fix(chat-context): clean up session entries on disconnect

[axelray-dev]

Fixes #2951

Problem

The global chat_contexts dict in backend/chainlit/chat_context.py accumulates a message list per session_id but never removes entries when sessions disconnect. Over time this causes unbounded memory growth and eventual OOM.

Root Cause

The disconnect handler in socket.py cleans up user_sessions and calls session.delete(), but does not remove the session's entry from chat_contexts.

Fix

1. Added ChatContext.delete_session(session_id) to remove a session's entry from chat_contexts.
2. Called it from the clear() function inside the disconnect handler, alongside the existing user_sessions cleanup.

Tests

3 new tests in backend/tests/test_chat_context.py:

• test_delete_session_removes_entry: verifies entry is removed after adding a message
• test_delete_session_nonexistent: verifies no error for unknown session ID
• test_delete_session_without_session: verifies deletion works without an active Chainlit context

All 31 tests pass: PYTHONPATH=. python -m pytest tests/test_chat_context.py -v

---

Summary by cubic

Fixes a memory leak by deleting session entries from chat_contexts on disconnect. Stops unbounded memory growth and OOM on long-running servers.

• Bug Fixes
  • Added ChatContext.delete_session(session_id) and call it in socket clear() after user_sessions cleanup.
  • Added tests for removal, unknown IDs, and no active context.

^{Written for commit 5485c3f. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files

_{Re-trigger cubic}

[dokterbob]

@codex review

[dokterbob]

@axelray-dev This looks good to me but I would love it if at least one other user/dev could validate that this doesn't have unintended side-effects. Unfortunately, I lack the time to do this investigation myself.