diff --git a/.cursor/rules/constraints.mdc b/.cursor/rules/constraints.mdc
index 43c61f6..f1ccf78 100644
--- a/.cursor/rules/constraints.mdc
+++ b/.cursor/rules/constraints.mdc
@@ -5,6 +5,8 @@ alwaysApply: true
 
 # Constraints
 
+These rules apply to the Rust `squid` library in `crates/squid` (and its wasm/napi shims must stay thin).
+
 ## Never re-implement Poulpy internals
 
 If a primitive exists in `poulpy-core`, `poulpy-schemes`, `poulpy-hal`, or `poulpy-cpu-ref`, use it. Writing a "simpler" version in squid defeats the purpose and will drift from Poulpy's correctness guarantees.
diff --git a/.cursor/rules/conventions.mdc b/.cursor/rules/conventions.mdc
index 7633e74..e34674d 100644
--- a/.cursor/rules/conventions.mdc
+++ b/.cursor/rules/conventions.mdc
@@ -1,20 +1,22 @@
 ---
 description: Coding conventions for squid
-globs: src/**/*.rs, examples/**/*.rs
+globs: crates/squid/src/**/*.rs, crates/squid/examples/**/*.rs
 alwaysApply: false
 ---
 
 # Coding conventions
 
+Paths below are under `crates/squid/`.
+
 ## Structure
 
-- `lib.rs` is module declarations and `pub use` re-exports only. No logic ever goes there.
+- `src/lib.rs` is module declarations and `pub use` re-exports only. No logic ever goes there.
 - All public operations are methods on `Context`. If a user needs to import a type from `keys` or `ciphertext` directly, re-export it from `lib.rs` instead.
 - `scratch` is a `pub mod`, but every item in `scratch.rs` is `pub(crate)` — treat it as internal; it is not re-exported from `lib.rs` and is not part of the supported API.
 
 ## Types
 
-- The backend is selected at compile time via `crate::backend::BE` (see `src/backend.rs`). `type Mod = Module<crate::backend::BE>` in `context.rs`. Do not add `<BE: Backend>` generics to any public type. Use `crate::backend::BE` everywhere internally instead of hard-coding `FFT64Ref`.
+- The backend is selected at compile time via `crate::backend::BE` (see `src/backend.rs` in `crates/squid`). `type Mod = Module<crate::backend::BE>` in `context.rs`. Do not add `<BE: Backend>` generics to any public type. Use `crate::backend::BE` everywhere internally instead of hard-coding `FFT64Ref`.
 - Layout fields on `Params` and its nested structs use Poulpy newtypes (`Degree`, `Base2K`, etc.). Prefer `Params::unsecure()` for the Poulpy `bdd_arithmetic` example bundle (not a security claim). For a custom `Params`, keep all layouts self-consistent (same `n_glwe`, `base2k`, `rank`, … across `glwe_layout`, `ggsw_layout`, `bdd_layout`).
 - `Ciphertext<T>` is always in standard (`Vec<u8>`) form. `FheUintPrepared` must never escape `eval_binary`.
 
@@ -29,6 +31,7 @@ Stay close to Poulpy's vocabulary when naming wrapper types so users who read Po
 ## User-facing choices
 
 Every feature that gives the end user a choice must have a sensible default that works without configuration. Alternatives (e.g. feature flags, optional parameters, variant constructors) must be documented with:
+
 - what the alternative does differently from the default
 - when the user should prefer it over the default
 - any trade-offs or requirements (e.g. hardware, security implications, performance cost)
diff --git a/.cursor/rules/modules.mdc b/.cursor/rules/modules.mdc
index a2a6736..4ae0327 100644
--- a/.cursor/rules/modules.mdc
+++ b/.cursor/rules/modules.mdc
@@ -1,22 +1,24 @@
 ---
 description: Module responsibilities and boundaries for squid
-globs: src/**/*.rs
+globs: crates/squid/src/**/*.rs
 alwaysApply: false
 ---
 
 # Module responsibilities
 
-| Module | File | Responsibility |
-|---|---|---|
-| `context` | `src/context.rs` | Single user entry point. Owns `Module<BE>` and `Params`. Allocates `scratch::Arena` per operation using Poulpy `*_tmp_bytes`. All public API flows through `Context`. |
-| `backend` | `src/backend.rs` | Compile-time `BE` alias (`FFT64Ref` or `FFT64Avx` via `backend-avx`). `pub(crate)` only; not re-exported from `lib.rs`. |
-| `scratch` | `src/scratch.rs` | Scratch arena (`Arena`): `new_arena` and `borrow` over `ScratchOwned<BE>`. `Context` sizes each allocation from Poulpy `*_tmp_bytes` at call sites. `pub(crate)`; not part of the supported public API. |
-| `keys` | `src/keys.rs` | `SecretKey` and `EvaluationKey` types. Holds standard-form and prepared-form key material. Hides all lifecycle transitions. |
-| `ciphertext` | `src/ciphertext.rs` | `Ciphertext<T>` newtype over `FheUint<Vec<u8>, T>`. The only ciphertext form users ever see. |
+Rust sources live under `crates/squid/src/`.
+
+| Module       | File                             | Responsibility                                                                                                                                                                                          |
+| ------------ | -------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| `context`    | `crates/squid/src/context.rs`    | Single user entry point. Owns `Module<BE>` and `Params`. Allocates `scratch::Arena` per operation using Poulpy `*_tmp_bytes`. All public API flows through `Context`.                                   |
+| `backend`    | `crates/squid/src/backend.rs`    | Compile-time `BE` alias (`FFT64Ref` or `FFT64Avx` via `backend-avx`). `pub(crate)` only; not re-exported from `lib.rs`.                                                                                 |
+| `scratch`    | `crates/squid/src/scratch.rs`    | Scratch arena (`Arena`): `new_arena` and `borrow` over `ScratchOwned<BE>`. `Context` sizes each allocation from Poulpy `*_tmp_bytes` at call sites. `pub(crate)`; not part of the supported public API. |
+| `keys`       | `crates/squid/src/keys.rs`       | `SecretKey` and `EvaluationKey` types. Holds standard-form and prepared-form key material. Hides all lifecycle transitions.                                                                             |
+| `ciphertext` | `crates/squid/src/ciphertext.rs` | `Ciphertext<T>` newtype over `FheUint<Vec<u8>, T>`. The only ciphertext form users ever see.                                                                                                            |
 
 ## lib.rs
 
-`lib.rs` is module declarations and `pub use` re-exports only. No logic. Declares `pub mod` for `context`, `scratch`, `keys`, and `ciphertext`, and a private `mod backend`.
+`crates/squid/src/lib.rs` is module declarations and `pub use` re-exports only. No logic. Declares `pub mod` for `context`, `scratch`, `keys`, and `ciphertext`, and a private `mod backend`.
 
 ## Ownership model
 
diff --git a/.cursor/rules/poulpy-concepts.mdc b/.cursor/rules/poulpy-concepts.mdc
index f1def41..8335bb2 100644
--- a/.cursor/rules/poulpy-concepts.mdc
+++ b/.cursor/rules/poulpy-concepts.mdc
@@ -1,6 +1,6 @@
 ---
 description: Key Poulpy concepts required before modifying squid code
-globs: src/**/*.rs
+globs: crates/squid/src/**/*.rs
 alwaysApply: false
 ---
 
@@ -16,11 +16,11 @@ Poulpy operations never heap-allocate on the hot path. Every operation accepts `
 
 Every ciphertext and key lives in one of three representations:
 
-| Layer | Storage | Use |
-|---|---|---|
-| Standard | `Vec<u8>`, serializable | Encrypt, decrypt, store, send |
-| Compressed | seed + body only | Reduced-size storage |
-| Prepared | DFT/NTT domain, backend-specific | Fast multiplication, key-switching |
+| Layer      | Storage                          | Use                                |
+| ---------- | -------------------------------- | ---------------------------------- |
+| Standard   | `Vec<u8>`, serializable          | Encrypt, decrypt, store, send      |
+| Compressed | seed + body only                 | Reduced-size storage               |
+| Prepared   | DFT/NTT domain, backend-specific | Fast multiplication, key-switching |
 
 squid hides this: users always hold Standard forms. Prepared forms are created transiently inside `Context` operations and never surface in the public API.
 
@@ -41,6 +41,7 @@ All arithmetic is expressed as trait methods on `Module<BE>`. The backend `BE` i
 ## 5. BDD key hierarchy
 
 `BDDKey` bundles three sub-keys:
+
 - `CircuitBootstrappingKey` — blind rotation key + automorphism key + tensor switching key
 - `GLWESwitchingKey` (optional) — rank reduction before LWE extraction
 - `GLWEToLWESwitchingKey` — GLWE -> LWE extraction
diff --git a/.cursor/rules/project.mdc b/.cursor/rules/project.mdc
index 9024f19..22b3c5c 100644
--- a/.cursor/rules/project.mdc
+++ b/.cursor/rules/project.mdc
@@ -7,6 +7,21 @@ alwaysApply: true
 
 `squid` is an ergonomic Rust wrapper over [Poulpy](https://github.com/phantomzone-org/poulpy), a low-level, modular FHE toolkit. Poulpy exposes the full machinery of lattice-based homomorphic encryption and leaves resource management entirely to the caller. squid wraps it with a smaller, opinionated API.
 
+## Monorepo layout
+
+This repository is a **Cargo workspace** and a **pnpm workspace**:
+
+| Path                | Role                                                                  |
+| ------------------- | --------------------------------------------------------------------- |
+| `crates/squid`      | Rust library (package name `squid`); primary focus of the rules below |
+| `crates/squid-wasm` | `wasm-bindgen` crate for the browser                                  |
+| `crates/squid-napi` | napi-rs native addon for Node                                         |
+| `packages/squid-js` | TypeScript package: client (wasm), server (`.node`)                   |
+| `demo`              | Next.js walkthrough app (`@squid-js/demo`)                            |
+| `tests`             | Playwright e2e (`@squid-js/e2e`)                                      |
+
+Root scripts: `pnpm run build:squid-js`, `pnpm run build:demo`, `pnpm test`.
+
 ## Current scope
 
 squid currently wraps `poulpy-schemes::bin_fhe::bdd_arithmetic` only — the one fully exposed end-to-end capability in `poulpy-schemes`. That means:
@@ -23,10 +38,10 @@ The scope will expand as `poulpy-schemes` adds more scheme-level implementations
 
 Everything flows through `Context`. The user-facing types are:
 
-| Type | Role |
-|---|---|
-| `Context` | Owns `Module<BE>` and `Params`. Allocates Poulpy scratch per operation from `*_tmp_bytes` (not exposed). Entry point for all operations. |
-| `Params` | Layout parameter bundle. Use `Params::unsecure()` (demo / non-production) or construct custom. |
-| `SecretKey` | Private key material: standard GLWE + LWE secrets and prepared GLWE for encrypt/decrypt. Returned by `Context::keygen`. |
-| `EvaluationKey` | Public evaluation key bundle (`BDDKey` standard + prepared). Returned by `Context::keygen`. |
-| `Ciphertext<T>` | Encrypted `T` value (`u8`, `u16`, `u32`). All ops run through `Context`. |
+| Type            | Role                                                                                                                                     |
+| --------------- | ---------------------------------------------------------------------------------------------------------------------------------------- |
+| `Context`       | Owns `Module<BE>` and `Params`. Allocates Poulpy scratch per operation from `*_tmp_bytes` (not exposed). Entry point for all operations. |
+| `Params`        | Layout parameter bundle. Use `Params::unsecure()` (demo / non-production) or construct custom.                                           |
+| `SecretKey`     | Private key material: standard GLWE + LWE secrets and prepared GLWE for encrypt/decrypt. Returned by `Context::keygen`.                  |
+| `EvaluationKey` | Public evaluation key bundle (`BDDKey` standard + prepared). Returned by `Context::keygen`.                                              |
+| `Ciphertext<T>` | Encrypted `T` value (`u8`, `u16`, `u32`). All ops run through `Context`.                                                                 |
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 222d55a..7e6ae8e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -29,3 +29,43 @@ jobs:
         run: cargo clippy --all-targets --all-features -- -D warnings
       - name: cargo test
         run: cargo test --verbose
+
+  e2e:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: pnpm/action-setup@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: pnpm
+          cache-dependency-path: pnpm-lock.yaml
+
+      - uses: dtolnay/rust-toolchain@v1
+        with:
+          toolchain: nightly
+          targets: wasm32-unknown-unknown
+
+      - uses: Swatinem/rust-cache@v2
+
+      - uses: taiki-e/install-action@v2
+        with:
+          tool: wasm-pack
+
+      - name: Install JS dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Cache Playwright browsers
+        uses: actions/cache@v4
+        with:
+          path: ~/.cache/ms-playwright
+          key: playwright-${{ runner.os }}-${{ hashFiles('pnpm-lock.yaml') }}
+
+      - name: Build wasm, napi, and JS packages
+        run: pnpm run build
+
+      - name: Run E2E tests
+        run: pnpm test
diff --git a/.gitignore b/.gitignore
index 5b5a9d6..333ea5b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,3 +7,29 @@
 
 # macOS
 .DS_Store
+
+# Node
+node_modules/
+dist/
+pkg/
+*.node
+packages/squid-js/wasm/
+packages/squid-js/napi/
+
+# Next.js
+demo/.next/
+demo/data/*.bin
+
+# Playwright
+tests/playwright-report/
+tests/test-results/
+
+# Environment
+.env
+.env.local
+*.log
+*.tsbuildinfo
+
+# pnpm
+.pnpm-store/
+pnpm-debug.log*
diff --git a/Cargo.lock b/Cargo.lock
index 8c9c7e9..7666378 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,6 +2,15 @@
 # It is not intended for manual editing.
 version = 4
 
+[[package]]
+name = "aho-corasick"
+version = "1.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ddd31a130427c27518df266943a5308ed92d4b226cc639f5a8f1002816174301"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "anyhow"
 version = "1.0.102"
@@ -20,6 +29,12 @@ version = "2.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "843867be96c8daad0d758b57df9392b6d8d271134fce549de6ce169ff98a92af"
 
+[[package]]
+name = "bumpalo"
+version = "3.20.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5d20789868f4b01b2f2caec9f5c4e0213b41e3e5702a50157d699ae31ced2fcb"
+
 [[package]]
 name = "bytemuck"
 version = "1.25.0"
@@ -68,6 +83,25 @@ dependencies = [
  "cc",
 ]
 
+[[package]]
+name = "console_error_panic_hook"
+version = "0.1.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a06aeb73f470f66dcdbf7223caeebb85984942f22f1adb2a088cf9668146bbbc"
+dependencies = [
+ "cfg-if",
+ "wasm-bindgen",
+]
+
+[[package]]
+name = "convert_case"
+version = "0.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ec182b0ca2f35d8fc196cf3404988fd8b8c739a4d270ff118a398feb0cbec1ca"
+dependencies = [
+ "unicode-segmentation",
+]
+
 [[package]]
 name = "cpufeatures"
 version = "0.3.0"
@@ -77,6 +111,16 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "ctor"
+version = "0.2.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32a2785755761f3ddc1492979ce1e48d2c00d09311c39e4466429188f3dd6501"
+dependencies = [
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "dashu-base"
 version = "0.4.1"
@@ -141,9 +185,11 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "899def5c37c4fd7b2664648c28120ecec138e4d395b459e5ca34f9cce2dd77fd"
 dependencies = [
  "cfg-if",
+ "js-sys",
  "libc",
  "r-efi 5.3.0",
  "wasip2",
+ "wasm-bindgen",
 ]
 
 [[package]]
@@ -153,11 +199,13 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0de51e6874e94e7bf76d726fc5d13ba782deca734ff60d5bb2fb2607c7406555"
 dependencies = [
  "cfg-if",
+ "js-sys",
  "libc",
  "r-efi 6.0.0",
  "rand_core",
  "wasip2",
  "wasip3",
+ "wasm-bindgen",
 ]
 
 [[package]]
@@ -214,6 +262,16 @@ version = "1.0.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8f42a60cbdf9a97f5d2305f08a87dc4e09308d1276d28c869c684d7777685682"
 
+[[package]]
+name = "js-sys"
+version = "0.3.95"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2964e92d1d9dc3364cae4d718d93f227e3abb088e747d92e0395bfdedf1c12ca"
+dependencies = [
+ "once_cell",
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "leb128fmt"
 version = "0.1.0"
@@ -226,6 +284,16 @@ version = "0.2.184"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "48f5d2a454e16a5ea0f4ced81bd44e4cfc7bd3a507b61887c99fd3538b28e4af"
 
+[[package]]
+name = "libloading"
+version = "0.8.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d7c4b02199fee7c5d21a5ae7d8cfa79a6ef5bb2fc834d6e9058e89c825efdc55"
+dependencies = [
+ "cfg-if",
+ "windows-link",
+]
+
 [[package]]
 name = "libm"
 version = "0.2.16"
@@ -244,6 +312,63 @@ version = "2.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f8ca58f447f06ed17d5fc4043ce1b10dd205e060fb3ce5b979b8ed8e59ff3f79"
 
+[[package]]
+name = "napi"
+version = "2.16.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "55740c4ae1d8696773c78fdafd5d0e5fe9bc9f1b071c7ba493ba5c413a9184f3"
+dependencies = [
+ "bitflags",
+ "ctor",
+ "napi-derive",
+ "napi-sys",
+ "once_cell",
+]
+
+[[package]]
+name = "napi-build"
+version = "2.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d376940fd5b723c6893cd1ee3f33abbfd86acb1cd1ec079f3ab04a2a3bc4d3b1"
+
+[[package]]
+name = "napi-derive"
+version = "2.16.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7cbe2585d8ac223f7d34f13701434b9d5f4eb9c332cccce8dee57ea18ab8ab0c"
+dependencies = [
+ "cfg-if",
+ "convert_case",
+ "napi-derive-backend",
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "napi-derive-backend"
+version = "1.0.75"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1639aaa9eeb76e91c6ae66da8ce3e89e921cd3885e99ec85f4abacae72fc91bf"
+dependencies = [
+ "convert_case",
+ "once_cell",
+ "proc-macro2",
+ "quote",
+ "regex",
+ "semver",
+ "syn",
+]
+
+[[package]]
+name = "napi-sys"
+version = "2.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "427802e8ec3a734331fec1035594a210ce1ff4dc5bc1950530920ab717964ea3"
+dependencies = [
+ "libloading",
+]
+
 [[package]]
 name = "num-modular"
 version = "0.6.1"
@@ -454,6 +579,35 @@ dependencies = [
  "rand",
 ]
 
+[[package]]
+name = "regex"
+version = "1.12.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e10754a14b9137dd7b1e3e5b0493cc9171fdd105e0ab477f51b72e7f3ac0e276"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-automata",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-automata"
+version = "0.4.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6e1dd4122fc1595e8162618945476892eefca7b88c52820e74af6262213cae8f"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.8.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dc897dd8d9e8bd1ed8cdad82b5966c3e0ecae09fb1907d58efaa013543185d0a"
+
 [[package]]
 name = "rustversion"
 version = "1.0.22"
@@ -526,6 +680,28 @@ dependencies = [
  "poulpy-schemes",
 ]
 
+[[package]]
+name = "squid-napi"
+version = "0.1.0"
+dependencies = [
+ "napi",
+ "napi-build",
+ "napi-derive",
+ "squid",
+]
+
+[[package]]
+name = "squid-wasm"
+version = "0.1.0"
+dependencies = [
+ "console_error_panic_hook",
+ "getrandom 0.3.4",
+ "getrandom 0.4.2",
+ "js-sys",
+ "squid",
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "static_assertions"
 version = "1.1.0"
@@ -549,6 +725,12 @@ version = "1.0.24"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e6e4313cd5fcd3dad5cafa179702e2b244f760991f45397d14d4ebf38247da75"
 
+[[package]]
+name = "unicode-segmentation"
+version = "1.13.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9629274872b2bfaf8d66f5f15725007f635594914870f65218920345aa11aa8c"
+
 [[package]]
 name = "unicode-xid"
 version = "0.2.6"
@@ -573,6 +755,51 @@ dependencies = [
  "wit-bindgen",
 ]
 
