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/session-context-summary.ts

@@ -1,7 +1,7 @@
 import { Agent } from "@mastra/core/agent";
 
 import {
-  CONSULTATION_HISTORY_TAIL_MAX_CHARS,
+  consultationHistoryCheckpointChars,
   lastConsultationPair,
   parseSessionContextSummary,
   storedConsultationTurns,
@@ -98,7 +98,7 @@ export function sanitizeSessionContextSummary(raw: string): string | null {
 export function tailCharCount(
   messages: unknown,
   summary: SessionContextSummaryV1 | null,
-  options: { excludeRequestId?: string } = {},
+  options: { excludeRequestId?: string; contextWindow?: number | null } = {},
 ): number {
   const turns = storedConsultationTurns(messages, { excludeRequestId: options.excludeRequestId });
   const tail = summary
@@ -110,9 +110,10 @@ export function tailCharCount(
 export function shouldCheckpoint(
   messages: unknown,
   summary: SessionContextSummaryV1 | null,
-  options: { excludeRequestId?: string } = {},
+  options: { excludeRequestId?: string; contextWindow?: number | null } = {},
 ): boolean {
-  return tailCharCount(messages, summary, options) > CONSULTATION_HISTORY_TAIL_MAX_CHARS;
+  return tailCharCount(messages, summary, options)
+    > consultationHistoryCheckpointChars(options.contextWindow);
 }
 
 export function messagesForSummaryInput(
@@ -215,6 +216,19 @@ export function nextSessionContextSummary(
   };
 }
 
+export async function resolveInheritedContextSummary(input: {
+  continuedFromSessionId?: string | null;
+  loadOwnedSummary: (sessionId: string) => Promise<unknown>;
+}): Promise<SessionContextSummaryV1 | null> {
+  const sourceId = input.continuedFromSessionId?.trim();
+  if (!sourceId) return null;
+  try {
+    return parseSessionContextSummary(await input.loadOwnedSummary(sourceId));
+  } catch {
+    return null;
+  }
+}
+
 export async function writeSessionContextSummary(input: {
   seenUpdatedAt: string | null;
   summary: SessionContextSummaryV1;
@@ -228,13 +242,17 @@ export async function checkpointSessionContextSummary(input: {
   messages: unknown;
   summary: unknown;
   excludeRequestId?: string;
+  contextWindow?: number | null;
   now?: () => Date;
   generateText: (prompt: string, signal?: AbortSignal) => Promise<string>;
   update: (summary: SessionContextSummaryV1, seenUpdatedAt: string | null) => Promise<boolean>;
   timeoutMs?: number;
 }): Promise<"written" | "skipped" | "abandoned" | "failed"> {
   const previous = parseSessionContextSummary(input.summary);
-  if (!shouldCheckpoint(input.messages, previous, { excludeRequestId: input.excludeRequestId })) {
+  if (!shouldCheckpoint(input.messages, previous, {
+    excludeRequestId: input.excludeRequestId,
+    contextWindow: input.contextWindow,
+  })) {
     return "skipped";
   }
   try {