diff --git a/packages/core-shared/src/instrumentation/sentry/init-server.test.ts b/packages/core-shared/src/instrumentation/sentry/init-server.test.ts
new file mode 100644
index 0000000..2f34b7e
--- /dev/null
+++ b/packages/core-shared/src/instrumentation/sentry/init-server.test.ts
@@ -0,0 +1,102 @@
+// packages/core-shared/src/instrumentation/sentry/init-server.test.ts
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+vi.mock("@sentry/nextjs", () => ({
+  init: vi.fn(),
+  replayIntegration: vi.fn(() => ({ name: "Replay" })),
+}));
+
+import * as Sentry from "@sentry/nextjs";
+import { initSentryServer } from "@/instrumentation/sentry/init-server";
+
+describe("initSentryServer", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("calls Sentry.init with sendDefaultPii: false (R31)", () => {
+    initSentryServer({ dsn: "https://x@y/1", app: "web-next" });
+    expect(Sentry.init).toHaveBeenCalledTimes(1);
+    const call = (Sentry.init as ReturnType<typeof vi.fn>).mock.calls[0][0] as Record<
+      string,
+      unknown
+    >;
+    expect(call["sendDefaultPii"]).toBe(false);
+  });
+
+  it("passes the configured DSN", () => {
+    initSentryServer({ dsn: "https://x@y/1", app: "web-next" });
+    const call = (Sentry.init as ReturnType<typeof vi.fn>).mock.calls[0][0] as Record<
+      string,
+      unknown
+    >;
+    expect(call["dsn"]).toBe("https://x@y/1");
+  });
+
+  it("attaches beforeSend + beforeSendTransaction scrubbers", () => {
+    initSentryServer({ dsn: "https://x@y/1", app: "web-next" });
+    const call = (Sentry.init as ReturnType<typeof vi.fn>).mock.calls[0][0] as Record<
+      string,
+      unknown
+    >;
+    expect(typeof call["beforeSend"]).toBe("function");
+    expect(typeof call["beforeSendTransaction"]).toBe("function");
+  });
+
+  it("uses SENTRY_TRACES_SAMPLE_RATE env when set", () => {
+    const prev = process.env["SENTRY_TRACES_SAMPLE_RATE"];
+    process.env["SENTRY_TRACES_SAMPLE_RATE"] = "0.25";
+    initSentryServer({ dsn: "https://x@y/1", app: "web-next" });
+    const call = (Sentry.init as ReturnType<typeof vi.fn>).mock.calls[0][0] as Record<
+      string,
+      unknown
+    >;
+    expect(call["tracesSampleRate"]).toBe(0.25);
+    if (prev === undefined) delete process.env["SENTRY_TRACES_SAMPLE_RATE"];
+    else process.env["SENTRY_TRACES_SAMPLE_RATE"] = prev;
+  });
+
+  it("defaults tracesSampleRate to 1.0 in dev, 0.1 in production", () => {
+    const prevEnv = process.env["NODE_ENV"];
+    const prevRate = process.env["SENTRY_TRACES_SAMPLE_RATE"];
+    delete process.env["SENTRY_TRACES_SAMPLE_RATE"];
+
+    process.env["NODE_ENV"] = "development";
+    initSentryServer({ dsn: "https://x@y/1", app: "web-next" });
+    expect(
+      ((Sentry.init as ReturnType<typeof vi.fn>).mock.calls[0][0] as Record<string, unknown>)[
+        "tracesSampleRate"
+      ],
+    ).toBe(1.0);
+
+    (Sentry.init as ReturnType<typeof vi.fn>).mockClear();
+    process.env["NODE_ENV"] = "production";
+    initSentryServer({ dsn: "https://x@y/1", app: "web-next" });
+    expect(
+      ((Sentry.init as ReturnType<typeof vi.fn>).mock.calls[0][0] as Record<string, unknown>)[
+        "tracesSampleRate"
+      ],
+    ).toBe(0.1);
+
+    if (prevEnv === undefined) delete process.env["NODE_ENV"];
+    else process.env["NODE_ENV"] = prevEnv;
+    if (prevRate !== undefined) process.env["SENTRY_TRACES_SAMPLE_RATE"] = prevRate;
+  });
+
+  it("tags events with the app name", () => {
+    initSentryServer({ dsn: "https://x@y/1", app: "web-next" });
+    const call = (Sentry.init as ReturnType<typeof vi.fn>).mock.calls[0][0] as Record<
+      string,
+      unknown
+    >;
+    const initialScope = call["initialScope"] as { tags?: Record<string, string> };
+    expect(initialScope?.tags?.["app"]).toBe("web-next");
+  });
+
+  it("is a no-op when dsn is empty/undefined", () => {
+    initSentryServer({ dsn: "", app: "web-next" });
+    expect(Sentry.init).not.toHaveBeenCalled();
+    initSentryServer({ dsn: undefined as unknown as string, app: "web-next" });
+    expect(Sentry.init).not.toHaveBeenCalled();
+  });
+});
diff --git a/packages/core-shared/src/instrumentation/sentry/init-server.ts b/packages/core-shared/src/instrumentation/sentry/init-server.ts
new file mode 100644
index 0000000..c662a8f
--- /dev/null
+++ b/packages/core-shared/src/instrumentation/sentry/init-server.ts
@@ -0,0 +1,39 @@
+// packages/core-shared/src/instrumentation/sentry/init-server.ts
+import * as Sentry from "@sentry/nextjs";
+import { beforeSend, beforeSendTransaction } from "./scrub";
+
+export type InitServerOpts = {
+  dsn: string | undefined;
+  app: "web-next" | "cms" | "web-tanstack";
+  release?: string;
+};
+
+export function initSentryServer(opts: InitServerOpts): void {
+  if (!opts.dsn) return;
+
+  const isProd = process.env["NODE_ENV"] === "production";
+  const tracesSampleRate =
+    process.env["SENTRY_TRACES_SAMPLE_RATE"] !== undefined
+      ? Number(process.env["SENTRY_TRACES_SAMPLE_RATE"])
+      : isProd
+        ? 0.1
+        : 1.0;
+
+  const environment =
+    process.env["SENTRY_ENVIRONMENT"] ??
+    process.env["VERCEL_ENV"] ??
+    process.env["NODE_ENV"] ??
+    "development";
+  const release = opts.release ?? process.env["VERCEL_GIT_COMMIT_SHA"] ?? "unknown";
+
+  Sentry.init({
+    dsn: opts.dsn,
+    environment,
+    release,
+    tracesSampleRate,
+    sendDefaultPii: false, // R31 — non-negotiable
+    beforeSend, // R32
+    beforeSendTransaction, // R33
+    initialScope: { tags: { app: opts.app } },
+  });
+}