fix(history): strip base64 image data from REST endpoint responses (#3535)

ViewImageMiddleware persists full base64 image payloads in hide_from_ui
human messages inside checkpoints. All REST endpoints that returned
serialize_channel_values(channel_values) sent these multi-megabyte
payloads to the frontend, freezing the UI on threads with images.

Add strip_data_url_image_blocks() to remove data:-scheme image_url
content blocks from hide_from_ui messages, and
serialize_channel_values_for_api() as a convenience wrapper used by all
six affected call sites across threads, runs, and thread_runs routers.
SSE streaming is unaffected (still uses serialize_channel_values).

Fixes #3496

backend/app/gateway/routers/runs.py

@@ -18,7 +18,7 @@ from app.gateway.deps import get_checkpointer, get_feedback_repo, get_run_event_
 from app.gateway.pagination import trim_run_message_page
 from app.gateway.routers.thread_runs import RunCreateRequest
 from app.gateway.services import sse_consumer, start_run, wait_for_run_completion
-from deerflow.runtime import serialize_channel_values
+from deerflow.runtime import serialize_channel_values_for_api
 
 logger = logging.getLogger(__name__)
 router = APIRouter(prefix="/api/runs", tags=["runs"])
@@ -82,7 +82,7 @@ async def stateless_wait(body: RunCreateRequest, request: Request) -> dict:
             if checkpoint_tuple is not None:
                 checkpoint = getattr(checkpoint_tuple, "checkpoint", {}) or {}
                 channel_values = checkpoint.get("channel_values", {})
-                return serialize_channel_values(channel_values)
+                return serialize_channel_values_for_api(channel_values)
         except Exception:
             logger.exception("Failed to fetch final state for run %s", record.run_id)
 

backend/app/gateway/routers/thread_runs.py

@@ -23,7 +23,7 @@ from app.gateway.authz import require_permission
 from app.gateway.deps import get_checkpointer, get_current_user, get_feedback_repo, get_run_event_store, get_run_manager, get_run_store, get_stream_bridge
 from app.gateway.pagination import trim_run_message_page
 from app.gateway.services import sse_consumer, start_run, wait_for_run_completion
-from deerflow.runtime import RunRecord, RunStatus, serialize_channel_values
+from deerflow.runtime import RunRecord, RunStatus, serialize_channel_values_for_api
 
 logger = logging.getLogger(__name__)
 router = APIRouter(prefix="/api/threads", tags=["runs"])
@@ -192,7 +192,7 @@ async def wait_run(thread_id: str, body: RunCreateRequest, request: Request) ->
             if checkpoint_tuple is not None:
                 checkpoint = getattr(checkpoint_tuple, "checkpoint", {}) or {}
                 channel_values = checkpoint.get("channel_values", {})
-                return serialize_channel_values(channel_values)
+                return serialize_channel_values_for_api(channel_values)
         except Exception:
             logger.exception("Failed to fetch final state for run %s", record.run_id)
 

backend/app/gateway/routers/threads.py

@@ -25,7 +25,7 @@ from app.gateway.deps import get_checkpointer
 from app.gateway.internal_auth import get_trusted_internal_owner_user_id
 from app.gateway.utils import sanitize_log_param
 from deerflow.config.paths import Paths, get_paths
-from deerflow.runtime import serialize_channel_values
+from deerflow.runtime import serialize_channel_values_for_api
 from deerflow.runtime.user_context import get_effective_user_id
 from deerflow.utils.time import coerce_iso, now_iso
 
@@ -437,7 +437,7 @@ async def get_thread(thread_id: str, request: Request) -> ThreadResponse:
         created_at=coerce_iso(record.get("created_at", "")),
         updated_at=coerce_iso(record.get("updated_at", "")),
         metadata=record.get("metadata", {}),
-        values=serialize_channel_values(channel_values),
+        values=serialize_channel_values_for_api(channel_values),
     )
 
 
@@ -480,7 +480,7 @@ async def get_thread_state(thread_id: str, request: Request) -> ThreadStateRespo
     next_tasks = [t.name for t in tasks_raw if hasattr(t, "name")]
     tasks = [{"id": getattr(t, "id", ""), "name": getattr(t, "name", "")} for t in tasks_raw]
 
-    values = serialize_channel_values(channel_values)
+    values = serialize_channel_values_for_api(channel_values)
 
     return ThreadStateResponse(
         values=values,
@@ -588,7 +588,7 @@ async def update_thread_state(thread_id: str, body: ThreadStateUpdateRequest, re
                 logger.debug("Failed to sync title to thread_meta for %s (non-fatal)", sanitize_log_param(thread_id))
 
     return ThreadStateResponse(
-        values=serialize_channel_values(channel_values),
+        values=serialize_channel_values_for_api(channel_values),
         next=[],
         metadata=metadata,
         checkpoint_id=new_checkpoint_id,
@@ -640,7 +640,7 @@ async def get_thread_history(thread_id: str, body: ThreadHistoryRequest, request
             if is_latest_checkpoint:
                 messages = channel_values.get("messages")
                 if messages:
-                    values["messages"] = serialize_channel_values({"messages": messages}).get("messages", [])
+                    values["messages"] = serialize_channel_values_for_api({"messages": messages}).get("messages", [])
             is_latest_checkpoint = False
 
             # Derive next tasks