+[[package]]
+name = "wasm-bindgen"
+version = "0.2.118"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0bf938a0bacb0469e83c1e148908bd7d5a6010354cf4fb73279b7447422e3a89"
+dependencies = [
+ "cfg-if",
+ "once_cell",
+ "rustversion",
+ "wasm-bindgen-macro",
+ "wasm-bindgen-shared",
+]
+
+[[package]]
+name = "wasm-bindgen-macro"
+version = "0.2.118"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eeff24f84126c0ec2db7a449f0c2ec963c6a49efe0698c4242929da037ca28ed"
+dependencies = [
+ "quote",
+ "wasm-bindgen-macro-support",
+]
+
+[[package]]
+name = "wasm-bindgen-macro-support"
+version = "0.2.118"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9d08065faf983b2b80a79fd87d8254c409281cf7de75fc4b773019824196c904"
+dependencies = [
+ "bumpalo",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "wasm-bindgen-shared",
+]
+
+[[package]]
+name = "wasm-bindgen-shared"
+version = "0.2.118"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5fd04d9e306f1907bd13c6361b5c6bfc7b3b3c095ed3f8a9246390f8dbdee129"
+dependencies = [
+ "unicode-ident",
+]
+
 [[package]]
 name = "wasm-encoder"
 version = "0.244.0"
@@ -607,6 +834,12 @@ dependencies = [
  "semver",
 ]
 
+[[package]]
+name = "windows-link"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
+
 [[package]]
 name = "wit-bindgen"
 version = "0.51.0"
diff --git a/Cargo.toml b/Cargo.toml
index 17b44d4..bf0b2c2 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,20 +1,21 @@
-[package]
-name = "squid"
-version = "0.1.0-alpha.1"
+[workspace]
+resolver = "2"
+members = [
+    "crates/squid",
+    "crates/squid-wasm",
+    "crates/squid-napi",
+]
+
+[workspace.package]
+version = "0.1.0"
 edition = "2021"
-description = "An ergonomic Rust wrapper for Poulpy FHE."
 license = "MIT"
+authors = ["Omar Desogus <me@cedoor.dev>"]
 
-[features]
-backend-avx = ["dep:poulpy-cpu-avx"]
-
-[dependencies]
-poulpy-core = { git = "https://github.com/poulpy-fhe/poulpy.git", rev = "e5450f9a51884082c293c8a13846c8a6fb310626" }
-poulpy-schemes = { git = "https://github.com/poulpy-fhe/poulpy.git", rev = "e5450f9a51884082c293c8a13846c8a6fb310626" }
-poulpy-hal = { git = "https://github.com/poulpy-fhe/poulpy.git", rev = "e5450f9a51884082c293c8a13846c8a6fb310626" }
-poulpy-cpu-ref = { git = "https://github.com/poulpy-fhe/poulpy.git", rev = "e5450f9a51884082c293c8a13846c8a6fb310626" }
-poulpy-cpu-avx = { git = "https://github.com/poulpy-fhe/poulpy.git", rev = "e5450f9a51884082c293c8a13846c8a6fb310626", optional = true }
-getrandom = "0.3"
+[workspace.dependencies]
+squid = { path = "crates/squid", default-features = false }
 
-[target.'cfg(target_arch = "x86_64")'.dependencies]
-poulpy-cpu-avx = { git = "https://github.com/poulpy-fhe/poulpy.git", rev = "e5450f9a51884082c293c8a13846c8a6fb310626", optional = true, features = ["enable-avx"] }
+[profile.release]
+opt-level = 3
+lto = "thin"
+codegen-units = 1
diff --git a/README.md b/README.md
index 23a8282..8b4d4c8 100644
--- a/README.md
+++ b/README.md
@@ -1,16 +1,29 @@
 # 🦑 Squid
 
-**An ergonomic Rust wrapper for [Poulpy](https://github.com/phantomzone-org/poulpy), making Fully Homomorphic Encryption accessible without sacrificing control.**
+**An ergonomic Rust wrapper ([`squid`](crates/squid)) for [Poulpy](https://github.com/poulpy-fhe/poulpy) and the [`squid-js`](packages/squid-js) library for browser and Node (WebAssembly + napi-rs), making Fully Homomorphic Encryption accessible without sacrificing control.**
 
-[![License](https://img.shields.io/badge/license-MIT-blue.svg)](LICENSE) [![CI](https://github.com/cedoor/squid/actions/workflows/ci.yml/badge.svg)](https://github.com/cedoor/squid/actions) ![Status](https://img.shields.io/badge/status-early%20development-orange)
+[![License](https://img.shields.io/badge/license-MIT-blue.svg)](LICENSE) [![CI](https://github.com/cedoor/squid/actions/workflows/ci.yml/badge.svg)](https://github.com/cedoor/squid/actions) [![Live demo](https://img.shields.io/badge/demo-squid.cedoor.dev-blueviolet)](https://squid.cedoor.dev/) ![Status](https://img.shields.io/badge/status-early%20development-orange)
 
-Poulpy is a low-level, modular toolkit exposing the full machinery of lattice-based homomorphic encryption. That power comes with sharp edges: manual scratch arenas, explicit lifecycle transitions, trait-heavy APIs. `squid` wraps Poulpy with a smaller, opinionated surface so you can write FHE programs without managing every byte of workspace memory or tracking which representation a ciphertext currently lives in.
+Poulpy is a low-level, modular toolkit exposing the full machinery of lattice-based homomorphic encryption. That power comes with sharp edges: manual scratch arenas, explicit lifecycle transitions, trait-heavy APIs. [`squid`](crates/squid) wraps Poulpy with a smaller, opinionated surface so you can write FHE programs without managing every byte of workspace memory or tracking which representation a ciphertext currently lives in.
 
-**Current scope:** `squid` wraps Poulpy's `bin_fhe::bdd_arithmetic` layer: gate-level FHE on encrypted unsigned integers (`u8`, `u16`, `u32`). This is the only fully exposed end-to-end capability in `poulpy-schemes` today. The API will expand as Poulpy adds more scheme-level implementations.
+For JavaScript and TypeScript, **[`squid-js`](packages/squid-js)** exposes the same stack: **`squid-js/client`** runs keygen, encrypt, and decrypt in the browser over WebAssembly (typically inside a dedicated worker so crypto stays off the UI thread), while **`squid-js/server`** runs homomorphic evaluation in Node via a native addon (napi-rs). In the usual setup the secret key stays on the client; the server only receives the evaluation key and ciphertexts.
 
-There are also [JavaScript bindings](https://github.com/cedoor/poulpy-js/) (browser and Node, via WebAssembly and napi-rs) built on Squid’s Rust API.
+**Current scope:** [`squid`](crates/squid) wraps Poulpy's `bin_fhe::bdd_arithmetic` layer: gate-level FHE on encrypted unsigned integers (`u8`, `u16`, `u32`). This is the only fully exposed end-to-end capability in `poulpy-schemes` today. The API will expand as Poulpy adds more scheme-level implementations.
 
-## Usage
+## Monorepo structure
+
+| Path                                     | Description                                                      |
+| ---------------------------------------- | ---------------------------------------------------------------- |
+| [`crates/squid`](crates/squid)           | Rust library — ergonomic Poulpy wrapper (this is the main crate) |
+| [`crates/squid-wasm`](crates/squid-wasm) | WebAssembly bindings via `wasm-bindgen` (browser)                |
+| [`crates/squid-napi`](crates/squid-napi) | Node.js native bindings via `napi-rs` (server)                   |
+| [`packages/squid-js`](packages/squid-js) | npm package — browser client + Node evaluator                    |
+| [`demo`](demo)                           | Next.js demo: keygen in browser, homomorphic eval on server — **[live at squid.cedoor.dev](https://squid.cedoor.dev/)** |
+| [`tests`](tests)                         | Playwright end-to-end tests for the demo                         |
+
+The Cargo workspace ties the three Rust crates together. The pnpm workspace ties [`squid-js`](packages/squid-js), the demo, and the E2E tests together.
+
+## Usage (Rust)
 
 ### Quick start
 
@@ -46,7 +59,7 @@ Built-in bundles can be selected by string: `Params::by_name("unsecure")` and `P
 
