fix: index concurrent first chat saves atomically

db/services/chats.ts

@@ -68,17 +68,17 @@ export async function saveChat(
   if (!(await waitForSessionOwnership(scope, chat.sessionId))) return;
   await ensureScope(scope);
   const now = new Date();
-  const existing = await db
-    .select({ sessionId: chats.sessionId })
-    .from(chats)
-    .where(
-      and(
-        eq(chats.workspaceId, scope.workspaceId),
-        eq(chats.sessionId, chat.sessionId)
-      )
-    );
-  if (existing.length === 0) {
-    await db.insert(chats).values({
+  const updates: Partial<typeof chats.$inferInsert> = { updatedAt: now };
+  if (chat.channel !== undefined) updates.channel = chat.channel;
+  if (chat.title !== undefined) updates.title = chat.title;
+  if (chat.usage !== undefined) {
+    updates.costUsd = chat.usage.costUsd;
+    updates.inputTokens = chat.usage.inputTokens;
+    updates.outputTokens = chat.usage.outputTokens;
+  }
+  await db
+    .insert(chats)
+    .values({
       channel: chat.channel ?? null,
       costUsd: chat.usage?.costUsd ?? null,
       createdAt: now,
@@ -88,24 +88,10 @@ export async function saveChat(
       title: chat.title ?? "New chat",
       updatedAt: now,
       workspaceId: scope.workspaceId,
+    })
+    .onConflictDoUpdate({
+      target: chats.sessionId,
+      set: updates,
+      setWhere: eq(chats.workspaceId, scope.workspaceId),
     });
-    return;
-  }
-  const updates: Partial<typeof chats.$inferInsert> = { updatedAt: now };
-  if (chat.channel !== undefined) updates.channel = chat.channel;
-  if (chat.title !== undefined) updates.title = chat.title;
-  if (chat.usage !== undefined) {
-    updates.costUsd = chat.usage.costUsd;
-    updates.inputTokens = chat.usage.inputTokens;
-    updates.outputTokens = chat.usage.outputTokens;
-  }
-  await db
-    .update(chats)
-    .set(updates)
-    .where(
-      and(
-        eq(chats.workspaceId, scope.workspaceId),
-        eq(chats.sessionId, chat.sessionId)
-      )
-    );
 }

web/trpc/chat-concurrency.test.ts

@@ -0,0 +1,82 @@
+import { PGlite } from "@electric-sql/pglite";
+import { drizzle } from "drizzle-orm/pglite";
+import { migrate } from "drizzle-orm/pglite/migrator";
+import {
+  afterAll,
+  beforeAll,
+  beforeEach,
+  describe,
+  expect,
+  it,
+  vi,
+} from "vitest";
+import * as Database from "@db";
+import * as schema from "@db/schema";
+import { readChat, saveChat } from "@db/services/chats";
+import { ensureScope } from "@db/services/scope";
+import { claimSession } from "@db/services/sessions";
+import { appRouter } from "@web/trpc/router";
+
+const client = new PGlite();
+const database = drizzle(client, { schema });
+const scope = { userId: "chat-fixture", workspaceId: "workspace:chat-fixture" };
+const caller = appRouter.createCaller({ origin: "https://example.com", scope });
+
+beforeAll(async () => {
+  await migrate(database, { migrationsFolder: "db/migrations" });
+  // SAFETY: PGlite supplies the real Drizzle query-builder contract used by the service; only the database driver changes.
+  // oxlint-disable-next-line typescript/no-unsafe-type-assertion -- Exercise the committed migrations and real services against an isolated PostgreSQL-compatible database.
+  vi.spyOn(Database, "db", "get").mockReturnValue(database as never);
+}, 20_000);
+
+beforeEach(async () => {
+  await database.delete(schema.workspaces);
+  await ensureScope(scope);
+  await claimSession(scope, "chat-session");
+});
+
+afterAll(async () => {
+  vi.restoreAllMocks();
+  await client.close();
+});
+
+describe("chat indexing", () => {
+  it("preserves title and usage when the first UI saves overlap", async () => {
+    await Promise.all([
+      caller.chats.save({ sessionId: "chat-session", title: "Travel plans" }),
+      caller.chats.save({
+        sessionId: "chat-session",
+        usage: { costUsd: 0.25, inputTokens: 10, outputTokens: 4 },
+      }),
+    ]);
+    expect(await readChat(scope, "chat-session")).toMatchObject({
+      title: "Travel plans",
+      usage: { costUsd: 0.25, inputTokens: 10, outputTokens: 4 },
+    });
+  });
+
+  it("preserves sparse fields during sequential saves and denies another workspace", async () => {
+    await caller.chats.save({
+      sessionId: "chat-session",
+      title: "Travel plans",
+    });
+    await saveChat(scope, { channel: "http", sessionId: "chat-session" });
+    await caller.chats.save({
+      sessionId: "chat-session",
+      usage: { costUsd: 0.25, inputTokens: 10, outputTokens: 4 },
+    });
+    const before = await readChat(scope, "chat-session");
+    expect(before).toMatchObject({
+      channel: "http",
+      title: "Travel plans",
+      usage: { costUsd: 0.25, inputTokens: 10, outputTokens: 4 },
+    });
+    await appRouter
+      .createCaller({
+        origin: "https://example.com",
+        scope: { userId: "other-user", workspaceId: "workspace:other-user" },
+      })
+      .chats.save({ sessionId: "chat-session", title: "Other title" });
+    expect(await readChat(scope, "chat-session")).toEqual(before);
+  });
+});