Display version number that introduced schema

site/src/components/explorer/VersionLink.astro

@@ -0,0 +1,23 @@
+---
+import options from 'src/options.json';
+const { version } = Astro.props;
+const url = `${options.git.githubRepoUrl}/releases/tag/${version}`;
+---
+
+<style>
+  .VersionLink {
+    display: inline-block;
+    padding-inline: var(--space-xs);
+    border-radius: var(--radius-full);
+    font-size: var(--font-size-sm);
+    background-color: var(--color-bg-elevated);
+    border: 1px solid var(--color-border-default);
+    color: var(--color-fg-muted);
+    text-decoration: none;
+    font-weight: 400;
+  }
+</style>
+
+<a class="VersionLink" href={url} noreferrer noopener>
+  Since {version}
+</a>

site/src/components/page/SchemaPageHeader.astro

@@ -0,0 +1,38 @@
+---
+import path from 'node:path';
+import { getGitFirstTag } from 'astro-theme-docs';
+import VersionLink from '@components/explorer/VersionLink.astro';
+
+const { schema } = Astro.props;
+
+let firstVersion = null;
+const schemaPath = path.join('followthemoney', 'schema', `${schema.name}.yaml`);
+
+try {
+  firstVersion = await getGitFirstTag(schemaPath);
+} catch (error) {}
+---
+
+<style>
+  .SchemaPageHeader {
+    display: flex;
+    flex-direction: column;
+    row-gap: var(--space-sm);
+    align-items: start;
+  }
+
+  .SchemaPageHeader__name {
+    margin-block-end: 0;
+  }
+</style>
+
+<header class="SchemaPageHeader">
+  <h1 class="SchemaPageHeader__name alpha">{schema.label}</h1>
+  {firstVersion && <VersionLink version={firstVersion} />}
+
+  {
+    schema.description && (
+      <p class="SchemaPageHeader__description lead">{schema.description}</p>
+    )
+  }
+</header>

site/src/pages/explorer/schemata/[name].astro

@@ -2,6 +2,7 @@
 import { model } from '@util/ftm';
 import { Stack, TocNav } from 'astro-theme-docs/components';
 import ExplorerLayout from '@layouts/ExplorerLayout.astro';
+import SchemaPageHeader from '@components/page/SchemaPageHeader.astro';
 import SchemaExtends from '@components/explorer/SchemaExtends.astro';
 import SchemaSemantics from '@components/explorer/SchemaSemantics.astro';
 import SchemaProperties from '@components/explorer/SchemaProperties.astro';
@@ -27,11 +28,7 @@ const headings = [
   <TocNav {headings} slot="toc" />
 
   <Stack size="xl">
-    <header>
-      <h1 class="alpha">{schema.label}</h1>
-      {schema.description && <p class="lead">{schema.description}</p>}
-    </header>
-
+    <SchemaPageHeader schema={schema} />
     <SchemaExtends id="inheritance" schema={schema} />
     <SchemaSemantics id="semantics" schema={schema} />
     <SchemaProperties id="properties" schema={schema} />