diff --git a/api/routes.py b/api/routes.py
index 6b6ddcbb..88d49776 100644
--- a/api/routes.py
+++ b/api/routes.py
@@ -1568,6 +1568,75 @@ def _ensure_full_session_before_mutation(sid: str, session):
     return full_session
 
 
+def _get_or_materialize_session(sid: str):
+    """Get a session, materializing from CLI/agent metadata if not in WebUI store.
+
+    Mirrors the fallback logic in /api/session/archive (routes.py:~8530).
+    Raises:
+        KeyError: session not found in any store
+        PermissionError: session is read-only (messaging/Claude Code)
+    """
+    try:
+        s = get_session(sid)
+        s = _ensure_full_session_before_mutation(sid, s)
+        return s
+    except KeyError:
+        pass
+
+    # Fallback: try to materialize from CLI/agent session metadata
+    cli_meta = _lookup_cli_session_metadata(sid)
+    if not cli_meta:
+        raise KeyError(sid)
+
+    # Read-only guard: messaging sessions and Claude Code imports cannot be mutated
+    if cli_meta.get("read_only"):
+        raise PermissionError("read-only imported session")
+
+    # Preserve source metadata fields
+    def _apply_source_meta(s):
+        s.is_cli_session = True
+        s.source_tag = cli_meta.get("source_tag")
+        s.raw_source = cli_meta.get("raw_source") or cli_meta.get("source_tag")
+        s.session_source = cli_meta.get("session_source")
+        s.source_label = cli_meta.get("source_label")
+        s.user_id = cli_meta.get("user_id")
+        s.chat_id = cli_meta.get("chat_id")
+        s.chat_type = cli_meta.get("chat_type")
+        s.thread_id = cli_meta.get("thread_id")
+        s.session_key = cli_meta.get("session_key")
+        s.platform = cli_meta.get("platform")
+
+    if _is_messaging_session_record(cli_meta):
+        # Messaging sessions: lightweight Session with no messages (state.db is source of truth)
+        s = Session(
+            session_id=sid,
+            title=cli_meta.get("title") or title_from(get_cli_session_messages(sid), "CLI Session"),
+            workspace=get_last_workspace(),
+            model=cli_meta.get("model") or "unknown",
+            created_at=cli_meta.get("created_at"),
+            updated_at=cli_meta.get("updated_at"),
+        )
+        _apply_source_meta(s)
+        s.save(touch_updated_at=False)
+    else:
+        # Regular CLI/agent sessions: import full message history
+        msgs = get_cli_session_messages(sid)
+        if not msgs:
+            raise KeyError(sid)
+        s = import_cli_session(
+            sid,
+            cli_meta.get("title") or title_from(msgs, "CLI Session"),
+            msgs,
+            cli_meta.get("model") or "unknown",
+            profile=cli_meta.get("profile"),
+            created_at=cli_meta.get("created_at"),
+            updated_at=cli_meta.get("updated_at"),
+        )
+        _apply_source_meta(s)
+
+    return s
+
+
 def _reconcile_stale_stream_state_for_session_rows(session_rows) -> bool:
     """Clear stale persisted stream fields before /api/sessions serializes rows."""
     changed = False
@@ -7418,10 +7487,11 @@ def handle_post(handler, parsed) -> bool:
         except ValueError as e:
             return bad(handler, str(e))
         try:
-            s = get_session(body["session_id"])
-            s = _ensure_full_session_before_mutation(body["session_id"], s)
+            s = _get_or_materialize_session(body["session_id"])
         except KeyError:
             return bad(handler, "Session not found", 404)
+        except PermissionError:
+            return bad(handler, "Read-only imported sessions cannot be renamed from WebUI", 403)
         with _get_session_agent_lock(body["session_id"]):
             from api.session_ops import apply_session_title_rename
             apply_session_title_rename(s, body["title"])
@@ -7608,9 +7678,11 @@ def handle_post(handler, parsed) -> bool:
         except ValueError as e:
             return bad(handler, str(e))
         try:
-            s = get_session(body["session_id"])
+            s = _get_or_materialize_session(body["session_id"])
         except KeyError:
             return bad(handler, "Session not found", 404)
+        except PermissionError:
+            return bad(handler, "Read-only imported sessions cannot be updated from WebUI", 403)
         old_ws = getattr(s, "workspace", "")
         old_model = getattr(s, "model", None)
         old_provider = getattr(s, "model_provider", None)
@@ -8592,9 +8664,11 @@ def handle_post(handler, parsed) -> bool:
         except ValueError as e:
             return bad(handler, str(e))
         try:
-            s = get_session(body["session_id"])
+            s = _get_or_materialize_session(body["session_id"])
         except KeyError:
             return bad(handler, "Session not found", 404)
+        except PermissionError:
+            return bad(handler, "Read-only imported sessions cannot be moved from WebUI", 403)
         # #1614: refuse moves into a project owned by another profile.
         target_pid = body.get("project_id") or None
         if target_pid: