b098d87075
- promote research fetch quality + content_sha256 from ToolExecutionCompletedEvent metadata to first-class SourceFetchedEvent / LowQualityExtractionEvent (registered + serialization test); existing metadata write kept intact (additive) - emitted from SandboxedToolExecutor on research-fetch tool completion, guarded on the url/content_sha256/quality markers; reuses the extractor's LOW_QUALITY marker Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>