## Summary
This PR adds checkpoint/resume support for the GraphRAG
`extract_community` and `resolve_entities` stages.
The implementation stores successful intermediate results in the
document store so interrupted ingestion can resume without repeating
already-completed LLM work. Checkpoints are loaded before each stage,
reused when available, saved after successful batch/community
processing, and cleaned up after the stage completes successfully.
## Related Issue
Closes: #15518
## Change Type
- [x] Feature
- [x] Bug fix
- [x] Test
- [ ] Refactor
- [ ] Documentation
- [ ] Breaking change
## Real Behavior Proof
Validation commands run locally:
```bash
uv run python -m py_compile \
rag/graphrag/checkpoints.py \
rag/graphrag/general/community_reports_extractor.py \
rag/graphrag/entity_resolution.py \
rag/graphrag/general/index.py \
test/unit_test/rag/graphrag/test_checkpoints.py
```
Result:
```text
Passed
```
```bash
uv run pytest test/unit_test/rag/graphrag/test_checkpoints.py
```
Result:
```text
4 passed
```
```bash
uv run pytest \
test/unit_test/rag/graphrag/test_phase_markers.py \
test/unit_test/rag/graphrag/test_graphrag_utils.py \
test/unit_test/rag/graphrag/test_checkpoints.py
```
Result:
```text
95 passed
```
```bash
git diff --check
```
Result:
```text
Passed
```
## Checklist
- [x] Implemented checkpoint/resume support for `extract_community`.
- [x] Implemented checkpoint/resume support for `resolve_entities`.
- [x] Avoided touching unrelated API behavior.
- [x] Added unit tests for the new checkpoint helper logic.
- [x] Verified Python syntax compilation.
- [x] Ran related GraphRAG unit tests successfully.
- [x] Ran `git diff --check`.
- [ ] Ran full project test suite.
---------
Co-authored-by: Wang Qi <wangq8@outlook.com>
