feat: restore aggregate summaries endpoint + widget re-mount rehydration (#5054)

## Summary
- Restore the `GET /tasks/{id}/summaries/aggregate` Engine endpoint
(lost during PR #5002→#5013 squash). It synthesizes micro-summaries into
a single LLM-generated aggregate sentence via Gemini Flash Lite.
- Widget now shows proper aggregate summaries during live polling
(instead of falling back to raw micro-summaries)
- On re-mount (revisiting a conversation), widget calls
`backfillSummaries()` which fetches the last aggregate + micro-summaries
and renders one activity entry

## Changes
- **Engine**: `generate_aggregate_summary()` + `AGGREGATE_SYSTEM_PROMPT`
in `summarizer.py`, `AggregatedSummaryResponse` model, `GET
/{task_id}/summaries/aggregate` endpoint
- **MCP routes**: `api_progress` fetches aggregate for terminal tasks
without cursor (re-mount backfill)
- **Widget**: `backfillSummaries()` on re-mount, detects completed
status in `ontoolresult`

## Test plan
- [x] Engine tests pass (46)
- [x] MCP tests pass (351)
- [ ] Run task in Claude.ai, verify aggregate summaries appear in
Activity tab
- [ ] Switch away, switch back, verify last summary rehydrates

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Sourced from commit 1fea2f62212855b004be733de63b739e0a0554b1

Author: RafaelPo

futuresearch-mcp/src/futuresearch_mcp/routes.py

@@ -193,8 +193,10 @@ async def api_progress(request: Request) -> Response:
 
         payload = ts.model_dump(mode="json", exclude=_UI_EXCLUDE)
 
-        # Fetch aggregate + micro-summaries + partial rows for non-terminal tasks
-        if not ts.is_terminal:
+        # Fetch aggregate + micro-summaries for non-terminal tasks,
+        # or for terminal tasks without cursor (re-mount backfill).
+        backfill = ts.is_terminal and not request.query_params.get("cursor")
+        if not ts.is_terminal or backfill:
             cursor = request.query_params.get("cursor")
             aggregate, summaries, new_cursor = await _fetch_aggregate_rest(
                 client, task_id, cursor

futuresearch-mcp/src/futuresearch_mcp/templates.py

@@ -1001,12 +1001,31 @@
   });
 }
 
+/* ── fetch last aggregate summary (for re-mount when task already done) ── */
+async function backfillSummaries(){
+  if(!pollUrl||!pollToken)return;
+  try{
+    const opts=pollToken?{headers:{"Authorization":"Bearer "+pollToken}}:{};
+    const r=await fetch(pollUrl,opts);
+    if(!r.ok)return;
+    const d=await r.json();
+    if(d.aggregate_summary||d.summaries)renderProgress(d);
+  }catch{}
+}
+
 /* ── ontoolresult: unified entry point ── */
 app.ontoolresult=({content,structuredContent})=>{
   /* Entry 1: structuredContent from futuresearch_status (widget data) */
   if(structuredContent&&structuredContent.progress_url){
     enterProgressMode(structuredContent);
-    if(!pollTimer){pollUrl=structuredContent.progress_url;startPoll();}
+    /* If task already completed on re-mount, backfill summaries then fetch results */
+    const done=["completed","failed","revoked"].includes(structuredContent.status);
+    if(done){
+      wasDone=true;
+      backfillSummaries().then(()=>{if(!resultsFetched)autoFetchResults();});
+    } else if(!pollTimer){
+      pollUrl=structuredContent.progress_url;startPoll();
+    }
     return;
   }
 
@@ -1018,7 +1037,13 @@
         const d=JSON.parse(t.text);
         if(d.progress_url){
           enterProgressMode(d);
-          if(!pollTimer){pollUrl=d.progress_url;startPoll();}
+          const done=["completed","failed","revoked"].includes(d.status);
+          if(done){
+            wasDone=true;
+            backfillSummaries().then(()=>{if(!resultsFetched)autoFetchResults();});
+          } else if(!pollTimer){
+            pollUrl=d.progress_url;startPoll();
+          }
           return;
         }
       }catch{}