 The evaluation key is public material needed for every homomorphic op. Persist
 it once and reload it on the server that runs the circuits. The blob is
-versioned and tied to the [`Params`](src/context.rs) used at keygen — loading
+versioned and tied to the [`Params`](crates/squid/src/context.rs) used at keygen — loading
 under different parameters returns an `io::Error`.
 
 ```rust
@@ -179,12 +192,12 @@ The public API is identical regardless of which backend is selected.
 - [ ] Vetted Params presets: [#18](https://github.com/cedoor/squid/issues/18)
 - [ ] Refactor `context.rs`: [#20](https://github.com/cedoor/squid/issues/20)
 - [ ] Add CHANGELOG file: [#26](https://github.com/cedoor/squid/issues/26)
-- [x] [#22](https://github.com/cedoor/squid/issues/22) — closed: `Context` no longer keeps a persistent max-sized arena; scratch is allocated per operation from Poulpy’s `*_tmp_bytes` (supersedes the issue’s “split keygen vs runtime” split).
+- [x] [#22](https://github.com/cedoor/squid/issues/22) — closed: `Context` no longer keeps a persistent max-sized arena; scratch is allocated per operation from Poulpy's `*_tmp_bytes` (supersedes the issue's "split keygen vs runtime" split).
 
 ## Design goals
 
 - **Hide scratch management.** Callers never allocate or thread scratch buffers.
 - **Hide lifecycle transitions.** The Standard → Prepared → BDD-eval pipeline is handled internally; users see one coherent `Ciphertext<T>` type.
 - **Explicitly non-production defaults.** `Params::unsecure()` matches Poulpy's `bdd_arithmetic` example for demos; treat it as unaudited unless you analyse parameters yourself.
-- **No magic.** Every abstraction is traceable to the underlying Poulpy call. No hidden global state; scratch is sized with Poulpy’s `*_tmp_bytes` at each operation.
+- **No magic.** Every abstraction is traceable to the underlying Poulpy call. No hidden global state; scratch is sized with Poulpy's `*_tmp_bytes` at each operation.
 - **Safe defaults.** Every user-facing choice has a default that works without configuration. Alternatives are documented with their trade-offs and the conditions under which they should be preferred.
diff --git a/crates/squid-napi/Cargo.toml b/crates/squid-napi/Cargo.toml
new file mode 100644
index 0000000..b7aee46
--- /dev/null
+++ b/crates/squid-napi/Cargo.toml
@@ -0,0 +1,19 @@
+[package]
+name = "squid-napi"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+authors.workspace = true
+description = "napi-rs bindings for cedoor/squid (server-side evaluator)."
+publish = false
+
+[lib]
+crate-type = ["cdylib"]
+
+[dependencies]
+squid = { workspace = true }
+napi = { version = "2.16", default-features = false, features = ["napi8"] }
+napi-derive = "2.16"
+
+[build-dependencies]
+napi-build = "2"
diff --git a/crates/squid-napi/build.rs b/crates/squid-napi/build.rs
new file mode 100644
index 0000000..0f1b010
--- /dev/null
+++ b/crates/squid-napi/build.rs
@@ -0,0 +1,3 @@
+fn main() {
+    napi_build::setup();
+}
diff --git a/crates/squid-napi/src/lib.rs b/crates/squid-napi/src/lib.rs
new file mode 100644
index 0000000..2d63991
--- /dev/null
+++ b/crates/squid-napi/src/lib.rs
@@ -0,0 +1,56 @@
+//! napi-rs bindings over `squid` for server-side evaluation.
+//!
+//! The server only knows how to load an `EvaluationKey` and run ops on
+//! serialized ciphertexts. It never holds any secret key material.
+
+#![deny(clippy::all)]
+
+use napi::bindgen_prelude::*;
+use napi_derive::napi;
+use squid::{Context, EvaluationKey, Params};
+
+#[napi]
+pub struct Evaluator {
+    ctx: Context,
+    ek: EvaluationKey,
+}
+
+#[napi]
+impl Evaluator {
+    /// Rebuild a `Context` for the named parameter set (`"test"` or `"unsecure"`)
+    /// and load the serialized evaluation key produced by the browser client.
+    #[napi(factory)]
+    pub fn load(ek_bytes: Buffer, params_name: String) -> Result<Self> {
+        let params = Params::by_name(&params_name).ok_or_else(|| {
+            Error::from_reason(format!(
+                "unknown parameter set {params_name:?}; expected \"test\" or \"unsecure\""
+            ))
+        })?;
+        let mut ctx = Context::new(params);
+        let ek = ctx
+            .deserialize_evaluation_key(ek_bytes.as_ref())
+            .map_err(io_err)?;
+        Ok(Self { ctx, ek })
+    }
+
+    /// Homomorphic `a + b` over serialized `u32` ciphertexts. Returns the
+    /// serialized result.
+    #[napi]
+    pub fn add_u32(&mut self, a: Buffer, b: Buffer) -> Result<Buffer> {
+        let a_ct = self
+            .ctx
+            .deserialize_ciphertext::<u32>(a.as_ref())
+            .map_err(io_err)?;
+        let b_ct = self
+            .ctx
+            .deserialize_ciphertext::<u32>(b.as_ref())
+            .map_err(io_err)?;
+        let c = self.ctx.add(&a_ct, &b_ct, &self.ek);
+        let out = c.serialize().map_err(io_err)?;
+        Ok(out.into())
+    }
+}
+
+fn io_err(e: std::io::Error) -> Error {
+    Error::from_reason(e.to_string())
+}
diff --git a/crates/squid-wasm/Cargo.toml b/crates/squid-wasm/Cargo.toml
new file mode 100644
index 0000000..9ec07bc
--- /dev/null
+++ b/crates/squid-wasm/Cargo.toml
@@ -0,0 +1,28 @@
+[package]
+name = "squid-wasm"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+authors.workspace = true
+description = "wasm-bindgen bindings for cedoor/squid (portable backend)."
+publish = false
+
+[lib]
+crate-type = ["cdylib", "rlib"]
+
+[dependencies]
+squid = { workspace = true }
+wasm-bindgen = "0.2.95"
+js-sys = "0.3.72"
+console_error_panic_hook = "0.1.7"
+
+# On wasm32 we need getrandom's JS backend for every version that ends up
+# linked into the dep graph (squid uses 0.3, some transitive Poulpy deps pull
+# in 0.4). Cargo unifies features per-semver, so turning `wasm_js` on here is
+# enough to make every user of that major version compile.
+[target.'cfg(target_arch = "wasm32")'.dependencies]
+getrandom_03 = { package = "getrandom", version = "0.3", features = ["wasm_js"] }
+getrandom_04 = { package = "getrandom", version = "0.4", features = ["wasm_js"] }
+
+[features]
+default = []
diff --git a/crates/squid-wasm/src/lib.rs b/crates/squid-wasm/src/lib.rs
new file mode 100644
index 0000000..cb80cd0
--- /dev/null
+++ b/crates/squid-wasm/src/lib.rs
@@ -0,0 +1,113 @@
+//! wasm-bindgen bindings over `squid` for browser use.
+//!
+//! Public surface mirrors the plan: `Session` owns a `Context` + `(sk, ek)`
+//! and exposes byte-oriented helpers. Secret key material never leaves memory
+//! — only `KeygenSeeds` (96 bytes) and serialized `ek`/ciphertexts do.
+
+use squid::{Context, EvaluationKey, KeygenSeeds, Params, SecretKey};
+use wasm_bindgen::prelude::*;
+
+const SEEDS_LEN: usize = 96;
+
+fn params_from_name(name: &str) -> Result<Params, JsError> {
+    Params::by_name(name).ok_or_else(|| {
+        JsError::new(&format!(
+            "unknown parameter set {name:?}; expected \"test\" or \"unsecure\""
+        ))
+    })
+}
+
+#[wasm_bindgen(start)]
+pub fn __start() {
+    console_error_panic_hook::set_once();
+}
+
+#[wasm_bindgen]
+pub struct Session {
+    ctx: Context,
+    sk: SecretKey,
+    ek: EvaluationKey,
+    seeds: KeygenSeeds,
+}
+
+#[wasm_bindgen]
+impl Session {
+    /// Fresh keys from OS randomness. Returns a session whose seeds can be
+    /// exported via [`Session::seeds`] for later restoration.
+    #[wasm_bindgen(js_name = newRandom)]
+    pub fn new_random(params_name: &str) -> Result<Session, JsError> {
+        let params = params_from_name(params_name)?;
+        let mut ctx = Context::new(params);
+        let (sk, ek, seeds) = ctx.keygen_with_seeds();
+        Ok(Session { ctx, sk, ek, seeds })
+    }
+
+    /// Deterministic rebuild from a 96-byte seed blob produced by
+    /// [`Session::seeds`].
+    #[wasm_bindgen(js_name = fromSeeds)]
+    pub fn from_seeds(seeds: &[u8], params_name: &str) -> Result<Session, JsError> {
+        if seeds.len() != SEEDS_LEN {
+            return Err(JsError::new(&format!(
+                "expected {SEEDS_LEN}-byte seeds blob, got {}",
+                seeds.len()
+            )));
+        }
+        let mut lattice = [0u8; 32];
+        let mut bdd_mask = [0u8; 32];
+        let mut bdd_noise = [0u8; 32];
+        lattice.copy_from_slice(&seeds[0..32]);
+        bdd_mask.copy_from_slice(&seeds[32..64]);
+        bdd_noise.copy_from_slice(&seeds[64..96]);
+        let ks = KeygenSeeds {
+            lattice,
+            bdd_mask,
+            bdd_noise,
+        };
+        let params = params_from_name(params_name)?;
+        let mut ctx = Context::new(params);
+        let (sk, ek) = ctx.keygen_from_seeds(ks);
+        Ok(Session {
+            ctx,
+            sk,
+            ek,
+            seeds: ks,
+        })
+    }
+
+    /// 96-byte seed blob: `lattice || bdd_mask || bdd_noise`.
+    #[wasm_bindgen(js_name = seeds)]
+    pub fn seeds(&self) -> Vec<u8> {
+        let mut out = Vec::with_capacity(SEEDS_LEN);
+        out.extend_from_slice(&self.seeds.lattice);
+        out.extend_from_slice(&self.seeds.bdd_mask);
+        out.extend_from_slice(&self.seeds.bdd_noise);
+        out
+    }
+
+    /// Versioned little-endian evaluation key blob to ship to the server.
+    #[wasm_bindgen(js_name = evaluationKeyBytes)]
+    pub fn evaluation_key_bytes(&self) -> Result<Vec<u8>, JsError> {
+        self.ek.serialize().map_err(io_err)
+    }
+
+    /// Encrypt a `u32` value and return the serialized ciphertext.
+    #[wasm_bindgen(js_name = encryptU32)]
+    pub fn encrypt_u32(&mut self, value: u32) -> Result<Vec<u8>, JsError> {
+        let ct = self.ctx.encrypt::<u32>(value, &self.sk);
+        ct.serialize().map_err(io_err)
+    }
+
+    /// Deserialize + decrypt a `u32` ciphertext.
+    #[wasm_bindgen(js_name = decryptU32)]
+    pub fn decrypt_u32(&mut self, bytes: &[u8]) -> Result<u32, JsError> {
+        let ct = self
+            .ctx
+            .deserialize_ciphertext::<u32>(bytes)
+            .map_err(io_err)?;
+        Ok(self.ctx.decrypt::<u32>(&ct, &self.sk))
+    }
+}
+
+fn io_err(e: std::io::Error) -> JsError {
+    JsError::new(&e.to_string())
+}
diff --git a/crates/squid/Cargo.lock b/crates/squid/Cargo.lock
new file mode 100644
index 0000000..8c9c7e9
--- /dev/null
+++ b/crates/squid/Cargo.lock
@@ -0,0 +1,722 @@
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+version = "0.1.0-alpha.1"
+edition = "2021"
+description = "An ergonomic Rust wrapper for Poulpy FHE."
+license = "MIT"
+authors.workspace = true
+
+[features]
+backend-avx = ["dep:poulpy-cpu-avx"]
+
+[dependencies]
+poulpy-core = { git = "https://github.com/poulpy-fhe/poulpy.git", rev = "e5450f9a51884082c293c8a13846c8a6fb310626" }
+poulpy-schemes = { git = "https://github.com/poulpy-fhe/poulpy.git", rev = "e5450f9a51884082c293c8a13846c8a6fb310626" }
+poulpy-hal = { git = "https://github.com/poulpy-fhe/poulpy.git", rev = "e5450f9a51884082c293c8a13846c8a6fb310626" }
+poulpy-cpu-ref = { git = "https://github.com/poulpy-fhe/poulpy.git", rev = "e5450f9a51884082c293c8a13846c8a6fb310626" }
+poulpy-cpu-avx = { git = "https://github.com/poulpy-fhe/poulpy.git", rev = "e5450f9a51884082c293c8a13846c8a6fb310626", optional = true }
+getrandom = "0.3"
+
+[target.'cfg(target_arch = "x86_64")'.dependencies]
+poulpy-cpu-avx = { git = "https://github.com/poulpy-fhe/poulpy.git", rev = "e5450f9a51884082c293c8a13846c8a6fb310626", optional = true, features = ["enable-avx"] }
diff --git a/examples/add_u32.rs b/crates/squid/examples/add_u32.rs
similarity index 100%
rename from examples/add_u32.rs
rename to crates/squid/examples/add_u32.rs
diff --git a/src/backend.rs b/crates/squid/src/backend.rs
similarity index 100%
rename from src/backend.rs
rename to crates/squid/src/backend.rs
diff --git a/src/ciphertext.rs b/crates/squid/src/ciphertext.rs
similarity index 100%
rename from src/ciphertext.rs
rename to crates/squid/src/ciphertext.rs
diff --git a/src/context.rs b/crates/squid/src/context.rs
similarity index 100%
rename from src/context.rs
rename to crates/squid/src/context.rs
diff --git a/src/keys.rs b/crates/squid/src/keys.rs
similarity index 100%
rename from src/keys.rs
rename to crates/squid/src/keys.rs
diff --git a/src/lib.rs b/crates/squid/src/lib.rs
similarity index 100%
rename from src/lib.rs
rename to crates/squid/src/lib.rs
diff --git a/src/scratch.rs b/crates/squid/src/scratch.rs
similarity index 100%
rename from src/scratch.rs
rename to crates/squid/src/scratch.rs
diff --git a/tests/bdd_parallel.rs b/crates/squid/tests/bdd_parallel.rs
similarity index 100%
rename from tests/bdd_parallel.rs
rename to crates/squid/tests/bdd_parallel.rs
diff --git a/tests/ciphertext_serialization.rs b/crates/squid/tests/ciphertext_serialization.rs
similarity index 100%
rename from tests/ciphertext_serialization.rs
rename to crates/squid/tests/ciphertext_serialization.rs
diff --git a/tests/common/mod.rs b/crates/squid/tests/common/mod.rs
similarity index 100%
rename from tests/common/mod.rs
rename to crates/squid/tests/common/mod.rs
diff --git a/tests/evaluation_key_serialization.rs b/crates/squid/tests/evaluation_key_serialization.rs
similarity index 100%
rename from tests/evaluation_key_serialization.rs
rename to crates/squid/tests/evaluation_key_serialization.rs
diff --git a/tests/keygen_seeds.rs b/crates/squid/tests/keygen_seeds.rs
similarity index 100%
rename from tests/keygen_seeds.rs
rename to crates/squid/tests/keygen_seeds.rs
diff --git a/demo/next-env.d.ts b/demo/next-env.d.ts
new file mode 100644
index 0000000..830fb59
--- /dev/null
+++ b/demo/next-env.d.ts
@@ -0,0 +1,6 @@
+/// <reference types="next" />
+/// <reference types="next/image-types/global" />
+/// <reference path="./.next/types/routes.d.ts" />
+
+// NOTE: This file should not be edited
+// see https://nextjs.org/docs/app/api-reference/config/typescript for more information.
diff --git a/demo/next.config.ts b/demo/next.config.ts
new file mode 100644
index 0000000..31eaf24
--- /dev/null
+++ b/demo/next.config.ts
@@ -0,0 +1,25 @@
+import type { NextConfig } from 'next'
+
+const nextConfig: NextConfig = {
+  async headers() {
+    return [
+      {
+        source: '/(.*)',
+        headers: [
+          { key: 'Cross-Origin-Opener-Policy', value: 'same-origin' },
+          { key: 'Cross-Origin-Embedder-Policy', value: 'require-corp' },
+        ],
+      },
+    ]
+  },
+  serverExternalPackages: ['squid-js'],
+  webpack(config, { isServer }) {
+    if (!isServer) {
+      config.experiments = { ...config.experiments, asyncWebAssembly: true }
+      config.module.rules.push({ test: /\.wasm$/, type: 'asset/resource' })
+    }
+    return config
+  },
+}
+
+export default nextConfig
diff --git a/demo/package.json b/demo/package.json
new file mode 100644
index 0000000..82a1d65
--- /dev/null
+++ b/demo/package.json
@@ -0,0 +1,27 @@
+{
+  "name": "@squid-js/demo",
+  "version": "0.1.0",
+  "private": true,
+  "description": "Playful Next.js FHE demo — keygen, encrypt, evaluate, decrypt with squid-js.",
+  "scripts": {
+    "predev": "node scripts/ensure-demo-ek.mjs",
+    "dev": "next dev",
+    "prebuild": "node scripts/generate-demo-ek.mjs",
+    "gen-demo-ek": "node scripts/generate-demo-ek.mjs",
+    "build": "next build",
+    "start": "next start",
+    "lint": "next lint"
+  },
+  "dependencies": {
+    "next": "^15.3.1",
+    "squid-js": "workspace:*",
+    "react": "^19.0.0",
+    "react-dom": "^19.0.0"
+  },
+  "devDependencies": {
+    "@types/node": "^22",
+    "@types/react": "^19",
+    "@types/react-dom": "^19",
+    "typescript": "^5.6.3"
+  }
+}
diff --git a/demo/scripts/ensure-demo-ek.mjs b/demo/scripts/ensure-demo-ek.mjs
new file mode 100644
index 0000000..bd957a8
--- /dev/null
+++ b/demo/scripts/ensure-demo-ek.mjs
@@ -0,0 +1,15 @@
+import { existsSync } from 'node:fs'
+import { join, dirname } from 'node:path'
+import { fileURLToPath } from 'node:url'
+import { spawnSync } from 'node:child_process'
+
+const root = join(dirname(fileURLToPath(import.meta.url)), '..')
+const f = join(root, 'data', 'demo-ek.test.bin')
+if (!existsSync(f)) {
+  console.log('demo: generating data/demo-ek.test.bin (one-time, ~30 MiB)…')
+  const r = spawnSync(process.execPath, [join(root, 'scripts', 'generate-demo-ek.mjs')], {
+    stdio: 'inherit',
+    cwd: root,
+  })
+  process.exit(r.status ?? 1)
+}
diff --git a/demo/scripts/generate-demo-ek.mjs b/demo/scripts/generate-demo-ek.mjs
new file mode 100644
index 0000000..6ecdf6d
--- /dev/null
+++ b/demo/scripts/generate-demo-ek.mjs
@@ -0,0 +1,32 @@
+#!/usr/bin/env node
+/**
+ * Builds `data/demo-ek.test.bin` from the same 96-byte seed as `src/lib/demo-seed.ts`.
+ * Requires built squid-js wasm (workspace / published package).
+ */
+import { writeFileSync, mkdirSync, readFileSync } from 'node:fs'
+import { dirname, join } from 'node:path'
+import { fileURLToPath } from 'node:url'
+import { createRequire } from 'node:module'
+
+import init, { Session } from 'squid-js/wasm/squid_wasm.js'
+
+const __dirname = dirname(fileURLToPath(import.meta.url))
+const outDir = join(__dirname, '..', 'data')
+const outFile = join(outDir, 'demo-ek.test.bin')
+
+const require = createRequire(import.meta.url)
+const wasmPath = require.resolve('squid-js/wasm/squid_wasm_bg.wasm')
+
+const seeds = new Uint8Array(96)
+for (let i = 0; i < 96; i++) {
+  seeds[i] = (i * 13 + 1) & 0xff
+}
+
+const paramsSet = process.env.POULPY_PARAMS_SET ?? 'test'
+
+await init({ module_or_path: readFileSync(wasmPath) })
+const session = Session.fromSeeds(seeds, paramsSet)
+const ek = session.evaluationKeyBytes()
+mkdirSync(outDir, { recursive: true })
+writeFileSync(outFile, Buffer.from(ek))
+console.log(`wrote ${outFile} (${ek.length} bytes) for paramsSet=${paramsSet}`)
diff --git a/demo/src/app/api/add/route.ts b/demo/src/app/api/add/route.ts
new file mode 100644
index 0000000..f36aa60
--- /dev/null
+++ b/demo/src/app/api/add/route.ts
@@ -0,0 +1,24 @@
+import { NextRequest, NextResponse } from 'next/server'
+import { getDemoEvaluator } from '@/lib/load-demo-evaluator'
+
+export async function POST(req: NextRequest) {
+  const evaluator = getDemoEvaluator()
+  const body = Buffer.from(await req.arrayBuffer())
+  if (body.length < 4) {
+    return NextResponse.json({ error: 'body must be u32-le(a_len) || a || b' }, { status: 400 })
+  }
+  const aLen = body.readUInt32LE(0)
+  if (4 + aLen > body.length) {
+    return NextResponse.json({ error: 'a_len overruns body' }, { status: 400 })
+  }
+  const a = body.subarray(4, 4 + aLen)
+  const b = body.subarray(4 + aLen)
+  try {
+    const out = new Uint8Array(evaluator.addU32(a, b))
+    return new NextResponse(out, {
+      headers: { 'Content-Type': 'application/octet-stream' },
+    })
+  } catch (err) {
+    return NextResponse.json({ error: (err as Error).message }, { status: 400 })
+  }
+}
diff --git a/demo/src/app/globals.css b/demo/src/app/globals.css
new file mode 100644
index 0000000..883a0c7
--- /dev/null
+++ b/demo/src/app/globals.css
@@ -0,0 +1,124 @@
+:root {
+  --bg: oklch(0.975 0.01 80);
+  --bg-tint: oklch(0.955 0.015 80);
+  --card: oklch(0.995 0.004 80);
+  --ink: oklch(0.22 0.015 60);
+  --ink-soft: oklch(0.42 0.02 60);
+  --ink-faint: oklch(0.65 0.015 60);
+  --rule: oklch(0.88 0.012 70);
+  --rule-strong: oklch(0.78 0.015 70);
+
+  --plain: oklch(0.66 0.15 25);
+  --plain-soft: oklch(0.92 0.05 25);
+  --cipher: oklch(0.62 0.13 210);
+  --cipher-soft: oklch(0.93 0.04 210);
+  --key: oklch(0.62 0.13 290);
+  --key-soft: oklch(0.93 0.04 290);
+
+  --ok: oklch(0.62 0.14 150);
+  --warn: oklch(0.72 0.14 70);
+
+  --term-bg: oklch(0.2 0.015 260);
+  --term-ink: oklch(0.92 0.01 90);
+  --term-dim: oklch(0.62 0.015 90);
+
+  font-family: var(--font-sans), ui-sans-serif, system-ui, -apple-system, sans-serif;
+  font-size: 15px;
+  line-height: 1.45;
+  -webkit-font-smoothing: antialiased;
+}
+
+*, *::before, *::after {
+  box-sizing: border-box;
+}
+
+html, body {
+  margin: 0;
+  padding: 0;
+  background: var(--bg);
+  color: var(--ink);
+  min-height: 100vh;
+}
+
+button {
+  font: inherit;
+  color: inherit;
+}
+
+::selection {
+  background: var(--plain-soft);
+}
+
+@keyframes poulpy-wiggle {
+  0%, 100% { transform: rotate(0deg); }
+  50% { transform: rotate(2deg); }
+}
+
+@keyframes parcel {
+  0% { transform: translateX(-4px); opacity: 0; }
+  10% { opacity: 1; }
+  90% { opacity: 1; }
+  100% { transform: translateX(68px); opacity: 0; }
+}
+
+@keyframes pulse {
+  0%, 100% { opacity: 1; }
+  50% { opacity: 0.35; }
+}
+
+@keyframes blink {
+  0%, 49% { opacity: 1; }
+  50%, 100% { opacity: 0; }
+}
+
+.demo-github-link {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  width: 36px;
+  height: 36px;
+  border-radius: 10px;
+  color: var(--ink-soft);
+  background: oklch(0.98 0.01 80);
+  border: 1px solid var(--rule);
+  transition: color 0.15s, background 0.15s, border-color 0.15s;
+}
+
+.demo-github-link:hover {
+  color: var(--ink);
+  background: oklch(0.96 0.02 80);
+  border-color: var(--ink-faint);
+}
+
+.demo-root { padding: 28px 32px 40px; }
+.demo-header { flex-direction: row; align-items: center; gap: 18px; }
+.demo-header-title { font-size: 36px; }
+.demo-grid { display: grid; grid-template-columns: minmax(0, 1.35fr) minmax(360px, 1fr); gap: 22px; align-items: start; }
+.demo-sidebar { position: sticky; top: 20px; height: calc(100vh - 40px); min-height: 560px; }
+
+@media (max-width: 960px) {
+  .demo-root { padding: 20px 18px 32px; }
+  .demo-grid { grid-template-columns: 1fr; }
+  .demo-sidebar { position: static; height: auto; min-height: 340px; }
+  .demo-header-title { font-size: 30px; }
+}
+
+@media (max-width: 600px) {
+  :root { font-size: 14px; }
+  .demo-root { padding: 16px 14px 28px; gap: 16px !important; }
+  .demo-header { flex-wrap: wrap; gap: 12px !important; padding-bottom: 14px !important; justify-content: space-between !important; align-items: center; }
+  .demo-header-main { flex: 1 1 100% !important; order: 2 !important; }
+  .demo-header-title { font-size: 24px; letter-spacing: -0.3px; }
+  .demo-header-sub { font-size: 13px; }
+  .demo-card-2col { grid-template-columns: 1fr !important; }
+  .demo-send-grid { grid-template-columns: 1fr !important; }
+  .demo-send-arrow { transform: rotate(90deg); margin: 4px auto; }
+  .demo-numpad { grid-template-columns: repeat(8, 1fr) !important; }
+  .demo-decrypt-row { flex-direction: column !important; align-items: flex-start !important; gap: 14px !important; }
+  .demo-decrypt-explain { flex: 0 0 auto !important; min-width: 0 !important; }
+  .demo-decrypt-big { font-size: 56px !important; }
+  .demo-footer { flex-direction: column; align-items: flex-start; gap: 4px !important; }
+  .demo-sidebar { min-height: 280px; }
+  .demo-card { padding: 14px !important; }
+  .demo-card-accent { padding-left: 18px !important; }
+}
diff --git a/demo/src/app/layout.tsx b/demo/src/app/layout.tsx
new file mode 100644
index 0000000..52423e1
--- /dev/null
+++ b/demo/src/app/layout.tsx
@@ -0,0 +1,40 @@
+import type { Metadata } from 'next'
+import { Newsreader, Geist, Geist_Mono } from 'next/font/google'
+import './globals.css'
+
+const newsreader = Newsreader({
+  subsets: ['latin'],
+  weight: ['400', '500', '600'],
+  style: ['normal', 'italic'],
+  variable: '--font-serif',
+  display: 'swap',
+})
+
+const geist = Geist({
+  subsets: ['latin'],
+  variable: '--font-sans',
+  display: 'swap',
+})
+
+const geistMono = Geist_Mono({
+  subsets: ['latin'],
+  variable: '--font-mono',
+  display: 'swap',
+})
+
+export const metadata: Metadata = {
+  title: 'Poulpy FHE — Interactive Demo',
+  description:
+    'Add two numbers without the server ever seeing them — a CGGI homomorphic encryption walkthrough.',
+}
+
+export default function RootLayout({ children }: { children: React.ReactNode }) {
+  return (
+    <html
+      lang="en"
+      className={`${newsreader.variable} ${geist.variable} ${geistMono.variable}`}
+    >
+      <body>{children}</body>
+    </html>
+  )
+}
diff --git a/demo/src/app/page.tsx b/demo/src/app/page.tsx
new file mode 100644
index 0000000..8a1869b
--- /dev/null
+++ b/demo/src/app/page.tsx
@@ -0,0 +1,5 @@
+import { DemoLoader } from '@/components/DemoLoader'
+
+export default function Page() {
+  return <DemoLoader />
+}
diff --git a/demo/src/components/Demo.tsx b/demo/src/components/Demo.tsx
new file mode 100644
index 0000000..94efc8c
--- /dev/null
+++ b/demo/src/components/Demo.tsx
@@ -0,0 +1,273 @@
+'use client'
+
+import { useCallback } from 'react'
+import { Poulpy } from '@/components/mascot/Poulpy'
+import { Btn } from '@/components/atoms/Btn'
+import { ServerTerminal } from '@/components/terminal/ServerTerminal'
+import { Step1Keygen } from '@/components/steps/Step1Keygen'
+import { Step2Encrypt } from '@/components/steps/Step2Encrypt'
+import { Step3Evaluate } from '@/components/steps/Step3Evaluate'
+import { Step4Decrypt } from '@/components/steps/Step4Decrypt'
+import { useFhe } from '@/hooks/useFhe'
+
+const GITHUB_REPO = 'https://github.com/cedoor/squid'
+
+function GitHubLink() {
+  return (
+    <a
+      className="demo-github-link"
+      href={GITHUB_REPO}
+      target="_blank"
+      rel="noreferrer"
+      aria-label="View source on GitHub"
+    >
+      <svg
+        width={22}
+        height={22}
+        viewBox="0 0 98 96"
+        aria-hidden
+        focusable="false"
+      >
+        <path
+          fill="currentColor"
+          d="M48.854 0C21.839 0 0 22 0 49.217c0 21.756 13.993 40.172 33.405 46.69 2.427.49 3.316-1.059 3.316-2.362 0-1.141-.08-5.052-.08-9.127-13.59 2.934-16.42-5.867-16.42-5.867-2.184-5.704-5.42-7.17-5.42-7.17-4.448-3.015.324-3.015.324-3.015 4.934.326 7.523 5.052 7.523 5.052 4.367 7.496 11.404 5.378 14.235 4.074.404-3.178 1.699-5.378 3.074-6.6-10.839-1.141-22.23-5.378-22.23-24.188 0-5.378 1.94-9.778 5.014-13.2-.485-1.222-2.184-6.275.486-13.038 0 0 4.125-1.304 13.426 5.052a46.97 46.97 0 0 1 12.214-1.63c4.125 0 8.33.571 12.213 1.63 9.302-6.356 13.427-5.052 13.427-5.052 2.67 6.763.97 11.816.485 13.038 3.155 3.422 5.015 7.822 5.015 13.2 0 18.905-11.404 23.06-22.324 24.189 1.75 1.52 3.32 3.5 3.32 7.11 0 5.19-.04 9.3-.04 10.5 0 1.3.9 2.8 3.3 2.2 19.2-6.4 32.1-25 32.1-45.1C98 22 75.3 0 48.8 0z"
+        />
+      </svg>
+    </a>
+  )
+}
+
+function Footer() {
+  return (
+    <div
+      className="demo-footer"
+      style={{
+        marginTop: 4,
+        paddingTop: 14,
+        borderTop: '1px dashed var(--rule)',
+        display: 'flex',
+        justifyContent: 'space-between',
+        fontSize: 11.5,
+        color: 'var(--ink-faint)',
+        fontFamily: 'var(--font-mono)',
+        letterSpacing: 0.3,
+        flexWrap: 'wrap',
+        gap: 8,
+      }}
+    >
+      <span>scheme: CGGI · plaintext: u32</span>
+      <span>
+        legend:{' '}
+        <span style={{ color: 'var(--plain)' }}>● plaintext</span>{' '}
+        <span style={{ color: 'var(--cipher)' }}>● ciphertext</span>{' '}
+        <span style={{ color: 'var(--key)' }}>● keys</span>
+      </span>
+      <span>squid-js demo · not for production use</span>
+    </div>
+  )
+}
+
+export default function Demo() {
+  const { state, doKeygen, doEncrypt, doEvaluate, doDecrypt, doReset, setA, setB } = useFhe()
+  const { phase, skPreview, ekBytes, a, b, ctA, ctB, ctSum, result, logs, error } = state
+
+  const busy = phase !== 'idle'
+
+  // Mood: thinking while busy, brief happy flash after keygen/decrypt, locked on error
+  // Derive mood from state
+  let mood: 'idle' | 'thinking' | 'happy' | 'locked' = 'idle'
+  if (error) mood = 'locked'
+  else if (busy) mood = 'thinking'
+  else if (result !== null) mood = 'happy'
+
+  const handleEncrypt = useCallback(() => {
+    doEncrypt(a, b)
+  }, [doEncrypt, a, b])
+
+  const handleEvaluate = useCallback(() => {
+    if (ctA && ctB) {
+      doEvaluate(ctA, ctB)
+    }
+  }, [doEvaluate, ctA, ctB])
+
+  const handleDecrypt = useCallback(() => {
+    if (ctSum) doDecrypt(ctSum)
+  }, [doDecrypt, ctSum])
+
+  return (
+    <div
+      className="demo-root"
+      style={{
+        minHeight: '100vh',
+        maxWidth: 1400,
+        margin: '0 auto',
+        display: 'flex',
+        flexDirection: 'column',
+        gap: 22,
+      }}
+    >
+      {/* Header */}
+      <header
+        className="demo-header"
+        style={{
+          display: 'flex',
+          paddingBottom: 18,
+          borderBottom: '1px solid var(--rule)',
+        }}
+      >
+        <Poulpy size={68} mood={mood} tint="var(--plain)" />
+        <div className="demo-header-main" style={{ flex: 1 }}>
+          <div
+            style={{
+              fontSize: 11,
+              textTransform: 'uppercase',
+              letterSpacing: 2,
+              color: 'var(--ink-faint)',
+              fontFamily: 'var(--font-mono)',
+            }}
+          >
+            Poulpy · FHE playground
+          </div>
+          <h1
+            className="demo-header-title"
+            style={{
+              margin: '4px 0 2px',
+              fontFamily: 'var(--font-serif)',
+              fontWeight: 500,
+              letterSpacing: -0.6,
+              lineHeight: 1.1,
+            }}
+          >
+            Add two numbers{' '}
+            <em style={{ fontStyle: 'italic', color: 'var(--cipher)' }}>without</em> the server
+            ever seeing them.
+          </h1>
+          <div
+            className="demo-header-sub"
+            style={{ fontSize: 14, color: 'var(--ink-soft)', marginTop: 4, maxWidth: 780 }}
+          >
+            An end-to-end walkthrough of a CGGI homomorphic addition — keygen, encrypt, evaluate,
+            decrypt — using the{' '}
+            <a
+              href="https://github.com/poulpy-fhe/poulpy"
+              target="_blank"
+              rel="noreferrer"
+              style={{
+                color: 'var(--ink)',
+                textDecoration: 'underline',
+                textDecorationColor: 'var(--plain)',
+                textDecorationThickness: 2,
+              }}
+            >
+              Poulpy
+            </a>{' '}
+            library.
+          </div>
+          {error && (
+            <div
+              style={{
+                marginTop: 8,
+                fontSize: 13,
+                color: 'oklch(0.7 0.18 25)',
+                fontFamily: 'var(--font-mono)',
+              }}
+            >
+              ✗ {error}
+            </div>
+          )}
+        </div>
+        <div className="demo-header-actions" style={{ display: 'flex', alignItems: 'center', gap: 10 }}>
+          <Btn onClick={doReset} small>
+            Reset demo
+          </Btn>
+          <GitHubLink />
+        </div>
+      </header>
+
+      {/* Two-column grid */}
+      <div className="demo-grid">
+        {/* Left column — steps */}
+        <div style={{ display: 'flex', flexDirection: 'column', gap: 16 }}>
+          <Step1Keygen
+            skPreview={skPreview}
+            ekBytes={ekBytes}
+            phase={phase}
+            onGenerate={doKeygen}
+          />
+          <Step2Encrypt
+            hasKeys={!!ekBytes}
+            a={a}
+            b={b}
+            ctA={ctA}
+            ctB={ctB}
+            phase={phase}
+            onSelectA={setA}
+            onSelectB={setB}
+            onEncrypt={handleEncrypt}
+          />
+          <Step3Evaluate
+            ctA={ctA}
+            ctB={ctB}
+            ctSum={ctSum}
+            phase={phase}
+            onEvaluate={handleEvaluate}
+          />
+          <Step4Decrypt
+            ctSum={ctSum}
+            result={result}
+            phase={phase}
+            a={a}
+            b={b}
+            onDecrypt={handleDecrypt}
+          />
+          <Footer />
+        </div>
+
+        {/* Right column — server terminal */}
+        <div
+          className="demo-sidebar"
+          style={{
+            display: 'flex',
+            flexDirection: 'column',
+            gap: 10,
+          }}
+        >
+          <div
+            style={{
+              display: 'flex',
+              alignItems: 'baseline',
+              justifyContent: 'space-between',
+            }}
+          >
+            <div>
+              <div
+                style={{
+                  fontSize: 11,
+                  textTransform: 'uppercase',
+                  letterSpacing: 1.5,
+                  color: 'var(--ink-faint)',
+                }}
+              >
+                the other side
+              </div>
+              <h2
+                style={{
+                  margin: 0,
+                  fontFamily: 'var(--font-serif)',
+                  fontWeight: 500,
+                  fontSize: 22,
+                }}
+              >
+                Server log
+              </h2>
+            </div>
+            <span style={{ fontSize: 11.5, color: 'var(--ink-faint)' }}>
+              crypto runs in your browser
+            </span>
+          </div>
+          <ServerTerminal logs={logs} running={busy} />
+        </div>
+      </div>
+    </div>
+  )
+}
diff --git a/demo/src/components/DemoLoader.tsx b/demo/src/components/DemoLoader.tsx
new file mode 100644
index 0000000..9b8ba75
--- /dev/null
+++ b/demo/src/components/DemoLoader.tsx
@@ -0,0 +1,9 @@
+'use client'
+
+import dynamic from 'next/dynamic'
+
+const Demo = dynamic(() => import('./Demo'), { ssr: false })
+
+export function DemoLoader() {
+  return <Demo />
+}
diff --git a/demo/src/components/atoms/Btn.tsx b/demo/src/components/atoms/Btn.tsx
new file mode 100644
index 0000000..96c1fe2
--- /dev/null
+++ b/demo/src/components/atoms/Btn.tsx
@@ -0,0 +1,62 @@
+'use client'
+
+import { useState, type CSSProperties, type ReactNode } from 'react'
+
+interface BtnProps {
+  children: ReactNode
+  onClick?: () => void
+  disabled?: boolean
+  primary?: boolean
+  tone?: 'cipher' | 'plain' | 'key' | 'default'
+  small?: boolean
+  style?: CSSProperties
+}
+
+export function Btn({ children, onClick, disabled, primary, tone = 'default', small, style }: BtnProps) {
+  const [hover, setHover] = useState(false)
+
+  const base: CSSProperties = {
+    display: 'inline-flex',
+    alignItems: 'center',
+    gap: 8,
+    border: '1px solid var(--rule-strong)',
+    borderRadius: 999,
+    padding: small ? '6px 14px' : '9px 18px',
+    background: 'var(--card)',
+    color: 'var(--ink)',
+    fontWeight: 500,
+    fontSize: small ? 13 : 14,
+    cursor: disabled ? 'not-allowed' : 'pointer',
+    opacity: disabled ? 0.45 : 1,
+    transition: 'transform 0.08s ease, background 0.15s ease, border-color 0.15s ease',
+    transform: hover && !disabled ? 'translateY(-1px)' : 'none',
+    fontFamily: 'var(--font-sans)',
+  }
+
+  const primaryStyle: CSSProperties = primary
+    ? {
+        background:
+          tone === 'cipher'
+            ? 'var(--cipher)'
+            : tone === 'plain'
+            ? 'var(--plain)'
+            : tone === 'key'
+            ? 'var(--key)'
+            : 'var(--ink)',
+        color: 'var(--bg)',
+        borderColor: 'transparent',
+      }
+    : {}
+
+  return (
+    <button
+      onClick={disabled ? undefined : onClick}
+      onMouseEnter={() => setHover(true)}
+      onMouseLeave={() => setHover(false)}
+      disabled={disabled}
+      style={{ ...base, ...primaryStyle, ...style }}
+    >
+      {children}
+    </button>
+  )
+}
diff --git a/demo/src/components/atoms/ByteViewer.tsx b/demo/src/components/atoms/ByteViewer.tsx
new file mode 100644
index 0000000..380a3ef
--- /dev/null
+++ b/demo/src/components/atoms/ByteViewer.tsx
@@ -0,0 +1,32 @@
+import { bytesToHexPreview } from '@/lib/fingerprint'
+
+interface ByteViewerProps {
+  bytes: Uint8Array
+  label?: string
+  accent?: string
+  maxBytes?: number
+}
+
+export function ByteViewer({ bytes, label, accent = 'var(--cipher)', maxBytes = 24 }: ByteViewerProps) {
+  const hex = bytesToHexPreview(bytes, maxBytes)
+  return (
+    <div
+      style={{
+        fontFamily: 'var(--font-mono)',
+        fontSize: 11,
+        color: 'var(--ink-soft)',
+        background: 'var(--bg-tint)',
+        border: '1px dashed var(--rule)',
+        borderRadius: 8,
+        padding: '8px 10px',
+        lineHeight: 1.5,
+        wordBreak: 'break-all',
+      }}
+    >
+      {label && (
+        <span style={{ color: accent, fontWeight: 500 }}>{label} </span>
+      )}
+      <span style={{ color: 'var(--ink-faint)' }}>{hex}</span>
+    </div>
+  )
+}
diff --git a/demo/src/components/atoms/Card.tsx b/demo/src/components/atoms/Card.tsx
new file mode 100644
index 0000000..9240d20
--- /dev/null
+++ b/demo/src/components/atoms/Card.tsx
@@ -0,0 +1,28 @@
+import type { CSSProperties, ReactNode } from 'react'
+
+interface CardProps {
+  children: ReactNode
+  accent?: string
+  style?: CSSProperties
+}
+
+export function Card({ children, accent, style }: CardProps) {
+  return (
+    <div
+      className={accent ? 'demo-card demo-card-accent' : 'demo-card'}
+      style={{
+        background: 'var(--card)',
+        border: '1px solid var(--rule)',
+        borderRadius: 14,
+        padding: 18,
+        position: 'relative',
+        ...(accent
+          ? { boxShadow: `inset 4px 0 0 0 ${accent}`, paddingLeft: 22 }
+          : {}),
+        ...style,
+      }}
+    >
+      {children}
+    </div>
+  )
+}
diff --git a/demo/src/components/atoms/Chip.tsx b/demo/src/components/atoms/Chip.tsx
new file mode 100644
index 0000000..dadb144
--- /dev/null
+++ b/demo/src/components/atoms/Chip.tsx
@@ -0,0 +1,44 @@
+import type { CSSProperties, ReactNode } from 'react'
+
+type Tone = 'default' | 'plain' | 'cipher' | 'key' | 'ink' | 'ok' | 'warn'
+
+const toneStyles: Record<Tone, CSSProperties> = {
+  default: {},
+  plain: { background: 'var(--plain-soft)', color: 'oklch(0.35 0.1 25)', borderColor: 'transparent' },
+  cipher: { background: 'var(--cipher-soft)', color: 'oklch(0.32 0.08 210)', borderColor: 'transparent' },
+  key: { background: 'var(--key-soft)', color: 'oklch(0.32 0.08 290)', borderColor: 'transparent' },
+  ink: { background: 'var(--ink)', color: 'var(--bg)', borderColor: 'transparent' },
+  ok: { background: 'oklch(0.92 0.06 150)', color: 'oklch(0.28 0.08 150)', borderColor: 'transparent' },
+  warn: { background: 'oklch(0.92 0.06 70)', color: 'oklch(0.38 0.1 70)', borderColor: 'transparent' },
+}
+
+interface ChipProps {
+  children: ReactNode
+  tone?: Tone
+  style?: CSSProperties
+}
+
+export function Chip({ children, tone = 'default', style }: ChipProps) {
+  return (
+    <span
+      style={{
+        display: 'inline-flex',
+        alignItems: 'center',
+        gap: 6,
+        padding: '3px 9px',
+        borderRadius: 999,
+        fontSize: 11.5,
+        fontWeight: 500,
+        letterSpacing: 0.2,
+        border: '1px solid var(--rule)',
+        background: 'var(--bg-tint)',
+        color: 'var(--ink-soft)',
+        fontFamily: 'var(--font-mono)',
+        ...toneStyles[tone],
+        ...style,
+      }}
+    >
+      {children}
+    </span>
+  )
+}
diff --git a/demo/src/components/atoms/Fingerprint.tsx b/demo/src/components/atoms/Fingerprint.tsx
new file mode 100644
index 0000000..23cb972
--- /dev/null
+++ b/demo/src/components/atoms/Fingerprint.tsx
@@ -0,0 +1,35 @@
+import { useMemo } from 'react'
+import { deriveGrid } from '@/lib/fingerprint'
+
+interface FingerprintProps {
+  bytes: Uint8Array
+  size?: number
+  accent?: string
+  active?: boolean
+}
+
+export function Fingerprint({ bytes, size = 64, accent = 'var(--cipher)', active = true }: FingerprintProps) {
+  const cells = useMemo(() => deriveGrid(bytes), [bytes])
