fix: toolchain caching

Signed-off-by: Sam Gammon <sam@elide.ventures>

Author: sgammon

__tests__/releases-download.test.ts

@@ -56,9 +56,8 @@ mock.module('../src/command', () => ({
   elideInfo: jest.fn()
 }))
 
-const { downloadRelease, resolveLatestVersion } = await import(
-  '../src/releases'
-)
+const { downloadRelease, resolveLatestVersion, toSemverCacheKey } =
+  await import('../src/releases')
 const { default: buildOptions } = await import('../src/options')
 
 describe('resolveLatestVersion', () => {
@@ -116,6 +115,28 @@ describe('resolveLatestVersion', () => {
   })
 })
 
+describe('toSemverCacheKey', () => {
+  it('should pass through valid semver', () => {
+    expect(toSemverCacheKey('1.0.0')).toBe('1.0.0')
+    expect(toSemverCacheKey('1.0.0-beta10')).toBe('1.0.0-beta10')
+    expect(toSemverCacheKey('1.0.0-alpha9')).toBe('1.0.0-alpha9')
+    expect(toSemverCacheKey('2.1.3')).toBe('2.1.3')
+  })
+
+  it('should convert nightly tags to semver prerelease', () => {
+    expect(toSemverCacheKey('nightly-20260328')).toBe('0.0.0-nightly.20260328')
+    expect(toSemverCacheKey('nightly-2026-03-28')).toBe(
+      '0.0.0-nightly.20260328'
+    )
+    expect(toSemverCacheKey('nightly-20251231')).toBe('0.0.0-nightly.20251231')
+  })
+
+  it('should pass through unknown formats unchanged', () => {
+    expect(toSemverCacheKey('dev')).toBe('dev')
+    expect(toSemverCacheKey('custom-build')).toBe('custom-build')
+  })
+})
+
 describe('downloadRelease', () => {
   beforeEach(() => {
     debugMock.mockClear()
@@ -426,6 +447,59 @@ describe('downloadRelease', () => {
       expect(downloadToolMock).not.toHaveBeenCalled()
     })
 
+    it('nightly versions should use semver cache keys', async () => {
+      findMock.mockReturnValue('')
+      requestMock.mockResolvedValue({
+        data: { tag_name: 'nightly-20260328', name: 'Nightly' }
+      })
+      const options = buildOptions({
+        os: 'linux',
+        arch: 'amd64',
+        version: 'latest'
+      })
+      await downloadRelease(options)
+
+      // find should be called with the semver cache key, not the raw tag
+      expect(findMock).toHaveBeenCalledWith(
+        'elide',
+        '0.0.0-nightly.20260328',
+        'amd64'
+      )
+      // cacheDir should also use the semver key
+      expect(cacheDirMock).toHaveBeenCalledWith(
+        expect.any(String),
+        'elide',
+        '0.0.0-nightly.20260328',
+        'amd64'
+      )
+    })
+
+    it('second run with nightly should hit cache', async () => {
+      findMock.mockReturnValue(
+        '/cache/tools/elide/0.0.0-nightly.20260328/amd64'
+      )
+      requestMock.mockResolvedValue({
+        data: { tag_name: 'nightly-20260328', name: 'Nightly' }
+      })
+      const options = buildOptions({
+        os: 'linux',
+        arch: 'amd64',
+        version: 'latest'
+      })
+      const result = await downloadRelease(options)
+
+      expect(findMock).toHaveBeenCalledWith(
+        'elide',
+        '0.0.0-nightly.20260328',
+        'amd64'
+      )
+      expect(downloadToolMock).not.toHaveBeenCalled()
+      expect(result.cached).toBe(true)
+      expect(result.elideBin).toBe(
+        '/cache/tools/elide/0.0.0-nightly.20260328/amd64/bin'
+      )
+    })
+
     it('different architectures should not share cache', async () => {
       findMock.mockImplementation(
         (_name: string, _version: string, arch: string) => {

src/releases.ts

@@ -16,6 +16,34 @@ const GITHUB_DEFAULT_HEADERS = {
   'X-GitHub-Api-Version': GITHUB_API_VERSION
 }
 
+// Matches tags like "nightly-20260328" or "nightly-2026-03-28"
+const NIGHTLY_TAG_RE = /^nightly-(.+)$/
+
+/**
+ * Convert a release tag to a valid semver string for use with @actions/tool-cache.
+ *
+ * tool-cache's `find()` calls `semver.clean()` on the version, which returns null
+ * for non-semver strings like "nightly-20260328". This causes cache lookups to
+ * silently fail (never hit, never store correctly).
+ *
+ * Mapping:
+ *   "1.0.0"              → "1.0.0"          (already semver)
+ *   "1.0.0-beta10"       → "1.0.0-beta10"   (valid semver prerelease)
+ *   "nightly-20260328"   → "0.0.0-nightly.20260328"
+ *
+ * We use prerelease (not build metadata with +) because semver.clean strips
+ * build metadata, making it useless for cache key matching.
+ */
+export function toSemverCacheKey(tag: string): string {
+  const nightlyMatch = tag.match(NIGHTLY_TAG_RE)
+  if (nightlyMatch) {
+    // Use prerelease segment so semver.clean preserves it
+    const datePart = nightlyMatch[1].replaceAll('-', '')
+    return `0.0.0-nightly.${datePart}`
+  }
+  return tag
+}
+
 /**
  * Version info resolved for a release of Elide.
  */
@@ -359,12 +387,13 @@ async function maybeDownload(
   let elidePathTarget = elideHome
   let elideBin: string = `${elideHome}${sep}bin`
   let elideDir: string | null = null
+  const cacheVersion = toSemverCacheKey(version.tag_name)
 
   try {
     core.debug(
-      `Checking for cached tool 'elide' at version '${version.tag_name}'`
+      `Checking for cached tool 'elide' at version '${version.tag_name}' (cache key: ${cacheVersion})`
     )
-    elideDir = toolCache.find('elide', version.tag_name, options.arch)
+    elideDir = toolCache.find('elide', cacheVersion, options.arch)
   } catch (err) {
     core.debug(`Failed to locate Elide in tool cache: ${err}`)
   }
@@ -412,7 +441,7 @@ async function maybeDownload(
       const cachedPath = await toolCache.cacheDir(
         elideHome,
         'elide',
-        version.tag_name,
+        cacheVersion,
         options.arch
       )