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+---
+epic: 9
+story: 9.1
+title: "WASM Engine Integration"
+status: draft
+---
+
+## Epic 9 — Web App (React + WASM)
+**Goal:** Zero-install web experience with real-time collaboration.
+
+### Story 9.1: WASM Engine Integration
+
+As a web user,
+I want the CalcPad engine running natively in my browser via WebAssembly,
+So that I get full calculation fidelity without installing anything.
+
+**Acceptance Criteria:**
+
+**Given** the calcpad-engine Rust crate is configured with wasm-pack targets
+**When** the WASM module is compiled with `wasm-pack build --target web`
+**Then** a valid `.wasm` binary and JS glue code are produced
+**And** the gzipped WASM bundle is less than 500KB
+
+**Given** the web app is loaded in a browser
+**When** the WASM engine is initialized
+**Then** it is loaded inside a dedicated Web Worker thread
+**And** the main UI thread remains unblocked during computation
+
+**Given** the WASM engine is running in a Web Worker
+**When** the UI sends an evaluation request
+**Then** communication occurs via `postMessage` serialization
+**And** the worker returns the computed result back to the main thread via `postMessage`
+
+**Given** the WASM engine is initialized in the worker
+**When** a user types a valid CalcPad expression
+**Then** the engine evaluates it with identical results to the native Rust engine
+**And** all supported operations (arithmetic, units, conversions, variables, functions) produce matching output