# EDU-001 — Provider-neutral safe question content

- **Status:** done with recorded follow-up coverage
- **Type:** implementation
- **Phase:** 0 / core-loop prerequisite
- **Blockers:** EDU-000

## Student outcome

A student cannot receive or restore an apparently valid question when its type, visibility, or options are malformed. Student-visible question content and practice snapshot JSON do not expose answer-bearing fields.

## Scope delivered

- Shared question-type and option-shape contract.
- Option-backed, optionless, unsupported composite, and unknown type handling.
- Fail-closed single/page/collection safe projection.
- Fail-closed practice creation for disabled/unavailable provider, invisible question, and unsafe options.
- Strict practice snapshot restoration.
- Answer-free option snapshot JSON.

## Relevant files

- `docs/education/migration/11-question-content-safety-contract.md`
- `yudao-module-education/CONTEXT.md`
- `service/question/QuestionContentSafety.java`
- `service/question/QuestionCatalogServiceImpl.java`
- `service/practice/PracticeSessionServiceImpl.java`
- `service/practice/SessionResponseAssembler.java`
- corresponding focused tests

## Acceptance criteria

- [x] Invalid option-backed content fails closed.
- [x] Valid optionless content may have no options.
- [x] `reading` and unknown types fail closed until modeled.
- [x] Safe responses and option snapshot JSON exclude correctness and explanation fields.
- [x] Malformed persisted snapshots do not become empty valid options.
- [x] Disabled/unavailable providers and invisible questions cannot create sessions.
- [x] Focused safety tests pass.
- [x] Required compile and diff checks pass.

## Follow-up coverage

- Add a clean JavaCatalogProvider public-seam/PostgreSQL contract test when the native catalog test harness is established.
- Add explicit cross-tenant and `tenant_id=0` PUBLIC graph tests in the native catalog/graph-integrity slice.
- Do not test private provider parsing through reflection.

## Verification recorded

```text
Focused tests: 112 run, 0 failures, 0 errors
git diff --check: passed
yudao-server clean compile: BUILD SUCCESS
PostgreSQL migration: not applicable and not executed
```