Update image manifest (1 image)

generate-manifest.py

@@ -67,15 +67,31 @@ def find_images() -> list[dict]:
     return images
 
 
-def write_manifest(images: list[dict]) -> None:
+def write_manifest(images: list[dict]) -> bool:
+    """Write images.json. Returns True if the file changed.
+
+    If the image list is identical to what's already on disk, the file is left
+    untouched (keeping its timestamp) so a no-op run produces no commit.
+    """
+    plural = "" if len(images) == 1 else "s"
+
+    if OUT_FILE.exists():
+        try:
+            existing = json.loads(OUT_FILE.read_text(encoding="utf-8"))
+        except (json.JSONDecodeError, OSError):
+            existing = None
+        if isinstance(existing, dict) and existing.get("images") == images:
+            print(f"• Manifest unchanged ({len(images)} image{plural}).")
+            return False
+
     manifest = {
         "generatedAt": datetime.now(timezone.utc).isoformat().replace("+00:00", "Z"),
         "count": len(images),
         "images": images,
     }
     OUT_FILE.write_text(json.dumps(manifest, indent=2, ensure_ascii=False) + "\n", encoding="utf-8")
-    plural = "" if len(images) == 1 else "s"
     print(f"✓ Wrote {len(images)} image{plural} to {OUT_FILE.name}")
+    return True
 
 
 def git(*args: str, check: bool = True) -> subprocess.CompletedProcess:
@@ -117,7 +133,8 @@ def main() -> None:
     if args.no_commit:
         return
 
-    message = args.message or f"Update image manifest ({len(images)} images)"
+    plural = "" if len(images) == 1 else "s"
+    message = args.message or f"Update image manifest ({len(images)} image{plural})"
     commit(message)