### What problem does this PR solve?
This PR adds missing HTTP API test coverage for dataset
graph/GraphRAG/RAPTOR tasks, metadata summary, chat completions, agent
sessions/completions, and related questions. It also introduces minimal
HTTP test helpers to exercise these endpoints consistently with the
existing suite.
### Type of change
- [x] Other (please describe): Test coverage (HTTP API tests)
---------
Co-authored-by: Liu An <asiro@qq.com>
### What problem does this PR solve?
Updates pre-existing HTTP API and SDK tests to align with current
backend behavior (validation errors, 404s, and schema defaults). This
ensures p3 regression coverage is accurate without changing production
code.
### Type of change
- [x] Other (please describe): align p3 HTTP/SDK tests with current
backend behavior
---------
Co-authored-by: Liu An <asiro@qq.com>
### What problem does this PR solve?
as title.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
Signed-off-by: Jin Hai <haijin.chn@gmail.com>