+  const cell = size / 8
+  return (
+    <svg width={size} height={size} style={{ display: 'block', borderRadius: 6 }}>
+      <rect width={size} height={size} fill="var(--bg-tint)" />
+      {cells.map((b, i) => {
+        const x = (i % 8) * cell
+        const y = Math.floor(i / 8) * cell
+        const alpha = (b / 255) * (active ? 1 : 0.4)
+        return (
+          <rect
+            key={i}
+            x={x + 0.5}
+            y={y + 0.5}
+            width={cell - 1}
+            height={cell - 1}
+            fill={accent}
+            opacity={0.15 + alpha * 0.75}
+          />
+        )
+      })}
+    </svg>
+  )
+}
diff --git a/demo/src/components/atoms/NoiseMeter.tsx b/demo/src/components/atoms/NoiseMeter.tsx
new file mode 100644
index 0000000..f9b2cf4
--- /dev/null
+++ b/demo/src/components/atoms/NoiseMeter.tsx
@@ -0,0 +1,62 @@
+import { deriveNoise } from '@/lib/fingerprint'
+
+interface NoiseMeterProps {
+  bytes: Uint8Array
+  opCount?: number
+  label?: string
+}
+
+export function NoiseMeter({ bytes, opCount = 0, label = 'noise' }: NoiseMeterProps) {
+  const noise = deriveNoise(bytes, opCount)
+  const pct = Math.min(1, Math.max(0, noise))
+  const danger = pct > 0.4
+  const color = danger ? 'var(--warn)' : 'var(--ok)'
+  return (
+    <div>
+      <div
+        style={{
+          display: 'flex',
+          justifyContent: 'space-between',
+          fontSize: 11,
+          color: 'var(--ink-faint)',
+        }}
+      >
+        <span style={{ textTransform: 'uppercase', letterSpacing: 1 }}>{label}</span>
+        <span style={{ fontFamily: 'var(--font-mono)' }}>
+          {(pct * 100).toFixed(1)}%{' '}
+          <span style={{ color: 'var(--ink-faint)' }}>/ 50% margin</span>
+        </span>
+      </div>
+      <div
+        style={{
+          marginTop: 4,
+          height: 6,
+          borderRadius: 999,
+          background: 'var(--bg-tint)',
+          border: '1px solid var(--rule)',
+          overflow: 'hidden',
+          position: 'relative',
+        }}
+      >
+        <div
+          style={{
+            position: 'absolute',
+            left: '50%',
+            top: -2,
+            bottom: -2,
+            width: 1,
+            background: 'var(--rule-strong)',
+          }}
+        />
+        <div
+          style={{
+            width: `${pct * 100}%`,
+            height: '100%',
+            background: color,
+            transition: 'width 0.5s ease',
+          }}
+        />
+      </div>
+    </div>
+  )
+}
diff --git a/demo/src/components/atoms/NumberPad.tsx b/demo/src/components/atoms/NumberPad.tsx
new file mode 100644
index 0000000..6eb9ada
--- /dev/null
+++ b/demo/src/components/atoms/NumberPad.tsx
@@ -0,0 +1,63 @@
+'use client'
+
+interface NumberPadProps {
+  value: number
+  onChange: (n: number) => void
+  accent?: string
+  label?: string
+  disabled?: boolean
+}
+
+export function NumberPad({ value, onChange, accent = 'var(--plain)', label, disabled }: NumberPadProps) {
+  return (
+    <div style={{ display: 'flex', flexDirection: 'column', gap: 8 }}>
+      {label && (
+        <div
+          style={{
+            fontSize: 11.5,
+            color: 'var(--ink-faint)',
+            textTransform: 'uppercase',
+            letterSpacing: 1,
+          }}
+        >
+          {label}
+        </div>
+      )}
+      <div
+        className="demo-numpad"
+        style={{
+          display: 'grid',
+          gridTemplateColumns: 'repeat(8, 1fr)',
+          gap: 4,
+        }}
+      >
+        {Array.from({ length: 16 }, (_, i) => i).map((n) => {
+          const selected = n === value
+          return (
+            <button
+              key={n}
+              onClick={() => !disabled && onChange(n)}
+              disabled={disabled}
+              style={{
+                aspectRatio: '1',
+                border: '1px solid var(--rule)',
+                background: selected ? accent : 'var(--card)',
+                color: selected ? 'var(--bg)' : 'var(--ink-soft)',
+                borderColor: selected ? 'transparent' : 'var(--rule)',
+                borderRadius: 8,
+                fontFamily: 'var(--font-mono)',
+                fontSize: 13,
+                fontWeight: 500,
+                cursor: disabled ? 'not-allowed' : 'pointer',
+                transition: 'all 0.12s ease',
+                opacity: disabled ? 0.5 : 1,
+              }}
+            >
+              {n}
+            </button>
+          )
+        })}
+      </div>
+    </div>
+  )
+}
diff --git a/demo/src/components/atoms/StepHeader.tsx b/demo/src/components/atoms/StepHeader.tsx
new file mode 100644
index 0000000..d504100
--- /dev/null
+++ b/demo/src/components/atoms/StepHeader.tsx
@@ -0,0 +1,51 @@
+interface StepHeaderProps {
+  n: string | number
+  title: string
+  subtitle?: string
+  accent?: string
+  done?: boolean
+}
+
+export function StepHeader({ n, title, subtitle, accent = 'var(--ink)', done }: StepHeaderProps) {
+  return (
+    <div style={{ display: 'flex', alignItems: 'flex-start', gap: 14, marginBottom: 16 }}>
+      <div
+        style={{
+          width: 34,
+          height: 34,
+          borderRadius: '50%',
+          background: done ? accent : 'var(--card)',
+          color: done ? 'var(--bg)' : accent,
+          border: `1.5px solid ${accent}`,
+          display: 'flex',
+          alignItems: 'center',
+          justifyContent: 'center',
+          fontFamily: 'var(--font-serif)',
+          fontSize: 18,
+          fontWeight: 500,
+          flexShrink: 0,
+          transition: 'all 0.3s ease',
+        }}
+      >
+        {done ? '✓' : n}
+      </div>
+      <div style={{ flex: 1, paddingTop: 2 }}>
+        <h3
+          style={{
+            margin: 0,
+            fontFamily: 'var(--font-serif)',
+            fontWeight: 500,
+            fontSize: 22,
+            letterSpacing: -0.2,
+            lineHeight: 1.15,
+          }}
+        >
+          {title}
+        </h3>
+        {subtitle && (
+          <div style={{ fontSize: 13, color: 'var(--ink-soft)', marginTop: 3 }}>{subtitle}</div>
+        )}
+      </div>
+    </div>
+  )
+}
diff --git a/demo/src/components/atoms/StripePlaceholder.tsx b/demo/src/components/atoms/StripePlaceholder.tsx
new file mode 100644
index 0000000..4baef75
--- /dev/null
+++ b/demo/src/components/atoms/StripePlaceholder.tsx
@@ -0,0 +1,28 @@
+interface StripePlaceholderProps {
+  label: string
+  height?: number
+}
+
+export function StripePlaceholder({ label, height = 80 }: StripePlaceholderProps) {
+  return (
+    <div
+      style={{
+        height,
+        borderRadius: 8,
+        background:
+          'repeating-linear-gradient(45deg, var(--bg-tint), var(--bg-tint) 8px, var(--rule) 8px, var(--rule) 9px)',
+        border: '1px dashed var(--rule-strong)',
+        display: 'flex',
+        alignItems: 'center',
+        justifyContent: 'center',
+        fontFamily: 'var(--font-mono)',
+        fontSize: 11,
+        color: 'var(--ink-faint)',
+        letterSpacing: 1,
+        textTransform: 'uppercase',
+      }}
+    >
+      {label}
+    </div>
+  )
+}
diff --git a/demo/src/components/mascot/Poulpy.tsx b/demo/src/components/mascot/Poulpy.tsx
new file mode 100644
index 0000000..652f3ae
--- /dev/null
+++ b/demo/src/components/mascot/Poulpy.tsx
@@ -0,0 +1,93 @@
+import type { CSSProperties } from 'react'
+import type { MascotMood } from '@/lib/fhe-types'
+
+interface PouplypProps {
+  size?: number
+  mood?: MascotMood
+  tint?: string
+}
+
+export function Poulpy({ size = 120, mood = 'idle', tint = 'var(--plain)' }: PouplypProps) {
+  const eyeShift = mood === 'thinking' ? -1.2 : 0
+  const eyeY = mood === 'happy' ? 38 : 40
+  const eyeScaleY = mood === 'happy' ? 0.25 : 1
+  const mouth =
+    mood === 'happy'
+      ? 'M 46 54 Q 60 62 74 54'
+      : mood === 'thinking'
+      ? 'M 52 56 Q 60 56 68 56'
+      : mood === 'locked'
+      ? 'M 52 56 L 68 56'
+      : 'M 52 56 Q 60 58 68 56'
+
+  const tentacles: Array<{ d: string; delay: number }> = [
+    { d: 'M 22 60 Q 10 76 14 96 Q 20 108 12 116', delay: 0 },
+    { d: 'M 32 70 Q 24 92 32 108 Q 38 116 32 122', delay: 0.2 },
+    { d: 'M 48 76 Q 46 100 52 116 Q 56 122 50 128', delay: 0.4 },
+    { d: 'M 72 76 Q 74 100 68 116 Q 64 122 70 128', delay: 0.3 },
+    { d: 'M 88 70 Q 96 92 88 108 Q 82 116 88 122', delay: 0.1 },
+    { d: 'M 98 60 Q 110 76 106 96 Q 100 108 108 116', delay: 0.5 },
+  ]
+
+  return (
+    <svg
+      viewBox="0 0 120 140"
+      width={size}
+      height={size * (140 / 120)}
+      style={{ display: 'block', overflow: 'visible' }}
+      aria-hidden
+    >
+      <ellipse cx="60" cy="128" rx="34" ry="4" fill="oklch(0 0 0 / 0.08)" />
+      <g fill="none" stroke={tint} strokeWidth="8" strokeLinecap="round" opacity="0.9">
+        {tentacles.map((t, i) => (
+          <path
+            key={i}
+            d={t.d}
+            style={
+              {
+                transformOrigin: '60px 60px',
+                animation: `poulpy-wiggle 3.2s ease-in-out ${t.delay}s infinite`,
+              } as CSSProperties
+            }
+          />
+        ))}
+      </g>
+      <path
+        d="M 18 56 Q 18 22 60 22 Q 102 22 102 56 Q 102 72 88 76 L 32 76 Q 18 72 18 56 Z"
+        fill={tint}
+      />
+      <ellipse cx="44" cy="36" rx="10" ry="6" fill="oklch(1 0 0 / 0.35)" />
+      <g fill="oklch(0.2 0.015 60)">
+        <ellipse cx={48 + eyeShift} cy={eyeY} rx="3" ry={3 * eyeScaleY} />
+        <ellipse cx={72 + eyeShift} cy={eyeY} rx="3" ry={3 * eyeScaleY} />
+      </g>
+      {mood !== 'happy' && (
+        <g fill="oklch(1 0 0 / 0.9)">
+          <circle cx={49 + eyeShift} cy={eyeY - 1} r="0.8" />
+          <circle cx={73 + eyeShift} cy={eyeY - 1} r="0.8" />
+        </g>
+      )}
+      <path
+        d={mouth}
+        stroke="oklch(0.2 0.015 60)"
+        strokeWidth="1.8"
+        fill="none"
+        strokeLinecap="round"
+      />
+      <circle cx="38" cy="52" r="3.5" fill="oklch(0.75 0.12 20 / 0.35)" />
+      <circle cx="82" cy="52" r="3.5" fill="oklch(0.75 0.12 20 / 0.35)" />
+      {mood === 'locked' && (
+        <g transform="translate(50, 62)">
+          <rect x="0" y="5" width="20" height="14" rx="3" fill="oklch(0.5 0.12 290)" />
+          <path
+            d="M 4 5 Q 4 0 10 0 Q 16 0 16 5"
+            stroke="oklch(0.5 0.12 290)"
+            strokeWidth="2.5"
+            fill="none"
+          />
+          <circle cx="10" cy="12" r="2" fill="var(--bg)" />
+        </g>
+      )}
+    </svg>
+  )
+}
diff --git a/demo/src/components/steps/Step1Keygen.tsx b/demo/src/components/steps/Step1Keygen.tsx
new file mode 100644
index 0000000..20b0666
--- /dev/null
+++ b/demo/src/components/steps/Step1Keygen.tsx
@@ -0,0 +1,149 @@
+import { Card } from '@/components/atoms/Card'
+import { Chip } from '@/components/atoms/Chip'
+import { Btn } from '@/components/atoms/Btn'
+import { ByteViewer } from '@/components/atoms/ByteViewer'
+import { StripePlaceholder } from '@/components/atoms/StripePlaceholder'
+import { StepHeader } from '@/components/atoms/StepHeader'
+import { formatBytes } from '@/lib/pack'
+import type { Phase } from '@/lib/fhe-types'
+
+interface Step1KeygenProps {
+  skPreview: Uint8Array | null
+  ekBytes: Uint8Array | null
+  phase: Phase
+  onGenerate: () => void
+}
+
+function KeyIcon({ color, outline }: { color: string; outline?: boolean }) {
+  return (
+    <svg width="18" height="18" viewBox="0 0 18 18">
+      <circle cx="6" cy="9" r="3.5" fill={outline ? 'none' : color} stroke={color} strokeWidth="1.5" />
+      <path
+        d="M 9.5 9 L 16 9 M 14 9 L 14 12 M 12 9 L 12 11.5"
+        stroke={color}
+        strokeWidth="1.5"
+        fill="none"
+        strokeLinecap="round"
+      />
+    </svg>
+  )
+}
+
+export function Step1Keygen({ skPreview, ekBytes, phase, onGenerate }: Step1KeygenProps) {
+  const busy = phase !== 'idle'
+  const done = !!skPreview && !!ekBytes
+
+  return (
+    <Card accent="var(--key)">
+      <StepHeader
+        n="1"
+        title="Derive keys from the shared demo seed"
+        subtitle="The client rebuilds SK and EK deterministically — no randomness, always the same keys."
+        accent="var(--key)"
+        done={done}
+      />
+
+      {/* Shared-seed callout */}
+      <div
+        style={{
+          display: 'flex',
+          alignItems: 'flex-start',
+          gap: 10,
+          padding: '10px 12px',
+          borderRadius: 8,
+          background: 'var(--key-soft)',
+          border: '1px solid oklch(0.85 0.04 290)',
+          marginBottom: 14,
+          fontSize: 12.5,
+          color: 'oklch(0.32 0.08 290)',
+          lineHeight: 1.5,
+        }}
+      >
+        <span style={{ fontSize: 16, flexShrink: 0, marginTop: 1 }}>🔑</span>
+        <span>
+          Both sides share a fixed 96-byte seed committed to this repo. The server derives and
+          pre-loads EK at deploy time from that same seed — so <strong>no EK upload ever
+          happens</strong> (saving ~16 MiB per session).
+        </span>
+      </div>
+
+      <div className="demo-card-2col" style={{ display: 'grid', gridTemplateColumns: '1fr 1fr', gap: 14, marginBottom: 14 }}>
+        {/* Secret key card */}
+        <div
+          style={{
+            border: '1px solid var(--rule)',
+            borderRadius: 10,
+            padding: 12,
+            background: skPreview ? 'var(--key-soft)' : 'var(--bg-tint)',
+            opacity: skPreview ? 1 : 0.55,
+            transition: 'all 0.4s ease',
+          }}
+        >
+          <div style={{ display: 'flex', alignItems: 'center', gap: 8, marginBottom: 8, flexWrap: 'wrap' }}>
+            <KeyIcon color="oklch(0.35 0.12 290)" />
+            <span style={{ fontWeight: 500, fontSize: 13 }}>Secret key</span>
+            <Chip tone="key" style={{ fontSize: 10 }}>sk</Chip>
+          </div>
+          <div style={{ fontSize: 11.5, color: 'var(--ink-soft)', marginBottom: 8 }}>
+            Stays in this browser. Used only for decryption.
+          </div>
+          {skPreview ? (
+            <div style={{ display: 'flex', flexDirection: 'column', gap: 6 }}>
+              <ByteViewer bytes={skPreview} accent="oklch(0.35 0.12 290)" />
+              <div style={{ fontSize: 11, color: 'var(--ink-faint)', fontFamily: 'var(--font-mono)' }}>
+                seed preview · LWE n=630
+              </div>
+            </div>
+          ) : (
+            <StripePlaceholder label="sk — not yet derived" height={52} />
+          )}
+        </div>
+
+        {/* Evaluation key card */}
+        <div
+          style={{
+            border: '1px solid var(--rule)',
+            borderRadius: 10,
+            padding: 12,
+            background: ekBytes ? 'var(--key-soft)' : 'var(--bg-tint)',
+            opacity: ekBytes ? 1 : 0.55,
+            transition: 'all 0.4s ease',
+          }}
+        >
+          <div style={{ display: 'flex', alignItems: 'center', gap: 8, marginBottom: 8, flexWrap: 'wrap' }}>
+            <KeyIcon color="oklch(0.35 0.12 290)" outline />
+            <span style={{ fontWeight: 500, fontSize: 13 }}>Evaluation key</span>
+            <Chip tone="key" style={{ fontSize: 10 }}>ek</Chip>
+            {ekBytes && (
+              <Chip style={{ fontSize: 10, background: 'oklch(0.88 0.04 150)', color: 'oklch(0.3 0.1 150)', borderColor: 'transparent' }}>
+                pre-loaded on server
+              </Chip>
+            )}
+          </div>
+          <div style={{ fontSize: 11.5, color: 'var(--ink-soft)', marginBottom: 8 }}>
+            Enables homomorphic ops. Already on the server — never uploaded.
+          </div>
+          {ekBytes ? (
+            <div style={{ display: 'flex', flexDirection: 'column', gap: 6 }}>
+              <ByteViewer bytes={ekBytes} accent="oklch(0.35 0.12 290)" />
+              <div style={{ fontSize: 11, color: 'var(--ink-faint)', fontFamily: 'var(--font-mono)' }}>
+                {formatBytes(ekBytes.byteLength)} · bootstrapping key
+              </div>
+            </div>
+          ) : (
+            <StripePlaceholder label="ek — not yet derived" height={52} />
+          )}
+        </div>
+      </div>
+
+      <div style={{ display: 'flex', alignItems: 'center', gap: 12 }}>
+        <Btn onClick={onGenerate} disabled={busy} primary tone="key">
+          {phase === 'keygen' ? 'Deriving…' : done ? 'Re-derive keys' : 'Derive keys'}
+        </Btn>
+        <span style={{ fontSize: 12, color: 'var(--ink-faint)' }}>
+          CGGI over the torus · σ ≈ 2<sup>−15</sup> · plaintext space: 32 bits
+        </span>
+      </div>
+    </Card>
+  )
+}
diff --git a/demo/src/components/steps/Step2Encrypt.tsx b/demo/src/components/steps/Step2Encrypt.tsx
new file mode 100644
index 0000000..6fc6d1c
--- /dev/null
+++ b/demo/src/components/steps/Step2Encrypt.tsx
@@ -0,0 +1,151 @@
+import { Card } from '@/components/atoms/Card'
+import { Chip } from '@/components/atoms/Chip'
+import { Btn } from '@/components/atoms/Btn'
+import { Fingerprint } from '@/components/atoms/Fingerprint'
+import { NoiseMeter } from '@/components/atoms/NoiseMeter'
+import { NumberPad } from '@/components/atoms/NumberPad'
+import { StripePlaceholder } from '@/components/atoms/StripePlaceholder'
+import { StepHeader } from '@/components/atoms/StepHeader'
+import { formatBytes } from '@/lib/pack'
+import type { Phase } from '@/lib/fhe-types'
+
+interface Step2EncryptProps {
+  hasKeys: boolean
+  a: number
+  b: number
+  ctA: Uint8Array | null
+  ctB: Uint8Array | null
+  phase: Phase
+  onSelectA: (n: number) => void
+  onSelectB: (n: number) => void
+  onEncrypt: () => void
+}
+
+function EncryptSlot({
+  label,
+  value,
+  setValue,
+  ct,
+  disabled,
+}: {
+  label: string
+  value: number
+  setValue: (n: number) => void
+  ct: Uint8Array | null
+  disabled: boolean
+}) {
+  return (
+    <div
+      style={{
+        border: '1px solid var(--rule)',
+        borderRadius: 10,
+        padding: 14,
+        background: 'var(--card)',
+        opacity: disabled ? 0.5 : 1,
+      }}
+    >
+      <NumberPad value={value} onChange={setValue} label={label} disabled={disabled} />
+
+      <div style={{ display: 'flex', alignItems: 'center', gap: 10, marginTop: 12 }}>
+        <div
+          style={{
+            fontFamily: 'var(--font-serif)',
+            fontSize: 40,
+            lineHeight: 1,
+            color: 'var(--plain)',
+            fontWeight: 500,
+            width: 54,
+            textAlign: 'center',
+          }}
+        >
+          {value}
+        </div>
+        <div style={{ color: 'var(--ink-faint)', fontFamily: 'var(--font-mono)', fontSize: 13 }}>
+          → Enc →
+        </div>
+        <div style={{ flex: 1 }}>
+          {ct ? (
+            <div style={{ display: 'flex', alignItems: 'center', gap: 10 }}>
+              <Fingerprint bytes={ct} size={56} />
+              <div style={{ flex: 1, minWidth: 0 }}>
+                <Chip tone="cipher" style={{ fontSize: 10 }}>
+                  ct_{label.split(' ')[1]}
+                </Chip>
+                <div
+                  style={{
+                    fontSize: 11,
+                    color: 'var(--ink-faint)',
+                    fontFamily: 'var(--font-mono)',
+                    marginTop: 4,
+                  }}
+                >
+                  {formatBytes(ct.byteLength)}
+                </div>
+              </div>
+            </div>
+          ) : (
+            <StripePlaceholder label="ciphertext" height={56} />
+          )}
+        </div>
+      </div>
+      {ct && (
+        <div style={{ marginTop: 10 }}>
+          <NoiseMeter bytes={ct} opCount={0} label="initial noise" />
+        </div>
+      )}
