Fix immutable header on static image (vercel#25914)

This PR fixes a bug where the first request has the correct immutable header but subsequent requests do not.

Depends on vercel#25909

packages/next/next-server/server/image-optimizer.ts

@@ -163,7 +163,12 @@ export async function imageOptimizer(
         const contentType = getContentType(extension)
         const fsPath = join(hashDir, file)
         if (now < expireAt) {
-          res.setHeader('Cache-Control', 'public, max-age=0, must-revalidate')
+          res.setHeader(
+            'Cache-Control',
+            isStatic
+              ? 'public, max-age=315360000, immutable'
+              : 'public, max-age=0, must-revalidate'
+          )
           if (sendEtagResponse(req, res, etag)) {
             return { finished: true }
           }

test/integration/image-optimizer/test/index.test.js

@@ -512,11 +512,21 @@ function runTests({ w, isDev, domains }) {
         q: 100,
       }
       const opts = { headers: { accept: 'image/webp' } }
-      const res = await fetchViaHTTP(appPort, '/_next/image', query, opts)
-      expect(res.status).toBe(200)
-      expect(res.headers.get('cache-control')).toBe(
+
+      const res1 = await fetchViaHTTP(appPort, '/_next/image', query, opts)
+      expect(res1.status).toBe(200)
+      expect(res1.headers.get('cache-control')).toBe(
+        'public, max-age=315360000, immutable'
+      )
+      await expectWidth(res1, w)
+
+      // Ensure subsequent request also has immutable header
+      const res2 = await fetchViaHTTP(appPort, '/_next/image', query, opts)
+      expect(res2.status).toBe(200)
+      expect(res2.headers.get('cache-control')).toBe(
         'public, max-age=315360000, immutable'
       )
+      await expectWidth(res2, w)
     }
   })