fix(consult): drop traces, budget checkpoints, silent summary inherit

BUG-729: dropped history rounds leave an omission marker in the model-visible summary slot.
BUG-730: checkpoint threshold is 0.4 of historyBudgetChars (128k still 16,000).
BUG-731: session_full new chat copies owned context_summary on the server; clients send only continued_from_session_id.

frontend/src/app/api/sessions/route.ts

@@ -1,6 +1,12 @@
 import { NextResponse } from "next/server";
-import { chatSessionCreateSchema, ChatSessionBodyTooLargeError, readChatSessionJson } from "@/lib/chat-session-write-contract";
+import {
+  chatSessionCreateInsertRow,
+  chatSessionCreateSchema,
+  ChatSessionBodyTooLargeError,
+  readChatSessionJson,
+} from "@/lib/chat-session-write-contract";
 import { consumeUserRequestRateLimit } from "@/lib/request-rate-limit";
+import { resolveInheritedContextSummary } from "@/lib/session-context-summary";
 import { isSupabaseConfigurationError } from "@/lib/supabase/config";
 import { createServerSupabaseClient } from "@/lib/supabase/server";
 import {
@@ -94,13 +100,28 @@ export async function POST(request: Request) {
     }
     const parsed = chatSessionCreateSchema.safeParse(await readChatSessionJson(request));
     if (!parsed.success) return NextResponse.json({ error: "聊天记录格式不正确" }, { status: 400 });
-    const { id, updated_at: _ignoredClientClock, ...values } = parsed.data;
-    const { error } = await supabase.from("chat_sessions").insert({
-      id,
-      user_id: user.id,
-      ...values,
-      updated_at: new Date().toISOString(),
+    const { id, updated_at: _ignoredClientClock, continued_from_session_id: continuedFromSessionId, ...values } = parsed.data;
+    const inheritedSummary = await resolveInheritedContextSummary({
+      continuedFromSessionId,
+      loadOwnedSummary: async (sourceId) => {
+        const { data } = await supabase
+          .from("chat_sessions")
+          .select("context_summary")
+          .eq("id", sourceId)
+          .eq("user_id", user.id)
+          .maybeSingle();
+        return data?.context_summary ?? null;
+      },
     });
+    const { error } = await supabase.from("chat_sessions").insert(
+      chatSessionCreateInsertRow({
+        id,
+        userId: user.id,
+        values,
+        inheritedSummary,
+        updatedAt: new Date().toISOString(),
+      }),
+    );
     if (error) return NextResponse.json({ error: "聊天记录暂时无法同步" }, { status: 500 });
     return NextResponse.json({ ok: true }, { status: 201 });
   } catch (error) {