# Contract: Build Version Display

Version: 1.0

## Purpose

Every web application must display the current build version in the page footer so that users and support staff can identify exactly which version is running.

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## Rule

The build version **must** be visible in the footer on every page of the web application.

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## Requirements

- The version is shown in the footer on **all** pages, including error pages (404, 500, etc.).
- The version string is injected at **build time** — it is never hardcoded in source and never fetched at runtime.
- The version value comes from a single authoritative source (e.g. `package.json`, `version.go`, a CI environment variable). It is not duplicated manually.
- Format: any human-readable string that uniquely identifies the build — a semver tag, a git commit SHA, or a combination (e.g. `1.4.2`, `1.4.2-abc1234`, `abc1234`).
- The version text must be legible but visually subordinate — use a muted color and small font size so it does not compete with page content.

---

## Recommended implementation

**Frontend (JS/TS build tools)**

Expose the version through an environment variable at build time and reference it in the footer component:

```ts
// vite.config.ts / webpack.config.js
define: {
  __APP_VERSION__: JSON.stringify(process.env.APP_VERSION ?? "dev"),
}

// Footer component
<footer>v{__APP_VERSION__}</footer>
```

**Go (server-rendered HTML)**

Inject via `-ldflags` at build time and pass to the template:

```go
// main.go
var Version = "dev"

// Build: go build -ldflags "-X main.Version=1.4.2"
```

```html
<!-- base template -->
<footer>v{{ .Version }}</footer>
```

---

## What is NOT allowed

- Omitting the version from any page, including error pages.
- Fetching the version from an API endpoint at runtime (network dependency for a static value).
- Hardcoding a version string in source code.
- Storing the version in more than one place.