diff --git a/backend/AGENTS.md b/backend/AGENTS.md
index f460fc239..73caca7c8 100644
--- a/backend/AGENTS.md
+++ b/backend/AGENTS.md
@@ -427,7 +427,7 @@ Localhost persistence deliberately reads the direct request `Host` and ignores `
 | **Skills** (`/api/skills`) | `GET /` - list skills; `GET /{name}` - details; `PUT /{name}` - update enabled; `POST /install` - install from .skill archive (accepts standard optional frontmatter like `version`, `author`, `compatibility`); `POST /reload` - admin-only process-local prompt-cache invalidation after trusted external filesystem changes |
 | **Memory** (`/api/memory`) | `GET /` - memory data; `POST /reload` - force reload; `GET /config` - config; `GET /status` - config + data |
 | **Uploads** (`/api/threads/{id}/uploads`) | `POST /` - upload files (auto-converts PDF/PPT/Excel/Word); `GET /list` - list; `DELETE /{filename}` - delete |
-| **Threads** (`/api/threads/{id}`) | `DELETE /` - remove DeerFlow-managed local thread data after LangGraph thread deletion; `POST /branches` - create a new main-thread branch from a completed assistant turn checkpoint and, when an addressable pre-user replay checkpoint exists, materialize it into the branch namespace so the inherited response remains regeneratable. Workspace files are not checkpointed, so the branch only best-effort copies the current workspace when branching from the **latest** turn (`workspace_clone_mode="current_thread_best_effort"`); branching from an older/historical turn skips the copy (`workspace_clone_mode="skipped_historical_turn"`) so the branch never inherits files that only exist in a later timeline. Branch creation also seeds the new thread's run-event feed from the branch checkpoint's visible messages (`history_seed_mode` in the response): the thread feed reads run_events, not checkpoints, so without the seed the inherited history disappears from the UI after the branch's first run (#4380); `GET /goal`, `PUT /goal`, `DELETE /goal` - read, set, and clear the active thread goal; `POST /compact` - manually summarize older active context into `summary_text` and retain the recent message window, blocked while a run is in flight; unexpected failures are logged server-side and return a generic 500 detail |
+| **Threads** (`/api/threads/{id}`) | `DELETE /` - remove DeerFlow-managed local thread data after LangGraph thread deletion; `POST /branches` - create a new main-thread branch from a completed assistant turn checkpoint and, when an addressable pre-user replay checkpoint exists, materialize it into the branch namespace so the inherited response remains regeneratable. Workspace files are not checkpointed, so the branch only best-effort copies the current workspace when branching from the **latest** turn (`workspace_clone_mode="current_thread_best_effort"`); branching from an older/historical turn skips the copy (`workspace_clone_mode="skipped_historical_turn"`) so the branch never inherits files that only exist in a later timeline. Branch creation also seeds the new thread's run-event feed from the branch checkpoint's visible messages (`history_seed_mode` in the response): the thread feed reads run_events, not checkpoints, so without the seed the inherited history disappears from the UI after the branch's first run (#4380). Seeded rows are grouped into one synthetic run per inherited turn (`branch-seed-{thread_id}-{n}`, a new turn opening at every persisted human message, including an allowlisted hidden `ask_clarification` reply) because `run_id` is a turn identity to the feed's consumers, not a provenance tag: regenerating an inherited answer supersedes that row's whole `run_id` in `GET /messages/page`, so one shared id for the entire seed deleted the complete inherited history on a branch's first regenerate (#4458); `GET /goal`, `PUT /goal`, `DELETE /goal` - read, set, and clear the active thread goal; `POST /compact` - manually summarize older active context into `summary_text` and retain the recent message window, blocked while a run is in flight; unexpected failures are logged server-side and return a generic 500 detail |