+    </div>
+  )
+}
+
+export function Step2Encrypt({
+  hasKeys,
+  a,
+  b,
+  ctA,
+  ctB,
+  phase,
+  onSelectA,
+  onSelectB,
+  onEncrypt,
+}: Step2EncryptProps) {
+  const busy = phase !== 'idle'
+  const done = !!ctA && !!ctB
+
+  return (
+    <Card accent="var(--plain)">
+      <StepHeader
+        n="2"
+        title="Choose two numbers, then encrypt"
+        subtitle="Each integer (0–15) becomes an LWE ciphertext. Same value encrypts differently every time."
+        accent="var(--plain)"
+        done={done}
+      />
+
+      <div className="demo-card-2col" style={{ display: 'grid', gridTemplateColumns: '1fr 1fr', gap: 16 }}>
+        <EncryptSlot
+          label="input a"
+          value={a}
+          setValue={onSelectA}
+          ct={ctA}
+          disabled={!hasKeys || busy}
+        />
+        <EncryptSlot
+          label="input b"
+          value={b}
+          setValue={onSelectB}
+          ct={ctB}
+          disabled={!hasKeys || busy}
+        />
+      </div>
+
+      <div style={{ display: 'flex', alignItems: 'center', gap: 12, marginTop: 16 }}>
+        <Btn onClick={onEncrypt} disabled={!hasKeys || busy} primary>
+          {phase === 'encrypting' ? 'Encrypting…' : done ? 'Re-encrypt' : 'Encrypt a & b'}
+        </Btn>
+        {!hasKeys && (
+          <span style={{ fontSize: 12, color: 'var(--ink-faint)' }}>↑ Generate keys first</span>
+        )}
+      </div>
+    </Card>
+  )
+}
diff --git a/demo/src/components/steps/Step3Evaluate.tsx b/demo/src/components/steps/Step3Evaluate.tsx
new file mode 100644
index 0000000..53e9d31
--- /dev/null
+++ b/demo/src/components/steps/Step3Evaluate.tsx
@@ -0,0 +1,314 @@
+import { Card } from '@/components/atoms/Card'
+import { Chip } from '@/components/atoms/Chip'
+import { Btn } from '@/components/atoms/Btn'
+import { Fingerprint } from '@/components/atoms/Fingerprint'
+import { ByteViewer } from '@/components/atoms/ByteViewer'
+import { NoiseMeter } from '@/components/atoms/NoiseMeter'
+import { StepHeader } from '@/components/atoms/StepHeader'
+import { formatBytes } from '@/lib/pack'
+import type { Phase } from '@/lib/fhe-types'
+
+interface Step3EvaluateProps {
+  ctA: Uint8Array | null
+  ctB: Uint8Array | null
+  ctSum: Uint8Array | null
+  phase: Phase
+  onEvaluate: () => void
+}
+
+function PayloadRow({
+  icon,
+  label,
+  value,
+  tone,
+}: {
+  icon: React.ReactNode
+  label: string
+  value: string
+  tone: 'key' | 'cipher'
+}) {
+  return (
+    <div
+      style={{
+        display: 'flex',
+        alignItems: 'center',
+        gap: 8,
+        padding: '6px 8px',
+        borderRadius: 6,
+        background: 'var(--card)',
+        border: '1px solid var(--rule)',
+      }}
+    >
+      <div style={{ width: 18, display: 'flex', alignItems: 'center', justifyContent: 'center' }}>
+        {icon}
+      </div>
+      <Chip tone={tone} style={{ fontSize: 10 }}>
+        {label}
+      </Chip>
+      <div style={{ flex: 1 }} />
+      <div style={{ fontSize: 11, fontFamily: 'var(--font-mono)', color: 'var(--ink-soft)' }}>
+        {value}
+      </div>
+    </div>
+  )
+}
+
+export function Step3Evaluate({ ctA, ctB, ctSum, phase, onEvaluate }: Step3EvaluateProps) {
+  const busy = phase !== 'idle'
+  const ready = !!ctA && !!ctB
+  const sending = phase === 'sending' || phase === 'evaluating'
+  const done = !!ctSum
+
+  return (
+    <Card accent="var(--cipher)">
+      <StepHeader
+        n="3"
+        title="Send ciphertexts, add homomorphically"
+        subtitle="Client sends only ctₐ and ct_b — the server already holds the EK. It never sees the plaintext values."
+        accent="var(--cipher)"
+        done={done}
+      />
+
+      {/* Transit diagram */}
+      <div
+        className="demo-send-grid"
+        style={{
+          display: 'grid',
+          gridTemplateColumns: '1fr auto 1fr',
+          alignItems: 'center',
+          gap: 16,
+          padding: '8px 4px 12px',
+        }}
+      >
+        {/* Outbound payload */}
+        <div
+          style={{
+            border: '1px dashed var(--rule-strong)',
+            borderRadius: 10,
+            padding: 12,
+            background: 'var(--bg-tint)',
+          }}
+        >
+          <div
+            style={{
+              fontSize: 11,
+              textTransform: 'uppercase',
+              letterSpacing: 1.2,
+              color: 'var(--ink-faint)',
+              marginBottom: 6,
+            }}
+          >
+            outbound payload
+          </div>
+          <div style={{ display: 'flex', flexDirection: 'column', gap: 5 }}>
+            <PayloadRow
+              icon={ctA ? <Fingerprint bytes={ctA} size={14} /> : null}
+              label="ctₐ"
+              value={ctA ? formatBytes(ctA.byteLength) : '—'}
+              tone="cipher"
+            />
+            <PayloadRow
+              icon={ctB ? <Fingerprint bytes={ctB} size={14} /> : null}
+              label="ct_b"
+              value={ctB ? formatBytes(ctB.byteLength) : '—'}
+              tone="cipher"
+            />
+          </div>
+          {/* EK note */}
+          <div
+            style={{
+              marginTop: 8,
+              fontSize: 10.5,
+              color: 'var(--ink-faint)',
+              fontFamily: 'var(--font-mono)',
+              display: 'flex',
+              alignItems: 'center',
+              gap: 5,
+            }}
+          >
+            <svg width="11" height="11" viewBox="0 0 18 18">
+              <circle cx="6" cy="9" r="3.5" fill="none" stroke="currentColor" strokeWidth="1.5" />
+              <path d="M 9.5 9 L 16 9 M 14 9 L 14 12 M 12 9 L 12 11.5" stroke="currentColor" strokeWidth="1.5" fill="none" strokeLinecap="round" />
+            </svg>
+            ek pre-loaded on server · not sent
+          </div>
+        </div>
+
+        {/* Transit arrow + parcel animation */}
+        <div
+          className="demo-send-arrow"
+          style={{
+            display: 'flex',
+            flexDirection: 'column',
+            alignItems: 'center',
+            gap: 4,
+            minWidth: 90,
+          }}
+        >
+          <div style={{ position: 'relative', width: 80, height: 28 }}>
+            <svg width="80" height="28" viewBox="0 0 80 28" style={{ overflow: 'visible' }}>
+              <path
+                d="M 2 14 L 78 14"
+                stroke="var(--rule-strong)"
+                strokeWidth="1.2"
+                strokeDasharray="3 3"
+              />
+              <polygon points="78,14 72,10 72,18" fill="var(--rule-strong)" />
+            </svg>
+            {sending && (
+              <div
+                style={{
+                  position: 'absolute',
+                  top: 6,
+                  left: 0,
+                  animation: 'parcel 1.2s linear infinite',
+                }}
+              >
+                <div
+                  style={{
+                    width: 16,
+                    height: 16,
+                    borderRadius: 3,
+                    background: 'var(--cipher)',
+                    boxShadow: '0 2px 6px oklch(0 0 0 / 0.15)',
+                  }}
+                />
+              </div>
+            )}
+          </div>
+          <div
+            style={{
+              fontSize: 10,
+              textTransform: 'uppercase',
+              letterSpacing: 1.5,
+              color: 'var(--ink-faint)',
+            }}
+          >
+            https
+          </div>
+        </div>
+
+        {/* Server compute box */}
+        <div
+          style={{
+            border: '1px dashed var(--rule-strong)',
+            borderRadius: 10,
+            padding: 12,
+            background: 'var(--term-bg)',
+            color: 'var(--term-ink)',
+          }}
+        >
+          <div
+            style={{
+              fontSize: 11,
+              textTransform: 'uppercase',
+              letterSpacing: 1.2,
+              color: 'var(--term-dim)',
+              marginBottom: 6,
+            }}
+          >
+            server computes
+          </div>
+          <div
+            style={{
+              fontFamily: 'var(--font-mono)',
+              fontSize: 13,
+              color: 'var(--term-ink)',
+              padding: '8px 0',
+              textAlign: 'center',
+            }}
+          >
+            <span style={{ color: 'var(--term-dim)' }}>out ←</span>{' '}
+            <span style={{ color: 'oklch(0.8 0.12 210)' }}>ctₐ ⊞ ct_b</span>
+          </div>
+          <div
+            style={{
+              fontSize: 11,
+              color: 'var(--term-dim)',
+              fontFamily: 'var(--font-mono)',
+              textAlign: 'center',
+            }}
+          >
+            {ctSum ? 'done · ' + formatBytes(ctSum.byteLength) : 'awaiting input…'}
+          </div>
+        </div>
+      </div>
+
+      {/* Result ciphertext */}
+      <div
+        style={{
+          marginTop: 10,
+          padding: 14,
+          borderRadius: 10,
+          background: ctSum ? 'var(--cipher-soft)' : 'var(--bg-tint)',
+          border: '1px solid var(--rule)',
+          opacity: ctSum ? 1 : 0.55,
+          transition: 'all 0.4s ease',
+        }}
+      >
+        <div style={{ display: 'flex', alignItems: 'center', gap: 12 }}>
+          <div style={{ flexShrink: 0 }}>
+            {ctSum ? (
+              <Fingerprint bytes={ctSum} size={64} />
+            ) : (
+              <div
+                style={{
+                  width: 64,
+                  height: 64,
+                  background: 'var(--card)',
+                  border: '1px dashed var(--rule)',
+                  borderRadius: 6,
+                }}
+              />
+            )}
+          </div>
+          <div style={{ flex: 1, minWidth: 0 }}>
+            <div
+              style={{
+                display: 'flex',
+                alignItems: 'center',
+                gap: 8,
+                marginBottom: 6,
+                flexWrap: 'wrap',
+              }}
+            >
+              <span style={{ fontFamily: 'var(--font-serif)', fontSize: 18, fontWeight: 500 }}>
+                Encrypted result
+              </span>
+              {ctSum && (
+                <Chip tone="cipher" style={{ fontSize: 10 }}>
+                  ct_sum
+                </Chip>
+              )}
+            </div>
+            {ctSum ? (
+              <>
+                <ByteViewer bytes={ctSum} />
+                <div style={{ marginTop: 8 }}>
+                  <NoiseMeter bytes={ctSum} opCount={1} label="accumulated noise" />
+                </div>
+              </>
+            ) : (
+              <div style={{ fontSize: 12, color: 'var(--ink-faint)' }}>
+                The server will return a fresh ciphertext encoding the sum.
+              </div>
+            )}
+          </div>
+        </div>
+      </div>
+
+      <div style={{ display: 'flex', alignItems: 'center', gap: 12, marginTop: 14 }}>
+        <Btn onClick={onEvaluate} disabled={!ready || busy} primary tone="cipher">
+          {phase === 'sending' || phase === 'evaluating'
+            ? 'Computing on server…'
+            : done
+            ? 'Run again'
+            : 'Send & evaluate'}
+        </Btn>
+        {!ready && !done && (
+          <span style={{ fontSize: 12, color: 'var(--ink-faint)' }}>↑ Encrypt inputs first</span>
+        )}
+      </div>
+    </Card>
+  )
+}
diff --git a/demo/src/components/steps/Step4Decrypt.tsx b/demo/src/components/steps/Step4Decrypt.tsx
new file mode 100644
index 0000000..f92dc97
--- /dev/null
+++ b/demo/src/components/steps/Step4Decrypt.tsx
@@ -0,0 +1,130 @@
+import { Card } from '@/components/atoms/Card'
+import { Chip } from '@/components/atoms/Chip'
+import { Btn } from '@/components/atoms/Btn'
+import { Fingerprint } from '@/components/atoms/Fingerprint'
+import { StepHeader } from '@/components/atoms/StepHeader'
+import type { Phase } from '@/lib/fhe-types'
+
+interface Step4DecryptProps {
+  ctSum: Uint8Array | null
+  result: number | null
+  phase: Phase
+  a: number
+  b: number
+  onDecrypt: () => void
+}
+
+export function Step4Decrypt({ ctSum, result, phase, a, b, onDecrypt }: Step4DecryptProps) {
+  const busy = phase !== 'idle'
+  const ready = !!ctSum
+  const done = result !== null
+  const expected = a + b
+
+  return (
+    <Card accent="var(--plain)">
+      <StepHeader
+        n="4"
+        title="Decrypt on the client"
+        subtitle="Apply sk to the encrypted result. Works while noise stays under the 50% margin."
+        accent="var(--plain)"
+        done={done}
+      />
+
+      <div className="demo-decrypt-row" style={{ display: 'flex', alignItems: 'center', gap: 20, flexWrap: 'wrap' }}>
+        {/* The encrypted result */}
+        <div style={{ display: 'flex', alignItems: 'center', gap: 10 }}>
+          {ctSum ? (
+            <Fingerprint bytes={ctSum} size={54} />
+          ) : (
+            <div
+              style={{
+                width: 54,
+                height: 54,
+                borderRadius: 6,
+                background: 'var(--bg-tint)',
+                border: '1px dashed var(--rule)',
+              }}
+            />
+          )}
+          <div>
+            <Chip tone="cipher" style={{ fontSize: 10 }}>
+              ct_sum
+            </Chip>
+            <div
+              style={{
+                fontSize: 11,
+                color: 'var(--ink-faint)',
+                fontFamily: 'var(--font-mono)',
+                marginTop: 4,
+              }}
+            >
+              {ctSum ? `${ctSum.byteLength} B` : '—'}
+            </div>
+          </div>
+        </div>
+
+        {/* Dec arrow */}
+        <div
+          style={{
+            display: 'flex',
+            alignItems: 'center',
+            gap: 6,
+            fontFamily: 'var(--font-mono)',
+            color: 'var(--ink-faint)',
+            fontSize: 13,
+            flexShrink: 0,
+          }}
+        >
+          <span>⟶ Dec(</span>
+          <svg width="18" height="18" viewBox="0 0 18 18">
+            <circle cx="6" cy="9" r="3.5" fill="oklch(0.35 0.12 290)" stroke="oklch(0.35 0.12 290)" strokeWidth="1.5" />
+            <path d="M 9.5 9 L 16 9 M 14 9 L 14 12 M 12 9 L 12 11.5" stroke="oklch(0.35 0.12 290)" strokeWidth="1.5" fill="none" strokeLinecap="round" />
+          </svg>
+          <span>sk) ⟶</span>
+        </div>
+
+        {/* Big result number */}
+        <div
+          className="demo-decrypt-big"
+          data-testid="decrypt-result"
+          style={{
+            fontFamily: 'var(--font-serif)',
+            fontSize: 72,
+            lineHeight: 1,
+            color:
+              done ? 'var(--plain)' : 'var(--rule-strong)',
+            fontWeight: 500,
+            textAlign: 'center',
+            minWidth: 80,
+            transition: 'color 0.3s ease',
+            flexShrink: 0,
+          }}
+        >
+          {done ? result : '·'}
+        </div>
+
+        {/* Explanation */}
+        <div className="demo-decrypt-explain" style={{ fontSize: 12, color: 'var(--ink-soft)', flex: '1 1 240px', minWidth: 220 }}>
+          {done ? (
+            <>
+              <div style={{ fontFamily: 'var(--font-mono)', fontSize: 13, color: 'var(--ink)' }}>
+                {a} + {b} = <b>{result}</b>
+              </div>
+              <div style={{ marginTop: 2, color: 'var(--ink-faint)' }}>
+                Matches the plaintext sum ({expected}) — the server never saw either operand.
+              </div>
+            </>
+          ) : (
+            'The server returned ct_sum. Press below to recover the plaintext locally.'
+          )}
+        </div>
+      </div>
+
+      <div style={{ display: 'flex', alignItems: 'center', gap: 12, marginTop: 18 }}>
+        <Btn onClick={onDecrypt} disabled={!ready || busy} primary>
+          {phase === 'decrypting' ? 'Decrypting…' : done ? 'Decrypt again' : 'Decrypt result'}
+        </Btn>
+      </div>
+    </Card>
+  )
+}
diff --git a/demo/src/components/terminal/ServerTerminal.tsx b/demo/src/components/terminal/ServerTerminal.tsx
new file mode 100644
index 0000000..7d240c0
--- /dev/null
+++ b/demo/src/components/terminal/ServerTerminal.tsx
@@ -0,0 +1,160 @@
+'use client'
+
+import { useEffect, useRef } from 'react'
+import type { LogEntry, LogKind } from '@/lib/fhe-types'
+
+interface ServerTerminalProps {
+  logs: LogEntry[]
+  running: boolean
+}
+
+const colorFor: Record<LogKind, string> = {
+  info: 'var(--term-ink)',
+  dim: 'var(--term-dim)',
+  ok: 'oklch(0.78 0.14 150)',
+  warn: 'oklch(0.82 0.14 70)',
+  err: 'oklch(0.7 0.18 25)',
+  in: 'oklch(0.78 0.12 210)',
+  out: 'oklch(0.78 0.12 290)',
+}
+
+const prefixFor: Record<LogKind, string> = {
+  info: '·',
+  dim: ' ',
+  ok: '✓',
+  warn: '!',
+  err: '✗',
+  in: '←',
+  out: '→',
+}
+
+function Caret() {
+  return (
+    <span
+      style={{
+        display: 'inline-block',
+        width: 7,
+        height: 13,
+        background: 'var(--term-ink)',
+        verticalAlign: 'text-bottom',
+        animation: 'blink 1s step-end infinite',
+      }}
+    />
+  )
+}
+
+function TermLine({ line }: { line: LogEntry }) {
+  return (
+    <div style={{ color: colorFor[line.kind], whiteSpace: 'pre-wrap' }}>
+      <span style={{ color: 'var(--term-dim)', marginRight: 8 }}>[{line.ts}]</span>
+      <span style={{ marginRight: 6 }}>{prefixFor[line.kind]}</span>
+      {line.text}
+    </div>
+  )
+}
+
+export function ServerTerminal({ logs, running }: ServerTerminalProps) {
+  const scrollerRef = useRef<HTMLDivElement>(null)
+
+  useEffect(() => {
+    const el = scrollerRef.current
+    if (el) el.scrollTop = el.scrollHeight
+  }, [logs])
+
+  return (
+    <div
+      style={{
+        background: 'var(--term-bg)',
+        color: 'var(--term-ink)',
+        borderRadius: 14,
+        border: '1px solid oklch(0.28 0.02 260)',
+        overflow: 'hidden',
+        display: 'flex',
+        flexDirection: 'column',
+        height: '100%',
+        minHeight: 420,
+      }}
+    >
+      {/* Terminal chrome */}
+      <div
+        style={{
+          display: 'flex',
+          alignItems: 'center',
+          gap: 8,
+          padding: '10px 14px',
+          borderBottom: '1px solid oklch(0.28 0.02 260)',
+          background: 'oklch(0.16 0.015 260)',
+        }}
+      >
+        <div style={{ display: 'flex', gap: 6 }}>
+          <div style={{ width: 10, height: 10, borderRadius: '50%', background: 'oklch(0.68 0.16 25)' }} />
+          <div style={{ width: 10, height: 10, borderRadius: '50%', background: 'oklch(0.82 0.14 85)' }} />
+          <div style={{ width: 10, height: 10, borderRadius: '50%', background: 'oklch(0.7 0.14 150)' }} />
+        </div>
+        <div
+          style={{
+            flex: 1,
+            textAlign: 'center',
+            fontFamily: 'var(--font-mono)',
+            fontSize: 11.5,
+            color: 'var(--term-dim)',
+            letterSpacing: 0.5,
+          }}
+        >
+          server ~ poulpy-eval · cggi
+        </div>
+        <div
+          style={{
+            display: 'flex',
+            alignItems: 'center',
+            gap: 5,
+            fontFamily: 'var(--font-mono)',
+            fontSize: 10.5,
+            color: running ? 'oklch(0.75 0.15 150)' : 'var(--term-dim)',
+          }}
+        >
+          <span
+            style={{
+              width: 7,
+              height: 7,
+              borderRadius: '50%',
+              background: running ? 'oklch(0.75 0.15 150)' : 'var(--term-dim)',
+              animation: running ? 'pulse 1.1s ease-in-out infinite' : 'none',
+            }}
+          />
+          {running ? 'busy' : 'idle'}
+        </div>
+      </div>
