Checkpoint prerequisite files for cross-container --script mode

download_private_prerequisites.py downloads files (puf_2015.csv,
demographics_2015.csv, soi.csv, np2023_d5_mid.csv, policy_data.db)
to the local filesystem, which vanishes when the container exits.
In --script mode, each script runs in a separate container, so
subsequent scripts couldn't find the prerequisites.

Fix: save prerequisite files to the checkpoint volume after download,
and restore them before running any other script.

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

Author: anth-volk

modal_app/data_build.py

@@ -98,6 +98,17 @@
     "small_enhanced_cps": "policyengine_us_data/datasets/cps/small_enhanced_cps.py",
 }
 
+# Files downloaded by download_private_prerequisites.py that must be
+# checkpointed so subsequent --script calls in separate containers
+# can access them.
+PREREQUISITE_FILES = [
+    "policyengine_us_data/storage/puf_2015.csv",
+    "policyengine_us_data/storage/demographics_2015.csv",
+    "policyengine_us_data/storage/soi.csv",
+    "policyengine_us_data/storage/np2023_d5_mid.csv",
+    "policyengine_us_data/storage/calibration/policy_data.db",
+]
+
 
 def setup_gcp_credentials():
     """Write GCP credentials JSON to a temp file for google.auth.default()."""
@@ -700,7 +711,10 @@ def run_single_script(
     # Handle download_prerequisites specially (no SCRIPT_OUTPUTS entry)
     if script_name == "download_prerequisites":
         run_script(script_path)
-        checkpoint_volume.commit()
+        # Checkpoint prerequisite files so subsequent containers can
+        # restore them.
+        for prereq in PREREQUISITE_FILES:
+            save_checkpoint(branch, prereq, checkpoint_volume)
         return f"Completed {script_name}"
 
     output_files = SCRIPT_OUTPUTS.get(script_path)
@@ -710,6 +724,10 @@ def run_single_script(
             f"Valid names: {', '.join(SCRIPT_SHORT_NAMES.keys())}"
         )
 
+    # Restore prerequisite files from checkpoint volume
+    for prereq in PREREQUISITE_FILES:
+        restore_from_checkpoint(branch, prereq)
+
     # Restore any existing checkpoints for dependencies
     for dep_path, dep_outputs in SCRIPT_OUTPUTS.items():
         if dep_path == script_path: