feat(sdk): 59787 merge events

[namrataghadi-galileo]

Summary

• add an optional SDK-side merged-event path so local and server ControlExecutionEvents can be emitted together after evaluation
• keep event generation separate from evaluation by reconstructing events after evaluation results are available, instead of sending full event payloads over the wire
• reduce wire transfer for the merged path by keeping server evaluation responses focused on evaluation semantics and reconstructing server events in the SDK
• preserve event identity consistency during reconstruction by using ControlDefinition.observability_identity() for composite conditions
• add a merged-event sink interface in the SDK and a server-side merge-mode signal so the SDK can become the final emitter when needed

Behavior

• default behavior remains unchanged: local events are reconstructed in the SDK and enqueued through the existing SDK observability pipeline, while server-side evaluation still builds and ingests its own events on the server
• when a control event sink is registered, the SDK switches to the merged-event path: it reconstructs local and server events after evaluation, sends X-Agent-Control-Merge-Events: true to the server, and emits one merged batch through the registered sink
• server-side merge mode skips final server ingestion but still returns the same evaluation semantics, so the SDK can merge results and reconstruct the final event batch locally
• trace/span correlation is preserved in both paths through the tracing resolver and reconstructed control metadata

What changed

• added shared SDK event reconstruction helpers in evaluation_events.py
• updated evaluation.py to support:
• local reconstruction + default enqueue path
• optional merged-event sink path
• SDK reconstruction of server events from the lean server response plus cached control definitions
• added merged-event sink registration helpers in event_sink.py
• updated server evaluation.py so the server:
• still ingests events in the default path
• skips final ingestion when X-Agent-Control-Merge-Events: true is set

Testing

• SDK and server tests were updated to cover:
• default local enqueue behavior
• merged-event emission behavior
• provider-backed trace/span propagation
• server merge-mode skip-ingest behavior

[codecov]

Codecov Report

❌ Patch coverage is 93.84615% with 8 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
sdks/python/src/agent_control/evaluation_events.py	89.79%	5 Missing ⚠️
sdks/python/src/agent_control/evaluation.py	93.75%	3 Missing ⚠️

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