Make module-stage LLM handling resilient and report warnings

docs/architecture/public-contract.md

@@ -93,6 +93,7 @@ Current values:
 `--report-json` output and diagnostics run-dir `report.json` use the same report schema metadata.
 
 Validator decision/rejection records in reports use stable validator keys in `validator_name`.
+Module results may also include warning records for malformed module-stage LLM payloads.
 Report diagnostics metadata includes artifact-path fields for utilization diagnostics and correction ledger when diagnostics initialization succeeds.
 
 ## Diagnostics directory behavior
@@ -123,6 +124,7 @@ Success behavior:
 - with `--output`, stdout is empty
 - without `--output`, stdout contains only transcript JSON in selected output schema
 - report JSON is not written to stdout
+- success stderr remains empty even when reports/diagnostics contain module warnings
 
 Failure behavior:
 - stderr contains human-readable error summary
@@ -149,6 +151,7 @@ Config files should reference secrets via environment variable names (`api_key_e
 ## Compatibility and deprecation policy
 
 - Existing stable schema names, report metadata keys, and top-level command behavior are treated as public contract.
+- Existing stable validator keys remain public contract values even when validator semantics are refined.
 - Compatibility inputs (legacy flags/env aliases) may remain during transition windows.
 - Any planned removal or behavior change should include clear compatibility notes and migration guidance.