[codex] Fix audit findings

[duncanita]

Summary

• convert effect idempotency conflicts into durable terminal workflow failures
• make event bus publishing best-effort after storage commits in runner and mutation flows
• tighten JSON/coordinate validation for graph metadata, proposed mutations, and memory storage events
• add focused regression tests for each fixed path

Validation

• bundle exec rake
• git diff --check

[chatgpt-codex-connector]

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