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/lib/chat-session-write-contract.ts

@@ -59,6 +59,7 @@ export const chatSessionCreateSchema = z.object({
   messages: z.array(chatMessageSchema).max(0),
   session_type: z.enum(["consultation", "birth_time_rectification"]),
   rectification_case_id: z.string().uuid().nullable(),
+  continued_from_session_id: z.string().uuid().optional(),
   ...chartBindingSchema,
   updated_at: z.string().datetime().optional(),
 }).strict();
@@ -148,11 +149,41 @@ export type ChatSessionCreate = Readonly<{
   messages: readonly [];
   session_type: "consultation" | "birth_time_rectification";
   rectification_case_id: string | null;
+  continued_from_session_id?: string;
   chart_profile_id?: string | null;
   chart_profile_name?: string | null;
   chart_profile_role?: "self" | "other" | null;
 }>;
 
+export type ChatSessionCreateInsertValues = Readonly<{
+  title: string;
+  theme: ConsultationDomain;
+  model_id: string;
+  messages: readonly unknown[];
+  session_type: "consultation" | "birth_time_rectification";
+  rectification_case_id: string | null;
+  chart_profile_id?: string | null;
+  chart_profile_name?: string | null;
+  chart_profile_role?: "self" | "other" | null;
+}>;
+
+export function chatSessionCreateInsertRow(input: {
+  id: string;
+  userId: string;
+  values: ChatSessionCreateInsertValues;
+  inheritedSummary?: unknown;
+  updatedAt: string;
+}): Record<string, unknown> {
+  const row: Record<string, unknown> = {
+    id: input.id,
+    user_id: input.userId,
+    ...input.values,
+    updated_at: input.updatedAt,
+  };
+  if (input.inheritedSummary) row.context_summary = input.inheritedSummary;
+  return row;
+}
+
 export type ChatSessionWrite = Readonly<{
   title: string;
   theme: ConsultationDomain;