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/tests/chat-session-write.test.ts

@@ -1,7 +1,14 @@
 import assert from "node:assert/strict";
 import { readFileSync } from "node:fs";
 import test from "node:test";
-import { chatSessionCreateSchema, chatSessionMetadataPatchSchema, chatSessionWriteSchema, writeChatSession, type ChatSessionWrite } from "../src/lib/chat-session-write-contract.ts";
+import {
+  chatSessionCreateInsertRow,
+  chatSessionCreateSchema,
+  chatSessionMetadataPatchSchema,
+  chatSessionWriteSchema,
+  writeChatSession,
+  type ChatSessionWrite,
+} from "../src/lib/chat-session-write-contract.ts";
 import { metadataUpdateValues } from "../src/lib/session-metadata-update.ts";
 import { homeSurface } from "./home-surface.ts";
 
@@ -41,6 +48,61 @@ test("create schema keeps the client-generated session id after transcript limit
   assert.equal(parsed.messages.length, 0);
 });
 
+test("create schema accepts continued_from_session_id and rejects client-supplied context_summary", () => {
+  const parsed = chatSessionCreateSchema.parse({
+    id: sessionId,
+    ...createValues,
+    continued_from_session_id: "22222222-2222-4222-8222-222222222222",
+  });
+  assert.equal(parsed.continued_from_session_id, "22222222-2222-4222-8222-222222222222");
+  assert.equal("context_summary" in parsed, false);
+  assert.equal("context_summary" in chatSessionCreateSchema.shape, false);
+
+  const withSummary = chatSessionCreateSchema.safeParse({
+    id: sessionId,
+    ...createValues,
+    context_summary: { version: 1, text: "injected" },
+  });
+  assert.equal(withSummary.success, false);
+
+  const badId = chatSessionCreateSchema.safeParse({
+    id: sessionId,
+    ...createValues,
+    continued_from_session_id: "not-a-uuid",
+  });
+  assert.equal(badId.success, false);
+});
+
+test("create insert copies an owned summary and omits a missing one", () => {
+  const source = {
+    version: 1 as const,
+    text: "已问过的问题\n事业时机",
+    throughRequestId: "a1",
+    throughMessageIndex: 3,
+    messageCount: 4,
+    updatedAt: "2026-09-15T00:00:00.000Z",
+  };
+  const copied = chatSessionCreateInsertRow({
+    id: sessionId,
+    userId: "owner",
+    values: createValues,
+    inheritedSummary: source,
+    updatedAt: "2026-09-16T00:00:00.000Z",
+  });
+  assert.deepEqual(copied.context_summary, source);
+  assert.equal("continued_from_session_id" in copied, false);
+
+  const skipped = chatSessionCreateInsertRow({
+    id: sessionId,
+    userId: "owner",
+    values: createValues,
+    inheritedSummary: null,
+    updatedAt: "2026-09-16T00:00:00.000Z",
+  });
+  assert.equal("context_summary" in skipped, false);
+  assert.equal(skipped.user_id, "owner");
+});
+
 test("create schema rejects a non-empty transcript", () => {
   // Former value: create accepted up to CHAT_SESSION_MAX_MESSAGES and was a
   // history-import path. Create is now only an empty session.
@@ -122,6 +184,19 @@ test("metadata patch accepts pin and archive fields without a transcript", () =>
   assert.deepEqual(chatSessionMetadataPatchSchema.parse({ archived_at: null }), { archived_at: null });
 });
 
+test("create write may carry continued_from_session_id and never context_summary", async () => {
+  const calls: Array<Record<string, unknown>> = [];
+  await writeChatSession(sessionId, {
+    ...createValues,
+    continued_from_session_id: "22222222-2222-4222-8222-222222222222",
+  }, "create", async (_url, init) => {
+    calls.push(JSON.parse(String(init?.body)));
+    return Response.json({ ok: true }, { status: 201 });
+  });
+  assert.equal(calls[0]?.continued_from_session_id, "22222222-2222-4222-8222-222222222222");
+  assert.equal("context_summary" in (calls[0] ?? {}), false);
+});
+
 test("chat session writes use same-origin API instead of browser-to-Supabase requests", async () => {
   const calls: Array<{ url: string; init?: RequestInit }> = [];
   await writeChatSession(sessionId, metadataPatch, "update", async (url, init) => {
@@ -205,8 +280,17 @@ test("session API owns create and update while answer UI keeps sync failures out
   assert.match(itemRoute, /readChatSessionJson/);
   assert.match(collectionRoute, /ChatSessionBodyTooLargeError/);
   assert.match(itemRoute, /ChatSessionBodyTooLargeError/);
-  // Former value: `const { id, ...values } = parsed.data` trusted the client clock.
-  assert.match(collectionRoute, /const \{ id, updated_at: _ignoredClientClock, \.\.\.values \} = parsed\.data/);
+  // Former value: `const { id, updated_at: _ignoredClientClock, ...values } = parsed.data`
+  // New value: also peel `continued_from_session_id` so it is never inserted as a column.
+  assert.match(
+    collectionRoute,
+    /const \{ id, updated_at: _ignoredClientClock, continued_from_session_id: continuedFromSessionId, \.\.\.values \} = parsed\.data/,
+  );
+  assert.match(collectionRoute, /resolveInheritedContextSummary/);
+  assert.match(collectionRoute, /chatSessionCreateInsertRow/);
+  assert.match(collectionRoute, /\.eq\("user_id", user\.id\)/);
+  assert.match(collectionRoute, /status: 201/);
+  assert.doesNotMatch(collectionRoute, /context_summary: parsed/);
   assert.match(contract, /function limitTranscriptSize<Output extends \{ messages: Array<\{ text: string; thinkingText\?: string; thinkingSections\?: unknown \}> \}>/);
   assert.match(contract, /\): z\.ZodType<Output> \{/);
   assert.match(page, /chartSnapshotForSession/);