tsk-52ujjr [OPEN] fix-forward #2924 (tsk-omud2i): add the missing 42

Author: jaylfc

commit_message.txt

@@ -0,0 +1,21 @@
+tests: add Discord 429/Retry-After and Slack cursor regression tests with red-first proof
+
+RED (origin/dev, before fix):
+```
+FAILED tests/channel_hub/test_connector_rate_limit.py::TestDiscordRateLimit::test_429_arms_rate_limit_and_skips_handle
+FAILED tests/channel_hub/test_connector_rate_limit.py::TestDiscordRateLimit::test_poll_loop_skips_rate_limited_channel
+FAILED tests/channel_hub/test_connector_rate_limit.py::TestDiscordRateLimit::test_200_empty_does_not_arm_rate_limit
+FAILED tests/channel_hub/test_connector_rate_limit.py::TestSlackCursorNotAdvancedOnRaise::test_handle_message_raise_preserves_cursor
+4 failed in 0.39s
+```
+
+GREEN (HEAD, after fix):
+```
+4 passed in 0.20s
+```
+
+Add tests/channel_hub/test_connector_rate_limit.py with:
+- Discord: _check_channel receiving 429 with Retry-After: 3 arms _last_rate_limit to roughly now+3 and does NOT call _handle_message; a following _poll_loop iteration skips that channel while the window is open; a 200 with [] must NOT arm a window.
+- Slack: when _handle_message raises on the first message of a batch, _last_timestamps[channel_id] is NOT advanced.
+
+Also correct the changelog wording from at-most-once to at-least-once, and remove unused import time from slack_connector.py.