feat: add GET /sessions endpoint with pagination

[sharma-sugurthi]

Fixes #218

What it does

Adds a GET /sessions endpoint that returns a paginated list of active session IDs with message counts.

Query parameters

Param	Type	Default	Description
offset	int	0	Starting index
limit	int	20	Max sessions per page

Response format

{
  "sessions": [
    {"session_id": "abc-123", "message_count": 4}
  ],
  "total": 1,
  "offset": 0,
  "limit": 20
}

[sharma-sugurthi]

@berviantoleo
get_all_sessions() accepts an optional user_id parameter (currently defaults to None) so that once authentication lands (#78), we can filter sessions by the authenticated user without changing the function signature or the endpoint contract.

right now, no session endpoint (POST, DELETE, GET message history) filters by user either, this is consistent with the current state of the codebase.

also included pagination as discussed on PR #196 , offset and limit query params with defaults of 0 and 20 respectively.

[berviantoleo]

Most likely, I'll hold this until we have a proper handling of the session.

[sharma-sugurthi]

Yeah @berviantoleo . Holding this until and unless,good handling of the session, what i also thought of..

[divyansh-cyber]

Overall this is a good addition. The schema design is clean, pagination is reasonable, and the new tests cover the basic happy paths well. get_all_sessions is straightforward and correctly guarded by the lock.
some points that i want to address:
The GET /sessions/{session_id}/message route has been removed from chatbot.py. This breaks the existing message history functionality and needs to be restored before this can be merged.
There is no validation on offset and limit in the route handler. Negative values or very large limits are currently accepted. These should be constrained using Query parameters.
test_list_sessions_pagination_custom only checks the number of returned sessions, not which sessions are returned. It should assert specific session IDs to properly validate pagination behavior.
Ensure get_all_sessions exists in memory.py in the same PR. If not, the import will cause a startup failure.
coming to my final verdict ,the rest of the changes look well-structured and reasonable.

[sharma-sugurthi]

@divyansh-cyber thanks..

"GET /sessions/{session_id}/message route removed" This route is not touched by this PR - you can verify by checking the diff. The GET message history endpoint is part of PR #196 (separate branch). Our diff only adds the new GET /sessions list endpoint. The POST /sessions/{session_id}/message and POST .../upload routes are untouched.

"No validation on offset and limit" ,"test_list_sessions_pagination_custom should assert specific session IDs", Good catch and i update that those two of the things.But many be it will be holding this updates too, as @berviantoleo holding this feature enhancement. As sooner, this feature gets attention to make this enhancement concrete. I shall fix those.

"Ensure get_all_sessions exists in memory.py" It does - it's part of this PR's diff in
api/services/memory.py

. You can see it in the files changed

@berviantoleo any comments??

[divyansh-cyber]

@divyansh-cyber thanks..

"GET /sessions/{session_id}/message route removed" This route is not touched by this PR - you can verify by checking the diff. The GET message history endpoint is part of PR #196 (separate branch). Our diff only adds the new GET /sessions list endpoint. The POST /sessions/{session_id}/message and POST .../upload routes are untouched.

"No validation on offset and limit" ,"test_list_sessions_pagination_custom should assert specific session IDs", Good catch and i update that those two of the things.But many be it will be holding this updates too, as @berviantoleo holding this feature enhancement. As sooner, this feature gets attention to make this enhancement concrete. I shall fix those.

"Ensure get_all_sessions exists in memory.py" It does - it's part of this PR's diff in api/services/memory.py

. You can see it in the files changed

@berviantoleo any comments??

Thanks for the clarification. I see now that the GET /sessions/{session_id}/message route is handled in PR #196 and not part of this change.
Good to know get_all_sessions is included in the memory.py diff as well.
The pagination validation and test improvements sound reasonable whenever the feature moves forward. Thanks for taking a look at those.