Enable scoped LFS publication and add synthetic round-trip probe

.gitattributes

@@ -1,3 +1,5 @@
 # Preserve historical source bytes and SHA-256 across platforms. No EOL conversion.
 * -text
 *.jsonl.gz binary
+artifacts/**/*.tar.zst filter=lfs diff=lfs merge=lfs -text
+artifacts/lfs-smoke/*.bin filter=lfs diff=lfs merge=lfs -text

.gitignore

@@ -34,3 +34,5 @@ id_ed25519*
 /registry/verification-runs/
 # Historical learned deltas/checkpoints are not source files.
 /models/learned/
+# Explicit publication exports only; original scientific directories stay ignored.
+!/artifacts/**/*.tar.zst