feat: always post fresh review, supersede old with collapsed body

Closes #34

- Remove reviewUnchanged() skip logic — every push gets a fresh review
- Remove edit-in-place (PATCH same body) — always POST new
- Supersede old review: PATCH with struck-through banner + collapsed
  original body in <details> for historical reference
- Add commit footer to every review: 'Evaluated against <sha>'
- Remove --update-existing flag (no longer needed)
- Add CommitID field to Review struct
- Add TestBuildSupersededBody tests

cmd/review-bot/main.go

@@ -67,7 +67,6 @@ func main() {
 	patternsRepo := flag.String("patterns-repo", envOrDefault("PATTERNS_REPO", ""), "Repo with language patterns (e.g. rodin/elixir-patterns)")
 	patternsFiles := flag.String("patterns-files", envOrDefault("PATTERNS_FILES", "README.md"), "Comma-separated file paths to fetch from patterns repo")
 	dryRun := flag.Bool("dry-run", false, "Print review to stdout instead of posting")
-	updateExisting := flag.Bool("update-existing", envOrDefaultBool("UPDATE_EXISTING", true), "Delete previous review from same bot before posting (default true)")
 	llmTemp := flag.Float64("llm-temperature", envOrDefaultFloat("LLM_TEMPERATURE", 0), "LLM temperature (0 = server default)")
 	llmTimeout := flag.Int("llm-timeout", envOrDefaultInt("LLM_TIMEOUT", 300), "LLM request timeout in seconds (default 300)")
 	llmProvider := flag.String("llm-provider", envOrDefault("LLM_PROVIDER", "openai"), "LLM API provider: openai or anthropic")
@@ -279,6 +278,16 @@ func main() {
 
 	// Step 10: Format and post review
 	reviewBody := review.FormatMarkdown(result, *reviewerName)
+
+	// Add commit footer so readers know which commit was evaluated
+	if pr.Head.Sha != "" {
+		shortSHA := pr.Head.Sha
+		if len(shortSHA) > 8 {
+			shortSHA = shortSHA[:8]
+		}
+		reviewBody += fmt.Sprintf("\n\n---\n*Evaluated against %s*", shortSHA)
+	}
+
 	event := review.GiteaEvent(result.Verdict)
 
 	if *dryRun {
@@ -307,56 +316,33 @@ func main() {
 	}
 
 	// --- Review update strategy ---
-	// 1. No existing review → POST new
-	// 2. Existing review, same state → PATCH body in place (preserves threads)
-	// 3. Existing review, state change → PATCH old to "Superseded", POST new
-	if *updateExisting && *reviewerName != "" {
+	// Always post a fresh review on the current commit. If a previous review
+	// exists, mark it as superseded (preserves old threads as navigable history).
+	// Never skip posting — the fresh review must land on HEAD to clear stale badges.
+	if *reviewerName != "" {
 		existingReviews, err := giteaClient.ListReviews(ctx, owner, repoName, prNumber)
 		if err != nil {
 			slog.Warn("could not list existing reviews", "pr", prNumber, "error", err)
 		} else {
-			// Detect shared-token misconfiguration: if detected, skip all
-			// update logic (PATCH/supersede) to avoid clobbering a sibling's review.
+			// In shared-token mode, skip superseding to avoid clobbering sibling reviews.
 			sharedToken := hasSharedToken(existingReviews, sentinel)
-			if sharedToken {
-				slog.Warn("shared token mode: skipping update-in-place logic to avoid clobbering sibling review")
-			} else {
+			if !sharedToken {
 				existing := findOwnReview(existingReviews, sentinel)
-
 				if existing != nil {
-					if reviewUnchanged(existingReviews, reviewBody, event, sentinel) {
-						slog.Info("review unchanged from previous run; skipping to preserve threads", "pr", prNumber)
-						return
-					}
-
-					// Same state → PATCH in place
-					if existing.State == event {
-						commentID, err := giteaClient.GetTimelineReviewCommentID(ctx, owner, repoName, prNumber, sentinel)
-						if err != nil {
-							slog.Warn("could not find review comment ID, falling back to new post", "error", err)
-						} else {
-							if err := giteaClient.EditComment(ctx, owner, repoName, commentID, reviewBody); err != nil {
-								slog.Warn("could not edit review, falling back to new post", "comment_id", commentID, "error", err)
-							} else {
-								slog.Info("review updated in place", "comment_id", commentID, "pr", prNumber)
-								return
-							}
-						}
+					commentID, err := giteaClient.GetTimelineReviewCommentID(ctx, owner, repoName, prNumber, sentinel)
+					if err != nil {
+						slog.Warn("could not find old review comment ID for supersede", "error", err)
 					} else {
-						// State change → mark old as superseded, post new below
-						commentID, err := giteaClient.GetTimelineReviewCommentID(ctx, owner, repoName, prNumber, sentinel)
-						if err != nil {
-							slog.Warn("could not find old review comment ID", "error", err)
+						supersededBody := buildSupersededBody(existing.Body, existing.CommitID, sentinel)
+						if err := giteaClient.EditComment(ctx, owner, repoName, commentID, supersededBody); err != nil {
+							slog.Warn("could not mark old review as superseded", "comment_id", commentID, "error", err)
 						} else {
-							supersededBody := fmt.Sprintf("~~*This review has been superseded by a newer review below.*~~\n\n%s", sentinel)
-							if err := giteaClient.EditComment(ctx, owner, repoName, commentID, supersededBody); err != nil {
-								slog.Warn("could not mark old review as superseded", "comment_id", commentID, "error", err)
-							} else {
-								slog.Info("marked old review as superseded", "old_state", existing.State, "new_state", event, "pr", prNumber)
-							}
+							slog.Info("marked old review as superseded", "old_state", existing.State, "pr", prNumber)
 						}
 					}
 				}
+			} else {
+				slog.Warn("shared token mode: skipping supersede to avoid clobbering sibling review")
 			}
 		}
 	}
@@ -526,22 +512,23 @@ func validateReviewerName(name string) error {
 	return nil
 }
 
-// reviewUnchanged checks if an existing review with the same sentinel
-// already has identical body and state. Returns true if a re-post would
-// produce the same result (skip to preserve conversation threads).
-func reviewUnchanged(reviews []gitea.Review, newBody, newEvent, sentinel string) bool {
-	for _, r := range reviews {
-		if r.Stale {
-			continue
-		}
-		if !strings.Contains(r.Body, sentinel) {
-			continue
-		}
-		if r.State == newEvent && r.Body == newBody {
-			return true
-		}
+// buildSupersededBody creates the body for a superseded review: struck-through banner
+// with collapsed original content and the commit it was evaluated against.
+func buildSupersededBody(originalBody, commitSHA, sentinel string) string {
+	shortSHA := commitSHA
+	if len(shortSHA) > 8 {
+		shortSHA = shortSHA[:8]
 	}
-	return false
+	var sb strings.Builder
+	sb.WriteString("~~Original review~~\n\n")
+	sb.WriteString("**Superseded** \u2014 see current review for up-to-date findings.\n\n")
+	sb.WriteString("<details><summary>Previous findings (commit ")
+	sb.WriteString(shortSHA)
+	sb.WriteString(")</summary>\n\n")
+	sb.WriteString(originalBody)
+	sb.WriteString("\n\n</details>\n\n")
+	sb.WriteString(sentinel)
+	return sb.String()
 }
 
 // hasSharedToken detects if another review-bot role posted under the same