 | **Artifacts** (`/api/threads/{id}/artifacts`) | `GET /{path}` - serve artifacts; active content types (`text/html`, `application/xhtml+xml`, `image/svg+xml`) are always forced as download attachments to reduce XSS risk; `?download=true` still forces download for other file types |
 | **Suggestions** (`/api/suggestions`) | `GET /config` - returns global suggestions config boolean; `POST /threads/{id}/suggestions` - generate follow-up questions; rich list/block model content is normalized and inline reasoning (`<think>...</think>`, including unclosed/truncated blocks from reasoning models like MiniMax-M3) is stripped before JSON parsing |
 | **Input Polish** (`/api/input-polish`) | `POST /` - rewrite a composer draft before it is sent. This is a short authenticated `runs:create` LLM request using `input_polish` config; it does not create a LangGraph run, persist a message, or modify thread state. Shares the non-graph one-shot LLM path (`deerflow.utils.oneshot_llm.run_oneshot_llm`) with the suggestions route so model build + Langfuse metadata + invoke stay in one place; validates the same stripped view of the draft it sends to the model, and preserves literal `<think>` substrings in the rewrite (`strip_think_blocks(truncate_unclosed=False)`) |
diff --git a/backend/app/gateway/routers/threads.py b/backend/app/gateway/routers/threads.py
index b5ba42527..0e323a18b 100644
--- a/backend/app/gateway/routers/threads.py
+++ b/backend/app/gateway/routers/threads.py
@@ -888,7 +888,7 @@ async def branch_thread(thread_id: str, body: ThreadBranchRequest, request: Requ
         seed_events = build_branch_history_seed_events(
             _checkpoint_messages(snapshot),
             thread_id=new_thread_id,
-            run_id=f"branch-seed-{new_thread_id}",
+            run_id_prefix=f"branch-seed-{new_thread_id}",
             parent_thread_id=thread_id,
         )
         if seed_events:
diff --git a/backend/packages/harness/deerflow/runtime/journal.py b/backend/packages/harness/deerflow/runtime/journal.py
index bf5706a33..2112fcffc 100644
--- a/backend/packages/harness/deerflow/runtime/journal.py
+++ b/backend/packages/harness/deerflow/runtime/journal.py
@@ -91,7 +91,7 @@ def build_branch_history_seed_events(
     messages: Sequence[Any],
     *,
     thread_id: str,
-    run_id: str,
+    run_id_prefix: str,
     parent_thread_id: str,
 ) -> list[dict]:
     """Serialize a branch checkpoint's messages into run-event message rows.
@@ -104,6 +104,18 @@ def build_branch_history_seed_events(
     checkpoint snapshot the branch was created from keeps the feed
     consistent with what the branch actually contains.
 
+    Rows are grouped into one synthetic run per inherited turn
+    (``{run_id_prefix}-{n}``), a new turn starting at every persisted human
+    message — the same boundary a real run has, since a run begins with a
+    human input (including the allowlisted hidden ``ask_clarification``
+    reply, which resumes as its own run). ``run_id`` is a *turn* identity to
+    the feed's consumers, not merely a provenance tag: regenerating the last
+    inherited answer resolves that row's ``run_id`` as the superseded source
+    (``_find_target_run_id``) and ``GET /messages/page`` then drops **every**
+    row carrying it. One shared id for the whole seed therefore deleted the
+    complete inherited history on the branch's first regenerate (#4458); one
+    id per turn confines the drop to the turn actually regenerated.
+
     Mirrors RunJournal's message-event contract so seeded rows are
     indistinguishable from journaled ones except by the ``branch_seed``
     marker: same event types, ``category="message"``, ``content=
@@ -125,6 +137,8 @@ def build_branch_history_seed_events(
     events: list[dict] = []
     created_at = datetime.now(UTC).isoformat()
     seed_metadata = {"branch_seed": True, "branch_parent_thread_id": parent_thread_id}
+    # Messages ahead of the first human turn (none in practice) stay in turn 0.
