Summary

Replace the assert statement in load_physical_aiavdataset() with a ValueError, mirroring the pattern of merged PR #50 (which made the same change in helper.create_message()).

Why

assert statements are stripped when Python runs with -O (optimization mode), so the t0_us validation would silently disappear and downstream timestamp arithmetic would produce confusing failures (negative offsets, out-of-range queries) instead of a clear input-validation error.

ValueError is the correct exception type for invalid argument values and is always raised regardless of optimization flags.

Change

src/alpamayo_r1/load_physical_aiavdataset.py:

-    assert t0_us > num_history_steps * time_step * 1_000_000, (
-        "t0_us must be greater than the history time range"
-    )
+    history_time_range_us = num_history_steps * time_step * 1_000_000
+    if t0_us <= history_time_range_us:
+        raise ValueError(
+            f"{t0_us=} must be greater than the history time range "
+            f"({history_time_range_us=} us)"
+        )

The error message now includes the actual computed threshold so the caller can see which value they violated.

Test plan

• python -c "import ast; ast.parse(open('src/alpamayo_r1/load_physical_aiavdataset.py').read())" — syntax OK
• Behavior preserved: passing t0_us greater than num_history_steps * time_step * 1_000_000 proceeds as before; smaller/equal values now raise ValueError with a descriptive message instead of AssertionError.
• Reviewer: confirm the message format f"{name=}" is consistent with the project style (already used in helper.py after Replace assert with ValueError in create_message() #50).

References

• PR Replace assert with ValueError in create_message() #50 — same pattern applied to create_message() in helper.py