simplify: drop SWR cache, always upload fresh to S3

Always overwrites S3 on every preview request — no stale content.
Removed sync.Map cache and background goroutines.
Blob-by-SHA paths still skip upload if already exists (immutable).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

routers/web/repo/preview.go

@@ -8,7 +8,6 @@ import (
 	"io"
 	"net/http"
 	"os"
-	"sync"
 
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/log"
@@ -18,19 +17,8 @@ import (
 	"code.gitea.io/gitea/services/context"
 )
 
-// previewCache tracks known blob SHAs on S3 to skip Stat calls.
+// HTMLPreview serves an HTML file via S3.
-// Key: S3 object path, Value: blob SHA that was uploaded.
+// Always uploads the current blob (overwrite), then redirects to presigned S3 URL.
-var previewCache sync.Map
-
-// HTMLPreview serves an HTML file via S3 with stale-while-revalidate caching.
-//
-// Flow:
-//  1. Resolve the git blob for the requested file path
-//  2. Build the S3 object key: preview/{owner}/{repo}/{path}
-//  3. Check in-memory cache for the blob SHA
-//  4. HIT+fresh (SHA matches current blob) → redirect to S3 presigned URL
-//  5. HIT+stale (SHA mismatch) → redirect to S3 immediately, revalidate async
-//  6. MISS → upload synchronously, then redirect
 func HTMLPreview(ctx *context.Context) {
 	if !setting.HTMLPreview.Enabled {
 		ctx.NotFound(fmt.Errorf("HTML preview is not enabled"))
@@ -43,7 +31,6 @@ func HTMLPreview(ctx *context.Context) {
 		return
 	}
 
-	// Get the blob
 	entry, err := ctx.Repo.Commit.GetTreeEntryByPath(treePath)
 	if err != nil {
 		if git.IsErrNotExist(err) {
@@ -59,34 +46,9 @@ func HTMLPreview(ctx *context.Context) {
 	}
 
 	blob := entry.Blob()
-	blobSHA := blob.ID.String()
 	s3Key := buildPreviewS3Key(ctx)
 
-	// Check in-memory cache
+	if err := uploadPreview(s3Key, blob); err != nil {
-	if cachedSHA, ok := previewCache.Load(s3Key); ok {
-		if cachedSHA.(string) == blobSHA {
-			// Cache HIT + fresh — redirect directly
-			redirectToS3(ctx, s3Key, treePath)
-			return
-		}
-		// Cache HIT + stale — redirect to old version, revalidate in background
-		go revalidatePreview(s3Key, blob, blobSHA)
-		redirectToS3(ctx, s3Key, treePath)
-		return
-	}
-
-	// Cache MISS — check if S3 has it (cold start)
-	_, err = storage.HTMLPreview.Stat(s3Key)
-	if err == nil {
-		// S3 has a version — serve it and revalidate in background
-		previewCache.Store(s3Key, "") // mark as known but unknown SHA
-		go revalidatePreview(s3Key, blob, blobSHA)
-		redirectToS3(ctx, s3Key, treePath)
-		return
-	}
-
-	// No cached version — upload synchronously
-	if err := uploadPreview(s3Key, blob, blobSHA); err != nil {
 		ctx.ServerError("uploadPreview", err)
 		return
 	}
@@ -111,16 +73,16 @@ func HTMLPreviewByID(ctx *context.Context) {
 	}
 
 	blobSHA := blob.ID.String()
-	// For blob-by-SHA, use a content-addressed key (immutable)
 	s3Key := fmt.Sprintf("blobs/%s", blobSHA)
 
+	// Content-addressed: same SHA = same content, skip if exists
 	_, err = storage.HTMLPreview.Stat(s3Key)
 	if err == nil {
 		redirectToS3(ctx, s3Key, blobSHA+".html")
 		return
 	}
 
-	if err := uploadPreview(s3Key, blob, blobSHA); err != nil {
+	if err := uploadPreview(s3Key, blob); err != nil {
 		ctx.ServerError("uploadPreview", err)
 		return
 	}
@@ -140,7 +102,6 @@ func redirectToS3(ctx *context.Context, s3Key, name string) {
 		ContentType: "text/html; charset=utf-8",
 	})
 	if err != nil {
-		// Fallback: serve directly through Gitea
 		servePreviewDirect(ctx, s3Key)
 		return
 	}
@@ -171,7 +132,7 @@ func servePreviewDirect(ctx *context.Context, s3Key string) {
 	_, _ = io.Copy(ctx.Resp, obj)
 }
 
-func uploadPreview(s3Key string, blob *git.Blob, blobSHA string) error {
+func uploadPreview(s3Key string, blob *git.Blob) error {
 	dataRc, err := blob.DataAsync()
 	if err != nil {
 		return fmt.Errorf("blob DataAsync: %w", err)
@@ -183,15 +144,8 @@ func uploadPreview(s3Key string, blob *git.Blob, blobSHA string) error {
 		return fmt.Errorf("S3 save: %w", err)
 	}
 
-	previewCache.Store(s3Key, blobSHA)
+	log.Debug("HTMLPreview: uploaded %s (%d bytes)", s3Key, blob.Size())
-	log.Debug("HTMLPreview: uploaded %s (blob %s)", s3Key, blobSHA[:8])
 	return nil
 }
 
-func revalidatePreview(s3Key string, blob *git.Blob, blobSHA string) {
-	if err := uploadPreview(s3Key, blob, blobSHA); err != nil {
-		log.Error("HTMLPreview revalidate failed for %s: %v", s3Key, err)
-	}
-}
-
 // isHTMLTreePath is defined in view_file.go