Add pubsub.LiveEventSubscriber (subscribe_to_changes)

[winrid]

What

Adds live subscription support to the Python SDK, porting the Java SDK's LiveEventSubscriber / subscribeToChanges. Consumers can now receive real-time comment events (new comments, votes, edits, notifications, etc.) over a WebSocket.

from pubsub import LiveEventSubscriber

subscriber = LiveEventSubscriber()
result = subscriber.subscribe_to_changes(
    tenant_id_ws="YOUR_TENANT_ID",
    url_id="page-url-id",
    url_id_ws="page-url-id",
    user_id_ws="a-unique-presence-id",
    handle_live_event=lambda event: print(event.type),
    region=None,  # "eu" for the EU region
)
# ...later:
result.close()

How

New hand-written pubsub/ module, packaged alongside sso/ (survives client regeneration since update.sh only touches ./client):

• pubsub/live_event_subscriber.py — LiveEventSubscriber.subscribe_to_changes(...). Runs the connection on a background daemon thread, transparently reconnects with jitter, and fetches events missed while disconnected from the event-log endpoint on reconnect. Optional can_see_comments visibility filter, on_connection_status_change callback, disable_live_commenting short-circuit, and LiveEventSubscriber.create_testing() for a short NAT-friendly ping interval.
• pubsub/subscribe_to_changes_result.py — SubscribeToChangesResult.close().
• pyproject.toml — new pubsub optional extra (fastcomments[client] + websocket-client>=1.5.0); package discovery and coverage include pubsub; dev extra pulls it in.
• README.md — usage section + install/import notes.

EU region fix (baked in)

The event-log fallback defaults its REST host from region: when region="eu" and the caller hasn't overridden api_host/api_client, it targets https://eu.fastcomments.com instead of silently querying US infra and getting nothing back. (The Java SDK had the identical bug in its fallback — fixed in FastComments/fastcomments-java#16.)

Testing

tests/test_pubsub.py — 11 unit tests, WebSocket and event-log API mocked (no real network): URL/region routing, message dispatch, can_see_comments filtering, connection-status callback, intentional-close-prevents-reconnect, event-log missed-event replay, and EU/US/override host selection.

pytest tests/test_pubsub.py tests/test_sso.py
33 passed

Note

websocket-client requires Python >= 3.9 while the base package floor is 3.8. It's only pulled in via the optional pubsub extra, so the base/SSO install (floor 3.8) is unaffected.