_here():
     assert "window.chatModule.resendUserMessage(userMsgEl, { replaceFromHere: true });" in renderer
 
 
-def test_replace_and_regenerate_keep_the_original_user_message():
-    chat = _CHAT_JS.read_text(encoding="utf-8")
-    resend = chat[
-        chat.index("export async function resendUserMessage("):
-        chat.index("export async function regenerateFrom(")
-    ]
-    regenerate = chat[
-        chat.index("export async function regenerateFrom("):
-        chat.index("// Pending variants from a regeneration", chat.index("export async function regenerateFrom("))
-    ]
+def test_regenerate_replace_paths_keep_user_row_and_mark_resubmit():
+    body = _resend_body()
+    src = _CHAT_JS.read_text(encoding="utf-8")
+    regen = src[src.index("export async function regenerateFrom("):src.index("// Pending variants", src.index("export async function regenerateFrom("))]
+    replace_branch = body[body.index("if (replaceFromHere)"):body.index("_pendingRegenAttachments = _ids;")]
+    normal_resubmit = body[body.index("_pendingRegenAttachments = _ids;"):]
 
-    assert "const keepCount = msgIndex + 1;" in resend
-    assert "const keepCount = userIndex + 1;" in regenerate
-    assert "const keepCount = msgIndex;" not in resend
-    assert "const keepCount = userIndex;" not in regenerate
+    assert "const keepCount = msgIndex + 1;" in body
+    assert "const keepCount = userIndex + 1;" in regen
+    assert replace_branch.count("_pendingRegenerateSend = true;") == 1
+    assert "_pendingRegenerateSend = true;" not in normal_resubmit
+    assert regen.count("_pendingRegenerateSend = true;") == 1
+    assert "if (regenerateSend) fd.append('regenerate', 'true');" in src
+    assert "const keepCount = msgIndex;" not in body
+    assert "const keepCount = userIndex;" not in regen