+
+      {/* Log area */}
+      <div
+        ref={scrollerRef}
+        style={{
+          flex: 1,
+          padding: '14px 16px',
+          fontFamily: 'var(--font-mono)',
+          fontSize: 12,
+          lineHeight: 1.65,
+          overflowY: 'auto',
+        }}
+      >
+        {logs.length === 0 && (
+          <div style={{ color: 'var(--term-dim)' }}>
+            <span style={{ color: 'oklch(0.75 0.15 150)' }}>$</span> ./poulpy-server --scheme cggi --listen :3001
+            <br />
+            <span style={{ color: 'var(--term-dim)' }}>waiting for client… </span>
+            <Caret />
+          </div>
+        )}
+        {logs.map((l) => (
+          <TermLine key={l.id} line={l} />
+        ))}
+        {running && (
+          <div style={{ color: 'var(--term-dim)' }}>
+            <Caret />
+          </div>
+        )}
+      </div>
+    </div>
+  )
+}
diff --git a/demo/src/hooks/useFhe.ts b/demo/src/hooks/useFhe.ts
new file mode 100644
index 0000000..adeb959
--- /dev/null
+++ b/demo/src/hooks/useFhe.ts
@@ -0,0 +1,218 @@
+'use client'
+
+import { useCallback, useEffect, useReducer, useRef } from 'react'
+import type { FheState, LogEntry, LogKind, Phase } from '@/lib/fhe-types'
+import { DEMO_KEY_SEED } from '@/lib/demo-seed'
+import { formatBytes, packCiphertexts } from '@/lib/pack'
+
+const API_BASE = '/api'
+const PARAMS_SET =
+  (process.env.NEXT_PUBLIC_POULPY_PARAMS_SET as string | undefined) ?? 'test'
+const OCTET = 'application/octet-stream'
+
+// ---------------------------------------------------------------------------
+// Reducer
+// ---------------------------------------------------------------------------
+
+type Action =
+  | { type: 'SET_PHASE'; phase: Phase }
+  | { type: 'KEYGEN_DONE'; skPreview: Uint8Array; ekBytes: Uint8Array }
+  | { type: 'ENCRYPT_DONE'; ctA: Uint8Array; ctB: Uint8Array }
+  | { type: 'EVALUATE_DONE'; ctSum: Uint8Array }
+  | { type: 'DECRYPT_DONE'; result: number }
+  | { type: 'SET_A'; a: number }
+  | { type: 'SET_B'; b: number }
+  | { type: 'LOG'; entry: LogEntry }
+  | { type: 'ERROR'; message: string }
+  | { type: 'RESET' }
+
+const initial: FheState = {
+  phase: 'idle',
+  skPreview: null,
+  ekBytes: null,
+  a: 7,
+  b: 5,
+  ctA: null,
+  ctB: null,
+  ctSum: null,
+  result: null,
+  logs: [],
+  error: null,
+}
+
+function reducer(state: FheState, action: Action): FheState {
+  switch (action.type) {
+    case 'SET_PHASE':
+      return { ...state, phase: action.phase, error: null }
+    case 'KEYGEN_DONE':
+      return {
+        ...state,
+        phase: 'idle',
+        skPreview: action.skPreview,
+        ekBytes: action.ekBytes,
+        ctA: null,
+        ctB: null,
+        ctSum: null,
+        result: null,
+        error: null,
+      }
+    case 'ENCRYPT_DONE':
+      return { ...state, phase: 'idle', ctA: action.ctA, ctB: action.ctB, ctSum: null, result: null, error: null }
+    case 'EVALUATE_DONE':
+      return { ...state, phase: 'idle', ctSum: action.ctSum, result: null, error: null }
+    case 'DECRYPT_DONE':
+      return { ...state, phase: 'idle', result: action.result, error: null }
+    case 'SET_A':
+      return { ...state, a: action.a, ctA: null, ctB: null, ctSum: null, result: null }
+    case 'SET_B':
+      return { ...state, b: action.b, ctA: null, ctB: null, ctSum: null, result: null }
+    case 'LOG':
+      return { ...state, logs: [...state.logs, action.entry] }
+    case 'ERROR':
+      return { ...state, phase: 'idle', error: action.message }
+    case 'RESET':
+      return { ...initial, logs: [] }
+    default:
+      return state
+  }
+}
+
+// ---------------------------------------------------------------------------
+// Hook
+// ---------------------------------------------------------------------------
+
+export function useFhe() {
+  const [state, dispatch] = useReducer(reducer, initial)
+  const clientRef = useRef<import('squid-js/client').PoulpyClient | null>(null)
+  const logIdRef = useRef(0)
+  const startRef = useRef(Date.now())
+
+  const log = useCallback((kind: LogKind, text: string) => {
+    const elapsed = (Date.now() - startRef.current) / 1000
+    dispatch({
+      type: 'LOG',
+      entry: { id: logIdRef.current++, ts: elapsed.toFixed(2) + 's', kind, text },
+    })
+  }, [])
+
+  const doKeygen = useCallback(async () => {
+    dispatch({ type: 'SET_PHASE', phase: 'keygen' })
+    startRef.current = Date.now()
+    logIdRef.current = 0
+    log('info', 'client: building CGGI session from demo seed (deterministic)…')
+    log('dim', `  scheme=CGGI  paramsSet=${PARAMS_SET}`)
+    try {
+      const { PoulpyClient } = await import('squid-js/client')
+      const client = await PoulpyClient.create({ paramsSet: PARAMS_SET, seeds: DEMO_KEY_SEED })
+      clientRef.current = client
+
+      const seeds = await client.exportSeeds()
+      const skPreview = seeds.slice(0, 48)
+      const ekBytes = client.evaluationKey
+
+      log('ok', `client: sk ready (${formatBytes(seeds.byteLength)}) — stays local`)
+      log('info', 'client: EK matches server (same seed; server loads demo-ek at deploy)')
+      log('dim', 'server: stateless /api/add, waiting for ciphertexts…')
+
+      dispatch({ type: 'KEYGEN_DONE', skPreview, ekBytes })
+    } catch (err) {
+      log('err', `client: keygen failed — ${(err as Error).message}`)
+      dispatch({ type: 'ERROR', message: (err as Error).message })
+    }
+  }, [log])
+
+  const doEncrypt = useCallback(
+    async (a: number, b: number) => {
+      const client = clientRef.current
+      if (!client) return
+      dispatch({ type: 'SET_PHASE', phase: 'encrypting' })
+      log('info', `client: encrypting a=${a}`)
+      try {
+        const ctA = await client.encryptU32(a)
+        log('ok', `client: ctₐ ready (${formatBytes(ctA.byteLength)})`)
+        log('info', `client: encrypting b=${b}`)
+        const ctB = await client.encryptU32(b)
+        log('ok', `client: ct_b ready (${formatBytes(ctB.byteLength)})`)
+        dispatch({ type: 'ENCRYPT_DONE', ctA, ctB })
+      } catch (err) {
+        log('err', `client: encrypt failed — ${(err as Error).message}`)
+        dispatch({ type: 'ERROR', message: (err as Error).message })
+      }
+    },
+    [log],
+  )
+
+  const doEvaluate = useCallback(
+    async (ctA: Uint8Array, ctB: Uint8Array) => {
+      dispatch({ type: 'SET_PHASE', phase: 'sending' })
+      const payloadSize = formatBytes(ctA.byteLength + ctB.byteLength)
+      log('info', `client → server: POST /api/add (${payloadSize})`)
+      try {
+        const body = packCiphertexts(ctA, ctB)
+        dispatch({ type: 'SET_PHASE', phase: 'evaluating' })
+        log('in', 'server: received ciphertexts, computing ctₐ ⊞ ct_b')
+        const resp = await fetch(`${API_BASE}/add`, {
+          method: 'POST',
+          headers: { 'Content-Type': OCTET },
+          body: body as BodyInit,
+        })
+        if (!resp.ok) {
+          const body2 = (await resp.json().catch(() => ({}))) as { error?: string }
+          throw new Error(body2.error ?? `/add failed (${resp.status})`)
+        }
+        const ctSum = new Uint8Array(await resp.arrayBuffer())
+        log('ok', `server: ct_sum ready (${formatBytes(ctSum.byteLength)})`)
+        log('out', 'server → client: 200 OK')
+        dispatch({ type: 'EVALUATE_DONE', ctSum })
+      } catch (err) {
+        log('err', `evaluate failed — ${(err as Error).message}`)
+        dispatch({ type: 'ERROR', message: (err as Error).message })
+      }
+    },
+    [log],
+  )
+
+  const doDecrypt = useCallback(
+    async (ctSum: Uint8Array) => {
+      const client = clientRef.current
+      if (!client) return
+      dispatch({ type: 'SET_PHASE', phase: 'decrypting' })
+      log('info', 'client: Dec(sk, ct_sum)…')
+      try {
+        const result = await client.decryptU32(ctSum)
+        log('ok', `client: plaintext = ${result}`)
+        dispatch({ type: 'DECRYPT_DONE', result })
+      } catch (err) {
+        log('err', `client: decrypt failed — ${(err as Error).message}`)
+        dispatch({ type: 'ERROR', message: (err as Error).message })
+      }
+    },
+    [log],
+  )
+
+  const doReset = useCallback(() => {
+    clientRef.current = null
+    dispatch({ type: 'RESET' })
+  }, [])
+
+  const setA = useCallback((a: number) => dispatch({ type: 'SET_A', a }), [])
+  const setB = useCallback((b: number) => dispatch({ type: 'SET_B', b }), [])
+
+  // Cleanup worker on unmount
+  useEffect(() => {
+    return () => {
+      clientRef.current = null
+    }
+  }, [])
+
+  return {
+    state,
+    doKeygen,
+    doEncrypt,
+    doEvaluate,
+    doDecrypt,
+    doReset,
+    setA,
+    setB,
+  }
+}
diff --git a/demo/src/lib/demo-seed.ts b/demo/src/lib/demo-seed.ts
new file mode 100644
index 0000000..9feaa85
--- /dev/null
+++ b/demo/src/lib/demo-seed.ts
@@ -0,0 +1,8 @@
+/** 96-byte keygen seeds — must match `scripts/generate-demo-ek.mjs` and `data/demo-ek.test.bin`. */
+export const DEMO_KEY_SEED = ((() => {
+  const s = new Uint8Array(96)
+  for (let i = 0; i < 96; i++) {
+    s[i] = (i * 13 + 1) & 0xff
+  }
+  return s
+})())
diff --git a/demo/src/lib/fhe-types.ts b/demo/src/lib/fhe-types.ts
new file mode 100644
index 0000000..141be4d
--- /dev/null
+++ b/demo/src/lib/fhe-types.ts
@@ -0,0 +1,37 @@
+export type Phase =
+  | 'idle'
+  | 'keygen'
+  | 'encrypting'
+  | 'sending'
+  | 'evaluating'
+  | 'decrypting'
+
+export type MascotMood = 'idle' | 'thinking' | 'happy' | 'locked'
+
+export type LogKind = 'info' | 'dim' | 'ok' | 'warn' | 'err' | 'in' | 'out'
+
+export interface LogEntry {
+  id: number
+  ts: string
+  kind: LogKind
+  text: string
+}
+
+export interface FheState {
+  phase: Phase
+  // Step 1 — Keygen
+  skPreview: Uint8Array | null
+  ekBytes: Uint8Array | null
+  // Step 2 — Encrypt
+  a: number
+  b: number
+  ctA: Uint8Array | null
+  ctB: Uint8Array | null
+  // Step 3 — Evaluate
+  ctSum: Uint8Array | null
+  // Step 4 — Decrypt
+  result: number | null
+  // Terminal
+  logs: LogEntry[]
+  error: string | null
+}
diff --git a/demo/src/lib/fingerprint.ts b/demo/src/lib/fingerprint.ts
new file mode 100644
index 0000000..39726a5
--- /dev/null
+++ b/demo/src/lib/fingerprint.ts
@@ -0,0 +1,37 @@
+/**
+ * Returns 64 byte values (0–255) deterministically from ciphertext bytes.
+ * Used to render the 8×8 fingerprint grid.
+ */
+export function deriveGrid(bytes: Uint8Array): number[] {
+  const out: number[] = []
+  for (let i = 0; i < 64; i++) {
+    out.push(bytes[(i * 7 + 3) % bytes.length])
+  }
+  return out
+}
+
+/**
+ * Returns a simulated noise fraction (0–1) from ciphertext bytes.
+ * Fresh ciphertexts land at ~6–12%. After homomorphic add: ~14–22%.
+ * opCount=0 → fresh, opCount=1 → after one server add.
+ */
+export function deriveNoise(bytes: Uint8Array, opCount = 0): number {
+  let h = 0
+  for (let i = 0; i < Math.min(bytes.length, 16); i++) {
+    h = ((h * 31) ^ bytes[i]) >>> 0
+  }
+  const base = opCount === 0 ? 0.05 : 0.13
+  const spread = 0.07
+  const frac = (h % 1000) / 1000
+  return Math.min(0.48, base + frac * spread)
+}
+
+/** Returns the first maxBytes bytes as a hex string, e.g. "0a 3f c1 …" */
+export function bytesToHexPreview(bytes: Uint8Array, maxBytes = 24): string {
+  const len = Math.min(bytes.length, maxBytes)
+  const parts: string[] = []
+  for (let i = 0; i < len; i++) {
+    parts.push(bytes[i].toString(16).padStart(2, '0'))
+  }
+  return parts.join(' ') + (bytes.length > maxBytes ? ' …' : '')
+}
diff --git a/demo/src/lib/load-demo-evaluator.ts b/demo/src/lib/load-demo-evaluator.ts
new file mode 100644
index 0000000..6f86265
--- /dev/null
+++ b/demo/src/lib/load-demo-evaluator.ts
@@ -0,0 +1,21 @@
+import { readFileSync, existsSync } from 'node:fs'
+import { join } from 'node:path'
+import { Evaluator } from 'squid-js/server'
+
+const PARAMS_SET = process.env.POULPY_PARAMS_SET ?? 'test'
+
+const ekPath =
+  process.env.POULPY_DEMO_EK_PATH ?? join(process.cwd(), 'data', 'demo-ek.test.bin')
+
+let cached: Evaluator | null = null
+
+export function getDemoEvaluator(): Evaluator {
+  if (cached) return cached
+  if (!existsSync(ekPath)) {
+    throw new Error(
+      `Missing demo evaluation key at ${ekPath}. Run: pnpm --filter @squid-js/demo run gen-demo-ek`,
+    )
+  }
+  cached = Evaluator.load(readFileSync(ekPath), PARAMS_SET)
+  return cached
+}
diff --git a/demo/src/lib/pack.ts b/demo/src/lib/pack.ts
new file mode 100644
index 0000000..8c53a35
--- /dev/null
+++ b/demo/src/lib/pack.ts
@@ -0,0 +1,14 @@
+/** Pack two ciphertexts as u32-le(a.length) || a || b. */
+export function packCiphertexts(a: Uint8Array, b: Uint8Array): Uint8Array {
+  const out = new Uint8Array(4 + a.length + b.length)
+  new DataView(out.buffer).setUint32(0, a.length, true)
+  out.set(a, 4)
+  out.set(b, 4 + a.length)
+  return out
+}
+
+export function formatBytes(n: number): string {
+  if (n < 1024) return `${n} B`
+  if (n < 1024 * 1024) return `${(n / 1024).toFixed(1)} KiB`
+  return `${(n / (1024 * 1024)).toFixed(2)} MiB`
+}
diff --git a/demo/tsconfig.json b/demo/tsconfig.json
new file mode 100644
index 0000000..b6bf469
--- /dev/null
+++ b/demo/tsconfig.json
@@ -0,0 +1,24 @@
+{
+  "compilerOptions": {
+    "target": "ES2017",
+    "lib": ["dom", "dom.iterable", "esnext"],
+    "allowJs": false,
+    "skipLibCheck": true,
+    "strict": true,
+    "noEmit": true,
+    "esModuleInterop": true,
+    "module": "esnext",
+    "moduleResolution": "bundler",
+    "resolveJsonModule": true,
+    "isolatedModules": true,
+    "jsx": "preserve",
+    "incremental": true,
+    "baseUrl": ".",
+    "paths": {
+      "@/*": ["./src/*"]
+    },
+    "plugins": [{ "name": "next" }]
+  },
+  "include": ["next-env.d.ts", "**/*.ts", "**/*.tsx", ".next/types/**/*.ts"],
+  "exclude": ["node_modules"]
+}
diff --git a/demo/vercel.json b/demo/vercel.json
new file mode 100644
index 0000000..4f3bb9b
--- /dev/null
+++ b/demo/vercel.json
@@ -0,0 +1,4 @@
+{
+  "$schema": "https://openapi.vercel.sh/vercel.json",
+  "installCommand": "pnpm install --no-link-workspace-packages --no-lockfile"
+}
diff --git a/package.json b/package.json
new file mode 100644
index 0000000..177f4e4
--- /dev/null
+++ b/package.json
@@ -0,0 +1,23 @@
+{
+  "name": "squid-monorepo",
+  "version": "0.1.0",
+  "private": true,
+  "description": "Squid FHE monorepo: Rust wrapper, wasm bindings, Node bindings, and a client/server demo.",
+  "scripts": {
+    "build:squid-js": "pnpm --filter squid-js build",
+    "build:demo": "pnpm --filter @squid-js/demo build",
+    "build": "pnpm run build:squid-js && pnpm run build:demo",
+    "dev": "pnpm --filter @squid-js/demo dev",
+    "test": "pnpm --filter @squid-js/e2e test",
+    "clean": "rimraf target packages/squid-js/wasm packages/squid-js/napi packages/squid-js/dist demo/.next"
+  },
+  "devDependencies": {
+    "concurrently": "^9.0.1",
+    "rimraf": "^6.0.1",
+    "typescript": "^5.6.3"
+  },
+  "packageManager": "pnpm@9.12.0",
+  "engines": {
+    "node": ">=20"
+  }
+}
diff --git a/packages/squid-js/README.md b/packages/squid-js/README.md
new file mode 100644
index 0000000..9008d0a
--- /dev/null
+++ b/packages/squid-js/README.md
@@ -0,0 +1,44 @@
+# Squid JS
+
+JavaScript bindings for [Squid](https://github.com/cedoor/squid) (ergonomic Rust wrapper for [Poulpy](https://github.com/poulpy-fhe/poulpy) FHE): a **browser** client (WebAssembly in a dedicated worker so keygen and crypto stay off the UI thread) and a **Node** evaluator (napi-rs). The client holds the secret key; the server only receives the evaluation key and ciphertexts.
+
+## Install
+
+```sh
+npm install squid-js
+```
+
+Use `pnpm add squid-js` or `yarn add squid-js` if you prefer. The server entry point ships a native addon; install on the platform you run Node on.
+
+## Usage
+
+**Browser** — import `squid-js/client`:
+
+```ts
+import { PoulpyClient } from "squid-js/client";
+
+const client = await PoulpyClient.create({ paramsSet: "test" }); // or "unsecure" — must match the server
+const ct = await client.encryptU32(42);
+// Send `client.evaluationKey` and `ct` to the server; decrypt results with `await client.decryptU32(...)`.
+```
+
+**Node** — import `squid-js/server` (native addon; not for bundlers targeting the browser):
+
+```ts
+import { Evaluator } from "squid-js/server";
+
+const ev = Evaluator.load(evaluationKeyBytes, "test");
+const sum = ev.addU32(ctA, ctB);
+```
+
+The `./wasm/*` export serves the built `.wasm` assets for hosting or custom `init()` URLs. Call `init()` only if you use the wasm `Session` on the main thread (no `Worker`); otherwise wasm loads inside the worker when you call `PoulpyClient.create()`.
+
+## Build
+
+Requires Rust (`wasm-pack`), and for the server target, a normal napi build environment.
+
+```sh
+pnpm run build
+```
+
+This runs `build:wasm`, `build:napi`, and `build:ts` in order (emitting `dist/squid-worker.js` next to `dist/client.js`). Node **≥ 20** is required.
diff --git a/packages/squid-js/build-linux-napi.Dockerfile b/packages/squid-js/build-linux-napi.Dockerfile
new file mode 100644
index 0000000..3e4f076
--- /dev/null
+++ b/packages/squid-js/build-linux-napi.Dockerfile
@@ -0,0 +1,43 @@
+# Linux-only glibc napi build for `squid-js` (e.g. `squid.linux-x64-gnu.node` for Vercel / linux/amd64).
+# Darwin: run `pnpm run build` in this package on your Mac; this image cannot produce macOS .node files.
+#
+# Build context: monorepo root (so Cargo.toml, crates/, packages/, pnpm-lock.yaml are available).
+# On Apple Silicon, force amd64 to match a typical Vercel Node (x86_64 glibc) runtime, from monorepo root:
+#   docker build --platform=linux/amd64 -f packages/squid-js/build-linux-napi.Dockerfile -t squid-linux:local .
+# Baked build + copy napi/ into this package (runs docker build, then copies napi/ out; see scripts/build-linux-napi.sh):
+#   pnpm --filter squid-js run build:squid:linux
+#   (from packages/squid-js: pnpm run build:squid:linux)
+#
+# Mount workflow (from monorepo root; rewrites the tree under /squid):
+#   docker run --rm -v "$PWD":/squid -w /squid squid-linux:local \
+#     bash -c 'pnpm install --no-frozen-lockfile && pnpm run build:squid-js'
+#
+# The image is built on Debian bookworm, Node 20, Rust nightly (see /squid/rust-toolchain.toml for wasm), wasm-pack, pnpm@9.12.0.
+# Use `docker build --platform=linux/amd64` (do not hardcode platform in FROM; BuildKit warns on constant FromPlatform).
+
+FROM node:20-bookworm
+
+ENV DEBIAN_FRONTEND=noninteractive
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    build-essential \
+    ca-certificates \
+    curl \
+    pkg-config \
+    && rm -rf /var/lib/apt/lists/*
+
+# Rust (nightly + wasm32 per rust-toolchain.toml; native .node target matches the build platform, e.g. linux/amd64 when using --platform=linux/amd64)
+ENV PATH="/root/.cargo/bin:${PATH}"
+RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
+RUN rustup default nightly && rustup target add wasm32-unknown-unknown
+
+# wasm-pack (uses cargo from the active nightly toolchain)
+RUN curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | sh
+
+RUN corepack enable && corepack prepare pnpm@9.12.0 --activate
+
+WORKDIR /squid
+COPY . .
+
+# --no-frozen-lockfile: after version bumps, package.json can change before pnpm-lock.yaml; frozen would fail the image build.
+RUN pnpm install --no-frozen-lockfile && pnpm run build:squid-js
diff --git a/packages/squid-js/package.json b/packages/squid-js/package.json
new file mode 100644
index 0000000..63109c0
--- /dev/null
+++ b/packages/squid-js/package.json
@@ -0,0 +1,47 @@
+{
+  "name": "squid-js",
+  "version": "0.1.2",
+  "description": "Browser FHE client and Node evaluator over Squid. `squid-js/client` uses wasm; `squid-js/server` uses a napi-rs native addon.",
