base: experimentally add .cursor/rules.

.cursor/rules/deno-testing.mdc

@@ -0,0 +1,46 @@
+---
+description: Mandatory Deno-based testing requirements for HPKE-JS code modifications
+globs: ["**/*.ts", "**/*.js", "test/**/*"]
+alwaysApply: true
+---
+
+# Deno Testing Requirements for HPKE-JS
+
+## Mandatory Testing for Code Changes
+- All code modifications MUST be accompanied by appropriate tests to verify functionality
+- Tests MUST be written using Deno's native testing framework
+- Use `@std/testing/bdd` for behavior-driven testing when appropriate
+- Use `@std/assert` for assertions
+
+## Deno Task Usage
+- ALWAYS use the predefined Deno tasks from `deno.json` instead of running commands directly
+- Primary testing command: `deno task test:deno` for comprehensive testing
+- For specific package testing, use: `deno task test:deno:<package-name>`
+
+Available package-specific test tasks:
+- `deno task test:deno:common`
+- `deno task test:deno:core`
+- `deno task test:deno:chacha20poly1305`
+- `deno task test:deno:dhkem-x25519`
+- `deno task test:deno:dhkem-x448`
+- `deno task test:deno:dhkem-secp256k1`
+- `deno task test:deno:hybridkem-x-wing`
+- `deno task test:deno:hpke-js`
+- `deno task test:deno:ml-kem`
+
+## Testing Workflow
+1. Before making changes: Run relevant tests to establish baseline
+2. After making changes: Run tests to verify functionality
+3. Use `deno task test:deno` for full project testing
+4. Use package-specific tasks for focused testing during development
+
+## Test File Conventions
+- Test files MUST be placed in the `test/` directory within each package
+- Test files MUST follow the naming convention: `*.test.ts`
+- Import test utilities from `@std/assert` and `@std/testing/bdd`
+
+## Code Quality Integration
+- `deno task test:deno` includes formatting, linting, type checking, and tests
+- Individual quality checks: `deno task check` for type checking
+- Coverage enabled with `--coverage=coverage`
+- Use `deno task cov` to generate coverage reports

.cursor/rules/development-workflow.mdc

@@ -0,0 +1,28 @@
+---
+description: Development workflow standards for HPKE-JS project
+globs: ["src/**/*", "test/**/*"]
+alwaysApply: false
+---
+
+# Development Workflow Standards
+
+## Pre-Commit Testing
+- Run `deno task test:deno` before committing changes
+- Ensure all tests pass before requesting code reviews
+- Use package-specific tasks during active development for faster feedback
+
+## Error Handling Protocol
+- If tests fail, investigate and fix issues before proceeding
+- Check both test logic and implementation code
+- Use `deno task check` to identify type-related issues
+- Use formatting and linting to catch style issues
+
+## Multi-Runtime Considerations
+- For significant changes, consider running the full test suite: `deno task test`
+- This includes Deno, Node.js, browser, Cloudflare Workers, and Bun testing
+- For quick iterations, focus on Deno tests: `deno task test:deno`
+
+## Test Execution Features
+- Tests run with `--fail-fast` flag for quick feedback
+- Tests run with `--parallel` flag for faster execution
+- Tests include documentation tests (`--doc`) to verify code examples

.cursor/rules/package-specific-testing.mdc

@@ -0,0 +1,30 @@
+---
+description: Package-specific testing guidance for HPKE-JS components
+globs: ["packages/*/src/**/*", "packages/*/test/**/*"]
+alwaysApply: false
+---
+
+# Package-Specific Testing Guidance
+
+## Available Packages and Test Commands
+
+### Core Packages
+- **common**: `deno task test:deno:common` - Common utilities and base functionality
+- **core**: `deno task test:deno:core` - Core HPKE implementation
+- **hpke-js**: `deno task test:deno:hpke-js` - Main HPKE library
+
+### Cryptographic Packages
+- **chacha20poly1305**: `deno task test:deno:chacha20poly1305` - ChaCha20-Poly1305 AEAD
+- **dhkem-x25519**: `deno task test:deno:dhkem-x25519` - X25519 DHKEM
+- **dhkem-x448**: `deno task test:deno:dhkem-x448` - X448 DHKEM
+- **dhkem-secp256k1**: `deno task test:deno:dhkem-secp256k1` - secp256k1 DHKEM
+- **ml-kem**: `deno task test:deno:ml-kem` - ML-KEM post-quantum cryptography
+
+### Hybrid KEM Packages
+- **hybridkem-x-wing**: `deno task test:deno:hybridkem-x-wing` - X-Wing hybrid KEM
+
+## Package-Specific Development Tips
+- Use focused package testing during active development
+- Run individual package tests for faster feedback loops
+- Each package has its own `test/` directory with `*.test.ts` files
+- Package tests include conformance tests for cryptographic standards

.cursor/rules/test-templates.mdc

@@ -0,0 +1,74 @@
+---
+description: Test file templates and patterns for HPKE-JS
+globs: ["test/**/*.ts", "**/*.test.ts"]
+alwaysApply: false
+---
+
+# Test File Templates and Patterns
+
+## Basic Test Structure
+Use this template when creating new test files:
+
+```typescript
+import { assertEquals, assertRejects, assertThrows } from "@std/assert";
+import { describe, it } from "@std/testing/bdd";
+
+describe("YourModule", () => {
+  it("should perform expected behavior", () => {
+    // Arrange
+    const input = "test input";
+
+    // Act
+    const result = yourFunction(input);
+
+    // Assert
+    assertEquals(result, expectedOutput);
+  });
+
+  it("should handle error cases", () => {
+    assertThrows(() => {
+      yourFunction(invalidInput);
+    }, Error, "Expected error message");
+  });
+});
+```
+
+## Async Test Pattern
+For testing asynchronous operations:
+
+```typescript
+import { assertEquals } from "@std/assert";
+import { describe, it } from "@std/testing/bdd";
+
+describe("AsyncModule", () => {
+  it("should handle async operations", async () => {
+    const result = await yourAsyncFunction();
+    assertEquals(result, expectedValue);
+  });
+
+  it("should reject with proper error", async () => {
+    await assertRejects(
+      async () => await yourAsyncFunction(invalidInput),
+      Error,
+      "Expected error message"
+    );
+  });
+});
+```
+
+## Import Patterns
+Standard imports for HPKE-JS tests:
+
+```typescript
+// For assertions
+import { assertEquals, assertRejects, assertThrows } from "@std/assert";
+
+// For BDD-style tests
+import { describe, it, beforeEach, afterEach } from "@std/testing/bdd";
+
+// For cryptographic testing
+import { CipherSuite } from "../src/cipherSuite.ts";
+import type { AeadInterface } from "../src/interfaces/aeadInterface.ts";
+```
+
+@packages/common/test/hmac.test.ts