Carry snapshot diagnostics into execution

[Pigbibi]

Summary

• carry snapshot manifest diagnostic metadata from runtime evaluation into execution payloads
• lets signal snapshots and notifications show price/universe/source fallback details even for no-execute monthly cadence decisions
• add regression coverage in decision mapper

Tests

• PYTHONPATH=/home/ubuntu/Projects/LongBridgePlatform:/home/ubuntu/Projects/QuantPlatformKit/src:/home/ubuntu/Projects/UsEquityStrategies/src:/home/ubuntu/Projects/HkEquityStrategies/src /tmp/useq-snapshot-guardrails-venv/bin/python -m pytest tests -q
• /tmp/useq-snapshot-guardrails-venv/bin/python -m py_compile decision_mapper.py application/signal_snapshot.py notifications/renderers.py notifications/telegram.py
• git diff --check

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve original decision diagnostics when attaching snapshot data

When a no_execute decision carries snapshot manifest fields in decision.diagnostics, _normalize_to_value_target_decision replaces it with a synthetic hold-current decision whose diagnostics are empty, so passing normalized_decision here drops the very fields this helper tries to copy into execution. In that scenario the signal snapshot/notification still won't show the manifest dates or fallback status unless the same values also happen to be duplicated in runtime_metadata; use the original decision (or merge its diagnostics before normalization) for this attachment step.

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