---
id: S04
parent: M004
milestone: M004
provides:
  - TechniquePageVersion model and migration
  - Version list/detail API endpoints
  - Pipeline metadata capture helper (_capture_pipeline_metadata)
  - Frontend version count display and fetchTechniqueVersions API function
requires:
  []
affects:
  []
key_files:
  - backend/models.py
  - alembic/versions/002_technique_page_versions.py
  - backend/pipeline/stages.py
  - backend/schemas.py
  - backend/routers/techniques.py
  - backend/tests/test_public_api.py
  - frontend/src/api/public-client.ts
  - frontend/src/pages/TechniquePage.tsx
key_decisions:
  - D018: Best-effort versioning — snapshot INSERT failure logs ERROR but does not block page update
  - Composite unique index on (technique_page_id, version_number) enforces version ordering at DB level
  - Version count only displayed in frontend when > 0 to avoid clutter on pages with no history
  - source_quality enum stored as string .value in JSONB snapshot for serialization compatibility
patterns_established:
  - Pre-overwrite snapshot pattern: before mutating an existing DB row, capture its current state into a version table with pipeline metadata for audit/benchmarking
  - _capture_pipeline_metadata() helper collects prompt file hashes + model config — reusable for any pipeline stage that needs reproducibility metadata
observability_surfaces:
  - INFO log in stage 5 when version snapshot is created (includes version_number and page slug)
  - ERROR log if snapshot INSERT fails (with exception details)
  - SELECT * FROM technique_page_versions ORDER BY created_at DESC LIMIT 5 — inspect recent versions
  - GET /techniques/{slug}/versions — API surface for version history
drill_down_paths:
  - .gsd/milestones/M004/slices/S04/tasks/T01-SUMMARY.md
  - .gsd/milestones/M004/slices/S04/tasks/T02-SUMMARY.md
  - .gsd/milestones/M004/slices/S04/tasks/T03-SUMMARY.md
duration: ""
verification_result: passed
completed_at: 2026-03-30T07:21:14.192Z
blocker_discovered: false
---

# S04: Article Versioning + Pipeline Tuning Metadata

**Added technique page version tracking with pipeline metadata capture, snapshot-on-write in stage 5, version list/detail API endpoints, and frontend version count display.**

## What Happened

This slice added a full article versioning stack across all three layers — database model, API, and frontend.

**T01 (Model + Migration + Pipeline Hook):** Added `TechniquePageVersion` model with UUID PK, FK to technique_pages (CASCADE delete), version_number, content_snapshot (JSONB), pipeline_metadata (JSONB), and created_at. Created Alembic migration 002 with a composite unique index on (technique_page_id, version_number). Added `_capture_pipeline_metadata()` helper that hashes all prompt template files (SHA-256) and collects model/modality config from settings. Modified `stage5_synthesis` to snapshot all 9 content fields (title, slug, topic_category, topic_tags, summary, body_sections, signal_chains, plugins, source_quality) before any attribute mutations, with best-effort error handling — INSERT failures log ERROR but don't block the page update.

**T02 (API + Tests):** Added three Pydantic schemas (TechniquePageVersionSummary, TechniquePageVersionDetail, TechniquePageVersionListResponse) and a version_count field on TechniquePageDetail. Added GET /{slug}/versions (list, DESC order) and GET /{slug}/versions/{version_number} (detail with full content_snapshot) endpoints. Modified get_technique to include version_count. Wrote 6 integration tests covering empty list, populated list ordering, detail with snapshot content, 404 for missing version, 404 for missing slug, and version_count on technique detail. All pass alongside 8 pre-existing tests.

**T03 (Frontend):** Added TypeScript interfaces mirroring the backend schemas, a fetchTechniqueVersions API function, and conditional version count display in TechniquePage meta stats (only when > 0). Frontend builds with zero TypeScript errors.

## Verification

All slice-level verification checks pass:
1. `cd backend && python -c "from models import TechniquePageVersion; print('Model OK')"` → exit 0
2. `test -f alembic/versions/002_technique_page_versions.py` → exit 0
3. `grep -q '_capture_pipeline_metadata' backend/pipeline/stages.py` → exit 0
4. `grep -q 'TechniquePageVersion' backend/pipeline/stages.py` → exit 0
5. `cd backend && python -c "from schemas import TechniquePageVersionSummary, TechniquePageVersionDetail, TechniquePageVersionListResponse"` → exit 0
6. `cd frontend && npm run build` → exit 0, zero errors
7. `grep -q 'version_count' frontend/src/api/public-client.ts && grep -q 'version_count' frontend/src/pages/TechniquePage.tsx && grep -q 'fetchTechniqueVersions' frontend/src/api/public-client.ts` → exit 0

## Requirements Advanced

- R013 — Pipeline metadata now captures prompt file SHA-256 hashes at synthesis time, creating a traceable link between prompt versions and output quality — directly supports the 're-run extraction' workflow in R013

## Requirements Validated

None.

## New Requirements Surfaced

None.

## Requirements Invalidated or Re-scoped

None.

## Deviations

None.

## Known Limitations

1. Version list endpoint returns all versions without pagination — acceptable since version count per page is expected to be small (single-digit to low tens).
2. Backend integration tests require PostgreSQL on ub01:5433 and cannot run locally on this machine.
3. Pre-existing creator test failures (5 tests) and test_search.py deadlock issues exist but are unrelated to versioning.
4. Pipeline metadata capture hashes prompt files at snapshot time — if prompt files are deleted or moved, the hash will be empty (logged as WARNING).

## Follow-ups

None.

## Files Created/Modified

- `backend/models.py` — Added TechniquePageVersion model with UUID PK, FK, version_number, content_snapshot (JSONB), pipeline_metadata (JSONB), created_at. Added versions relationship on TechniquePage.
- `alembic/versions/002_technique_page_versions.py` — New migration creating technique_page_versions table with composite unique index on (technique_page_id, version_number)
- `backend/pipeline/stages.py` — Added _capture_pipeline_metadata() helper and pre-overwrite snapshot logic in stage5_synthesis
- `backend/schemas.py` — Added TechniquePageVersionSummary, TechniquePageVersionDetail, TechniquePageVersionListResponse schemas; added version_count to TechniquePageDetail
- `backend/routers/techniques.py` — Added GET /{slug}/versions and GET /{slug}/versions/{version_number} endpoints; modified get_technique to include version_count
- `backend/tests/test_public_api.py` — Added 6 integration tests for version endpoints
- `frontend/src/api/public-client.ts` — Added version_count to TechniquePageDetail, TechniquePageVersionSummary/ListResponse interfaces, fetchTechniqueVersions function
- `frontend/src/pages/TechniquePage.tsx` — Conditional version count display in meta stats line
