diff --git a/gnommo/cli.py b/gnommo/cli.py
index 6e012e4..35264a6 100644
--- a/gnommo/cli.py
+++ b/gnommo/cli.py
@@ -4817,10 +4817,28 @@ def _cmd_render_impl(
         print(f"  Warning: {w}")
     print("  Passed.")
 
-    # Stage 3: Transform (alignment, unless a prior events.json pins the times)
+    # Stage 3: Transform.
+    #   build (plan_only): align the manuscript to the transcript (or reuse an
+    #     existing events.json), producing the timing layer.
+    #   render: NEVER aligns — it requires the precomputed events.json/scaffold.json
+    #     and executes them. If they're missing it errors, so `down` + `render` is
+    #     all the rig ever needs and the output can't silently diverge from the build.
     from . import scaffold as _scaffold
 
     _existing_events = None if realign else _scaffold.read_events(project_path)
+    if not plan_only:
+        if _existing_events is None or _scaffold.read_scaffold(project_path) is None:
+            print(
+                f"Error: render requires the precomputed timing layer "
+                f"({_scaffold.EVENTS_FILE} + {_scaffold.SCAFFOLD_FILE}), which is missing.",
+                file=sys.stderr,
+            )
+            print(
+                f"  Render does not align — run 'gnommo -p {project_path.name} build' first "
+                f"(then 'up'; on the rig, 'down' brings them over).",
+                file=sys.stderr,
+            )
+            return 1
     _timings_override = (
         _scaffold.events_to_marker_timings(_existing_events) if _existing_events else None
     )
@@ -4895,10 +4913,10 @@ def _cmd_render_impl(
     ]
     _write_tasks_file(project_path, missing_videos, alignment_issues)
 
-    # --- Timing layer: derive events, keep hand-edits, persist events.json + scaffold.json ---
-    # Only for a full-timeline pass — partial (--slides) and internal chunk renders
-    # read the override but must never overwrite the complete events.json/scaffold.json.
-    if slide_range is None and _output_path_override is None:
+    # --- Timing layer (BUILD only): derive events, keep hand-edits, persist
+    # events.json + scaffold.json, and print the plan. Render never runs this — it
+    # only consumes the files — so the timing layer is written exactly once, by build.
+    if plan_only and slide_range is None and _output_path_override is None:
         _events = _scaffold.derive_events(marker_timings, slides, videos, audio)
         # merge restores each id's human `adjustment` (the relative tweak).
         _events = _scaffold.merge_events(_events, _existing_events)
diff --git a/gnommo/transfer.py b/gnommo/transfer.py
index 379206c..9d69e02 100644
--- a/gnommo/transfer.py
+++ b/gnommo/transfer.py
@@ -27,7 +27,10 @@ from typing import Optional
 
 _COMMITS_LOG = "commits.log"
 
-# Dirs/patterns excluded on down (mirrors what up never pushes).
+# Dirs/patterns excluded on down (mirrors what up never pushes). Note: events.json
+# and scaffold.json are NOT excluded — they must reach the rig so `down` + `render`
+# is all that's needed there. The render never rewrites them, so they stay identical
+# on both ends (no clobbering).
 _DOWN_EXCLUDES = [
     "media/narration/processed/",
     "media/narration/intermediate/",
@@ -57,8 +60,18 @@ def _build_manifest(project_path: Path) -> list[str]:
         except (json.JSONDecodeError, OSError):
             pass
 
-    # Fixed project-root files
-    for fixed in ["project.json", "manuscript.txt", _COMMITS_LOG, "citations.json"]:
+    # Fixed project-root files. events.json / scaffold.json are the precomputed
+    # timing layer the render needs — events.json also carries the human `adjustment`
+    # tweaks — so they must travel UP to the rig. (They're excluded on `down` so the
+    # rig's regenerated copies can't clobber the local edits.)
+    for fixed in [
+        "project.json",
+        "manuscript.txt",
+        _COMMITS_LOG,
+        "citations.json",
+        "events.json",
+        "scaffold.json",
+    ]:
         if (project_path / fixed).exists():
             files.add(fixed)