# Task 011: Evidence Matrix And Claim Gate

Development description: Build claim extraction, claim-to-evidence mapping, unsupported-claim visibility, insufficient-evidence plan revision, and high-risk unsupported-claim blocking.

## Implementation Details

- Backend endpoints:
  - `GET /api/articles/{article_id}/evidence`
  - `PATCH /api/articles/{article_id}/evidence/{evidence_id}`
  - Claim review operations under article evidence routes.
- Evidence matrix maps:
  - Plan sections.
  - Claims.
  - Evidence items.
  - Source quality score.
  - Support status.
  - Risk level.
- If research cannot find enough acceptable evidence for the approved plan:
  - Move workflow to `PLAN_REVISION_REQUIRED`.
  - Do not allow drafting.
  - Show missing evidence reasons to Editor.
- High-risk unsupported claims:
  - Are visible in review screens.
  - Block final approval until resolved.
- Editor can approve/reject evidence and add/remove evidence manually.

## Public Interface

- Editor views evidence by section and claim.
- Editor can filter unsupported claims.
- Workflow refuses to draft if evidence is structurally insufficient.

## Acceptance Criteria

- [ ] TDD pre-requirement: before implementation, write one failing behavior test showing insufficient evidence returns the article to `PLAN_REVISION_REQUIRED`; proceed one claim/evidence behavior at a time and record evidence in `Result`.
- [ ] Every factual claim is mapped to at least one evidence item or marked unsupported.
- [ ] Unsupported claims are visible by section.
- [ ] High-risk unsupported claims block final approval.
- [ ] Insufficient acceptable evidence blocks draft production and triggers plan revision.
- [ ] Editor can approve, reject, add, and remove evidence.
- [ ] Evidence UI supports section and unsupported-claim filters.
- [ ] Evidence item retains URL, title, source type, summary, quality score, retrieval timestamp, and manifest reference.

## Verification

- Run evidence matrix API tests.
- Run frontend evidence UI tests.
- Run a smoke flow with both sufficient and insufficient fake research fixtures.

## Result

- Status: Pending execution.
- TDD plan: To be filled during execution.
- Red evidence: To be filled during execution.
- Green evidence: To be filled during execution.
- Refactor notes: To be filled during execution.
- Verification output: To be filled during execution.