Agent explainability tech specs (#655)

* Query time provenance tech spec

* Extraction provenance placeholder

docs/tech-specs/extraction-time-provenance.md

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+# Extraction-Time Provenance: Source Layer
+
+## Status
+
+Notes - Not yet started
+
+## Overview
+
+This document captures notes on extraction-time provenance for future specification work. Extraction-time provenance records the "source layer" - where data came from originally, how it was extracted and transformed.
+
+This is separate from query-time provenance (see `query-time-provenance.md`) which records agent reasoning.
+
+## Current State
+
+Source metadata is already partially stored in the knowledge graph (~40% solved):
+- Documents have source URLs, timestamps
+- Some extraction metadata exists
+
+## Scope
+
+Extraction-time provenance should capture:
+
+### Source Layer (Origin)
+- URL / file path
+- Retrieval timestamp
+- Funding sources
+- Authorship / authority
+- Document metadata (title, date, version)
+
+### Transformation Layer (Extraction)
+- Extraction tool used (e.g., PDF parser, table extractor)
+- Extraction method / version
+- Confidence scores
+- Raw-to-structured mapping
+- Parent-child relationships (PDF → table → row → fact)
+
+## Key Questions for Future Spec
+
+1. What metadata is already captured today?
+2. What gaps exist?
+3. How to structure the extraction DAG?
+4. How does query-time provenance link to extraction-time nodes?
+5. Storage format - RDF triples? Separate schema?
+
+## References
+
+- Query-time provenance: `docs/tech-specs/query-time-provenance.md`
+- PROV-O standard for provenance modeling
+- Existing source metadata in knowledge graph (needs audit)