otel: Session Lifecycle Instrumentation

[schloerke]

Goal: Add OTel spans for session start/end and HTTP/WebSocket connections.

Tasks

• Modify AppSession._run() method to wrap server initialization in session.start span
  • Updated in Phase 3: Moved span to wrap only app.server() call, not entire session loop
• Modify _run_session_ended_tasks() to wrap session-ended callbacks in session.end span
• Create shiny/otel/_attributes.py with:
  • extract_http_attributes(scope) - Extract HTTP attributes from ASGI scope
  • Attributes: server.address, server.port, url.path, url.scheme
• Apply HTTP attributes to session start span
• Include session ID in all session spans

Acceptance Criteria

• Session lifecycle creates spans when SHINY_OTEL_COLLECT >= session
• Spans include session.id attribute
• Spans include HTTP metadata (address, port, path, scheme)
• No spans created when SHINY_OTEL_COLLECT=none
• Async context propagates correctly through session lifecycle
• session.start span only wraps server initialization (fixed in Phase 3)

Implementation

Files Created

• shiny/otel/_attributes.py - HTTP attribute extraction utilities

Files Modified

• shiny/session/_session.py - Session lifecycle instrumentation
  • session.start span wraps app.server() call (server initialization)
  • session.end span wraps session cleanup callbacks
• tests/pytest/test_otel_session.py - 9 comprehensive tests

Status

✅ COMPLETED - Phase 2 complete with Phase 3 refinement

Note: The session.start span scope was refined in Phase 3 (commit 8e0420f8) to only wrap the server function initialization instead of the entire session event loop. This provides a more accurate measurement of server initialization time.

---

Closed by PR #2144