Validate training completion handoff

docs/CODEX_EXECUTION_LOG.md

@@ -11799,6 +11799,11 @@ Deployment evidence:
   `results.png` appears. The bound command permits up to 20 iterations, keeps
   protected test/background closed until calibration passes, and preserves
   the exact AdamW, 180-degree rotation, flip, scale and translation contract.
+- Extracted and tested strict completion-command validation. Only a non-empty
+  JSON list of non-empty argv strings is accepted; mappings, empty arguments,
+  malformed JSON and filesystem errors produce an explicit fail-closed
+  supervisor state before any subprocess is started. The updated supervisor
+  was activated live with one remaining v37 GPU process.
 - Added those aerial augmentation parameters to the orchestrator CLI and
   training command, preventing later failure-driven checkpoints from silently
   reverting to generic orientation assumptions.