+    turn_index = 0
     for raw_message in messages:
         message = _coerce_seed_message(raw_message)
         if not isinstance(message, BaseMessage):
@@ -132,6 +146,7 @@ def build_branch_history_seed_events(
         if isinstance(message, HumanMessage):
             if not _should_persist_human_input_message(message):
                 continue
+            turn_index += 1
             event_type = "llm.human.input"
             content = restore_original_human_message(message).model_dump()
             metadata: dict[str, Any] = {"caller": "lead_agent", **seed_metadata}
@@ -149,7 +164,7 @@ def build_branch_history_seed_events(
         events.append(
             {
                 "thread_id": thread_id,
-                "run_id": run_id,
+                "run_id": f"{run_id_prefix}-{turn_index}",
                 "event_type": event_type,
                 "category": "message",
                 "content": content,
diff --git a/backend/tests/test_branch_history_seed.py b/backend/tests/test_branch_history_seed.py
index 4d391910d..c5ca0de88 100644
--- a/backend/tests/test_branch_history_seed.py
+++ b/backend/tests/test_branch_history_seed.py
@@ -19,7 +19,7 @@ def _seed(messages):
     return build_branch_history_seed_events(
         messages,
         thread_id="branch-thread",
-        run_id="branch-seed-branch-thread",
+        run_id_prefix="branch-seed-branch-thread",
         parent_thread_id="parent-thread",
     )
 
@@ -36,7 +36,7 @@ def test_seed_serializes_visible_history_in_order() -> None:
     assert [event["event_type"] for event in events] == ["llm.human.input", "llm.ai.response", "llm.tool.result"]
     assert all(event["category"] == "message" for event in events)
     assert all(event["thread_id"] == "branch-thread" for event in events)
-    assert all(event["run_id"] == "branch-seed-branch-thread" for event in events)
+    assert all(event["run_id"] == "branch-seed-branch-thread-1" for event in events)
     assert [event["content"]["id"] for event in events] == ["h1", "a1", "t1"]
     # Human/AI rows carry the journal's caller tag; every row carries the
     # seed provenance marker.
@@ -159,6 +159,60 @@ def test_seed_restores_original_user_content() -> None:
     assert "original_user_content" not in events[0]["content"]["additional_kwargs"]
 
 
+def test_seed_scopes_one_synthetic_run_per_inherited_turn() -> None:
+    """``run_id`` is a turn identity to the feed, not a provenance tag: the
+    regenerate path supersedes a whole ``run_id``, so packing every inherited
+    turn into one id deleted the complete history on the first regenerate
+    (#4458). Each human message opens the next synthetic run."""
+    events = _seed(
+        [
+            HumanMessage(id="h1", content="turn one"),
+            AIMessage(id="a1", content="answer one"),
+            HumanMessage(id="h2", content="turn two"),
+            AIMessage(id="a2", content="calling a tool", tool_calls=[{"name": "search", "args": {}, "id": "call-1", "type": "tool_call"}]),
+            ToolMessage(id="t2", content="tool output", tool_call_id="call-1"),
+            AIMessage(id="a2b", content="answer two"),
+        ]
+    )
+
+    assert [(event["content"]["id"], event["run_id"]) for event in events] == [
+        ("h1", "branch-seed-branch-thread-1"),
+        ("a1", "branch-seed-branch-thread-1"),
+        ("h2", "branch-seed-branch-thread-2"),
+        ("a2", "branch-seed-branch-thread-2"),
+        ("t2", "branch-seed-branch-thread-2"),
+        ("a2b", "branch-seed-branch-thread-2"),
+    ]
+
+
+def test_seed_opens_a_new_turn_at_a_hidden_clarification_reply() -> None:
+    """An answered clarification resumes as its own run, so the reply is a turn
+    boundary exactly like a visible user message."""
+    response = {
+        "version": 1,
+        "kind": "human_input_response",
+        "source": "ask_clarification",
+        "request_id": "req-1",
+        "value": "yes",
+        "response_kind": "text",
+    }
+    events = _seed(
+        [
+            HumanMessage(id="h1", content="question"),
+            AIMessage(id="a1", content="which one?"),
+            HumanMessage(id="h-response", content="yes", additional_kwargs={"hide_from_ui": True, "human_input_response": response}),
+            AIMessage(id="a2", content="answer"),
+        ]
+    )
+
+    assert [event["run_id"] for event in events] == [
+        "branch-seed-branch-thread-1",
+        "branch-seed-branch-thread-1",
+        "branch-seed-branch-thread-2",
+        "branch-seed-branch-thread-2",
+    ]
+
+
 def test_seed_roundtrips_through_memory_store_feed() -> None:
     """put_batch preserves order and list_messages returns the seeded feed."""
     store = MemoryRunEventStore()
diff --git a/backend/tests/test_thread_messages_page.py b/backend/tests/test_thread_messages_page.py
index 246bd00c1..07bfb6129 100644
--- a/backend/tests/test_thread_messages_page.py
+++ b/backend/tests/test_thread_messages_page.py
@@ -9,10 +9,12 @@ from unittest.mock import AsyncMock, MagicMock
 import pytest
 from _router_auth_helpers import make_authed_test_app
 from fastapi.testclient import TestClient
+from langchain_core.messages import AIMessage, HumanMessage
 
 from app.gateway.routers import thread_runs
 from deerflow.runtime import RunRecord
 from deerflow.runtime.events.store.memory import MemoryRunEventStore
+from deerflow.runtime.journal import build_branch_history_seed_events
 
 
 def _make_app(event_store: MemoryRunEventStore, *, superseded: set[str] | None = None, records=None, feedback=None):
@@ -185,6 +187,45 @@ def test_thread_page_filters_all_successfully_superseded_runs_before_filling():
     assert body["next_before_seq"] is None
 
 
+def test_thread_page_keeps_earlier_branch_turns_when_the_last_one_is_regenerated():
+    """Regenerating a branch's inherited answer must not delete the turns before
+    it (#4458).
+
+    Supersession is run-scoped, so it can only stay confined to the regenerated
+    turn while each seeded turn owns its own synthetic run id — this pins the
+    seed builder's turn scoping against the filter that consumes it.
+    """
+    store = MemoryRunEventStore()
+    branch_thread = "thread-1"
+
+    async def seed():
+        seed_events = build_branch_history_seed_events(
+            [
+                HumanMessage(id="h1", content="turn one"),
+                AIMessage(id="a1", content="answer one"),
+                HumanMessage(id="h2", content="turn two"),
+                AIMessage(id="a2", content="answer two"),
+            ],
+            thread_id=branch_thread,
+            run_id_prefix=f"branch-seed-{branch_thread}",
+            parent_thread_id="parent-thread",
+        )
+        await store.put_batch(seed_events)
+        # The regenerate run re-journals the same human id plus a fresh answer.
+        await _put_message(store, "live-run", "human", "h2")
+        await _put_message(store, "live-run", "ai", "a2-new")
+        # Resolve the superseded source the way `_find_target_run_id` does:
+        # the run id carried by the regenerated assistant row itself.
+        return next(event["run_id"] for event in seed_events if event["content"]["id"] == "a2")
+
+    superseded_run_id = asyncio.run(seed())
+    app = _make_app(store, superseded={superseded_run_id})
+    with TestClient(app) as client:
+        body = client.get("/api/threads/thread-1/messages/page?limit=50").json()
+
+    assert [row["content"]["id"] for row in body["data"]] == ["h1", "a1", "h2", "a2-new"]
+
+
 def test_thread_page_logs_rows_missing_sequence_values(caplog):
     store = AsyncMock()
     store.list_messages.return_value = [{"run_id": "run-1", "content": {"type": "human"}}]
diff --git a/backend/tests/test_threads_router.py b/backend/tests/test_threads_router.py
index df2c702f9..99a937a26 100644
--- a/backend/tests/test_threads_router.py
+++ b/backend/tests/test_threads_router.py
@@ -2013,7 +2013,8 @@ def test_branch_seeds_run_events_with_parent_history(monkeypatch, mode) -> None:
     assert [row["content"]["id"] for row in rows] == ["h1", "t1", "a1"]
     assert [row["event_type"] for row in rows] == ["llm.human.input", "llm.tool.result", "llm.ai.response"]
     assert all(row["category"] == "message" for row in rows)
-    assert all(row["run_id"] == f"branch-seed-{branch_thread_id}" for row in rows)
+    # One synthetic run per inherited turn (#4458): this source has a single turn.
+    assert all(row["run_id"] == f"branch-seed-{branch_thread_id}-1" for row in rows)
     assert all((row.get("metadata") or {}).get("branch_seed") is True for row in rows)
     seqs = [row["seq"] for row in rows]
     assert seqs == sorted(seqs)