fix(loop): prevent runtime event NPEs for null tool metadata

[alexk-dev]

Summary

• replace Map.of(...) runtime event payload construction in DefaultToolLoopSystem with a null-safe builder so incomplete tool call metadata does not abort the turn before the tool executes
• cover the shared failure mode with regression tests for missing toolCallId/tool fields and for stopOnToolFailure when the outcome has no toolName
• keep the runtime event contract stable while allowing nullable tool metadata to pass through the event service instead of crashing the tool loop

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
86.7% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud