security: cookie + session hardening (#41)

Three related fixes:
- Cookie secure flag now tracks AUTH_URL scheme (https → Secure),
  not NODE_ENV — staging over HTTPS with NODE_ENV!=production used
  to ship Set-Cookie without Secure. Cookie name gains __Host-
  prefix when Secure is on.
- jwt() callback no longer swallows session-registry write failures;
  concurrent-session cap is now fail-closed.
- Session callback no longer copies token.sid onto session.user.jti.
  The tRPC route handler reads the JTI directly from the encrypted
  JWT via getToken() so it stays server-side.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/web/src/app/api/trpc/[trpc]/route.ts

@@ -2,6 +2,7 @@ import { createTRPCContext, loadRoleDefaults } from "@capakraken/api";
 import { appRouter } from "@capakraken/api/router";
 import { prisma } from "@capakraken/db";
 import { fetchRequestHandler } from "@trpc/server/adapters/fetch";
+import { getToken } from "next-auth/jwt";
 import type { NextRequest } from "next/server";
 import { auth } from "~/server/auth.js";
 
@@ -42,9 +43,19 @@ const handler = async (req: NextRequest) => {
   // Sessions kicked by concurrent-session limits or manual logout are rejected immediately.
   // Fail-open: if the table doesn't exist yet (pending migration) the check is skipped.
   // In E2E test mode the jwt callback skips registration, so skip validation too.
+  //
+  // We decode the JWT directly (not session.user.jti) because the session
+  // token is client-visible and therefore must not carry internal
+  // session-revocation identifiers — see security ticket #41.
   const isE2eTestMode = process.env["E2E_TEST_MODE"] === "true";
   if (session?.user && !isE2eTestMode) {
-    const jti = (session.user as typeof session.user & { jti?: string }).jti;
+    const secret = process.env["AUTH_SECRET"] ?? process.env["NEXTAUTH_SECRET"] ?? "";
+    const cookieName =
+      (process.env["AUTH_URL"] ?? "").startsWith("https://") || process.env["VERCEL"] === "1"
+        ? "__Host-authjs.session-token"
+        : "authjs.session-token";
+    const jwt = secret ? await getToken({ req, secret, salt: cookieName }) : null;
+    const jti = (jwt?.["sid"] as string | undefined) ?? undefined;
     if (jti) {
       try {
         const activeSession = await prisma.activeSession.findUnique({ where: { jti } });