Adds Flagsmith adapter

.changeset/dull-kings-pump.md

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+---
+'@flags-sdk/flagsmith': major
+'flags': minor
+---
+
+Adds Flagsmith Adapter

packages/adapter-flagsmith/.eslintrc.cjs

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+module.exports = {
+  root: true,
+  extends: [require.resolve('@pyra/eslint-config/components')],
+};

packages/adapter-flagsmith/.gitignore

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+.vercel
+.env*.local

packages/adapter-flagsmith/README.md

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+# Flags SDK - Flagsmith Provider
+
+A provider adapter for the Flags SDK that integrates with [Flagsmith](https://flagsmith.com/), allowing you to use Flagsmith's feature flags and remote configuration in your application.
+
+## Installation
+
+```bash
+npm install @flags-sdk/flagsmith
+```
+
+## Usage
+
+An Environment ID must be provided using the `FLAGSMITH_ENVIRONMENT_ID` environment variable.
+
+```typescript
+import { flagsmithAdapter } from '@flags-sdk/flagsmith';
+import { flag } from 'flags';
+
+// Boolean flags - returns flagState.enabled
+const myBooleanFlag = flag({
+  key: 'my-boolean-feature',
+  adapter: flagsmithAdapter.booleanValue(),
+});
+
+// String flags - returns flagState.value when enabled
+const myStringFlag = flag({
+  key: 'my-string-feature',
+  adapter: flagsmithAdapter.stringValue(),
+});
+
+// Number flags - returns flagState.value when enabled
+const myNumberFlag = flag({
+  key: 'my-number-feature',
+  adapter: flagsmithAdapter.numberValue(),
+});
+```
+
+## API
+
+The adapter provides three methods for different flag types:
+
+### `booleanValue()`
+
+Returns an adapter for boolean flags. Uses `flagState.enabled` directly.
+
+```typescript
+const booleanAdapter = flagsmithAdapter.booleanValue();
+const value = await booleanAdapter.decide({
+  key: 'my-flag',
+  defaultValue: false,
+  entities: { identifier: 'user-123' },
+});
+```
+
+### `stringValue()`
+
+Returns an adapter for string flags. Returns `flagState.value` when the flag is enabled, otherwise returns the default value.
+
+```typescript
+const stringAdapter = flagsmithAdapter.stringValue();
+const value = await stringAdapter.decide({
+  key: 'my-flag',
+  defaultValue: 'default',
+  entities: { identifier: 'user-123' },
+});
+```
+
+### `numberValue()`
+
+Returns an adapter for number flags. Returns `flagState.value` when the flag is enabled, otherwise returns the default value.
+
+```typescript
+const numberAdapter = flagsmithAdapter.numberValue();
+const value = await numberAdapter.decide({
+  key: 'my-flag',
+  defaultValue: 0,
+  entities: { identifier: 'user-123' },
+});
+```
+
+## Identity Handling
+
+The adapter supports Flagsmith identity management. Pass an `IIdentity` object to the `entities` parameter:
+
+```typescript
+const identity: IIdentity = {
+  identifier: 'user-123',
+  traits: {
+    email: 'user@example.com',
+    plan: 'premium',
+  },
+};
+
+const value = await adapter.decide({
+  key: 'my-flag',
+  defaultValue: false,
+  entities: identity,
+});
+```
+
+## Configuration
+
+The adapter automatically initializes Flagsmith with the following configuration:
+
+- `environmentId`: From `FLAGSMITH_ENVIRONMENT_ID` environment variable
+
+## Features
+
+- **Type-safe flag definitions**: Each method returns a properly typed adapter
+- **Automatic initialization**: Flagsmith client can be lazily initialized
+- **Identity support**: Full support for Flagsmith identity and traits
+- **Default value handling**: Proper fallback to default values when flags are disabled or not found
+- **Boolean flag optimization**: Boolean flags use the `enabled` state directly for better performance
+
+## Environment Variables
+
+- `FLAGSMITH_ENVIRONMENT_ID` (required): Your Flagsmith environment ID
+
+## License
+
+MIT

packages/adapter-flagsmith/package.json

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+{
+  "name": "@flags-sdk/flagsmith",
+  "version": "0.1.0",
+  "description": "Flagsmith provider for the Flags SDK",
+  "keywords": [
+    "flags-sdk",
+    "flagsmith-nodejs",
+    "vercel",
+    "feature flags",
+    "flags"
+  ],
+  "homepage": "https://flags-sdk.dev",
+  "bugs": {
+    "url": "https://github.com/vercel/flags/issues"
+  },
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/vercel/flags.git"
+  },
+  "license": "MIT",
+  "author": "",
+  "sideEffects": false,
+  "type": "module",
+  "exports": {
+    ".": {
+      "import": "./dist/index.js",
+      "require": "./dist/index.cjs"
+    }
+  },
+  "main": "./dist/index.js",
+  "typesVersions": {
+    "*": {
+      ".": [
+        "dist/*.d.ts",
+        "dist/*.d.cts"
+      ]
+    }
+  },
+  "files": [
+    "dist",
+    "CHANGELOG.md"
+  ],
+  "scripts": {
+    "build": "rimraf dist && tsup",
+    "dev": "tsup --watch --clean=false",
+    "eslint": "eslint-runner",
+    "eslint:fix": "eslint-runner --fix",
+    "test": "vitest --run",
+    "test:watch": "vitest",
+    "type-check": "tsc --noEmit"
+  },
+  "dependencies": {
+    "flagsmith": "^9.0.5"
+  },
+  "devDependencies": {
+    "@types/node": "20.11.17",
+    "eslint-config-custom": "workspace:*",
+    "flags": "workspace:*",
+    "msw": "2.6.4",
+    "rimraf": "6.0.1",
+    "tsconfig": "workspace:*",
+    "tsup": "8.0.1",
+    "typescript": "5.6.3",
+    "vite": "5.1.1",
+    "vitest": "1.4.0"
+  },
+  "publishConfig": {
+    "access": "public"
+  }
+}