+  "type": "module",
+  "exports": {
+    "./client": {
+      "types": "./dist/client.d.ts",
+      "import": "./dist/client.js"
+    },
+    "./server": {
+      "browser": "./dist/server-browser-stub.js",
+      "types": "./dist/server.d.ts",
+      "import": "./dist/server.js"
+    },
+    "./wasm/*": "./wasm/*"
+  },
+  "files": [
+    "dist",
+    "wasm",
+    "napi",
+    "src"
+  ],
+  "napi": {
+    "name": "squid",
+    "triples": {
+      "defaults": true
+    }
+  },
+  "scripts": {
+    "build:wasm": "wasm-pack build ../../crates/squid-wasm --target web --out-dir ../../packages/squid-js/wasm --out-name squid_wasm && node -e \"try { require('fs').unlinkSync('wasm/.gitignore'); } catch (e) { if (e.code !== 'ENOENT') throw e; }\"",
+    "build:napi": "napi build --cargo-cwd ../../crates/squid-napi --platform --release --js index.js --dts index.d.ts napi && node -e \"require('fs').writeFileSync('napi/package.json', '{\\\"type\\\":\\\"commonjs\\\"}\\n')\"",
+    "build:ts": "tsc -p tsconfig.json",
+    "build": "pnpm run build:wasm && pnpm run build:napi && pnpm run build:ts",
+    "build:squid:linux": "bash scripts/build-linux-napi.sh",
+    "prepublishOnly": "pnpm run build && pnpm run build:squid:linux",
+    "dev": "tsc -p tsconfig.json --watch"
+  },
+  "devDependencies": {
+    "@napi-rs/cli": "^2.18.4",
+    "@types/node": "^22.7.5",
+    "typescript": "^5.6.3"
+  },
+  "engines": {
+    "node": ">=20"
+  }
+}
diff --git a/packages/squid-js/scripts/build-linux-napi.sh b/packages/squid-js/scripts/build-linux-napi.sh
new file mode 100644
index 0000000..31f52e5
--- /dev/null
+++ b/packages/squid-js/scripts/build-linux-napi.sh
@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+# Build the Linux Docker image, then copy napi/ from that image into this package (replaces napi/ contents).
+# Usage: packages/squid-js/scripts/build-linux-napi.sh [image-tag]   default: squid-linux:local
+set -euo pipefail
+PKG_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+REPO_ROOT="$(cd "$PKG_ROOT/../.." && pwd)"
+IMG="${1:-squid-linux:local}"
+
+echo "docker build: $REPO_ROOT -> $IMG"
+docker build --platform=linux/amd64 -f "$PKG_ROOT/build-linux-napi.Dockerfile" -t "$IMG" "$REPO_ROOT"
+
+echo "docker cp: $IMG napi/ -> $PKG_ROOT/napi/"
+cd "$PKG_ROOT"
+mkdir -p napi
+cid=$(docker create "$IMG")
+docker cp "$cid":/squid/packages/squid-js/napi/. napi/
+docker rm "$cid" >/dev/null
+echo "Done."
diff --git a/packages/squid-js/src/client.ts b/packages/squid-js/src/client.ts
new file mode 100644
index 0000000..4b56bf4
--- /dev/null
+++ b/packages/squid-js/src/client.ts
@@ -0,0 +1,132 @@
+import initWasm, { Session } from "../wasm/squid_wasm.js";
+
+let initPromise: Promise<void> | null = null;
+
+type Pending = Map<number, { resolve: (v: unknown) => void; reject: (e: Error) => void }>;
+
+function rpc(
+  worker: Worker,
+  pending: Pending,
+  id: number,
+  msg: object,
+  transfer?: Transferable[],
+): Promise<unknown> {
+  return new Promise((resolve, reject) => {
+    pending.set(id, { resolve, reject });
+    worker.postMessage({ ...msg, id }, transfer ?? []);
+  });
+}
+
+/** Main-thread wasm init; no-op when a Worker is used (wasm loads in the worker). */
+export function init(wasmUrl?: string | URL | Request): Promise<void> {
+  if (typeof Worker !== "undefined") return Promise.resolve();
+  return (initPromise ??= initWasm(wasmUrl ? { module_or_path: wasmUrl } : undefined).then(() => {}));
+}
+
+export interface CreateOptions {
+  seeds?: Uint8Array;
+  paramsSet: string;
+  wasmUrl?: string | URL | Request;
+}
+
+/** Browser: wasm + `Session` in a worker so crypto does not block the UI. No Worker: main thread after {@link init}. */
+export class PoulpyClient {
+  readonly evaluationKey: Uint8Array;
+  private readonly session: Session | null;
+  private readonly worker: Worker | null;
+  private nextId = 1;
+  private readonly pending: Pending;
+
+  private constructor(ek: Uint8Array, session: Session | null, worker: Worker | null, pending: Pending) {
+    this.evaluationKey = ek;
+    this.session = session;
+    this.worker = worker;
+    this.pending = pending;
+  }
+
+  static async create(opts: CreateOptions): Promise<PoulpyClient> {
+    if (typeof Worker !== "undefined") return PoulpyClient.#workerCreate(opts);
+    await init(opts.wasmUrl);
+    const { paramsSet } = opts;
+    const session = opts.seeds ? Session.fromSeeds(opts.seeds, paramsSet) : Session.newRandom(paramsSet);
+    return new PoulpyClient(session.evaluationKeyBytes(), session, null, new Map());
+  }
+
+  static async #workerCreate(opts: CreateOptions): Promise<PoulpyClient> {
+    const worker = new Worker(new URL("./squid-worker.js", import.meta.url), { type: "module" });
+    const pending: Pending = new Map();
+    const fail = (e: Error) => {
+      pending.forEach((p) => p.reject(e));
+      pending.clear();
+    };
+    worker.onmessage = (ev) => {
+      const d = ev.data as { id: number; ok: boolean; error?: string };
+      const p = pending.get(d.id);
+      if (!p) return;
+      pending.delete(d.id);
+      d.ok === false ? p.reject(new Error(d.error ?? "worker error")) : p.resolve(ev.data);
+    };
+    worker.onmessageerror = () => fail(new Error("squid-js: worker message error"));
+    worker.onerror = (e) => fail(new Error(e.message));
+
+    const seeds = opts.seeds?.slice().buffer;
+    let res: { evaluationKey?: ArrayBuffer };
+    try {
+      res = (await rpc(
+        worker,
+        pending,
+        0,
+        {
+          kind: "create",
+          paramsSet: opts.paramsSet,
+          seeds,
+          wasmUrl: opts.wasmUrl != null ? String(opts.wasmUrl) : undefined,
+        },
+        seeds ? [seeds] : [],
+      )) as { evaluationKey?: ArrayBuffer };
+    } catch (e) {
+      worker.terminate();
+      throw e;
+    }
+    const ek = res.evaluationKey;
+    if (!ek) {
+      worker.terminate();
+      throw new Error("squid-js: worker create missing evaluationKey");
+    }
+    return new PoulpyClient(new Uint8Array(ek), null, worker, pending);
+  }
+
+  #rpc<T>(msg: object, transfer?: Transferable[]): Promise<T> {
+    const w = this.worker;
+    if (!w) return Promise.reject(new Error("squid-js: no worker"));
+    return rpc(w, this.pending, this.nextId++, msg, transfer) as Promise<T>;
+  }
+
+  encryptU32(value: number): Promise<Uint8Array> {
+    if (!Number.isInteger(value) || value < 0 || value > 0xff_ff_ff_ff) {
+      return Promise.reject(new RangeError(`encryptU32: ${value} is out of u32 range`));
+    }
+    const s = this.session;
+    if (s) return Promise.resolve(s.encryptU32(value));
+    return this.#rpc<{ ciphertext: ArrayBuffer }>({ kind: "encrypt", value }).then(
+      (r) => new Uint8Array(r.ciphertext),
+    );
+  }
+
+  decryptU32(ciphertext: Uint8Array): Promise<number> {
+    const s = this.session;
+    if (s) return Promise.resolve(s.decryptU32(ciphertext));
+    const ct = ciphertext.slice();
+    return this.#rpc<{ value: number }>({ kind: "decrypt", ciphertext: ct.buffer }, [ct.buffer]).then(
+      (r) => r.value,
+    );
+  }
+
+  exportSeeds(): Promise<Uint8Array> {
+    const s = this.session;
+    if (s) return Promise.resolve(s.seeds());
+    return this.#rpc<{ seeds: ArrayBuffer }>({ kind: "exportSeeds" }).then((r) => new Uint8Array(r.seeds));
+  }
+}
+
+export { Session };
diff --git a/packages/squid-js/src/server-browser-stub.ts b/packages/squid-js/src/server-browser-stub.ts
new file mode 100644
index 0000000..057a8cd
--- /dev/null
+++ b/packages/squid-js/src/server-browser-stub.ts
@@ -0,0 +1,4 @@
+throw new Error(
+  "squid-js/server is the Node-only entry point (napi native addon); import squid-js/client in the browser.",
+);
+export {};
diff --git a/packages/squid-js/src/server.ts b/packages/squid-js/src/server.ts
new file mode 100644
index 0000000..ee6aeb0
--- /dev/null
+++ b/packages/squid-js/src/server.ts
@@ -0,0 +1,8 @@
+import { createRequire } from "node:module";
+import type { Evaluator as EvaluatorClass } from "../napi/index.js";
+
+const require = createRequire(import.meta.url);
+const addon = require("../napi/index.js") as { Evaluator: typeof EvaluatorClass };
+
+export const Evaluator = addon.Evaluator;
+export type Evaluator = EvaluatorClass;
diff --git a/packages/squid-js/src/squid-worker.ts b/packages/squid-js/src/squid-worker.ts
new file mode 100644
index 0000000..a6c1937
--- /dev/null
+++ b/packages/squid-js/src/squid-worker.ts
@@ -0,0 +1,54 @@
+import initWasm, { Session } from "../wasm/squid_wasm.js";
+
+const send = (msg: object, transfer?: Transferable[]) =>
+  (self as unknown as { postMessage: (m: object, t?: Transferable[]) => void }).postMessage(
+    msg,
+    transfer,
+  );
+
+let wasmReady = false;
+let session: Session | null = null;
+
+async function ensureWasm(url?: string) {
+  if (!wasmReady) {
+    await initWasm(url ? { module_or_path: url } : undefined);
+    wasmReady = true;
+  }
+}
+
+self.onmessage = async (ev: MessageEvent<Record<string, unknown>>) => {
+  const d = ev.data;
+  const id = d.id as number;
+  const kind = d.kind as string;
+  try {
+    if (kind === "create") {
+      await ensureWasm(d.wasmUrl as string | undefined);
+      session?.free();
+      session = d.seeds
+        ? Session.fromSeeds(new Uint8Array(d.seeds as ArrayBuffer), d.paramsSet as string)
+        : Session.newRandom(d.paramsSet as string);
+      const u = new Uint8Array(session.evaluationKeyBytes());
+      send({ id, ok: true, evaluationKey: u.buffer }, [u.buffer]);
+      return;
+    }
+    if (!session) throw new Error("squid-worker: no session");
+    if (kind === "encrypt") {
+      const u = new Uint8Array(session.encryptU32(d.value as number));
+      send({ id, ok: true, ciphertext: u.buffer }, [u.buffer]);
+    } else if (kind === "decrypt") {
+      const v = session.decryptU32(new Uint8Array(d.ciphertext as ArrayBuffer));
+      send({ id, ok: true, value: v });
+    } else if (kind === "exportSeeds") {
+      const u = new Uint8Array(session.seeds());
+      send({ id, ok: true, seeds: u.buffer }, [u.buffer]);
+    } else {
+      throw new Error(`squid-worker: unknown kind ${kind}`);
+    }
+  } catch (err) {
+    send({
+      id,
+      ok: false,
+      error: err instanceof Error ? err.message : String(err),
+    });
+  }
+};
diff --git a/packages/squid-js/tsconfig.json b/packages/squid-js/tsconfig.json
new file mode 100644
index 0000000..9e1fef2
--- /dev/null
+++ b/packages/squid-js/tsconfig.json
@@ -0,0 +1,21 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ES2022",
+    "moduleResolution": "Bundler",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "declaration": true,
+    "declarationMap": true,
+    "sourceMap": true,
+    "outDir": "dist",
+    "rootDir": "src",
+    "lib": ["ES2022", "DOM"],
+    "types": ["node"],
+    "allowJs": false,
+    "resolveJsonModule": true
+  },
+  "include": ["src/**/*.ts"],
+  "exclude": ["dist", "wasm", "napi", "node_modules"]
+}
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
new file mode 100644
index 0000000..329c6a4
--- /dev/null
+++ b/pnpm-lock.yaml
@@ -0,0 +1,910 @@
+lockfileVersion: '9.0'
+
+settings:
+  autoInstallPeers: true
+  excludeLinksFromLockfile: false
+
+importers:
+
+  .:
+    devDependencies:
+      concurrently:
+        specifier: ^9.0.1
+        version: 9.2.1
+      rimraf:
+        specifier: ^6.0.1
+        version: 6.1.3
+      typescript:
+        specifier: ^5.6.3
+        version: 5.9.3
+
+  demo:
+    dependencies:
+      next:
+        specifier: ^15.3.1
+        version: 15.5.15(@playwright/test@1.59.1)(react-dom@19.2.5(react@19.2.5))(react@19.2.5)
+      react:
+        specifier: ^19.0.0
+        version: 19.2.5
+      react-dom:
+        specifier: ^19.0.0
+        version: 19.2.5(react@19.2.5)
+      squid-js:
+        specifier: workspace:*
+        version: link:../packages/squid-js
+    devDependencies:
+      '@types/node':
+        specifier: ^22
+        version: 22.19.17
+      '@types/react':
+        specifier: ^19
+        version: 19.2.14
+      '@types/react-dom':
+        specifier: ^19
+        version: 19.2.3(@types/react@19.2.14)
+      typescript:
+        specifier: ^5.6.3
+        version: 5.9.3
+
+  packages/squid-js:
+    devDependencies:
+      '@napi-rs/cli':
+        specifier: ^2.18.4
+        version: 2.18.4
+      '@types/node':
+        specifier: ^22.7.5
+        version: 22.19.17
+      typescript:
+        specifier: ^5.6.3
+        version: 5.9.3
+
+  tests:
+    devDependencies:
+      '@playwright/test':
+        specifier: ^1.48.0
+        version: 1.59.1
+      '@types/node':
+        specifier: ^22.7.5
+        version: 22.19.17
+
+packages:
+
+  '@emnapi/runtime@1.10.0':
+    resolution: {integrity: sha512-ewvYlk86xUoGI0zQRNq/mC+16R1QeDlKQy21Ki3oSYXNgLb45GV1P6A0M+/s6nyCuNDqe5VpaY84BzXGwVbwFA==}
+
+  '@img/colour@1.1.0':
+    resolution: {integrity: sha512-Td76q7j57o/tLVdgS746cYARfSyxk8iEfRxewL9h4OMzYhbW4TAcppl0mT4eyqXddh6L/jwoM75mo7ixa/pCeQ==}
+    engines: {node: '>=18'}
+
+  '@img/sharp-darwin-arm64@0.34.5':
+    resolution: {integrity: sha512-imtQ3WMJXbMY4fxb/Ndp6HBTNVtWCUI0WdobyheGf5+ad6xX8VIDO8u2xE4qc/fr08CKG/7dDseFtn6M6g/r3w==}
+    engines: {node: ^18.17.0 || ^20.3.0 || >=21.0.0}
+    cpu: [arm64]
+    os: [darwin]
+
+  '@img/sharp-darwin-x64@0.34.5':
+    resolution: {integrity: sha512-YNEFAF/4KQ/PeW0N+r+aVVsoIY0/qxxikF2SWdp+NRkmMB7y9LBZAVqQ4yhGCm/H3H270OSykqmQMKLBhBJDEw==}
+    engines: {node: ^18.17.0 || ^20.3.0 || >=21.0.0}
+    cpu: [x64]
+    os: [darwin]
+
+  '@img/sharp-libvips-darwin-arm64@1.2.4':
+    resolution: {integrity: sha512-zqjjo7RatFfFoP0MkQ51jfuFZBnVE2pRiaydKJ1G/rHZvnsrHAOcQALIi9sA5co5xenQdTugCvtb1cuf78Vf4g==}
+    cpu: [arm64]
+    os: [darwin]
+
+  '@img/sharp-libvips-darwin-x64@1.2.4':
+    resolution: {integrity: sha512-1IOd5xfVhlGwX+zXv2N93k0yMONvUlANylbJw1eTah8K/Jtpi15KC+WSiaX/nBmbm2HxRM1gZ0nSdjSsrZbGKg==}
+    cpu: [x64]
+    os: [darwin]
+
+  '@img/sharp-libvips-linux-arm64@1.2.4':
+    resolution: {integrity: sha512-excjX8DfsIcJ10x1Kzr4RcWe1edC9PquDRRPx3YVCvQv+U5p7Yin2s32ftzikXojb1PIFc/9Mt28/y+iRklkrw==}
+    cpu: [arm64]
+    os: [linux]
+
+  '@img/sharp-libvips-linux-arm@1.2.4':
+    resolution: {integrity: sha512-bFI7xcKFELdiNCVov8e44Ia4u2byA+l3XtsAj+Q8tfCwO6BQ8iDojYdvoPMqsKDkuoOo+X6HZA0s0q11ANMQ8A==}
+    cpu: [arm]
+    os: [linux]
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+    optional: true
+
+  '@img/sharp-linuxmusl-x64@0.34.5':
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+    optional: true
+
+  '@img/sharp-wasm32@0.34.5':
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+      picocolors: 1.1.1
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+      scheduler: 0.27.0
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+    optional: true
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+      detect-libc: 2.1.2
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+      '@img/sharp-linuxmusl-arm64': 0.34.5
+      '@img/sharp-linuxmusl-x64': 0.34.5
+      '@img/sharp-wasm32': 0.34.5
+      '@img/sharp-win32-arm64': 0.34.5
+      '@img/sharp-win32-ia32': 0.34.5
+      '@img/sharp-win32-x64': 0.34.5
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+      is-fullwidth-code-point: 3.0.0
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+    dependencies:
+      ansi-regex: 5.0.1
+
+  styled-jsx@5.1.6(react@19.2.5):
+    dependencies:
+      client-only: 0.0.1
+      react: 19.2.5
+
+  supports-color@7.2.0:
+    dependencies:
+      has-flag: 4.0.0
+
+  supports-color@8.1.1:
+    dependencies:
+      has-flag: 4.0.0
+
+  tree-kill@1.2.2: {}
+
+  tslib@2.8.1: {}
+
+  typescript@5.9.3: {}
+
+  undici-types@6.21.0: {}
+
+  wrap-ansi@7.0.0:
+    dependencies:
+      ansi-styles: 4.3.0
+      string-width: 4.2.3
+      strip-ansi: 6.0.1
+
+  y18n@5.0.8: {}
+
+  yargs-parser@21.1.1: {}
+
+  yargs@17.7.2:
+    dependencies:
+      cliui: 8.0.1
+      escalade: 3.2.0
+      get-caller-file: 2.0.5
+      require-directory: 2.1.1
+      string-width: 4.2.3
+      y18n: 5.0.8
+      yargs-parser: 21.1.1
diff --git a/pnpm-workspace.yaml b/pnpm-workspace.yaml
new file mode 100644
index 0000000..5c0355a
--- /dev/null
+++ b/pnpm-workspace.yaml
@@ -0,0 +1,4 @@
+packages:
+  - "packages/*"
+  - "demo"
+  - "tests"
diff --git a/tests/index.spec.ts b/tests/index.spec.ts
new file mode 100644
index 0000000..61dd427
--- /dev/null
+++ b/tests/index.spec.ts
@@ -0,0 +1,43 @@
+import { test, expect } from "@playwright/test";
+
+// Keygen runs in a wasm worker; duration depends on the chosen `paramsSet`
+// (demo default `test`). Allow extra time for cold CI / slow runners.
+const KEYGEN_TIMEOUT_MS = 30_000;
+const COMPUTE_TIMEOUT_MS = 15_000;
+
+test.setTimeout(KEYGEN_TIMEOUT_MS + COMPUTE_TIMEOUT_MS + 30_000);
+
+test("browser keygen → server FHE add → browser decrypt", async ({ page }) => {
+  page.on("pageerror", (err) => console.log(`[e2e] pageerror: ${err.message}`));
+  page.on("requestfailed", (req) =>
+    console.log(
+      `[e2e] requestfailed: ${req.method()} ${req.url()} — ${req.failure()?.errorText}`,
+    ),
+  );
+
+  await page.goto("/");
+
+  // Step 1 — derive keys from demo seed (WASM keygen in worker, may take a while)
+  await page.getByRole("button", { name: /Derive keys/i }).click();
+  await expect(
+    page.getByRole("button", { name: /Encrypt a & b/i }),
+  ).toBeEnabled({ timeout: KEYGEN_TIMEOUT_MS });
+
+  // Step 2 — encrypt (defaults: a=7, b=5)
+  await page.getByRole("button", { name: /Encrypt a & b/i }).click();
+  await expect(
+    page.getByRole("button", { name: /Send & evaluate/i }),
+  ).toBeEnabled({ timeout: 10_000 });
+
+  // Step 3 — send to server and evaluate homomorphically
+  await page.getByRole("button", { name: /Send & evaluate/i }).click();
+  await expect(
+    page.getByRole("button", { name: /Decrypt result/i }),
+  ).toBeEnabled({ timeout: COMPUTE_TIMEOUT_MS });
+
+  // Step 4 — decrypt result locally; 7 + 5 = 12
+  await page.getByRole("button", { name: /Decrypt result/i }).click();
+  await expect(page.getByTestId("decrypt-result")).toHaveText("12", {
+    timeout: 10_000,
+  });
+});
diff --git a/tests/package.json b/tests/package.json
new file mode 100644
index 0000000..4a900c9
--- /dev/null
+++ b/tests/package.json
@@ -0,0 +1,15 @@
+{
+  "name": "@squid-js/e2e",
+  "version": "0.1.0",
+  "private": true,
+  "description": "End-to-end tests for the squid-js client/server demo.",
+  "type": "module",
+  "scripts": {
+    "pretest": "playwright install chromium",
+    "test": "playwright test"
+  },
+  "devDependencies": {
+    "@playwright/test": "^1.48.0",
+    "@types/node": "^22.7.5"
+  }
+}
diff --git a/tests/playwright.config.ts b/tests/playwright.config.ts
new file mode 100644
index 0000000..365b853
--- /dev/null
+++ b/tests/playwright.config.ts
@@ -0,0 +1,21 @@
+import { defineConfig } from "@playwright/test";
+
+// The root `pnpm dev` runs the Next.js demo; reuseExistingServer lets a
+// developer keep it open and just run `pnpm test` on the side.
+export default defineConfig({
+  testDir: ".",
+  timeout: 120_000,
+  fullyParallel: false,
+  workers: 1,
+  use: {
+    baseURL: "http://localhost:3000",
+  },
+  webServer: {
+    command: "pnpm -w dev",
+    url: "http://localhost:3000",
+    reuseExistingServer: !process.env.CI,
+    timeout: 120_000,
+    stdout: "pipe",
+    stderr: "pipe",
+  },
+});
diff --git a/tests/tsconfig.json b/tests/tsconfig.json
new file mode 100644
index 0000000..4f0a331
--- /dev/null
+++ b/tests/tsconfig.json
@@ -0,0 +1,11 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "Bundler",
+    "strict": true,
+    "noEmit": true,
+    "skipLibCheck": true
+  },
+  "include": ["playwright.config.ts", "index.spec.ts"]
+}